HK1229078B - Series-resonance oscillator - Google Patents

Description

Series Resonant Oscillator

Technical Field

The present disclosure relates to an oscillator circuit, a method of operating an oscillator circuit, and a wireless communication device including an oscillator circuit.

Background Art

A harmonic oscillator, known in the art and implemented in an integrated circuit chip, comprises an inductor and a capacitor, generally referred to as a tank, operating at the tank's resonant frequency. Typically, such an oscillator injects a pulse waveform into the tank, which filters out higher current harmonics and generates a sinusoidal voltage waveform at its output. The tank comprises an inductor and a capacitor coupled in parallel and operates in a parallel resonant mode, where the parallel impedance (i.e., the impedance of the parallel-coupled inductor and capacitor) is high, generating a relatively high oscillating voltage from a relatively low bias current.

In some applications, such as wireless communication devices, oscillators with extremely low phase noise combined with low power consumption are required. This combination is difficult to achieve, particularly when the available supply voltage _V is low, as is often the case with today's nanometer complementary metal oxide semiconductor (CMOS) processes. Increasing the oscillation voltage swing can reduce the oscillator's phase noise. However, conventional oscillators are limited by the maximum voltage swing they can provide, which ranges from a peak single-ended voltage of 2 _V to 3 _V , the latter being possible in so-called Class D oscillators. Reducing the inductor's inductance and increasing the capacitor's capacitance can also reduce phase noise. However, if the required inductance is very small, such as tens of picohenries, this approach can become unmanageable due to the parasitic inductance and resistance of the integrated circuit, which begin to dominate. Furthermore, the quality factor of very small inductors is lower than that for larger inductors, resulting in higher power consumption for a given phase noise level.

Figure 1 illustrates a typical Clapp oscillator operating in parallel resonant mode. Referring to Figure 1 , the Clapp oscillator has a first energy tank, _{TA ,} comprising a first inductor, _LA , and a first capacitor, _CA. The first inductor, _LA , and the first capacitor, CA _, are coupled in series to the drain of a first transistor, _QA . To provide a differential tank voltage, _VOUT , the Clapp oscillator also has a second energy tank, _{TB ,} comprising a second inductor, _LB , and a second capacitor, _CB . The second inductor, _LB , and the second capacitor, CB _, are coupled in series to the drain of a second transistor, _QB . The first and second transistors, _QA and _QB, have their gates biased with a constant bias voltage, _VDC . The Clapp oscillator is a current-mode oscillator, meaning that the first and second transistors, _QA and _QB, operate as transconductors, providing voltage-to-current conversion and delivering high current to their respective first and second energy tanks, _TA and _TB, without loading the energy tanks. Therefore, each transconductor must have a high parallel impedance. Although the first and second energy tanks _TA , _TB have a series-coupled inductor and capacitor, the Clapp oscillator does not oscillate at the series resonant frequency of the series-coupled inductor and capacitor. Instead, the Clapp oscillator oscillates at a frequency determined by the total reactive components in the energy tank, including the capacitances between the drain and source, and between the source and ground, of the first and second transistors _QA , _QB . These capacitances are also shown in FIG1 . For a given bias current supplied to the sources of the first and second transistors _QA , _QB , the oscillation amplitude is proportional to the bias current and the equivalent parallel tank resistance. Therefore, for the current-mode Clapp oscillator illustrated in FIG1 with the bias current I _BIAS provided by the first and second current sources _IA , _IB , the amplitude of the tank voltage V _OUT can be expressed as:

V _OUT = kI _BIAS .R _PEQ (1)

where R _PEQ is the equivalent parallel resistance of each tank in the energy storage, which is proportional to the quality factor Q of each tank in the energy storage, and k is a scaling factor. In a Clapp oscillator, the parallel resistance of each tank in the energy storage is degraded by feedback at the source of the transistor through capacitive taps between the drain and source and between the source and ground.

There is a need for improved oscillators.

Summary of the Invention

According to a first aspect, an oscillator circuit is provided, the oscillator circuit comprising:

a first tank circuit comprising an inductive element and a capacitive element coupled in series between the voltage rail and the first drive node; and

a feedback stage coupled to the first tank output of the first tank circuit and to the first drive node;

wherein the feedback stage is arranged to generate a first oscillating drive voltage at the first drive node in phase with the oscillating tank current flowing in the inductive element and the capacitive element in response to a first oscillating tank voltage present at the first tank output, thereby causing the oscillator circuit to oscillate in a series resonant mode of the inductive element and the capacitive element.

According to a second aspect, there is provided a method of operating an oscillator circuit comprising a first tank circuit, the first tank circuit comprising an inductive element and a capacitive element coupled in series between a voltage rail and a first drive node, the method comprising generating a first oscillating drive voltage at the first drive node in response to a first oscillating tank voltage present at the first tank output, wherein the first oscillating drive voltage is in phase with an oscillating tank current flowing in the inductive element and the capacitive element, thereby causing the oscillator to oscillate in a series resonant mode of the inductive element and the capacitive element.

Thus, the oscillator circuit is voltage driven and oscillates in series resonant mode. This enables high oscillation amplitude using only low supply voltage, which enables low phase noise.

The following embodiments provide different low-complexity solutions for implementing an oscillator circuit and a method of operating an oscillator circuit.

The feedback stage may be arranged to generate the first oscillating drive voltage having a substantially rectangular waveform.This feature enables a switching device to be used, thereby enabling low power consumption.

In a first preferred embodiment of the oscillator circuit, the first tank circuit may be arranged to generate a first oscillating tank voltage in phase with the first oscillating drive voltage in response to a first oscillating drive voltage, and the feedback stage may include a first driver arranged to generate the first oscillating drive voltage in phase with the first oscillating tank voltage in response to the first oscillating tank voltage. Similarly, a first preferred embodiment of the method may include: generating the first oscillating tank voltage in phase with the first oscillating drive voltage; and generating the first oscillating drive voltage in phase with the first oscillating tank voltage in response to the first oscillating tank voltage. The first preferred embodiment enables a single-ended oscillating signal to be generated in a low-complexity manner.

In a variation of the first preferred embodiment of the oscillator circuit, the first tank circuit may be arranged to generate a first oscillating tank voltage 180 degrees out of phase with the first oscillating tank voltage in response to the first oscillating drive voltage, and the feedback stage may include a first driver arranged to generate the first oscillating tank voltage 180 degrees out of phase with the first oscillating tank voltage by applying a signal inversion to the first oscillating tank voltage in response to the first oscillating drive voltage. Similarly, a variation of the first preferred embodiment of the method may include: generating the first oscillating tank voltage 180 degrees out of phase with the first oscillating drive voltage in response to the first oscillating drive voltage; and generating the first oscillating drive voltage 180 degrees out of phase with the first oscillating tank voltage in response to the first oscillating drive voltage by applying a signal inversion to the first oscillating tank voltage. This variation enables a single-ended oscillating signal to be generated in a low-complexity manner.

In a second preferred embodiment of the oscillator circuit, the first tank circuit may be arranged to generate, in response to the first oscillating drive voltage, a first oscillating tank voltage in phase with the first oscillating drive voltage, and the feedback stage may comprise:

a second driver arranged to generate a second oscillating drive voltage by applying a signal inverted to the first oscillating tank voltage;

a second tank circuit arranged to generate a second oscillating tank voltage in phase with the second oscillating drive voltage in response to the second oscillating drive voltage; and

A first driver is arranged to generate a first oscillating drive voltage by applying a signal inversion to the second oscillating tank voltage.

Similarly, a second preferred embodiment of the method may include:

generating a first oscillating energy storage voltage in phase with the first oscillating drive voltage in response to the first oscillating drive voltage;

generating a second oscillating drive voltage by applying a signal inversion to the first oscillating tank voltage;

generating a second oscillating tank voltage in phase with the second oscillating drive voltage in response to the second oscillating drive voltage; and

The first oscillating drive voltage is generated by applying a signal inversion to the second oscillating tank voltage.

The second preferred embodiment enables a balanced oscillating signal to be generated in a low-complexity manner.The use of a first and a second tank circuit enables an accurate phase difference to be provided in a low-complexity manner.

In a first variant of the second preferred embodiment of the oscillator circuit, the first tank circuit may be arranged to generate, in response to the first oscillating drive voltage, a first oscillating tank voltage that is one hundred eighty degrees out of phase with the first oscillating drive voltage, and the feedback stage may comprise:

a second driver arranged to generate a second oscillating drive voltage by applying a signal inverted to the first oscillating tank voltage;

a second tank circuit arranged to generate a second oscillating tank voltage in phase with the second oscillating drive voltage in response to the second oscillating drive voltage; and

A first driver is arranged to generate a first oscillating drive voltage that is in phase with the second oscillating tank voltage.

Similarly, a first variant of the second preferred embodiment of the method may include:

generating, in response to the first oscillating drive voltage, a first oscillating energy storage voltage one hundred eighty degrees out of phase with the first oscillating drive voltage;

generating a second oscillating drive voltage by applying a signal inverse to the first oscillating tank voltage;

generating a second oscillating tank voltage in phase with the second oscillating drive voltage in response to the second oscillating drive voltage; and

A first oscillating drive voltage is generated that is in phase with the second oscillating tank voltage.

This first variant enables a balanced oscillating signal to be generated in a low-complexity manner and enables an accurate phase difference to be provided with low complexity.

In a second variant of the second preferred embodiment of the oscillator circuit, the first tank circuit may be arranged to generate, in response to the first oscillating drive voltage, a first oscillating tank voltage that is one hundred eighty degrees out of phase with the first oscillating drive voltage, and the feedback stage may comprise:

a second driver arranged to generate, in response to the first oscillating tank voltage, a second oscillating drive voltage in phase with the first oscillating tank voltage;

a second tank circuit arranged to generate a second oscillating tank voltage in response to the second oscillating drive voltage that is one hundred eighty degrees out of phase with the second oscillating drive voltage; and

The first driver is arranged to generate a first oscillating drive voltage in phase with the second oscillating tank voltage in response to the second oscillating tank voltage.

Similarly, a second variant of the second preferred embodiment of the method may include:

generating, in response to the first oscillating drive voltage, a first oscillating energy storage voltage one hundred eighty degrees out of phase with the first oscillating drive voltage;

generating a second oscillating drive voltage in phase with the first oscillating tank voltage in response to the first oscillating tank voltage;

generating, in response to the second oscillating drive voltage, a second oscillating tank voltage that is one hundred eighty degrees out of phase with the second oscillating drive voltage; and

A first oscillating drive voltage in phase with the second oscillating tank voltage is generated in response to the second oscillating tank voltage.

This second variant enables a balanced oscillating signal to be generated in a low-complexity manner and enables an accurate phase difference to be provided with low complexity.

In the first and second preferred embodiments of the oscillator circuit and their variants, the first tank circuit may include a sensor device arranged to generate a first oscillating tank voltage in response to the first oscillating tank current. Similarly, the first and second preferred embodiments of the method and their variants may include generating the first oscillating tank voltage in the sensor device in response to the first oscillating tank current. The sensor device may include one of a resistive element and a transformer coupled in series with a first inductive element and a first capacitive element between the voltage rail and the first drive node. Alternatively, the sensor device may be magnetically coupled to the first inductive element for generating the first oscillating tank voltage by magnetic induction in response to the first oscillating tank current. These features enable feedback to be provided in a low-complexity manner.

In a third preferred embodiment of the oscillator circuit, the first energy storage circuit may be arranged to generate a first oscillating energy storage voltage having a phase lagging ninety degrees relative to the phase of the first oscillating energy storage voltage in response to the first oscillating drive voltage, and the feedback stage may include: a phase shift stage arranged to generate a first intermediate oscillating voltage by applying a phase lag of ninety degrees to the first oscillating energy storage voltage; and a first driver arranged to generate the first oscillating drive voltage by applying a signal inversion to the first intermediate oscillating voltage.

Similarly, a third preferred embodiment of the method may include:

generating, in response to the first oscillation driving voltage, a first oscillation tank voltage having a phase lagging ninety degrees behind a phase of the first oscillation driving voltage;

generating a first intermediate oscillating voltage by applying a ninety degree phase lag to the first oscillating tank voltage; and

The first oscillation drive voltage is generated by applying a signal inversion to the first intermediate oscillation voltage.

The third preferred embodiment enables orthogonal correlation signals to be generated in a low complexity manner.

In a fourth preferred embodiment of the oscillator circuit, the first energy storage circuit may be arranged to generate a first oscillating energy storage voltage having a phase that leads the phase of the first oscillating energy storage voltage by ninety degrees in response to the first oscillating drive voltage, and the feedback stage may include: a phase shift stage arranged to generate a first intermediate oscillating voltage by applying a phase lag of ninety degrees to the first oscillating energy storage voltage; and a first driver arranged to generate the first oscillating drive voltage in response to the first intermediate oscillating voltage and in phase therewith.

Similarly, a fourth preferred embodiment of the method may include:

generating, in response to the first oscillation driving voltage, a first oscillation tank voltage having a phase leading ninety degrees from a phase of the first oscillation driving voltage;

generating a first intermediate oscillating voltage by applying a ninety degree phase lag to the first oscillating tank voltage; and

A first oscillating drive voltage is generated in response to and in phase with the first intermediate oscillating voltage.

The fourth preferred embodiment enables orthogonal correlation signals to be generated in a low complexity manner.

In a fifth preferred embodiment of the oscillator circuit, the first tank circuit may be arranged to generate, in response to the first oscillating drive voltage, a first oscillating tank voltage having a phase that lags the phase of the first oscillating drive voltage by ninety degrees, and the feedback stage may comprise:

a first phase shift circuit arranged to generate a first intermediate oscillating voltage by applying a ninety degree phase lag to the first oscillating tank voltage;

a second driver arranged to generate, in response to the first intermediate oscillating voltage, a second oscillating drive voltage in phase with the first intermediate oscillating voltage;

a second tank circuit arranged to generate, in response to the second oscillating drive voltage, a second oscillating tank voltage having a phase that lags ninety degrees behind the phase of the second oscillating drive voltage;

a second phase shift circuit arranged to generate a second intermediate oscillating voltage by applying a ninety degree phase lag to the second oscillating tank voltage; and

The first driver is arranged to generate a first oscillating drive voltage in phase with the second intermediate oscillating voltage in response to the second intermediate oscillating voltage.

Similarly, a fifth preferred embodiment of the method may include:

generating, in response to the first oscillation driving voltage, a first oscillation tank voltage having a phase lagging ninety degrees behind a phase of the first oscillation driving voltage;

generating a first intermediate oscillating voltage by applying a ninety degree phase lag to the first oscillating tank voltage;

generating a second oscillation drive voltage in phase with the first intermediate oscillation voltage in response to the first intermediate oscillation voltage;

generating, in response to the second oscillating driving voltage, a second oscillating tank voltage having a phase lagging ninety degrees behind a phase of the second oscillating driving voltage;

generating a second intermediate oscillating voltage by applying a ninety degree phase lag to the second oscillating tank voltage; and

A first oscillation driving voltage in phase with the second intermediate oscillation voltage is generated in response to the second intermediate oscillation voltage.

The fifth preferred embodiment enables a balanced oscillating signal to be generated in a low-complexity manner.

In a sixth preferred embodiment of the oscillator circuit, the first tank circuit may be arranged to generate, in response to the first oscillating drive voltage, a first oscillating tank voltage having a phase that lags the phase of the first oscillating drive voltage by ninety degrees, and the feedback stage may comprise:

a first phase shift circuit arranged to generate a first intermediate oscillating voltage by applying a ninety degree phase lag to the first oscillating tank voltage;

a second driver arranged to generate a second oscillating drive voltage by applying a signal inverted to the first intermediate oscillating voltage;

a second tank circuit arranged to generate, in response to the second oscillating drive voltage, a second oscillating tank voltage having a phase leading the second oscillating drive voltage by ninety degrees;

a second phase shift circuit arranged to generate a second intermediate oscillating voltage by applying a ninety degree phase lag to the second oscillating tank voltage; and

The first driver is arranged to generate a first oscillating drive voltage in phase with the second intermediate oscillating voltage in response to the second intermediate oscillating voltage.

Similarly, a sixth preferred embodiment of the method may include:

generating a first oscillating tank voltage having a phase lagging ninety degrees behind a phase of the first oscillating drive voltage in response to the first oscillating drive voltage, and the feedback stage may include:

a first phase shifter arranged to generate a first intermediate oscillating voltage by applying a ninety degree phase lag to the first oscillating tank voltage;

a second driver arranged to generate a second oscillating drive voltage by applying a signal inverted to the first intermediate oscillating voltage;

a second tank circuit arranged to generate, in response to the second oscillating drive voltage, a second oscillating tank voltage having a phase leading the second oscillating drive voltage by ninety degrees;

a second phase shifter arranged to generate a second intermediate oscillating voltage by applying a ninety degree phase lag to the second oscillating tank voltage; and

The first driver is arranged to generate a first oscillating drive voltage in phase with the second intermediate oscillating voltage in response to the second intermediate oscillating voltage.

The sixth preferred embodiment enables a balanced oscillating signal to be generated in a low-complexity manner.

In a seventh preferred embodiment of the oscillator circuit, the first tank circuit may be arranged to generate, in response to the first oscillating drive voltage, a first oscillating tank voltage having a phase that lags the phase of the first oscillating drive voltage by ninety degrees, and the feedback stage may comprise:

a second driver arranged to generate a second oscillating drive voltage by applying a signal inverted to the first oscillating tank voltage;

a second tank circuit arranged to generate, in response to the second oscillating drive voltage, a second oscillating tank voltage having a phase that lags ninety degrees behind the phase of the second oscillating drive voltage; and

The first driver is arranged to generate a first oscillating drive voltage in phase with the second oscillating tank voltage in response to the second oscillating tank voltage.

Similarly, a seventh preferred embodiment of the method may include:

generating, in response to the first oscillation driving voltage, a first oscillation tank voltage having a phase lagging ninety degrees behind a phase of the first oscillation driving voltage;

generating a second oscillating drive voltage by applying a signal inversion to the first oscillating tank voltage;

generating, in response to the second oscillation driving voltage, a second oscillation tank voltage having a phase lagging ninety degrees behind a phase of the second oscillation driving voltage; and

A first oscillating drive voltage in phase with the second oscillating tank voltage is generated in response to the second oscillating tank voltage.

The seventh preferred embodiment enables a balanced oscillating signal to be generated in a low-complexity manner.

In an eighth preferred embodiment of the oscillator circuit, the first tank circuit may be arranged to generate, in response to the first oscillating drive voltage, a first oscillating tank voltage having a phase leading the phase of the first oscillating drive voltage by ninety degrees, and the feedback stage may comprise:

a second driver arranged to generate a second oscillating drive voltage by applying a signal inverted to the first oscillating tank voltage;

a second tank circuit arranged to generate a second oscillating tank voltage having a phase leading the second oscillating drive voltage by ninety degrees in response to the second oscillating drive voltage; and

The first driver is arranged to generate a first oscillating drive voltage in phase with the second oscillating tank voltage in response to the second oscillating tank voltage.

Similarly, an eighth preferred embodiment of the method may include:

generating, in response to the first oscillation driving voltage, a first oscillation tank voltage having a phase leading ninety degrees from a phase of the first oscillation driving voltage;

generating a second oscillating drive voltage by applying a signal inversion to the first oscillating tank voltage;

generating, in response to the second oscillation driving voltage, a second oscillation tank voltage having a phase leading by ninety degrees than a phase of the second oscillation driving voltage; and

A first oscillating drive voltage in phase with the second oscillating tank voltage is generated in response to the second oscillating tank voltage.

The eighth preferred embodiment enables orthogonal correlation signals to be generated in a low complexity manner.

In a ninth preferred embodiment of the oscillator circuit, the first tank circuit may be arranged to generate, in response to the first oscillating drive voltage, a first oscillating tank voltage having a phase leading the phase of the first oscillating drive voltage by ninety degrees, and the feedback stage may comprise:

a second driver arranged to generate, in response to the first oscillating tank voltage, a second oscillating drive voltage in phase with the first oscillating tank voltage;

a second tank circuit arranged to generate, in response to the second oscillating drive voltage, a second oscillating tank voltage having a phase that lags ninety degrees behind the phase of the second oscillating drive voltage; and

The first driver is arranged to generate a first oscillating drive voltage in phase with the second oscillating tank voltage in response to the second oscillating tank voltage.

Similarly, a ninth preferred embodiment of the method may include:

generating, in response to the first oscillation driving voltage, a first oscillation tank voltage having a phase leading ninety degrees from a phase of the first oscillation driving voltage;

generating a second oscillating drive voltage in phase with the first oscillating tank voltage in response to the first oscillating tank voltage;

generating, in response to the second oscillation driving voltage, a second oscillation tank voltage having a phase lagging ninety degrees behind a phase of the second oscillation driving voltage; and

A first oscillating drive voltage in phase with the second oscillating tank voltage is generated in response to the second oscillating tank voltage.

The ninth preferred embodiment enables orthogonally correlated oscillating signals to be generated in a low-complexity manner.

In a tenth preferred embodiment of the oscillator circuit, the first tank circuit may be arranged to generate, in response to the first oscillating drive voltage, a first oscillating tank voltage having a phase that lags the phase of the first oscillating drive voltage by ninety degrees, and the feedback stage may comprise:

a second driver arranged to generate, in response to the first oscillating tank voltage, a second oscillating drive voltage in phase with the first oscillating tank voltage;

a second tank circuit arranged to generate, in response to the second oscillating drive voltage, a second oscillating tank voltage having a phase that lags ninety degrees behind the phase of the second oscillating drive voltage;

a third driver arranged to generate, in response to the second oscillating tank voltage, a third oscillating drive voltage in phase with the second oscillating tank voltage;

a third tank circuit arranged to generate, in response to the third oscillating drive voltage, a third oscillating tank voltage having a phase that lags ninety degrees behind the phase of the third oscillating drive voltage;

a fourth driver arranged to generate, in response to the third oscillating tank voltage, a fourth oscillating drive voltage in phase with the third oscillating tank voltage;

a fourth tank circuit arranged to generate, in response to the fourth oscillating drive voltage, a fourth oscillating tank voltage having a phase lagging ninety degrees behind the phase of the fourth oscillating drive voltage; and

The first driver is arranged to generate a first oscillating drive voltage in phase with the fourth oscillating tank voltage in response to the fourth oscillating tank voltage.

Similarly, a tenth preferred embodiment of the method may include:

generating, in response to the first oscillation driving voltage, a first oscillation tank voltage having a phase lagging ninety degrees behind a phase of the first oscillation driving voltage;

generating a second oscillating drive voltage in phase with the first oscillating tank voltage in response to the first oscillating tank voltage;

generating, in response to the second oscillating driving voltage, a second oscillating tank voltage having a phase lagging ninety degrees behind a phase of the second oscillating driving voltage;

generating a third oscillating drive voltage in phase with the second oscillating tank voltage in response to the second oscillating tank voltage;

generating, in response to the third oscillation driving voltage, a third oscillation tank voltage having a phase lagging ninety degrees behind a phase of the third oscillation driving voltage;

generating a fourth oscillating drive voltage in phase with the third oscillating tank voltage in response to the third oscillating tank voltage;

generating, in response to the fourth oscillation driving voltage, a fourth oscillation tank voltage having a phase lagging ninety degrees behind the phase of the fourth oscillation driving voltage; and

A first oscillating drive voltage in phase with the fourth oscillating tank voltage is generated in response to the fourth oscillating tank voltage.

The tenth preferred embodiment enables orthogonally correlated balanced oscillating signals to be generated in a low-complexity manner.

In an eleventh preferred embodiment of the oscillator circuit, the first tank circuit may be arranged to generate, in response to the first oscillating drive voltage, a first oscillating tank voltage having a phase leading the phase of the first oscillating drive voltage by ninety degrees, and the feedback stage may comprise:

a second driver arranged to generate, in response to the first oscillating tank voltage, a second oscillating drive voltage in phase with the first oscillating tank voltage;

a second tank circuit arranged to generate, in response to the second oscillating drive voltage, a second oscillating tank voltage having a phase leading the second oscillating drive voltage by ninety degrees;

a third driver arranged to generate, in response to the second oscillating tank voltage, a third oscillating drive voltage in phase with the second oscillating tank voltage;

a third tank circuit arranged to generate, in response to the third oscillating drive voltage, a third oscillating tank voltage having a phase leading the phase of the third oscillating drive voltage by ninety degrees;

a fourth driver arranged to generate, in response to the third oscillating tank voltage, a fourth oscillating drive voltage in phase with the third oscillating tank voltage;

a fourth tank circuit arranged to generate, in response to the fourth oscillating drive voltage, a fourth oscillating tank voltage having a phase leading the fourth oscillating drive voltage by ninety degrees; and

The first driver is arranged to generate a first oscillating drive voltage in phase with the fourth oscillating tank voltage in response to the fourth oscillating tank voltage.

Similarly, an eleventh preferred embodiment of the method may include:

generating, in response to the first oscillation driving voltage, a first oscillation tank voltage having a phase leading ninety degrees from a phase of the first oscillation driving voltage;

generating a second oscillating drive voltage in phase with the first oscillating tank voltage in response to the first oscillating tank voltage;

generating, in response to the second oscillation driving voltage, a second oscillation tank voltage having a phase leading ninety degrees from the phase of the second oscillation driving voltage;

generating a third oscillating drive voltage in phase with the second oscillating tank voltage in response to the second oscillating tank voltage;

generating, in response to the third oscillation driving voltage, a third oscillation tank voltage having a phase leading ninety degrees from a phase of the third oscillation driving voltage;

generating a fourth oscillating drive voltage in phase with the third oscillating tank voltage in response to the third oscillating tank voltage;

generating a fourth oscillation tank voltage having a phase leading ninety degrees from the phase of the fourth oscillation drive voltage in response to the fourth oscillation drive voltage; and

A first oscillating drive voltage in phase with the fourth oscillating tank voltage is generated in response to the fourth oscillating tank voltage.

The eleventh preferred embodiment enables orthogonally correlated balanced oscillation signals to be generated in a low-complexity manner.

In the tenth and eleventh preferred embodiments of the oscillator circuit, the first driver may include:

a first transistor having a drain coupled to the first power rail, a source coupled to the output of the first driver, and a gate coupled to the input of the first driver through a first coupling capacitor; and a second transistor having a drain coupled to the output of the first driver, a source coupled to the second power rail, and a gate coupled to the first power rail through a first resistor;

And the third driver may include:

a third transistor having a drain coupled to the first power rail, a source coupled to the output of the third driver, and a gate coupled to the input of the third driver through a second coupling capacitor; and a fourth transistor having a drain coupled to the output of the third driver and a source coupled to the first power rail through a second resistor;

wherein a gate of the first transistor is coupled to a gate of the fourth transistor, and a gate of the third transistor is coupled to a gate of the second transistor; and wherein the first, second, third, and fourth transistors are n-channel complementary metal oxide silicon (CMOS) transistors.

Using n-channel CMOS transistors rather than p-channel CMOS transistors for coupling the first and third tank circuits to the third power rail enables the transistors to be implemented with less integrated circuit chip area and less parasitic capacitance.

In a twelfth preferred embodiment of the oscillator circuit, the first tank circuit may be arranged to generate, in response to the first oscillating drive voltage, a first oscillating tank voltage having a phase that lags the phase of the first oscillating drive voltage by ninety degrees, and the feedback stage may comprise:

a second driver arranged to generate a second oscillating drive voltage by applying a signal inverted to the first oscillating tank voltage;

a second tank circuit arranged to generate, in response to the second oscillating drive voltage, a second oscillating tank voltage having a phase that lags ninety degrees behind the phase of the second oscillating drive voltage;

a third driver arranged to generate a third oscillating drive voltage by applying a signal inversion to the second oscillating tank voltage;

a third tank circuit arranged to generate, in response to the third oscillating drive voltage, a third oscillating tank voltage having a phase that lags ninety degrees behind the phase of the third oscillating drive voltage;

a fourth driver arranged to generate a fourth oscillating drive voltage by applying a signal inversion to the third oscillating tank voltage;

a fourth tank circuit arranged to generate, in response to the fourth oscillating drive voltage, a fourth oscillating tank voltage having a phase lagging ninety degrees behind the phase of the fourth oscillating drive voltage; and

A first driver is arranged to generate a first oscillating drive voltage by applying a signal inversion to the fourth oscillating tank voltage.

Similarly, a twelfth preferred embodiment of the method may include:

generating, in response to the first oscillation driving voltage, a first oscillation tank voltage having a phase lagging ninety degrees behind a phase of the first oscillation driving voltage;

generating a second oscillating drive voltage by applying a signal inversion to the first oscillating tank voltage;

generating, in response to the second oscillating driving voltage, a second oscillating tank voltage having a phase lagging ninety degrees behind a phase of the second oscillating driving voltage;

generating a third oscillating drive voltage by applying a signal inversion to the second oscillating tank voltage;

generating, in response to the third oscillation driving voltage, a third oscillation tank voltage having a phase lagging ninety degrees behind a phase of the third oscillation driving voltage;

generating a fourth oscillating drive voltage by applying a signal inversion to the third oscillating tank voltage;

generating, in response to the fourth oscillation driving voltage, a fourth oscillation tank voltage having a phase lagging ninety degrees behind the phase of the fourth oscillation driving voltage; and

The first oscillating drive voltage is generated by applying a signal inversion to the fourth oscillating tank voltage.

The twelfth preferred embodiment enables orthogonally correlated balanced oscillation signals to be generated in a low-complexity manner.

In a thirteenth preferred embodiment of the oscillator circuit, the first tank circuit may be arranged to generate, in response to the first oscillating drive voltage, a first oscillating tank voltage having a phase leading the phase of the first oscillating drive voltage by ninety degrees, and the feedback stage may comprise:

a second driver arranged to generate a second oscillating drive voltage by applying a signal inverted to the first oscillating tank voltage;

a second tank circuit arranged to generate, in response to the second oscillating drive voltage, a second oscillating tank voltage having a phase leading the second oscillating drive voltage by ninety degrees;

a third driver arranged to generate a third oscillating drive voltage by applying a signal inversion to the second oscillating tank voltage;

a third tank circuit arranged to generate, in response to the third oscillating drive voltage, a third oscillating tank voltage having a phase leading the phase of the third oscillating drive voltage by ninety degrees;

a fourth driver arranged to generate a fourth oscillating drive voltage by applying a signal inversion to the third oscillating tank voltage;

a fourth tank circuit arranged to generate, in response to the fourth oscillating drive voltage, a fourth oscillating tank voltage having a phase leading the fourth oscillating drive voltage by ninety degrees; and

A first driver is arranged to generate a first oscillating drive voltage by applying a signal inversion to the fourth oscillating tank voltage.

Similarly, a thirteenth preferred embodiment of the method may include:

generating, in response to the first oscillation driving voltage, a first oscillation tank voltage having a phase leading ninety degrees from a phase of the first oscillation driving voltage;

generating a second oscillating drive voltage by applying a signal inversion to the first oscillating tank voltage;

generating, in response to the second oscillation driving voltage, a second oscillation tank voltage having a phase leading ninety degrees from the phase of the second oscillation driving voltage;

generating a third oscillating drive voltage by applying a signal inversion to the second oscillating tank voltage;

generating, in response to the third oscillation driving voltage, a third oscillation tank voltage having a phase leading ninety degrees from a phase of the third oscillation driving voltage;

generating a fourth oscillating drive voltage by applying a signal inversion to the third oscillating tank voltage;

generating a fourth oscillation tank voltage having a phase leading ninety degrees from the phase of the fourth oscillation drive voltage in response to the fourth oscillation drive voltage; and

The first oscillating drive voltage is generated by applying a signal inversion to the fourth oscillating tank voltage.

The thirteenth preferred embodiment enables orthogonally correlated balanced oscillation signals to be generated in a low-complexity manner.

In third, fifth, sixth, seventh, tenth and twelfth preferred embodiments of the oscillator circuit, a capacitive element may be coupled between the first drive node and the first energy tank output, and an inductive element may be coupled between the first energy tank output and the first voltage rail.

In the first, second, fourth, eighth, ninth, eleventh and thirteenth preferred embodiments of the oscillator circuit, an inductive element may be coupled between the first drive node and the first energy tank output, and a capacitive element may be coupled between the first energy tank output and the first voltage rail.

The third to ninth preferred embodiments may include a variable capacitance element coupled between the first energy storage output and the second energy storage output. This feature enables the oscillation frequency to be varied.

In the tenth and eleventh preferred embodiments, the second driver may include:

a fifth transistor having a drain coupled to the third power rail, a source coupled to the output of the second driver, and a gate coupled to the input of the second driver through a third coupling capacitor; and

a sixth transistor having a drain coupled to the output of the second driver, a source coupled to the fourth power rail, and a gate coupled to the third power rail through a third resistor;

The fourth driver may include:

a seventh transistor having a drain coupled to the third power rail, a source coupled to the output of the fourth driver, and a gate coupled to the input of the fourth driver through a fourth coupling capacitor; and

an eighth transistor having a drain coupled to the output of the fourth driver, a source coupled to the fourth power rail, and a gate coupled to the third power rail through a fourth resistor;

wherein the gate of the fifth transistor may be coupled to the gate of the eighth transistor, and the gate of the seventh transistor may be coupled to the gate of the sixth transistor; and

The fifth, sixth, seventh and eighth transistors may be n-channel CMOS transistors.

Using n-channel CMOS transistors rather than p-channel CMOS transistors for coupling the second and fourth tank circuits to the third power rail and for coupling the fifth and seventh transistors to the fifth power rail enables the transistors to be implemented with less integrated circuit chip area and less parasitic capacitance.

In the second and fifth to ninth preferred embodiments of the oscillator circuit and their variants, the first tank circuit and the second tank circuit may have equal resonant frequencies. In the tenth to thirteenth preferred embodiments of the oscillator circuit, the first, second, third, and fourth tank circuits may have equal resonant frequencies. These features enable high power efficiency.

In the second and fifth to ninth preferred embodiments of the oscillator circuit and their variations, the first tank circuit and the second tank circuit can have equal capacitance and equal inductance. In the tenth to thirteenth preferred embodiments of the oscillator circuit, the first, second, third, and fourth tank circuits can have equal capacitance and equal inductance. These features enable close matching of the resonant frequencies.

There is also provided a wireless communication device comprising the oscillator circuit according to the first aspect.

Preferred embodiments are described, by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of a prior art oscillator.

FIG. 2 is a schematic diagram illustrating the operating principle of an oscillator employing voltage-driven series resonance.

FIG3 is a schematic diagram of an oscillator circuit.

4 to 8 are schematic diagrams illustrating different energy storage configurations of the energy storage circuit.

9 to 18 are schematic diagrams of oscillator circuits.

FIG19 is a schematic diagram of a driver.

FIG20 is a schematic diagram of an oscillator circuit with a supply for tuning.

21 is a graph of phase noise as a function of frequency for the oscillator circuit described with reference to FIG. 18 .

FIG22 is a schematic diagram of a wireless communication device.

DETAILED DESCRIPTION

In the following description, an oscillator topology is disclosed that employs series resonance between an inductor and a capacitor rather than the parallel resonance of conventional oscillators, and in which the energy tank formed by the inductor and capacitor is voltage-driven. The operating principle of an oscillator circuit employing voltage-driven or voltage-mode series resonance is described with reference to FIG2 . Referring to FIG2 , an inductor or inductive element L and a capacitor or capacitive element C are coupled in series, thereby forming an energy tank circuit T or resonator. The inductive element L is coupled between a voltage rail at ground potential and junction 1, and the capacitive element C is coupled between junction 1 and a drive node 2. Thus, the inductive element L and the capacitive element C are coupled together at junction 1. If a sinusoidal drive or excitation voltage V _D = V _dd .sin(ωt) (where V _dd is the voltage supplied by power supply node 5, ω is the resonant frequency of the series-coupled inductive element L and capacitive element C in radians per second, and t is time) is applied to drive node 2 by voltage generator G, a tank voltage V _T = Q _{V dd} .sin(ωt-π/2) (where Q is the quality factor of the series-coupled inductive element L and capacitive element C) is generated at junction 1. Thus, the magnitude of the tank voltage V _T is Q times the magnitude of the drive voltage V _D and is shifted (i.e., delayed) in phase by π/2 radians (i.e., 90°) relative to the drive voltage V _D. Typically, with today's integrated circuit processes, the quality factor Q can be ten, and thus the tank voltage V _T can be high when the drive voltage V _D is small. It is not essential that the drive voltage _VD is sinusoidal, and alternatively it may have, for example, a square or rectangular waveform, or an approximately square or rectangular waveform with finite rise and fall times.

For the voltage-mode series resonant oscillator illustrated in Figure 2, the magnitude of the tank voltage _VT can be expressed as:

k.ωL.V _dd /R _SEQ ＝kQV _BIAS (2)

Where ωL is the impedance of the inductive element L at the resonant frequency ω, _Vdd is the amplitude of the driving voltage _VD determined by the power supply node 5 to drive the series resonance, _RSEQ is the equivalent series energy storage resistance, Q is the quality factor of the energy storage including the inductive element L and the capacitive element C, and k is the proportionality factor.

Comparison between equations (1) and (2) reveals a significant difference between a voltage-mode series resonant oscillator and a current-mode parallel resonant oscillator. In a current-mode parallel resonant oscillator, the oscillation amplitude is proportional to the bias current I _BIAS , and if the tank quality factor Q is high (i.e., if the parallel tank resistance is high), the bias current I _BIAS is low. Furthermore, the supply voltage of a current-mode parallel resonant oscillator limits the maximum oscillation amplitude. In a voltage-mode series resonant oscillator, if the tank quality factor Q is high (i.e., the series tank resistance is low), the current drawn from the supply is high, and the oscillation amplitude is also high, with the tank quality factor Q being inversely proportional to the series tank resistance. Furthermore, in a voltage-mode series resonant oscillator, there is no direct limit imposed on the amplitude of the oscillation by the value of the supply voltage V _dd , which enables very high oscillation amplitudes in the presence of very low supply voltages if the tank quality factor Q is high enough. This can enable very low phase noise in the oscillator despite large currents from the supply.

Continuing with reference to FIG. 2 , the drive voltage _VD and the energy storage voltage _VT have a quadrature phase relationship, or more succinctly, quadrature. Specifically, the phase of the drive voltage _VD leads the phase of the energy storage voltage _VT by 90°. In other words, the phase of the drive voltage _VD lags the phase of the energy storage voltage _VT by 90°. However, as described below, alternative configurations of energy storage may be used in which different phase relationships apply between the drive voltage _VD and the energy storage voltage _VT . In certain embodiments of a series resonant oscillator circuit employing energy storage, the oscillator circuit itself can provide the drive voltage _VD . For example, the drive voltage _VD can be generated from the energy storage voltage _VT or by switching the power supply voltage _Vdd on and off. Where the drive voltage _VD is generated from the energy storage voltage _VT , it is necessary to ensure the desired phase relationship between the energy storage voltage _VT and the drive voltage _VD in order to provide positive feedback to maintain oscillation.

Referring to FIG3 , oscillator circuit 100 includes a first tank circuit T1 and a feedback (FB) stage F. First tank circuit T1 has a first drive node 12 at which a first oscillating drive voltage V _D1 is applied to first tank circuit T1, and a first tank output 13 at which the first oscillating tank voltage V _T1 is delivered from first tank circuit T1. First tank circuit T1 of FIG3 can have one of several alternative tank configurations (described below) with an inductive element L and a capacitive element C coupled in series between first drive node 12 and voltage rail 14. Feedback stage F has an input 17 coupled to first tank output 13 for receiving the first oscillating tank voltage V _T1 , and an output 18 coupled to first drive node 12 for delivering the first oscillating tank voltage V _D1 to first drive node 12. The feedback stage F has one of different feedback configurations as described below and is arranged to generate, in response to the first oscillating tank voltage _VT1 , a first oscillating drive voltage _VD1 that is in phase with an oscillating tank current _IT flowing in the inductive element L and the capacitive element C between the first drive node 12 and the voltage rail 14, thereby causing the oscillator circuit 100 to oscillate in a series resonant mode of the inductive element L and the capacitive element C.

The energy storage configurations of the first tank circuit T1 are described with reference to Figures 4 to 8. In each of these energy storage configurations, a capacitive element C and an inductive element L are coupled in series between a first drive node 12 and a voltage rail 14, which may be at ground potential or another potential.

4 , a first tank configuration of the first tank circuit T1 has a capacitive element C coupled between the first drive node 12 and the junction 11, and an inductive element L coupled between the junction 11 and the voltage rail 14. Thus, this first tank configuration corresponds to the configuration of the tank circuit T illustrated in FIG2 . The junction 11 is coupled to the first tank output 13. In this first tank configuration, the first oscillating tank voltage _VT1 present at the first tank output 13 has a phase that lags the phase of the first oscillating drive voltage _VD1 by 90°.

5 , a second tank configuration of the first tank circuit T1 has an inductive element L coupled between the first drive node 12 and the junction 11, and a capacitive element C coupled between the junction 11 and the voltage rail 14. The junction 11 is coupled to the first tank output 13. Thus, this second tank configuration corresponds to the first tank configuration illustrated in FIG. 4 , but with the positions of the inductive element L and the capacitive element C swapped. In this second tank configuration, the first oscillating tank voltage _VT1 has a phase that leads the first oscillating drive voltage _VD1 by 90°.

6 , a third energy storage configuration of the first energy storage circuit T1 has a sensor device S coupled in series with an inductive element L and a capacitive element C between the first drive node 12 and the voltage rail 14. Specifically, the sensor device S is coupled between the inductive element L and the capacitive element C, but in non-illustrated variations of the third energy storage configuration, the sensor device S may alternatively be coupled between the first drive node 12 and the capacitive element C, or between the inductive element L and the voltage rail 14. In further non-illustrated variations of the third energy storage configuration, the positions of the inductive element L and the capacitive element C may be reversed, such that the sensor device S is coupled between the inductive element L and the capacitive element C, the capacitive element C is coupled between the voltage rail 14 and the sensor device S, and the inductive element L is coupled between the first drive node 12 and the sensor device S, or the sensor device S is alternatively coupled between the first drive node 12 and the inductive element L, or the sensor device S is alternatively coupled between the voltage rail 14 and the capacitive element C. An oscillating tank current _IT flows in response to a first oscillating drive voltage _VD1 , and the sensor device S is arranged to generate a first oscillating tank voltage _VT1 in response to the oscillating tank current _IT . In particular, in the third tank configuration illustrated in FIG6 , the sensor device S includes a resistive element R, and the first tank output 13 includes a pair of terminals 13a, 13b coupled to different terminals of the resistive element R. The oscillating tank current _IT flows through the resistive element R, thereby causing a first oscillating tank voltage _VT1 to appear across the resistive element R and, therefore, between the pair of terminals 13a, 13b. In those variations of the third tank configuration in which one of the terminals of the resistive element R is coupled directly to the voltage rail 14 (rather than via the inductive element L or via the capacitive element C), the first tank output 13 may alternatively be coupled only to the other terminal of the resistive element R, i.e., not directly to the voltage rail 14. The oscillating tank current _IT is in phase with the first oscillating drive voltage _VD1 , and the first oscillating tank voltage _VT1 is in phase with the oscillating tank current _IT , and therefore in phase with the first oscillating drive voltage _VD1 .

7 , a fourth tank configuration of the first tank circuit T1 has a sensor device S coupled in series with an inductive element L and a capacitive element C between the first drive node 12 and the voltage rail 14. In particular, the sensor device S is coupled between the inductive element L and the capacitive element C, but the alternative positions of the sensor device S described above with reference to FIG6 also apply to the sensor device S illustrated in the tank configuration of FIG7 . An oscillating tank current _IT flows in response to the first oscillating drive voltage _VD1 , and the sensor device S illustrated in FIG7 is arranged to generate a first oscillating tank voltage _VT1 in response to the oscillating tank current _IT . In particular, in the fourth energy tank configuration illustrated in FIG7 , the sensor device S includes a transformer X having a primary winding _XP coupled in series with an inductive element _L and a capacitive element C between a first drive node 12 and a voltage rail 14; a secondary winding _Xs coupled to a pair of terminals 13a, _13b of a first energy tank output 13; and a resistive element R coupled between the pair of terminals 13a, 13b in parallel with the secondary winding _Xs . The resistive element R has a resistance that is smaller than the impedance of the secondary winding Xs at the oscillation frequency, for example, one-tenth or less. An oscillating tank current _IT flows through the primary winding _XP , thereby inducing an oscillating sensor current to flow in the secondary winding Xs. The oscillating sensor current flows in the secondary winding _Xs and the resistive element R, thereby inducing a first oscillating tank voltage _VT1 between the pair of terminals 13a, 13b. Alternatively, one of the pair of terminals 13a, 13b can be coupled to the voltage rail 14, or to another voltage rail. In this case, the first energy tank output 13 can instead include a single terminal from the pair of terminals 13a, 13b. The oscillating tank current _IT is in phase with the first oscillating drive voltage _VD1 , and thus the oscillating sensor current flowing in the secondary winding _XS and the resistive element R is in phase with the oscillating tank current _IT and the first oscillating drive voltage _VD1 . The flow of the oscillating sensor current in the resistive element R causes a first oscillating tank voltage _VT1 that is in phase with the oscillating sensor current. Therefore, the first oscillating tank voltage _VT1 at the first energy tank output 13 is in phase with the oscillating tank current _IT and, therefore, with the first oscillating drive voltage _VD1 . In a variation of the fourth energy storage configuration described with reference to FIG7 , the resistive element R may be replaced by a transimpedance amplifier having: inputs coupled to respective terminals of the secondary winding _XS , rather than the secondary winding _XS being directly coupled to the pair of terminals 13 a, 13 b of the first energy storage output 13; and an output of the transimpedance amplifier coupled to the first energy storage output 13 or the pair of terminals 13 a, 13 b of the first energy storage output 13.

Referring to FIG8 , a fifth energy storage configuration of the first energy tank circuit T1 includes an inductive element L and a capacitive element C as illustrated in FIG4 , or alternatively, they may be arranged as illustrated in FIG5 . The first energy tank circuit T1 of FIG8 further includes a sensor device S magnetically coupled to the inductive element L. Specifically, a coil M of the sensor device S is magnetically coupled to the inductive element L, thereby forming a transformer Y, with the inductive element L being the primary winding of the transformer Y and the coil M being the secondary winding of the transformer Y. The coil M is coupled to a pair of terminals 13a, 13b of the first energy tank output 13, and a resistive element R is coupled between the pair of terminals 13a, 13b in parallel with the coil M. The resistive element R has a resistance that is less than the impedance of the coil M at the oscillation frequency, for example, one-tenth or less. In response to the first oscillating drive voltage V _D1 , an oscillating tank current _IT flows through the inductive element L, thereby inducing an oscillating sensor current to flow in the coil M. An oscillating sensor current flows in coil M and resistive element R, thereby inducing a first oscillating tank voltage V _T1 across the pair of terminals 13 a, 13 b. Thus, the sensor device S of FIG8 is arranged to generate the first oscillating tank voltage V _T1 by magnetic induction in response to the oscillating tank current _IT . Alternatively, one of the pair of terminals 13 a, 13 b may be coupled to voltage rail 14, or to another voltage rail, in which case first tank output 13 may instead comprise a single terminal from the pair of terminals 13 a, 13 b. The oscillating tank current _IT is in phase with the first oscillating drive voltage V _D1 , and thus the oscillating sensor current flowing in coil M and resistive element R is in phase with both the oscillating tank current _IT and the first oscillating drive voltage V _D1 . The flow of the oscillating sensor current in resistive element R induces the first oscillating tank voltage V _T1 to be in phase with the oscillating sensor current. Thus, the first oscillating tank voltage _VT1 at the first tank output 13 is in phase with the oscillating tank current _IT and, therefore, with the first oscillating drive voltage _VD1 . In a variation of the fifth tank configuration described with reference to FIG8 , the resistive element R can be replaced by a transimpedance amplifier having: inputs coupled to respective terminals of the coil M, rather than the coil M being directly coupled to the pair of terminals 13a, 13b of the first tank output 13; and an output of the transimpedance amplifier coupled to the first tank output 13 or the pair of terminals 13a, 13b of the first tank output 13.

In modified versions of the third, fourth, or fifth energy storage configurations described above, or variations thereof, the connections of the sensor S to the pair of terminals 13a, 13b may be reversed, thereby inverting the first oscillating tank voltage _VT1 , or equivalently, modifying the phase of the first oscillating tank voltage _VT1 by 180°. In this case, although the oscillating tank current _IT is in phase with the first oscillating drive voltage _VD1 , the first oscillating tank voltage _VT1 is 180° out of phase with the oscillating tank current _IT and, therefore, with the first oscillating drive voltage _VD1 .

Embodiments of an oscillator circuit 100 are described below with reference to FIG9 to FIG19 , including different energy storage configurations of the first tank circuit T1 described with reference to FIG4 to FIG8 , and having different feedback configurations of the feedback stage F. Some of these embodiments include a second tank circuit T2 in addition to the first tank circuit T1 , and some of these embodiments further include a third tank circuit T3 and a fourth tank circuit T4 in addition to the first and second tank circuits T1 , T2 . Such second, third and fourth tank circuits T2, T3, T4 may each have a tank configuration corresponding to one of the first to fifth tank configurations described with reference to Figures 4 to 8, and thus have: respective second, third and fourth drive nodes (labeled 22, 32, 42), at which respective second, third and fourth oscillating drive voltages _VD2 , _VD3 , _VD4 are applied; and respective second, third and fourth tank outputs (labeled 23, 33, 43), at which respective second, third and fourth oscillating tank voltages _VT2 , _VT3 , _VT4 are delivered.

The specific tank configuration that each of the first, second, third, and fourth tank circuits T1, T2, T3, and T4 can have depends on whether the corresponding tank circuit is required to generate a corresponding oscillating tank voltage that is in phase, 90° ahead of, 90° behind, or 180° out of phase with the corresponding first, second, third, and fourth oscillating drive voltages V _D1 , V _D2 , V _D3 , and V _D4 . In particular, where the first, second, third, or fourth tank circuit T1, T2, T3, and T4 is required to generate a corresponding first, second, third, or fourth oscillating tank voltage V _T1 , V _T2 , V _T3 , and V _T4 that has a phase that lags the phase of the corresponding first, second, third, or fourth oscillating drive voltage by 90°, the first, second, third, or fourth tank circuit T1, T2, T3, and T4 can have the first tank configuration described with reference to FIG. Where the first, second, third or fourth tank circuit T1, T2, T3, T4 is required to generate a corresponding first, second, third or fourth oscillating tank voltage _VT1 , _VT2 , _VT3 , _VT4 having a phase leading the phase of the corresponding first, second, third or fourth oscillating drive voltage by 90°, the first, second, third or fourth tank circuit T1, T2, T3, T4 may have the second tank configuration described with reference to FIG5 . Where the first, second, third or fourth tank circuit T1, T2, T3, T4 is required to generate the corresponding first, second, third or fourth oscillating tank voltage _VT1 , _VT2 , _VT3 , _VT4 that is in phase with the corresponding first, second, third or fourth oscillating drive voltage _VD1 , _VD2 , _VD3 , _VD4 , the first, second, third or fourth tank circuit T1, T2, T3, T4 may have any of the third, fourth or fifth tank configurations described with reference to Figures 6, 7 and 8 or their variations. Where the first, second, third or fourth tank circuit T1, T2, T3, T4 is required to generate a respective first, second, third or fourth oscillating tank voltage _VT1 , _VT2 , _VT3 , _VT4 that is 180° out of phase with the respective first, second, third or fourth oscillating drive voltage _VD1 , _VD2 , _VD3 , _VD4 , the first, second, third or fourth tank circuit T1, T2, T3, T4 may have a modified version of any of the third, fourth or fifth tank configurations or variations thereof described with reference to Figures 6, 7 and 8.

Although the first to fifth tank configurations described with reference to Figures 4 to 8 have the same voltage rail 14, any or all of the first, second, third or fourth tank circuits T1, T2, T3, T4 may have different voltage rails providing different voltages.

Referring to FIG9 , in a first preferred embodiment, an oscillator circuit 110 includes a first tank circuit T1 and a feedback stage F as described with respect to the oscillator circuit 100 of FIG3 . The feedback stage F has a first feedback configuration in which the feedback stage F includes a first driver D1 coupled in series between an input 17 of the feedback stage F and an output 18 of the feedback stage F. The first tank circuit T1 generates a first oscillating tank voltage _VT1 at a first tank output 13 in response to a first oscillating drive voltage _VD1 applied at a first drive node 12. The first tank output 13 is coupled to the input 17 of the feedback stage F, and the first drive node 12 is coupled to the output 18 of the feedback stage F. In the first preferred embodiment, the first tank circuit T1 generates a first oscillating tank voltage _{VT1 that is in phase with the first oscillating drive voltage VD1 and} , therefore, can have any of the third, fourth, or fifth tank configurations described above with reference to FIG6 , FIG7 , or FIG8 , or variations thereof. The first driver D1 generates the first oscillating drive voltage V _D1 in response to the first oscillating energy tank voltage _VT1 and in phase therewith, so no phase change is introduced, which is indicated by "0°" in the figure. The first driver D1 can have a positive input terminal and a negative input terminal coupled to the pair of terminals 13a, 13b of the first energy tank output 13, in other words, a differential input.

In a variation of the oscillator circuit 110 described with reference to FIG9 , the first tank circuit T1 generates a first oscillating tank voltage V _T1 that is 180° out of phase with the first oscillating drive voltage V _D1 , and thus may have any of the modified third, fourth, or fifth tank configurations described above with reference to FIG6 , FIG7 , or FIG8 , or variations thereof, and the first driver D1 applies a signal inversion to the first oscillating tank voltage V _T1 , thereby introducing a 180° phase change so that the first oscillating drive voltage V _D1 (as required to maintain oscillation) is 180° out of phase with the first oscillating tank voltage V _T1 .

In some applications, an oscillator circuit is required that generates differential or balanced oscillating signals, that is, generates a pair of signals in which one signal (also called the first signal component) is the inverse of the other signal (or the second signal component).

Referring to FIG10 , in a second embodiment, an oscillator circuit 115 generates such a balanced oscillating signal and includes a first tank circuit T1 and a feedback stage F as described with respect to the oscillator circuit 100 of FIG3 , with the feedback stage F having a second feedback configuration. In the second feedback configuration, the feedback stage F includes a second tank circuit T2 having a second drive node 22 for applying a second oscillating drive voltage V _D2 to the second tank circuit T2 and a second tank output 23 for delivering the second oscillating tank voltage V _T2 from the second tank circuit T2. The second tank output 23 is coupled to the output 18 of the feedback stage F via a first driver D1, and the second drive node 22 is coupled to the input 17 of the feedback stage F via a second driver D2. The first tank circuit T1 generates the first oscillating tank voltage V _T1 at the first tank output 13 in response to and in phase with the first oscillating drive voltage V _D1 applied at the first drive node 12. The second driver D2 generates a second oscillating drive voltage V _{D2 that is 180° out of phase with the first oscillating tank voltage V T1 by} applying a signal inverted to (or, in other words, inverting) the first oscillating tank voltage V _T1 . The second tank circuit T2 generates a second oscillating tank voltage V _T2 at the second tank output 23 in response to the second oscillating drive voltage V _D2 applied at the second drive node 22 and in phase therewith. The first driver D1 generates the first oscillating drive voltage V _D1 that is 180° out of phase with the second oscillating tank voltage V _T2 by applying a signal inverted to the second oscillating tank voltage V _T2 . Thus, as required to maintain oscillation, the first oscillating drive voltage V _D1 is generated in response to and in phase with the first oscillating tank voltage V _T1 . The second oscillating tank voltage V _T2 is 180° out of phase with the first oscillating tank voltage V _T1 , and thus the first and second oscillating tank voltages V _T1 and V _T2 can be used as the first and second signal components of a balanced oscillating signal.

In the first variation of the oscillator circuit 115 described with reference to FIG10 , the first tank circuit T1 generates a first oscillating tank voltage _VT1 that is 180° out of phase with the first oscillating drive voltage _VD1 , and the second driver D2 does not apply a signal inversion to the first oscillating tank voltage _VT1 so that the first oscillating drive voltage _VD1 is 180° out of phase with the first oscillating tank voltage _VT1 .

In the second variation of the oscillator circuit 115 described with reference to FIG10 , the first tank circuit T1 generates a first oscillating tank voltage V _T1 that is 180° out of phase with the first oscillating tank voltage V _D1 , the second driver D2 does not apply a signal inversion to the first oscillating tank voltage V _T1 , and thus the second oscillating tank voltage V _D2 is in phase with the first oscillating tank voltage V _T1 . The second tank circuit T2 generates a second oscillating tank voltage V _T2 that is 180° out of phase with the second oscillating tank voltage V _D2 , and the first driver does not apply a signal inversion to the second oscillating tank voltage V _T2 , resulting in the first oscillating tank voltage V _D1 being 180° out of phase with the first oscillating tank voltage V _T1 . Therefore, the second oscillating tank voltage V _T2 is 180° out of phase with the first oscillating tank voltage V _T1 , and thus the first and second oscillating tank voltages V _T1 and V _T2 can be used as the first and second signal components of a balanced oscillation signal.

In some applications, an oscillator circuit is required that generates a pair of oscillating signals having a quadrature relationship (i.e., 90° out of phase). Such oscillator circuits have applications, for example, in generating local oscillator signals in wireless communication devices. For the oscillator circuit 115 and its first and second variants described with reference to FIG10 , the phase relationship of the first and second oscillating tank voltages _VT1 and _VT2 has been described because this phase relationship is relevant to ensuring positive feedback that maintains oscillation, and also because these oscillating voltages can be used by an external device. Alternatively, the external device can use an oscillating voltage generated at another location in the respective first and second tank circuits T1 and T2, and this oscillating voltage can have a phase different from that of the first and second oscillating tank voltages _VT1 and _VT2 . For example, where the first and second tank circuits T1, T2 have any of the tank configurations described with reference to Figures 6, 7, and 8, the external device can utilize the oscillating voltage generated at: the junction 15 between the capacitive element C and the sensor S, or the junction 19 between the inductive element L and the sensor S in the tank configurations of Figures 6 and 7; or the junction 11 between the capacitive element and the inductive element in the tank configuration of Figure 8. Thus, depending on the choice of tank configuration and its variants (which need not be the same for both the first and second tank circuits T1, T2), the external device can utilize an oscillating voltage that leads or lags the first and second oscillating tank voltages _VT1 , _VT2 by 90°, and in particular, can provide oscillating voltages having a quadrature relationship.

Referring to FIG11 , in a third embodiment, an oscillator circuit 120 includes a first tank circuit T1 and a feedback stage F as described with respect to the oscillator circuit 100 of FIG3 , the feedback stage F having a third feedback configuration. The first tank circuit T1 generates a first oscillating tank voltage _VT1 at a first tank output 13 in response to a first oscillating drive voltage _VD1 present at a first tank input 12, having a phase that lags the first oscillating drive voltage _VD1 by 90°. In the third feedback configuration, the feedback stage F includes a phase shift stage P arranged to apply a 90° phase lag, and a first driver D1. The phase shift stage P is coupled to an input 17 of the feedback stage F for receiving the first oscillating tank voltage _VT1 from the first tank circuit T1. The phase shift stage P generates a first intermediate oscillating voltage _VI1 at an input 14 of the phase shift stage P and in response to the first oscillating tank voltage VT1 _{, having a phase that lags the first oscillating tank voltage VT1 by} 90°. The output 14 of the phase shift stage P is coupled to the output 18 of the feedback stage F via a first driver D1, which generates a first oscillating drive voltage V _D1 in response to the first intermediate oscillating voltage V _I1 by applying a signal inversion to the first intermediate oscillating voltage V _I1 . Due to the 90° phase shift provided by the first tank circuit T1, the 90° phase shift provided by the phase shift stage P, and the inversion provided by the first driver D1 (corresponding to a 180° phase shift), the first oscillating drive voltage V _D1 has a phase that leads the first oscillating tank voltage V _T1 by 90°, as required to maintain oscillation. The first oscillating tank voltage V _T1 and the first intermediate oscillating voltage V _I1 differ in phase by 90° and can therefore be used as orthogonally related oscillating signals.

12 , in a fourth embodiment, the oscillator circuit 130 is the same as the third embodiment described with reference to FIG11 , except that the first tank circuit T1 is arranged to generate a first oscillating tank voltage V _T1 at the first tank output 13 in response to the first oscillating drive voltage V _D1 present at the first tank output 12, having a phase that leads the first oscillating drive voltage V _D1 by 90°, and the first driver D1 does not apply signal inversion but generates the first oscillating drive voltage V _D1 in phase with the first intermediate oscillating voltage V _I1 in response to the first intermediate oscillating voltage V _I1 . As a result, the first oscillating drive voltage V _D1 has a phase that leads the first oscillating tank voltage V _T1 by 90° as required to maintain oscillation. The first oscillating tank voltage V _T1 and the first intermediate oscillating voltage V _I1 differ in phase by 90° and can therefore be used as orthogonally related oscillating signals.

Referring to FIG13 , a fifth embodiment of an oscillator circuit 140 includes a first tank circuit T1 and a feedback stage F as described with respect to the oscillator circuit 100 of FIG3 , wherein the feedback stage F has a fourth feedback configuration. The first tank circuit T1 generates a first oscillating tank voltage _VT1 at a first tank output 13 in response to a first oscillating drive voltage VD1 present at a first tank input ₁₂ , having a phase that lags the first oscillating drive voltage _VD1 by 90°. In a third feedback configuration, the feedback stage F includes a first phase shift circuit P1, a second phase shift circuit P2, a first driver D1, a second driver D2, and a second tank circuit T2. The first phase shift circuit P1 is coupled to an input 17 of the feedback stage F and generates a first intermediate oscillating voltage _VI1 at an output 15 of the first phase shift circuit P1 in response to the first oscillating tank voltage _VT1 , having a phase that lags the first oscillating tank voltage _VT1 by 90°. The output 15 of the first phase-shift circuit P1 is coupled to a second drive node 22 of the second tank circuit T2 via a second driver D2. The second driver D2 generates a second oscillating drive voltage V _D2 in phase with the first intermediate oscillating voltage V _I1 in response to the first intermediate oscillating voltage V _I1 . The second oscillating drive voltage V _D2 is delivered to the second drive node 22. The second tank circuit T2 generates a second oscillating tank voltage _VT2 at a second tank output 23 in response to the second oscillating drive voltage V _D2 , having a phase that lags the phase of the second oscillating tank voltage V _D2 by 90°. The second phase-shift circuit P2 is coupled to the second tank output 23 of the second tank circuit _T2 and generates a second intermediate oscillating voltage VT2 at an output 16 of the second phase-shift circuit P2 in response to the second oscillating tank voltage _VT2 , having a phase that lags the phase of the second oscillating tank voltage _VT2 by 90°. The output 16 of the second phase shift circuit P2 is coupled to the output 18 of the feedback stage F via the first driver _D1 . The first driver D1 generates a first oscillating drive voltage V _D1 in phase with the second intermediate oscillating voltage V _I2 in response to the second intermediate oscillating voltage V I2. The first and second oscillating tank voltages V _T1 and V _T2 differ in phase by 180° and can therefore be used as the first and second signal components of a balanced oscillating signal. The first oscillating drive voltage V _D1 delivered from the output 18 of the feedback stage F has a phase that lags the first oscillating tank voltage V _T1 by 270° (or equivalently, leads the first oscillating tank voltage V _T1 by 90°) as required to maintain oscillation.

14 , in a sixth embodiment, the oscillator circuit 150 is identical to the fifth embodiment described with reference to FIG13 , except that the second driver D2 applies a signal inverted to the first intermediate oscillating voltage V _I1 so that the second oscillating drive voltage V _D2 generated by the second driver D2 is 180° out of phase with respect to the first intermediate oscillating voltage V _I1 , and the second tank circuit T2 is arranged to generate a second oscillating tank voltage _VT2 at the second tank output 23 in response to the second oscillating drive voltage V D2 present at the second tank input 22, having a phase that lags the phase of the second oscillating drive voltage V _D2 by 90 _° . Thus, the first and second oscillating tank voltages _VT1 , _VT2 differ in phase by 180° and can therefore be used as first and second signal components of a balanced oscillation signal, with the first oscillating drive voltage V _D1 having a phase that leads the phase of the first oscillating tank voltage _VT1 by 90° as required to sustain oscillation.

Referring to FIG15 , in a seventh embodiment, an oscillator circuit 160 generates a pair of signals having a quadrature relationship and includes a first tank circuit T1 and a feedback stage F as described with respect to the oscillator circuit 100 of FIG3 , with the feedback stage F having a fifth feedback configuration. The first tank circuit T1 generates a first oscillating tank voltage V _T1 at a first tank output 13 in response to a first oscillating drive voltage V _D1 applied at a first drive node 12, with a phase that lags the first oscillating drive voltage V _D1 by 90°. In the fifth feedback configuration, the feedback stage F includes a second tank circuit T2 having a second drive node 22 for applying a second oscillating drive voltage V _D2 to the second tank circuit T2 and a second tank output 23 for delivering the second oscillating tank voltage V _T2 from the second tank circuit T2. The second tank output 23 is coupled to the output 18 of the feedback stage F via a first driver D1, and the second drive node 22 is coupled to the input 17 of the feedback stage F via a second driver D2. The second driver D2 generates a second oscillating drive voltage V _D2 that is 180° out of phase with the first oscillating tank voltage V _T1 by applying an inverted signal to the first oscillating tank voltage V _T1 . The second tank circuit T2 generates a second oscillating tank voltage V _T2 at the second tank output 23 in response to the second oscillating drive voltage V _D2 applied at the second drive node 22, having a phase that lags the second oscillating drive voltage V _D2 by 90°. The first driver D1 generates the first oscillating drive voltage V _D1 in response to and in phase with the second oscillating tank voltage V _T2 . Therefore, as required to maintain oscillation, the first oscillating drive voltage V _D1 is generated in response to and in phase with the first oscillating tank voltage V _T1 . The second oscillating tank voltage V _T2 is 180° out of phase with the first oscillating tank voltage V _T1 , and thus the first and second oscillating tank voltages V _T1 and V _T2 can be used as the first and second signal components of a balanced oscillating signal.

16 , in the eighth embodiment, the oscillator circuit 170 is the same as the seventh embodiment described with reference to FIG. 15 , except that the first tank circuit T1 generates a first oscillating tank voltage _VT1 having a phase that leads the first oscillating drive voltage _VD1 by 90°, and the second tank circuit T2 generates a second oscillating tank voltage _VT2 having a phase that leads the second oscillating drive voltage _VD2 by 90°. Therefore, the first and second oscillating tank voltages _VT1 , _VT2 differ in phase by 90° and therefore have an orthogonal relationship, and the first oscillating drive voltage _VD1 has a phase that lags the first oscillating tank voltage _VT1 by 90° as required to maintain oscillation.

17 , in a ninth embodiment, an oscillator circuit 180 is the same as the seventh embodiment described with reference to FIG. 15 , except that a first tank circuit T1 generates a first oscillating tank voltage _VT1 having a phase that leads the first oscillating drive voltage _VD1 by 90°, and a second driver D2 does not apply signal inversion so that the second oscillating drive voltage _VD2 is in phase with the first oscillating tank voltage _VT1 . Again, the first and second oscillating tank voltages _VT1 , _VT2 differ in phase by 90° and therefore have an orthogonal relationship, and the first oscillating drive voltage _VD1 has a phase that lags the first oscillating tank voltage _VT1 by 90° as required to maintain oscillation.

In some applications, an oscillator circuit is required that generates a pair of signals in quadrature (i.e., 90° out of phase) and that are balanced, both having first and second signal components. In this case, four signal components are required, having phases of 0°, 90°, 180°, and 270°. Such an oscillator circuit has applications, for example, in generating local oscillator signals in wireless communication devices.

18 , in a tenth embodiment, an oscillator circuit 190 generates balanced quadrature-correlated oscillating signals and includes a first tank circuit T1 and a feedback stage F as described with respect to the oscillator circuit 100 of FIG3 , wherein the feedback stage F has a sixth feedback configuration. The first tank circuit T1 generates a first oscillating tank voltage _VT1 at a first tank output 13 in response to a first oscillating drive voltage _VD1 applied at a first drive node 12, and has a phase that lags the phase of the first oscillating drive voltage _VD1 by 90°. In the sixth feedback configuration, the feedback stage F includes: a second tank circuit T2 having a second drive node 22 for applying a second oscillating drive voltage V _D2 to the second tank circuit T2, and a second tank output 23 for delivering the second oscillating tank voltage VT2 from the second tank circuit _T2 ; a third tank circuit T3 having a third drive node 32 for applying a third oscillating drive voltage V _D3 to the third tank circuit T3, and a third tank output 33 for delivering the third oscillating tank voltage VT3 from the third tank circuit _T3 ; and a fourth tank circuit T4 having a fourth drive node 42 for applying a fourth oscillating drive voltage V _D4 to the fourth tank circuit T4, and a fourth tank output 43 for delivering the fourth oscillating tank voltage VT4 from the fourth tank circuit _T4 . Feedback stage F further includes a first driver D1 having an input 703 coupled to fourth energy tank output 43 and an output 704 coupled to output 18 of feedback stage F and thereby to first drive node 12; a second driver D2 having an input 707 coupled to input 17 of feedback stage F and thereby to first energy tank output 13, and an output 708 coupled to second drive node 22; a third driver D3 having an input 733 coupled to second energy tank output 23 and an output 734 coupled to third drive node 32; and a fourth driver D4 having an input 737 coupled to third energy tank output 33 and an output 738 coupled to fourth drive node 42. The first driver D1 generates a first oscillating drive voltage V _D1 in response to and in phase with the fourth oscillating tank voltage _VT4 . The second driver D2 generates a second oscillating drive voltage V _D2 in response to and in phase with the first oscillating tank voltage _VT1 . The third driver D3 generates a third oscillating drive voltage V _D3 in response to the second oscillating tank voltage _VT2 and in phase therewith. The fourth driver D4 generates a fourth oscillating drive voltage V _D4 in response to the third oscillating tank voltage _VT3 and in phase therewith. The second oscillating tank voltage _VT2 has a phase that lags the first oscillating tank voltage _VT1 by 90°, the third oscillating tank voltage _VT3 has a phase that lags the second oscillating tank voltage _VT2 by 90°, and the fourth oscillating tank voltage _VT4 has a phase that lags the third oscillating tank voltage _VT3 by 90°, thereby providing two orthogonally related balanced oscillation signals. As required to maintain oscillation, the first oscillating drive voltage V _D1 leads the first oscillating tank voltage _VT1 by 90°.

The first variation of the oscillator circuit 190 described with reference to FIG18 differs from the oscillator circuit 190 in that each of the first, second, third and fourth drivers D1, D2, D3, D4 provides a signal inversion so that the second oscillating drive voltage _VD2 is 180° out of phase with the first oscillating energy tank voltage _VT1 , the third oscillating drive voltage _VD3 is 180° out of phase with the second oscillating energy tank voltage _VT2 , the fourth oscillating drive voltage _VD4 is 180° out of phase with the third oscillating energy tank voltage _VT3 , and the first oscillating drive voltage _VD1 is 180° out of phase with the fourth oscillating energy tank voltage _VT4 .

The second variation of the oscillator circuit 190 described with reference to FIG18 differs from the oscillator 190 in that the first tank circuit _T1 generates a first oscillating tank voltage _VT1 having a phase leading the first oscillation drive voltage VD1 by 90°, the second tank circuit _T2 generates a second oscillating tank voltage VT2 having a phase leading the second oscillation drive voltage _VD2 by 90°, the third tank circuit T3 generates a third oscillating tank voltage _VT3 having a phase leading the third oscillation drive voltage _VD3 by 90°, and the fourth tank circuit T4 generates a fourth oscillating tank voltage _VT4 having a phase leading the fourth oscillation drive voltage _VD4 by 90°.

The third variation of the oscillator circuit 190 described with reference to FIG18 differs from the oscillator circuit 190 in that each of the first, second, third and fourth drivers D1, D2, D3, D4 provides a signal inversion so that the second oscillating drive voltage _VD2 is 180° out of phase with the first oscillating energy tank voltage _VT1 , the third oscillating drive voltage _VD3 is 180° out of phase with the second oscillating energy tank voltage _VT2 , the fourth oscillating drive voltage _VD4 is 180° out of phase with the third oscillating energy tank voltage _VT3 , and the first oscillating drive voltage _VD1 is 180° out of phase with the fourth oscillating energy tank voltage _VT4 . In addition, the first tank circuit T1 generates a first oscillation tank voltage _VT1 having a phase leading the first oscillation drive voltage _VD1 by 90°, the second tank circuit T2 generates a second oscillation tank voltage _VT2 having a phase leading the second oscillation drive voltage _VD2 by 90°, the third tank circuit T3 generates a third oscillation tank voltage _VT3 having a phase leading the third oscillation drive voltage _VD3 by 90°, and the fourth tank circuit T4 generates a fourth oscillation tank voltage _VT4 having a phase leading the fourth oscillation drive voltage _VD4 by 90°.

Each of the first, second, and third variations of the oscillator circuit 190 described with reference to FIG. 18 generates balanced, quadrature-correlated oscillating signals.

Referring to FIG19 , a preferred embodiment of the first, second, third, and fourth drivers D1, D2, D3, and D4 of the oscillator circuit 190 illustrated in and described with reference to FIG18 is illustrated. The first driver D1 includes first and second transistors N1 and N2, which are n-channel CMOS transistors. The first transistor N1 has a drain N1d coupled to a first power rail 70 supplying a power supply voltage _Vdd1 ; a gate N1g coupled to an input 703 of the first driver D1 via a first coupling capacitor _Cb1 ; and a source N1s coupled to an output 704 of the first driver D1. The second transistor N2 has a drain N2d coupled to the output 704 of the first driver D1; a source coupled to a second power rail ₇₁ supplying a power supply voltage Vss1; and a gate N2g coupled to the first power rail 70 via a first resistor R1 for biasing. The third driver D3 includes third and fourth transistors N3 and N4, which are n-channel CMOS transistors. The third transistor N3 has a drain N3g coupled to the first power rail 70 and a gate N3g coupled to the third driver D3. The fourth transistor N4 has a drain N4d coupled to the output 734 of the first driver D1, a source N4s coupled to the second power rail 71, and a gate N4g coupled to the first power rail 70 via a second resistor R2 for biasing.

Continuing with FIG19 , the second driver D2 includes fifth and sixth transistors N5 and N6, which are n-channel CMOS transistors. The fifth transistor N5 has a drain N5d coupled to a third power rail 72 supplying a power supply voltage _Vdd2 (which may be the same as the power supply voltage _Vdd1 ); a gate N5g coupled to the input 707 of the second driver D2 via a third coupling capacitor _Cb3 ; and a source N5s coupled to the output 708 of the second driver D2. The sixth transistor N6 has a drain N6d coupled to the output 708 of the second driver D2; a source coupled to a fourth power rail 73 supplying a power supply voltage _Vss2 (which may be the same as the power supply voltage _Vss1 ); and a gate N6g coupled to the third power rail 72 via a third resistor R3 for biasing. The fourth driver D4 includes seventh and eighth transistors N7 and N8, which are n-channel CMOS transistors. The seventh transistor N7 has a drain N7g coupled to the second power rail 72, a gate N7g coupled to the input 737 of the fourth driver D4, and a source N7s coupled to the output 738 of the fourth driver D4. The eighth transistor N8 has a drain N8d coupled to the output 738 of the fourth driver D4, a source N8s coupled to the fourth power rail 73, and a gate N8g coupled to the third power rail 72 via a fourth resistor R4 for biasing.

The first coupling capacitor _Cb1 , together with the parasitic capacitance (not shown) of the gates N1g and N4g of the first and fourth transistors N1 and N4, respectively, forms a capacitive voltage divider for reducing the amplitude of the voltage applied to the gates N1g and N4g of the first and fourth transistors N1 and N4, respectively, to a tolerable value in response to the fourth oscillating tank voltage _VT4 present at the input 703 of the first driver D1. Similarly, the second coupling capacitor _Cb2 , together with the parasitic capacitance (not shown) of the gates N2g and N3g of the second and third transistors N2 and N3, respectively, forms a capacitive voltage divider for reducing the amplitude of the voltage applied to the gates N2g and N3g of the second and third transistors N2 and N3, respectively, to a tolerable value in response to the second oscillating tank voltage VT2 present at the input 733 of the third driver _D3 . Similarly, the third and fourth coupling capacitors _Cb3 , _Cb4 perform the corresponding function of reducing the magnitude of the voltage applied to the gates N5g, N6g, N7g, N8g of the fifth, sixth, seventh and eighth transistors N5, N6, N7, N8.

In those described embodiments of the oscillator circuit that include more than one tank circuit, the tank circuits have identical or substantially identical resonant frequencies, for example, within 5%. This contributes to high power efficiency. In particular, their respective inductive elements may have identical or substantially identical inductances, and their respective capacitive elements may have identical or substantially identical capacitances.

Each of the first, second, third, and fourth drivers D1, D2, D3, and D4 can be a linear or nonlinear amplifier, but preferably, for high power efficiency, is arranged to switch between two different voltage levels (typically the supply voltage) depending on the voltage at their respective inputs relative to a threshold. Thus, the respective first, second, third, and fourth oscillating drive voltages V _D1 , V _D2 , V _D3 , and V _D4 can have a square or rectangular waveform, or an approximately square or rectangular waveform with finite rise and fall times. The first, second, third, and fourth drivers D1, D2, D3, and D4 are arranged to deliver power to the respective first, second, third, and fourth tank circuits T1, T2, T3, and T4 in order to maintain oscillation. While embodiments of the first, second, third, and fourth drivers D1, D2, D3, and D4 and variations thereof have been described with reference to FIG19 with respect to the oscillator circuit 190 described with reference to FIG18 , these embodiments may also be employed in other oscillator circuits in the disclosed oscillator circuit. Furthermore, while embodiments have been described in which the first, second, third and fourth drivers D1, D2, D3, D4 include only n-channel CMOS transistors, this is not essential and variations including both p-channel CMOS transistors and n-channel CMOS transistors may instead be employed.

Optionally, a supply for tuning the oscillation frequency can be added to the disclosed oscillator circuit. For example, FIG20 illustrates the oscillator circuit 160 described with reference to FIG15 , but with an additional supply for tuning, including a variable capacitance element _CV coupled to the first energy tank output ₁₃ via a first additional capacitor _Cx and to the second energy tank output 23 via a second additional capacitor _Cy . The first and second additional capacitors _Cx , _Cy are included to attenuate the first and second oscillating energy tank voltages _VT1 , _VT2 applied to the variable capacitance element _CV to values tolerable by the variable capacitance element _CV . Depending on the voltage level tolerable by the variable capacitance element _CV , the first and second additional capacitors _Cx , _Cy can be omitted, and the variable capacitance element _CV instead directly coupled to the first and second energy tank outputs 13, 23, respectively. Typically, a frequency tuning range of approximately 10% can be provided by the variable capacitance element _CV .

FIG21 illustrates the phase noise of the oscillator circuit 190 described with reference to FIG18 as a function of frequency offset from the oscillation frequency for the following case: the inductive element of each of the first, second, third, and fourth tank circuits T1, T2, T3, T4 has an inductance of 0.5 nH, the oscillator circuit 190 is arranged to oscillate at an oscillation frequency of 6 GHz, the voltage rail 14 of each of the first, second, third, and fourth tank circuits T1, T2, T3, T4 provides 0.6 V, and the oscillator circuit 190 draws a current of 110 mA. Graph a) of FIG21 represents the total phase noise, graph b) represents the contribution of thermal noise to the total phase noise, and graph c) represents the contribution of flicker noise to the total phase noise. Despite the low supply voltage, very low phase noise is achieved, for example, -150 dBc/Hz at a 10 MHz offset from the oscillation frequency. Such a low phase noise level would require much larger capacitance and much lower inductance in a parallel resonant oscillator, resulting in a far less robust design.

22 , a wireless communication device 900 (such as a mobile phone) includes an antenna 910 coupled to an input of a low noise amplifier 920 for amplifying a radio frequency (RF) signal received by the antenna 910. The output of the low noise amplifier 920 is coupled to a first input 932 of a downconversion stage 930, which is used to downconvert the amplified RF signal to baseband by mixing the amplified RF signal with an orthogonally related component of a local oscillator signal present at a second input 934 of the downconversion stage 930. The output 936 of the downconversion stage 930 is coupled to an input 952 of a digital signal processor (DSP) 950 via an analog-to-digital converter (ADC) 940 that digitizes the baseband signal. The DSP 950 demodulates and decodes the digitized baseband signal. The DSP 950 also generates a baseband signal to be transmitted at an output 954 of the DSP 950. Output 954 of DSP 950 is coupled to a first input 972 of an upconversion stage 970 via a digital-to-analog converter (DAC) 960. Upconversion stage 970 upconverts the baseband signal to RF for transmission by mixing it with quadrature-related components of a local oscillator signal present at a second output 974 of upconversion stage 970. Output 976 of upconversion stage 970 is coupled to antenna 910 via a power amplifier 980, which amplifies the RF signal for transmission. Wireless communication device 900 includes oscillator circuit 100, as described with reference to FIG. 3 , which, in this embodiment, generates a first oscillating tank voltage V _T1 at a first tank output 13. The first tank output 13 of oscillator circuit 100 is coupled to an input 992 of a quadrature-phase generating element 990. Quadrature-phase generating element 990 generates quadrature-related components of the local oscillator signal at a first output 994 and a second output 996 of quadrature-phase generating element 990 from the first oscillating tank voltage V _T1 . A first output 994 of the quadrature phase generating element 990 is coupled to a second input 934 of the down-conversion stage 930, and a second output 996 of the quadrature phase generating element 990 is coupled to a second input 974 of the up-conversion stage 970. In applications where the local oscillator signal is required to be a balanced signal, the oscillator circuit 100 may employ any of the embodiments for generating a balanced oscillating signal, in particular the oscillator circuits 115, 140, 150, 160 described with reference to FIG. 10 , FIG. 13 , FIG. 14 , and FIG. 15 .

In a variation of the wireless communication device 900 , the oscillator circuit 100 and the quadrature phase generating element 990 may be replaced by one of the oscillator circuits 120 , 130 , 170 , 180 described with reference to FIGS. 11 , 12 , 16 , and 17 , which generate quadrature-correlated oscillation signals or quadrature-correlated balanced oscillation signals.

Other variations and modifications will be apparent to those skilled in the art. Such variations and modifications may involve equivalent and other features that are known and may be used instead of or in addition to the features described herein. Features described in the context of separate embodiments may be provided in combination in a single embodiment. Conversely, features described in the context of a single embodiment may also be provided separately or in any suitable subcombination.

It should be noted that the term "comprising" does not exclude other elements or steps, the term "a" or "an" does not exclude a plurality, a single feature may perform the functions of several features recited in the claims, and reference signs in the claims should not be construed as limiting the scope of the claims. It should also be noted that where a component is described as being "arranged to" or "adapted to" perform a particular function, it may be appropriate to consider the component as being merely "suitable for" performing that function, depending on the context in which the component is considered. Throughout the text, these terms are generally considered to be interchangeable, unless the specific context dictates otherwise. It should also be noted that the drawings are not necessarily to scale; instead, emphasis is generally placed on illustrating the principles of the invention.

Claims (25)

1. An oscillator circuit (100), comprising: The first energy storage circuit (T1) includes an inductive element (L) and a capacitive element (C) coupled in series between the voltage rail (14) and the first drive node (12); and The feedback stage (F) is coupled to the first energy storage output (13) of the first energy storage circuit (T1) and to the first drive node (12); The feedback stage (F) is arranged to generate a first oscillating drive voltage at the first drive node (12) in phase with the oscillating drive current flowing in the inductive element (L) and the capacitive element (C) in response to a first oscillating energy storage voltage present at the first energy storage output (13), thereby causing the oscillator circuit (100) to oscillate in a series resonant mode of the inductive element (L) and the capacitive element (C). 2. The oscillator circuit (100) according to claim 1, wherein the feedback stage (F) is arranged to generate the first oscillation drive voltage having a substantially rectangular waveform. 3. The oscillator circuit (110) according to claim 1 or claim 2, wherein the first energy storage circuit (T1) is arranged to generate a first oscillating energy storage voltage in phase with the first oscillating drive voltage in response to the first oscillating drive voltage, and wherein the feedback stage (F) includes a first driver (D1) arranged to generate a first oscillating drive voltage in phase with the first oscillating energy storage voltage in response to the first oscillating energy storage voltage. 4. The oscillator circuit (110) according to claim 1 or claim 2, wherein the first energy storage circuit (T1) is arranged to generate a first oscillating energy storage voltage that is 180 degrees out of phase with the first oscillating drive voltage in response to the first oscillating drive voltage, and wherein the feedback stage (F) includes a first driver (D1) arranged to generate the first oscillating drive voltage that is 180 degrees out of phase with the first oscillating energy storage voltage by applying a signal inverted to the first oscillating energy storage voltage in response to the first oscillating energy storage voltage. 5. The oscillator circuit (115) according to claim 1 or claim 2, wherein the first energy storage circuit (T1) is arranged to generate a first oscillating energy storage voltage in phase with the first oscillating drive voltage in response to the first oscillating drive voltage, and wherein the feedback stage (F) comprises: The second driver (D2) is arranged to generate a second oscillation drive voltage by applying a signal inverted to the first oscillation energy storage voltage; The second energy storage circuit (T2) is arranged to generate a second oscillating energy storage voltage in phase with the second oscillating drive voltage in response to the second oscillating drive voltage; and The first driver (D1) is arranged to generate the first oscillation drive voltage by applying a signal inverted to the second oscillation energy storage voltage. 6. The oscillator circuit (115) according to claim 1 or claim 2, wherein the first energy storage circuit (T1) is arranged to generate a first oscillating energy storage voltage that is 180 degrees out of phase with the first oscillating drive voltage in response to the first oscillating drive voltage, and wherein the feedback stage (F) comprises: The second driver (D2) is arranged to generate a second oscillation drive voltage by applying a signal inverted to the first oscillation energy storage voltage; The second energy storage circuit (T2) is arranged to generate a second oscillating energy storage voltage in phase with the second oscillating drive voltage in response to the second oscillating drive voltage; and The first driver (D1) is arranged to generate the first oscillating drive voltage that is in phase with the second oscillating energy storage voltage. 7. The oscillator circuit (115) according to claim 1 or claim 2, wherein the first energy storage circuit (T1) is arranged to generate a first oscillating energy storage voltage that is 180 degrees out of phase with the first oscillating drive voltage in response to the first oscillating drive voltage, and wherein the feedback stage (F) comprises: The second driver (D2) is arranged to generate a second oscillating drive voltage in phase with the first oscillating energy storage voltage in response to the first oscillating energy storage voltage; The second energy storage circuit (T2) is arranged to generate a second oscillating energy storage voltage that is 180 degrees out of phase with the second oscillating drive voltage in response to the second oscillating drive voltage: and The first driver (D1) is arranged to generate the first oscillating drive voltage in phase with the second oscillating energy storage voltage in response to the second oscillating energy storage voltage. 8. The oscillator circuit (110, 115) according to claim 3, wherein the first energy storage circuit (T1) includes a sensor device (S) arranged to generate the first oscillating energy storage voltage in response to the first oscillating energy storage current. 9. The oscillator circuit (110, 115) according to claim 8, wherein the sensor device (S) includes one of a resistive element (R) and a transformer (X) coupled in series with the inductive element (L) and the capacitive element (C) between the voltage rail (14) and the first drive node (12). 10. The oscillator circuit (110, 115) according to claim 8, wherein the sensor device (S) is magnetically coupled to the inductive element (L) for generating the first oscillating energy storage voltage by magnetic induction in response to the first oscillating energy storage current. 11. The oscillator circuit (120) according to claim 1 or claim 2, wherein the first energy storage circuit (T1) is arranged to generate a first oscillating energy storage voltage having a phase lag of 90 degrees compared to the first oscillating drive voltage in response to the first oscillating drive voltage, and wherein the feedback stage (F) includes a phase shift stage (P) arranged to generate a first intermediate oscillating voltage by applying a 90-degree phase lag to the first oscillating energy storage voltage, and the feedback stage (F) further includes a first driver (D1) arranged to generate the first oscillating drive voltage by applying a signal inverted to the first intermediate oscillating voltage. 12. The oscillator circuit (130) according to claim 1 or claim 2, wherein the first energy storage circuit (T1) is arranged to generate a first oscillating energy storage voltage having a phase leading the first oscillating drive voltage by ninety degrees in response to the first oscillating drive voltage, and wherein the feedback stage (F) includes a phase shift stage (P) arranged to generate a first intermediate oscillating voltage by applying a ninety-degree phase lag to the first oscillating energy storage voltage, the feedback stage (F) further including a first driver (D1) arranged to generate the first oscillating drive voltage in response to and in phase with the first intermediate oscillating voltage. 13. The oscillator circuit (140) according to claim 1 or claim 2, wherein the first energy storage circuit (T1) is arranged to generate a first oscillating energy storage voltage having a phase lag of ninety degrees behind the first oscillating drive voltage in response to the first oscillating drive voltage, and wherein the feedback stage (F) comprises: The first phase shift circuit (P1) is arranged to generate a first intermediate oscillation voltage by applying a 90-degree phase lag to the first oscillation energy storage voltage. The second driver (D2) is arranged to generate a second oscillation drive voltage in phase with the first intermediate oscillation voltage in response to the first intermediate oscillation voltage; The second energy storage circuit (T2) is arranged to generate a second oscillating energy storage voltage having a phase that lags ninety degrees behind the phase of the second oscillating drive voltage in response to the second oscillating drive voltage. The second phase shift circuit (P2) is arranged to generate a second intermediate oscillation voltage by applying a 90-degree phase lag to the second oscillation energy storage voltage; and The first driver (D1) is arranged to generate the first oscillation drive voltage in phase with the second intermediate oscillation voltage in response to the second intermediate oscillation voltage. 14. The oscillator circuit (150) according to claim 1 or claim 2, wherein the first energy storage circuit (T1) is arranged to generate a first oscillating energy storage voltage having a phase lag of 90 degrees behind the first oscillating drive voltage in response to the first oscillating drive voltage, and wherein the feedback stage (F) comprises: The first phase shift circuit (P1) is arranged to generate a first intermediate oscillation voltage by applying a 90-degree phase lag to the first oscillation energy storage voltage. The second driver (D2) is arranged to generate a second oscillation drive voltage by inverting a signal and applying it to the first intermediate oscillation voltage; The second energy storage circuit (T2) is arranged to generate a second oscillating energy storage voltage having a phase that leads the phase of the second oscillating drive voltage by ninety degrees in response to the second oscillating drive voltage. The second phase shift circuit (P2) is arranged to generate a second intermediate oscillation voltage by applying a 90-degree phase lag to the second oscillation energy storage voltage; and The first driver (D1) is arranged to generate the first oscillation drive voltage in phase with the second intermediate oscillation voltage in response to the second intermediate oscillation voltage. 15. The oscillator circuit (160) according to claim 1 or claim 2, wherein the first energy storage circuit (T1) is arranged to generate a first oscillating energy storage voltage having a phase lag of 90 degrees behind the first oscillating drive voltage in response to the first oscillating drive voltage, and wherein the feedback stage (F) comprises: The second driver (D2) is arranged to generate a second oscillation drive voltage by applying a signal inverted to the first oscillation energy storage voltage; The second energy storage circuit (T2) is arranged to generate a second oscillating energy storage voltage having a phase lag of ninety degrees behind the second oscillating drive voltage in response to the second oscillating drive voltage; and The first driver (D1) is arranged to generate the first oscillating drive voltage in phase with the second oscillating energy storage voltage in response to the second oscillating energy storage voltage. 16. The oscillator circuit (170) according to claim 1 or claim 2, wherein the first energy storage circuit (T1) is arranged to generate a first oscillating energy storage voltage having a phase leading the first oscillating drive voltage by ninety degrees in response to the first oscillating drive voltage, and wherein the feedback stage (F) comprises: The second driver (D2) is arranged to generate a second oscillation drive voltage by applying a signal inverted to the first oscillation energy storage voltage; The second energy storage circuit (T2) is arranged to generate a second oscillating energy storage voltage having a phase leading the second oscillating driving voltage by ninety degrees in response to the second oscillating driving voltage; and The first driver (D1) is arranged to generate the first oscillating drive voltage in phase with the second oscillating energy storage voltage in response to the second oscillating energy storage voltage. 17. The oscillator circuit (180) according to claim 1 or claim 2, wherein the first energy storage circuit (T1) is arranged to generate a first oscillating energy storage voltage having a phase leading the first oscillating drive voltage by ninety degrees in response to the first oscillating drive voltage, and wherein the feedback stage (F) comprises: The second driver (D2) is arranged to generate a second oscillating drive voltage in phase with the first oscillating energy storage voltage in response to the first oscillating energy storage voltage; The second energy storage circuit (T2) is arranged to generate a second oscillating energy storage voltage having a phase lag of ninety degrees behind the second oscillating drive voltage in response to the second oscillating drive voltage; and The first driver (D1) is arranged to generate the first oscillating drive voltage in phase with the second oscillating energy storage voltage in response to the second oscillating energy storage voltage. 18. The oscillator circuit (190) according to claim 1 or claim 2, wherein the first energy storage circuit (T1) is arranged to generate a first oscillating energy storage voltage having a phase lag of ninety degrees behind the phase of the first oscillating drive voltage in response to the first oscillating drive voltage, and wherein the feedback stage (F) comprises: The second driver (D2) is arranged to generate a second oscillating drive voltage in phase with the first oscillating energy storage voltage in response to the first oscillating energy storage voltage; The second energy storage circuit (T2) is arranged to generate a second oscillating energy storage voltage having a phase that lags ninety degrees behind the phase of the second oscillating drive voltage in response to the second oscillating drive voltage. The third driver (D3) is arranged to generate a third oscillating drive voltage in phase with the second oscillating energy storage voltage in response to the second oscillating energy storage voltage; The third energy storage circuit (T3) is arranged to generate a third oscillating energy storage voltage having a phase that lags behind the third oscillating driving voltage by ninety degrees in response to the third oscillating driving voltage. The fourth driver (D4) is arranged to generate a fourth oscillating drive voltage in phase with the third oscillating energy storage voltage in response to the third oscillating energy storage voltage; The fourth energy storage circuit (T4) is arranged to generate a fourth oscillating energy storage voltage having a phase lag of ninety degrees compared to the fourth oscillating drive voltage in response to the fourth oscillating drive voltage; and A first driver (D1) is arranged to generate a first oscillating drive voltage that is in phase with the fourth oscillating energy storage voltage in response to the fourth oscillating energy storage voltage. 19. The oscillator circuit (190) according to claim 1 or claim 2, wherein the first energy storage circuit (T1) is arranged to generate a first oscillating energy storage voltage having a phase leading the first oscillating drive voltage by ninety degrees in response to the first oscillating drive voltage, and wherein the feedback stage (F) comprises: The second driver (D2) is arranged to generate a second oscillating drive voltage in phase with the first oscillating energy storage voltage in response to the first oscillating energy storage voltage; The second energy storage circuit (T2) is arranged to generate a second oscillating energy storage voltage having a phase that leads the phase of the second oscillating drive voltage by ninety degrees in response to the second oscillating drive voltage. The third driver (D3) is arranged to generate a third oscillating drive voltage in phase with the second oscillating energy storage voltage in response to the second oscillating energy storage voltage; The third energy storage circuit (T3) is arranged to generate a third oscillating energy storage voltage having a phase that leads the phase of the third oscillating driving voltage by ninety degrees in response to the third oscillating driving voltage. The fourth driver (D4) is arranged to generate a fourth oscillating drive voltage in phase with the third oscillating energy storage voltage in response to the third oscillating energy storage voltage; The fourth energy storage circuit (T4) is arranged to generate a fourth oscillating energy storage voltage having a phase leading the fourth oscillating drive voltage by ninety degrees in response to the fourth oscillating drive voltage; and A first driver (D1) is arranged to generate a first oscillating drive voltage that is in phase with the fourth oscillating energy storage voltage in response to the fourth oscillating energy storage voltage. 20. The oscillator circuit (190) according to claim 1 or claim 2, wherein the first energy storage circuit (T1) is arranged to generate a first oscillating energy storage voltage having a phase lag of ninety degrees behind the first oscillating drive voltage in response to the first oscillating drive voltage, and wherein the feedback stage (F) comprises: The second driver (D2) is arranged to generate a second oscillation drive voltage by applying a signal inverted to the first oscillation energy storage voltage; The second energy storage circuit (T2) is arranged to generate a second oscillating energy storage voltage having a phase that lags ninety degrees behind the phase of the second oscillating drive voltage in response to the second oscillating drive voltage. The third driver (D3) is arranged to generate the third oscillation drive voltage by applying a signal inverted to the second oscillation energy storage voltage; The third energy storage circuit (T3) is arranged to generate a third oscillating energy storage voltage having a phase that lags behind the third oscillating driving voltage by ninety degrees in response to the third oscillating driving voltage. The fourth driver (D4) is arranged to generate the fourth oscillation drive voltage by inverting the signal and applying it to the third oscillation energy storage voltage; The fourth energy storage circuit (T4) is arranged to generate a fourth oscillating energy storage voltage having a phase lag of ninety degrees compared to the fourth oscillating drive voltage in response to the fourth oscillating drive voltage; and The first driver (D1) is arranged to generate the first oscillation drive voltage by applying a signal inverted to the fourth oscillation energy storage voltage. 21. The oscillator circuit (190) according to claim 1 or claim 2, wherein the first energy storage circuit (T1) is arranged to generate a first oscillating energy storage voltage having a phase leading the first oscillating drive voltage by ninety degrees in response to the first oscillating drive voltage, and wherein the feedback stage (F) comprises: The second driver (D2) is arranged to generate a second oscillation drive voltage by applying a signal inverted to the first oscillation energy storage voltage; The second energy storage circuit (T2) is arranged to generate a second oscillating energy storage voltage having a phase that leads the phase of the second oscillating drive voltage by ninety degrees in response to the second oscillating drive voltage. The third driver (D3) is arranged to generate the third oscillation drive voltage by applying a signal inverted to the second oscillation energy storage voltage; The third energy storage circuit (T3) is arranged to generate a third oscillating energy storage voltage having a phase that leads the phase of the third oscillating driving voltage by ninety degrees in response to the third oscillating driving voltage. The fourth driver (D4) is arranged to generate the fourth oscillation drive voltage by inverting the signal and applying it to the third oscillation energy storage voltage; The fourth energy storage circuit (T4) is arranged to generate a fourth oscillating energy storage voltage having a phase leading the fourth oscillating drive voltage by ninety degrees in response to the fourth oscillating drive voltage; and The first driver (D1) is arranged to generate the first oscillation drive voltage by applying a signal inverted to the fourth oscillation energy storage voltage. 22. The oscillator circuit (100) according to claim 8, wherein the capacitive element (C) is coupled between the first drive node (12) and the first energy storage output (13), and the inductive element (L) is coupled between the first energy storage output (13) and the voltage rail (14). 23. The oscillator circuit (100) according to claim 8, wherein the inductive element (L) is coupled between the first drive node (12) and the first energy storage output (13), and the capacitive element (C) is coupled between the first energy storage output (13) and the voltage rail (14). 24. A wireless communication device (900) comprising an oscillator circuit (100) according to any of the preceding claims. 25. A method of operating an oscillator circuit (100) including a first energy storage circuit (T1) comprising an inductive element (L) and a capacitive element (C) series coupled between a voltage rail (14) and a first drive node (12), the method comprising: generating a first oscillating drive voltage at the first drive node in response to a first oscillating energy storage voltage present at a first energy storage output (13), wherein the first oscillating drive voltage is in phase with a first oscillating energy storage current flowing in the inductive element (L) and the capacitive element (C), thereby causing the oscillator (100) to oscillate in a series resonant mode of the inductive element (L) and the capacitive element (C).