KR20060041141A - Amplifier circuit, gyrator circuit, filter device and signal amplification method - Google Patents

Abstract

The amplifier circuit includes a transducer device connected to the phase shifter section. The phase shifter section has an impedance adjustable phase shift that is at least partially dependent on the frequency of the input signal. In use, the adjustable phase shift is adjusted to have substantially the opposite value of the phase shift of the transducer device. In one embodiment, the phase shifter section includes an adjustable resistance device and a capacitor device including an amplifier device having an input contact for receiving a resistance control signal; A first output contact connected to the capacitor device and a second output contact connected to the transducer device. The amplifier circuit further includes a control device for providing a resistance control signal to an input contact of the amplifier device.

Description

Amplifier circuits, gyrator circuits, filter units and signal amplification {AN AMPLIFIER CIRCUIT, GYRATOR CIRCUIT, FILTER DEVICE AND METHOD FOR AMPLIFYING A SIGNAL}

The present invention relates to an amplifier circuit comprising at least one transducer device connected to at least one phase shifter section having an adjustable phase shift and an impedance at least partially dependent on the frequency of the input signal.

The invention also relates to circuits and devices comprising at least an amplifier circuit, for example a gyrator device and a filter circuit.

The amplifier can be implemented, for example, with an integrator and a capacitor used in integrated IF-filter devices. For example, "Analog circuit design, low-power low-voltage, integrated filters, smart power," published in Rudy J.van de Plassche, Willy MCSansen, Johan H. Huijsing, 1994, ISBN 0-7923-9513-1. It is known to implement an interconductance amplifier device and a capacitor to obtain the desired transfer characteristics of the filter device. The interconductance amplifier device can be used to realize the terminal impedance of the filter device. In addition, two interconductance amplifier devices can be used as a gyrator, ie an electronic device having an input impedance proportional to the inverse of the load impedance. Therefore, if the output of the gyrator is connected to a capacitor, i.e., if the load impedance is capacitance, then the input impedance acts like an inductance. Thus, such a gyrator-capacitor circuit has the characteristics of an inductor and has a frequency-dependent impedance. This feature is particularly useful for integrated circuit technology that is difficult and expensive to achieve physical inductors.

However, there is a problem that the interconductance amplifier device exhibits frequency-dependent transfer characteristics. This may cause a deviation between the characteristics and ideal characteristics of the gyrator device or filter device in which such a transconductance amplifier device is used. In addition, in the filter arrangement, the frequency dependence of the performance of the amplifier arrangement may affect the frequency attenuation outside the desired frequency passband of the filter, resulting in even unstable filter-systems.

In addition, in a polyphase filter, the image-rejection characteristic of the polyphase IF-filter is, in turn, determined by the matching characteristics between the circuits in the branches with different phases. This match can be obtained in complementary metal oxide semiconductor (CMOS) topologies by using transistors that occupy the largest area possible. The frequency dependence of the transconductance amplification of the transistors depends largely on their length because the blocking frequency of the transconductance is inversely proportional to the transistor-length square. Therefore, a trade-off between the passband tilt and / or stability of the gyrator device or filter device (determined by the transient phase shift of the mutual conductance stage) and the image-stopping property (set by the matching characteristics) is required.

Similar problems exist with interconductance amplifier devices in bipolar topology. In bipolar transistors, the unwanted frequency dependency of the amplifier is caused by the nonzero resistance of the base. The presence of the base resistor causes a frequency-dependent action between the external base-emitter voltage and the internal base-emitter voltage at which the gain of the transistor is proportional. As long as the match is associated with a bipolar transistor, the larger the transistor area, the better the match characteristics. Although the time constant equal to the product of the base resistance and the equivalent input capacitance is almost independent of scaling, if the transistor is scaled to a larger version, the base-emitter junction capacitance has a significant effect on the given collector-current. This, in turn, causes excessive phase shift of the interconductance gain for a given frequency. Therefore, it has also been found that in bipolar devices, there must also be a tradeoff between high frequency action and matching characteristics.

The present invention seeks to solve or at least alleviate the problems described. It is therefore an object of the present invention to provide an amplifier circuit having improved frequency independent propagation characteristics. Therefore, according to the invention, the amplifier device as described above is characterized in that, in use, the adjustable phase shift is adjusted to have substantially the opposite value of the phase shift of the interconductor device.

Because of the adjustable phase shift, the phase shift of the integrator can be set to compensate for the frequency dependent phase shift of the interconductor device. Due to this, the amplification degree of the amplifier is substantially frequency independent and the slope of the passband of the filter can be compensated for.

In addition, the stability problem can be avoided because the compensated adjustable phase shift acts in reverse with the filter's pole shift relative to the right half plane (RPH) caused by the transient phase shift. In addition, since larger transistors can be used for better matching characteristics without degrading the stability of the filter, it is less necessary to balance the image-saving requirements and stability requirements of the filter. In addition, if an automatic tuning system (ATS) is used, the time constant tuning system can be combined with the frequency tuning system of the filter device already available. The power consumption required for this compensation is very low, resulting in better performance at the same power consumption level.

Particular embodiments of the invention are described in the dependent claims.

Additional details, aspects, and embodiments of the invention are described below with reference to the accompanying drawings.

1 is a block diagram illustrating an example of one embodiment of an amplifier circuit according to the present invention in which an amplifier is used as an adjustable resistor;

2-6 are electrical circuit diagrams showing examples of capacitor-resistor circuits in which transistors are used as adjustable resistors.

7 is an electrical circuit diagram showing an example of one embodiment of a gyrator device according to the present invention;

8 is an electrical circuit diagram showing an example of one embodiment of a polyphase filter device according to the present invention;

9 is a block diagram showing a phase locked circuit with an example of an autotuning system for an amplifier circuit according to the present invention;

As used herein, resistors and capacitors include at least any device or device having primarily resistive or capacitive properties. 1 shows an example of an electrical circuit of an embodiment of an amplifier circuit A1 according to the present invention. The amplifier circuit comprises an interconductor device 1 having two input contacts Uin and two output contacts Uout. In general, the interconductor device outputs a current at the output contact based on the voltage of the input signal. The interconductor device 1 has its output contact Uout connected to the phase shifter section 2. The phase shifter device 2 comprises an adjustable resistor R and a capacitor C connected in series and is connected in parallel to the output contact Uout of the interconductor device 1.

The adjustable resistor R is an amplifier device R that can be tuned to any resistor. The amplifier device R has an input contact Rin and two output contacts Routl and Rout2, respectively. At the output contact, each of the currents I ₁ , I ₂ is provided in the direction indicated by arrows I ₁ , I ₂ . Typically, the currents I ₁ , I ₂ are the same. By applying a certain input signal to the input contact Rin, the output signal at the output contacts Rout1, Rout2 is controlled to generate some impedance to the output contacts. Thus, the impedance can be changed by changing the input signal.

Interconductor device 91 outputs an output current based on the voltage difference between the input contacts. The output current can be mathematically approximated as

This and equation, I _u represents the output current in the direction indicated by the arrow (I _u) of Figure 1, U _i represents a voltage applied across the input contacts (U _in), and g _m is a cross-conductor devices ( The gain of 1) is displayed.

The gain of the interconductor amplifier is generally dependent on the frequency of the signal provided to the input contact and can be approximated as g _m = g _o / (1 + jwτ), where g _o is applied to a signal having a frequency of substantially 0 Hz. Represents the cross-conductance of the cross-conductor device, ω represents the frequency of the input signal multiplied by 2π, j is the square root of -1, and τ is the time constant of the cross-conductor. The voltage-transfer of the amplifier circuit shown in FIG. 1 can be described by the following equation.

In equation (2), U _i and U _o represent the voltage difference between each of the input contacts and the output contact of the interconductor device 1; R denotes the resistance of the amplifier device R, and C denotes the capacitance of the capacitor C of FIG.

The phase shifter device 2 has a phase shift Δφ between the voltage between the first shifter contact portion 21 and the second shifter contact portion 22 and the current flowing through the shifter contact portion. The relationship between the voltage U _o and the current I _u over the shifter contacts 21, 22 can be described by the following equation.

This equation, and C indicates the capacitance of the capacitor (C), j is the square root of -1, ω represents the frequency, I _u is defined in the direction indicated by the arrow (I _u) In Figure 1, R Denotes the resistance of the amplifier device (R).

As described, the resistance of the amplifier device R over the output contacts Rout1, Rout2 can be controlled by a signal applied to the input contact Rin. Due to this, the phase shift of the phase shifter section 2 is also adjustable. The capacitor C can also be adjusted, for example a varactor device. Because of the adjustable resistance and / or capacitance, the phase shift can be set to compensate for the frequency dependence and / or phase-shift of the gain of the interconductor device 1.                 

Due to this, the time constant of the phase shifter device, which is the product of the resistance and the capacitance, is easily adjusted so that the time constant R * C becomes substantially equal to the time constant τ of the interconductor device. At this time, the entire transfer of the amplifier circuit A1 thereby can be described by the following equation.

This is the action of the ideal integrator.

The amplifier input may be connected to a control device in which the characteristics of the interconductor device are modeled. This control device then provides a signal to the amplifier device, so that the amplifier compensates for the change in interconductance as described above.

The amplifier device may be substantially similar or identical to the interconductor device. Because of this, the characteristics of the amplifier device and the interconductor device will have substantially the same dependency. As a result, there is no need for extra means to compensate for changes caused by temperature changes, for example.

The amplifier device in the resistor may be a transistor device, for example a field effect transistor (FET). In this application, the term 'amplifier' should be understood to include all transistors. If the adjustable resistor is a transistor device, the amplifier circuit can be implemented as a single integrated circuit. This is particularly suitable when the transistor is of the same type as the transistor used in other devices in the integrated circuit, such as the transistor in the interconductor device. In this case, the process of the integrated circuit is less complicated because the devices of the integrated circuit require substantially the same process.

2 to 6 show an example of a capacitor C connected to a transistor R used as an adjustable resistor device. In these figures, field effect transistors (FETs) are used as adjustable resistors, but other types of transistors may also be used. Resistor contacts Rout1, Rout2 are the drain and source of the FETs. The resistance of the FET can be adjusted by changing the voltage applied to the gates Rin, Rin1, Rin2 of the FETs relative to the substrate of the device. This results in a wider or tighter conduction channel in the FET between the source and drain, resulting in a lower or higher FET resistance between the source and drain. Since the drain-source is connected in series with the capacitor, no DC current flows through the resistor and power consumption is substantially zero or very low. 2-6, voltages are set across the source, drain, and gate of the FETs, allowing the transistor to operate in a triode region.

2 and 6, n-type FETs are used as resistors, and p-type FETs are used in Figs. In Fig. 5, an interactive FET is used. The complementary FETs comprise n-type FETs RF2 connected in anti-parallel to each other. In Fig. 5, each of the source and the drain of the FETs is connected to a capacitor having a capacitance of 2C. In Figures 2-6, the FETs may be replaced with another amplifier device, for example. The resistance of the amplifier device can then be adjusted by changing the voltage or current applied to the input of the amplifier device.

7 shows a gyrator device 10 comprising an amplifier circuit according to the invention. The gyrator device 10 has an input U _in and an output U _out . The gyrator comprises two interconductance amplifiers 101, 102 head-tailed to each other. The gain of the amplifier 102 is opposed to the gain of the amplifier 101, i.e., the amplifier 102, when an input signal is applied to the input contact U _i , is shown by the arrow I _u as shown in FIG. The current is output in the direction opposite to the direction of the output current of 101.

In the gyrator, the amplifiers 101 and 102 are connected to a phase shifter device comprising a capacitor C ₁ and a resistor R ₁ connected in series. Resistor R1 is an adjustable resistor and may be, for example, a FET connected to a capacitor or amplifier as described above in connection with FIGS.

When the resistance of the resistor R1 is set such that the time constant R ₁ * C ₁ is substantially equal to the time constant τ of the interconductors 101 and 102, the impedance of the gyrator is equal to the impedance of the ideal inductor × gain of the amplifier. Becomes the same as The gain of the amplifier can also be opposite and inverted against each other. In this case, the amplifier 102 outputs a current having an amplitude substantially equivalent to 1 over the amplitude of the output current of the amplifier 11, in which case the gyrator has the impedance of the ideal inductor. An RC-circuit comprising a resistor R2 and a capacitor C2 connected in series to the input contact U _i of the gyrator 10 is connected. Thus, the impedance of the circuit of FIG. 7 shown at the input contact U _i is substantially equal to the impedance of the ideal inductor and ideal capacitor in parallel with each other.

8 shows a polyphase IF filter. Currently, it is typically designed to implement channel selective (low) IF filters or IF anti-aliasing filters on the chip. Indeed, the selection of non-zero IF frequencies by combining quadrature mixers and polyphase IF filters offers significant advantages over conventional single mixer and IF filter combinations, since they essentially suppress the image frequency. This complex-frequency processing topology avoids the need for complex image-stop filters at the RF-frequency in front of the mixer. The image-frequency suppression level ultimately depends on the accuracy of the quadrature oscillator and the matching between in-phase and quadrature IF-branches. It should be noted that the filter of Figure 8 is an example of a polyphase filter and that the present invention can be applied to other types of polyphase filters.

The filter of Fig. 8 has two branches i and q with phase differences with respect to each other. In the example shown, it is assumed that the phase difference is 90 degrees. The illustrated filter device has two in-phase input contacts I _{in_i} to which a signal is provided and two phase shifted input contacts I _in-q that are identical in this example but provided a 90 degree phase shift. An output signal is provided to the in-phase output contact Uout_i. The same output signal but a 90 degree phase shift is provided to the phase shifted output contact Uout_q. The corresponding contacts are connected to each other via each of the resistors R5-R8. In-phase input contact I _{in_i} is connected to in-phase output contact U _{out_i} via _gyrator device 12 and two phase shifter devices F1, F2. The gyrator device 12 may be similar to the gyrator device of FIG. Both the input and output contacts of the gyrator device 12 are connected in parallel to each of the phase shifter devices F1 and F2, which comprise a capacitor and a resistor connected in series. The phase shifted input contact I _{in_q} and the phase shifted output contact U _{in_q are} connected to the gyrator device 14 and the phase shifters F3 and F4 in a similar manner. In-phase branch (i) and phase-shifted branch (q) are connected to each other through the Xi concentrator (11, 13) connected to the input contact (I _{in_i,} Iin_ _Q) respectively, the output contacts (U _{out_i,} U _{out_q)} . The filter has improved performance because the gyrator device with phase shifter behaves more like an ideal inductor due to the adjustable phase compensation of the phase shifters F1-F4.

The filter device shown is particularly suitable for implementation in a single integrated circuit, since only transistors, resistors and capacitors are needed. In addition, since the inductor is simulated using transistors and capacitors, the integrated circuit can be relatively small and have low power consumption. Therefore, this circuit is particularly suitable for devices with limited power sources, such as mobile phones and Bluetooth devices.

Indeed, the frequency-dependency of the gain of the interconductor device may not be known accurately enough because the action is poorly modeled, for example in an electronic circuit simulator. In addition, the spread of device characteristics after processing of electronic circuits is typically large, making it difficult to predict the behavior of a particular device. In the circuit of Figure 9, an automatic tuning system (ATS) matches the time constant of the adjustable resistor-capacitor circuit to the time constant (τ) of the interconductor device, so as to between the time constants of each of the resistor-capacitor circuit and the interconductor device. Obtaining the correct correspondence is shown. Elements constituting the ATS are indicated by dotted lines. It should be noted that the illustrated ATS is merely one example of a control system and that other control systems may likewise be used to control the resistance of the adjustable resistor of the amplifier circuit in accordance with the present invention.

The ATS of FIG. 9 is partially integrated in a phase locked circuit (PLL) 200 as is generally known in the art. PLL 200 has a PLL input 201 and PLL outputs 202, 203. PLL 200 includes a phase detector 204, a low pass filter 205, a voltage controlled oscillator (VCO) 206, a limiter device 208 and a frequency divider 207. An input signal of the reference frequency f _ref may be provided to the PLL input 201. In this case, the PLL provides a VCO signal at the output frequency f _out to the PLL outputs 202 and 203. Although the VCO signal is provided to the PLL outputs 202 and 203, there is a phase difference between the outputs. The VCO signal is generated by the VCO 206 based on the VCO input signal voltage. When the PLL 200 is synchronized, the output frequency f _out is equal to the reference frequency f _ref x division factor N.

f _out = _{Nf ref}

The VCO output signal frequency f _out is divided by the division ratio N by the frequency divider 207. This results in a signal at a divided frequency f _div equal to f _div = f _out / N.

The signal with the divided frequency f _div is compared by the phase detector 204 with the input signal at the reference frequency f _ref . The phase detector 204 outputs a difference signal based on the phase difference between the divided frequency f _div and the reference frequency f _ref . This difference signal is low pass filtered by filter 205 and used as the VCO input signal to control the oscillation of VCO 206.

The ATS of FIG. 9 includes a voltage controlled oscillator device (VCO) 206 of a PLL. In general, a VCO is an oscillator device that generates some frequency signal that follows the voltage applied to the input of the VCO. In FIG. 9, the VCO is a replica of the gyrator device as used in the filter and may be, for example, a gyrator device as shown in FIG. The amplifier circuit used in the VCO gyrator may be similar to the interconverter in the amplifier circuit that must be controlled by the ATS.

In the example of Fig. 9, the output of the filter 205 is connected to an unshown interconductor device in the amplifier device 8 according to the present invention. Thus, the output of filter 205 controls the interconductance gain of the interconductor device. The output of the filter 205 controls the oscillation frequency of the VCO, for example comprising the gyrator circuit according to the present invention, by controlling the gain of the interconductor device in the gyrator. The output of the VCO 206 is connected to a phase compensation processor (PC) device 71, which output signal can be used to control the resistance of the adjustable resistor, for example by controlling the gain of the amplifier in the adjustable resistor. To provide. In the example shown, the output signal of the PC device 71 is also fed back to the VCO 206 to control the gain of the amplifier in the adjustable resistor in the gyrator acting as the VCO.                 

Instead of the amplifier circuit 8, the polyphase filter or gyrator device according to the invention can be controlled by ATS. In addition, the ATS (part of) can be combined with the tune-loop (part of) of the filter, which tuning loop is usually already provided in the filter arrangement. This minimizes the additional power consumption required. In addition, the ATS may be standalone and may not be partially integrated within the PLL.

The amplifier circuit according to the present invention or the IF-filter according to the present invention can be usefully used in an electronic device for receiving a radio signal with a limited power supply. These electronic devices are, for example, devices that communicate via a Bluetooth protocol, such as a battery powered wireless device, a mobile phone or a laptop computer that communicates with a local area network via a Bluetooth link, or a personal digital assistant that communicates with a computer via a Bluetooth link. Can be.

Claims (13)

An amplifier circuit comprising at least one interconductor device connected to at least one phase shifter section having an impedance and an adjustable phase shift at least partially dependent on the frequency of the input signal, wherein in use the adjustable phase shift is substantially An amplifier circuit, adjusted to have an opposite value of a phase shift of the interconductor device, wherein the phase shifter portion comprises at least one capacitor device and one or more adjustable resistor devices. The adjustable resistor device comprises at least an amplifier device, the amplifier device comprising: One or more input contacts for receiving a resistance control signal; One or more first output contacts connected to at least one of the capacitor devices; And, One or more second output contacts connected to the interconductor device, The amplifier circuit further comprises a control device for providing the resistance control signal to the input contact. The method of claim 1, The amplifier device in the adjustable resistor device is substantially the same as the interconductor device. The method according to claim 1 or 2, And said interconductor device is a transistor device. The method according to any one of claims 1 to 3, The amplifier device in the adjustable device is a transistor device. The method according to claim 3 or 4, At least one of the transistor devices is a metal oxide semiconductor field effect transistor. The method according to any one of claims 1 to 5, The control device comprising at least a voltage controlled oscillator. The method of claim 6, The control device further comprises an amplifier device. The method of claim 7, wherein The voltage controlled oscillator circuit comprises at least two oscillator interconductor devices substantially similar to the interconductor device. As a gyrator circuit, At least one amplifier circuit as claimed in any one of claims 1 to 8, and  At least one amplifier device having an input contact connected to an output contact of an interconductor in the amplifier circuit, And the amplifier device has a gain that is substantially the inverse of the gain of the amplifier device in the amplifier circuit. As a filter device, One or more in-phase inputs, At least one gyrator device as claimed in claim 9 connected to said in-phase input, and At least one in-phase output connected to the gyrator device. The method of claim 10, One or more phase shifted inputs, At least one gyrator device as claimed in claim 9 connected to said phase shifted input, And at least one phase shifted output connected to the gyrator device. The method of claim 11, At least one first gyrator device coupled to the in-phase input and the phase shifted input, and At least one second gyrator device coupled to the in-phase output and the phase shifted output. As a method of amplifying an input signal, Generating a signal current based on the voltage of the input signal; Adjusting the phase shift of the resistor device to an opposite phase shift of the signal current generated in the generating step, the resistor device having an adjustable phase shift and an impedance at least partially dependent on the frequency of the input signal; step; Providing the signal current to a capacitor device; And, At least providing the current to the resistor device.

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