HK1110153A - Radio-receiver front-end and a method for frequency converting an input signal - Google Patents

Description

Radio receiver front-end and method for frequency converting an input signal

Technical Field

The present invention relates to an N-phase radio receiver front-end for converting an input signal having a first frequency to an output signal having a second frequency. The invention also relates to a method for converting an input signal having a first frequency to an output signal having a second frequency.

Background

Conventional radio receiver front-end designs incorporate conversion of an input Radio Frequency (RF) signal to one or more Intermediate Frequency (IF) signals, the final signal then being converted to baseband. The radio frequency receiver front-end may include a Low Noise Amplifier (LNA) with substantial voltage gain. One or several mixers for converting the input signal to an IF signal are provided after the low noise amplifier, said IF signal being provided at the output of the mixer.

A quadrature radio receiver front-end is designed to mix a differential or single-ended input signal with four local oscillator signals having different phases and to provide two output signals, one for the I channel and one for the Q channel.

The input signal may include superimposed out-of-band interference. In radio receiver front-ends known in the art, one or several filters are provided for processing the input signal. A pre-filter, such as a band selection filter, is placed before the LNA to reject out-of-band interference. Additional filters for processing the input signal may also be provided. To reduce the cost of the radio receiver front-end, it may be implemented as part of an integrated circuit. However, implementing a filter with on-chip design is difficult. Therefore, the filter must typically be implemented off-chip. This is a disadvantage because off-chip components make the radio receiver front-end more expensive, larger and more complex. Therefore, most of the off-chip filters have been removed in the development towards smaller and cheaper radio receivers. In today's homodyne receivers, one of the off-chip filters that remains is a band-select filter. Considerable cost and space can be saved if the band selection filter can also be eliminated. This is particularly applicable to multi-band radio receiver front-ends that require one band selection filter per frequency band. The impact is even greater if multiple antennas are also used.

Strong out-of-band interference can saturate the radio receiver if the pre-filter, e.g. band selection filter, is simply removed. In addition, it will cause intermodulation distortion and compression of the input signal. Different communication standards have different requirements for maximum out-of-band interference. In order to fulfill the requirements according to e.g. the GSM (global system for mobile communications) standard, out-of-band interference up to 0dBm has to be handled. Conventional radio receiver front-ends cannot fulfill this requirement without a pre-filter, e.g. a band selection filter.

In some radio receiver front-end designs, the band selection filter may be integrated on-chip. However, this solution does not fulfill the maximum out-of-band requirements of different mobile communication standards, such as the GSM or UMTS (universal mobile telecommunications standard) standards.

Disclosure of Invention

It is therefore an object of the present invention to provide a radio receiver front-end that is simpler than radio receiver front-ends known in the art and that can be implemented using on-chip technology. It is another object of the invention to provide a method for converting an input signal having a first frequency to an output signal having a second frequency.

According to a first aspect of the invention, these objects are achieved by an N-phase radio receiver front-end according to the invention, which is neither on-chip nor off-chip band selective filter.

The N-phase radio receiver front-end according to the invention comprises a low noise amplifier, a mixer arrangement and a signal generator. The input port of the N-phase radio receiver front-end is directly connected to the input port of the low noise amplifier. The mixer arrangement is a current mode mixer arrangement since the input signal has not been converted to a voltage before mixing. The output port of the low noise amplifier is directly connected to the input port of the mixer arrangement. The signal generator is adapted to generate N phase shifted local oscillator signals. The phase shifted local oscillator signal may be used to selectively activate mixer cores of the mixer arrangement.

The mixer arrangement may comprise N/2 mixer cores. Each mixer core may have an input terminal directly connected to an input port of the mixer arrangement. The mixer cores may be single-balanced or double-balanced mixer cores.

The low noise amplifier may be a single ended or differential amplifier.

The output port of the mixer arrangement may be connected to an active or passive frequency selective load. The frequency selective load may comprise N/2 current to voltage conversion means whereby out-of-band interference of signals input to the radio receiver front-end may be suppressed.

Each current-to-voltage conversion means may comprise a mixer load connected to a respective output terminal of the mixer core and to signal ground means, respectively. Each mixer load may be a resistor connected in parallel with a capacitor. The capacitor of each mixer load has a value effective to suppress out-of-band interference of a signal input to the radio receiver front-end when the signal is mixed. The capacitance of the capacitor of each mixer load may be variable for suppressing out-of-band interference of input signals having different bandwidths.

The signal generator may be an oscillator that provides a signal for driving the mixer core. The oscillator may be a voltage controlled oscillator.

The mixer arrangement may be connected to the voltage controlled oscillator by means of a transformer providing a local oscillator signal, e.g. a quadrature local oscillator signal. It is an advantage to supply the local oscillator signal with a transformer, since low frequency noise will not be introduced into the local oscillator terminals of the mixer arrangement.

The local oscillator may comprise a quadrature oscillator having an LC-tank. The inductor of the LC-tank may provide a primary winding of a transformer, and the inductor connected to the local oscillator input terminal of the mixer may provide a secondary winding of said transformer. Thus, no additional components for providing a transformer are required, apart from the inductor for providing the secondary winding.

The capacitor of each LC-tank may be a variable capacitor for adjusting the frequency of the local oscillator signal.

Alternatively, the signal generator may be provided by a high frequency oscillator and a frequency divider arranged to provide N non-overlapping local oscillator signals having a duty cycle of substantially 1/N. For quadrature oscillator signals, the duty cycle should be substantially 25% for each signal.

According to a second aspect of the invention the object is achieved by using an N-phase radio receiver front-end according to the invention for converting an input signal having a first frequency to a signal having a second frequency in a wireless electronic communication device.

According to a third aspect of the invention, the object is achieved by a wireless electronic communication device comprising an N-phase radio receiver front-end according to the invention.

According to a fourth aspect of the present invention, the object is achieved by a method in an N-phase radio receiver front-end for converting an input signal having a first frequency to an output signal having a second frequency. The method comprises the following steps: receiving an input signal at an input port of a radio receiver front-end; amplifying an input signal including out-of-band interference in a low noise amplifier; in a current mode mixer arrangement, an input signal and out-of-band interference are mixed with a plurality of phase shifted local oscillator signals having a second frequency to generate a mixed signal having the second frequency.

The mixed signal may include out-of-band interference. The method may further comprise the step of suppressing out-of-band interference of the mixed signal.

The suppressing step may include providing the mixed input signal including out-of-band interference to a passive or active frequency selective load. The frequency selective load may be a mixer load which is connected to a respective output terminal of the mixer arrangement and to the signal ground arrangement. The mixed signal may be an IF signal.

The suppressing step may comprise suppressing with a capacitor of the mixer load having a value effective to suppress out-of-band interference of the mixed signal.

The method may comprise adjusting a capacitance of a capacitor of the frequency selective load for suppressing out-of-band interference of mixed input signals having different bandwidths, said capacitor may be a variable capacitor.

The method may further comprise the steps of: generating a local oscillator signal, and supplying said generated local oscillator signal to N/2 mixer cores of the mixer arrangement.

Furthermore, the method may comprise adjusting a capacitance of a capacitor of an oscillator connected to the mixer arrangement for adjusting the frequency of the local oscillator signal.

Further embodiments of the invention are defined in the dependent claims.

An advantage of the present invention is that the size and complexity of a radio receiver front-end is reduced compared to conventional radio receiver front-ends.

It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Drawings

Further objects, features and advantages of the present invention will appear from the following detailed description of the invention, with reference to the accompanying drawings, in which:

fig. 1 is a front view of a mobile communication device including an N-phase radio receiver front end in accordance with the present invention;

fig. 2 is a block diagram of an N-phase radio receiver front end according to the present invention;

fig. 3 is a circuit diagram of an embodiment of an N-phase radio receiver front-end according to the present invention;

fig. 4a is a circuit diagram of a first embodiment of a voltage controlled oscillator for generating a low noise local oscillator signal;

FIG. 4b is a signal diagram of a local oscillator signal;

FIG. 5a is a block diagram of a high frequency oscillator connected to a frequency divider for generating a low noise local oscillator signal;

FIG. 5b is a signal diagram of a local oscillator signal;

fig. 6 is a circuit diagram of another embodiment of an N-phase radio receiver front end according to the present invention; and

fig. 7 is a flow chart of one embodiment of a method according to the present invention.

Detailed Description

Fig. 1 illustrates a mobile phone 1 as an example wireless electronic communication device in which an N-phase radio receiver front-end according to the present invention may be utilized. The invention is not limited to implementation in a mobile phone 1. The invention may be implemented in a wide variety of electronic devices in which a radio receiver front-end is required to receive and process Radio Frequency (RF) input signals, such as mobile radio terminals, pagers, communicators, electronic organizers (electronic organisers) or smart phones. The mobile phone 1 may comprise a first antenna 10 and a second auxiliary antenna 11 for receiving incoming signals. The microphone 12, speaker 13, keypad 14 and display 15 provide a man-machine interface for operating the mobile telephone 1.

The mobile phone may in operation be connected via a first radio link 22 to a radio station 20 (base station) of a mobile communication network 21, such as GSM, UMTS, PCS (personal communication system), and/or PDC (personal digital cellular), through a first antenna 10. Furthermore, the mobile phone 1 may in operation establish a second wireless link to the peripheral device 30 via the second radio link 31 through the auxiliary antenna 11. The second radio link 31 is for example Bluetooth^®A link established in the 2.4(2.400-2.480) GHz frequency range. In order to establish the radio links 22, 31, the mobile telephone 1 comprises radio resources adapted according to the relevant technology used. Thus, the mobile phone 1 includes: a first radio access device, such as a transceiver, that communicates radio signals with the base station 20; and a second radio access device that communicates radio signals with peripheral device 30. Alternatively, one radio access device may be switchable to communicate radio signals with the base station 20 or the peripheral device 30.

The peripheral device 30 may be any device having radio communication capabilities, such as according to Bluetooth^®Technology or any other Wireless Local Area Network (WLAN) technology. It comprises an antenna 32 for exchanging signals on the second link 31 and a transceiver (not shown) adapted according to the communication technology used by the peripheral device 30. The device may be a wireless headset, a remote server, a facsimile machine, a vending machine, a printer, a computer, etc. A wide variety of electronic devices may have such communication capabilities and have the need to communicate data wirelessly.

A received input signal having a Radio Frequency (RF) may be processed by a radio receiver front-end according to the present invention. The input signal may be single ended or differential. The input signal is converted to an Intermediate Frequency (IF) signal before further signal processing is applied. Thus, the radio receiver front-end of the mobile phone 1 may comprise mixer means comprising one or several mixer cores for converting a signal having a first frequency to a signal having a second frequency, as will be disclosed below.

Fig. 2 illustrates a radio receiver front-end according to the present invention. The antenna 10 may be directly connected to an input port of a Low Noise Amplifier (LNA) 50. The LNA 50 is linear or non-linear in nature so that it can handle out-of-band interference, for example according to the GSM standard, where out-of-band interference up to at least 0dBm should be handled. The RF signal input to the LNA 50 includes the desired signal and the superimposed out-of-band interference, which are amplified by the gain of the LNA 50.

The current input port of the N-phase mixer arrangement 50a is connected to the output port of the LNA 50. The mixer arrangement 50a may comprise N/2 mixer cores 51, 52. In the embodiments of fig. 2, 3 and 6, a quadrature radio receiver front-end is described. These mixer means 50a comprise a first and a second mixer core 51, 52 having input terminals. Each input port and output port of the mixer arrangement 50a and the LNA 50 may comprise one or several terminals.

The first mixer core 51 may be used for the I-channel of the input signal and the second mixer core 52 may be used for the Q-channel of the input signal. The output port of the LNA 50 is directly connected to the input port of the mixer arrangement 50a, i.e. the signal current from the LNA 50 is not transformed into a voltage by the load impedance. Due to the 0dBm interfering signal, the signal transformed to voltage will be too large to be processed. Mixing is thus performed in the current domain according to the present invention by controlling the mixer with phase shifted LO signals that selectively activate the mixer means 50a, e.g. selectively activate the mixer cores 51, 52. Thus, interference signals can be processed.

Each mixer core 51, 52 and thus the mixer arrangement 50a further comprises: a Local Oscillator (LO) input terminal for receiving an LO signal, the LO signal being generated by an LO signal generation device or LO signal generator for mixing with the amplified input signal. The first mixer core 51 is adapted to receive a first LO signal LO having a first phase_IAnd respond to it. The second mixer core 52 is adapted to receive and respond withA second LO signal LO in a second phase different from the first phase_Q。

Output ports of the mixer arrangement 50, e.g. output terminals of the first and second mixer cores 51, 52, may be connected to active or passive frequency selective loads.

The frequency selective load may comprise first and second current to voltage conversion means 53, 54. Thus, the input signal, now amplified and mixed to a lower frequency signal, can be converted to a voltage by the current-to-voltage conversion means. Thus, the I-channel and Q-channel output signals IF may be provided at the output port of the frequency selective load_I、IF_Q. Each output port of the frequency selective load may include first and second terminals.

The frequency selective load will also act as a suppression means for suppressing out-of-band interference.

Fig. 3 is a circuit diagram of one embodiment of an N-phase radio receiver front-end according to the present invention, where N-4. Thus, the radio receiver front-end according to fig. 3 is a quadrature radio receiver front-end. For the design according to the invention it is important that the linearity of the LNA is high enough to handle out-of-band interference, e.g. up to 0dBm, as described above. In the embodiment of fig. 3, the LNA is a common gate or common base LNA provided by an amplifier transistor 60, which amplifier transistor 60 may be an input transistor. The transistor 60 may be a FET (field effect transistor), such as a MOS (metal oxide semiconductor) transistor or a BJT (bipolar junction transistor) transistor. In the embodiment of FIG. 3, LNA 50 is provided by FET transistors. The input port of the quadrature radio receiver front-end is connected to the source terminal of the transistor 60.

The gate of amplifier transistor 60 is connected to a bias voltage V_bias1. Optionally, a bias input (gate) of the amplifier transistor 60 is connected to a common mode feedback circuit for controlling the bias of the amplifier transistor 60.

Since the mixer cores 51, 52 and the first and second current-to-voltage conversion means 53, 54 have a similar design, the first and second current-to-voltage conversion means are arranged in a first and a second frequency bandOnly the first mixer core 51 and the associated first current-to-voltage conversion means 53 will be described in detail here below. The first mixer core 51 may comprise first and second mixer transistors 61a, 62a connected to input terminals of the first mixer core 51. The mixer transistors 61a, 62a may be FET transistors or BJT transistors. BJT transistors have the advantage of being faster than FET transistors providing higher linearity. In the embodiment of fig. 3, the mixer transistors 61a, 62a are provided by BJT transistors. The mixer emitter of each mixer transistor 61a, 62a is connected to an input terminal of the first mixer core 51. The base of each mixer transistor is connected to an LO (local oscillator) input terminal of the first mixer core 51. Each mixer transistor 61a, 62a is responsive to a quadrature LO signal. The first mixer transistor 61a couples a first quadrature LO signal LO having a first phase_I+And responding. The second mixer transistor 62a couples a second LO signal LO having a second phase_I-In response, the second phase is 180 ° phase shifted with respect to the first phase. The collectors of the mixer transistors 61a, 62a are connected to a first and a second output terminal of the first mixer core 51, respectively.

The frequency selective load, e.g. the current to voltage conversion means, may comprise a capacitor 67a arranged between the input terminals of the frequency selective load. Thus, the frequency selective load will be operable to filter out-of-band interference and provide some channel filtering.

The mixer arrangement 50a and the mixer cores 51, 52 are current mode mixers operating in the current domain. The output signal from the first mixer core 51 is supplied to a frequency selective load. The frequency selective load may comprise a first current to voltage conversion means 53 which may convert the output signal from the first mixer core 51 into a voltage. The first current-to-voltage conversion means 53 may comprise a separate conversion means for each output signal. Each translation means may comprise passive components such as resistors 63a, 65a and capacitors 64a, 66a connected in parallel with the output terminals of the first mixer core 51 and signal ground means (such as a supply voltage). The first mixer transistor 61a is connected to a resistor 63a and a capacitor 64a, and the second mixer transistor 62a is connected to a resistor 65a and a capacitor 66 a.

The first and second current-to-voltage conversion means may further comprise active components. For example, a transistor connected as a resistor may replace the resistor 63a and/or the resistor 65 a. Optionally, the first and second current-to-voltage conversion means 53, 54 may comprise transimpedance amplifiers to convert the current signals output from the mixer means 50 a. The transfer function of such a transimpedance amplifier can be made frequency selective.

First IF (intermediate frequency) output signal IF of I channel_IMay be generated between the output terminals of the first mixer core 51. Capacitors 64a, 66a and 67a do not significantly attenuate the desired signal centered at low frequencies. However, by selecting appropriate values for capacitors 64a, 66a and 67a, out-of-band interference, which in GSM would occur at frequencies at least 20MHz away from the desired signal, can be greatly attenuated. Furthermore, LO-to-IF leakage is suppressed by capacitors 64a, 66a and 67a, which enable a single balanced mixer core and a single-ended LNA. The single-ended LNA eliminates the need for an external balun (balun). The external filter may perform a balun function. Thus, if a differential LNA is used, a separate external balun may need to be provided. The signal after the radio receiver front-end is differential, which is suitable for further processing on-chip.

Alternatively, the LNA 50 may be provided by a feedback LNA that is sufficiently linear to handle out-of-band interference up to 0dBm that meets GSM standards. However, the linearity requirements have to be taken into account in each particular case.

The second mixer core 52 may include first and second mixer transistors 61b, 62b and is configured as the first mixer core 51. The second current-to-voltage conversion means 54 comprises a mixer load provided by resistors 63b, 65b and capacitors 64a, 66b and a capacitor 67b arranged between the input terminals of the second current-to-voltage conversion means 54. The first mixer transistor 61b of the second mixer core 52 is responsive to a third quadrature LO signal having a third phaseLO_Q+The third phase is phase shifted by 90 ° with respect to the first phase. Second mixer transistor 62b of second mixer core 52 is responsive to a fourth LO signal LO having a fourth phase_Q-The fourth phase is phase shifted 270 deg. relative to the first phase. The collectors of the mixer transistors 61b, 62b of the second mixer core 52 are connected to the first and second output terminals of the second mixer core 52.

A second IF (intermediate frequency) output signal IF for the Q channel may be output between output terminals of the second mixer core 52_Q。

To provide bias current to the radio receiver front-end, a current device 68 is connected to the input port of the radio receiver front-end and to the input port of the LNA 50. The current device 68 may be provided, for example, by a resistor, an inductor, or a transistor connected as a current source. An inductor has the advantage that it causes a lower voltage drop than a resistor or a transistor connected as a current source. Furthermore, if current device 68 is provided by an inductor, it may detune the parasitic capacitance that appears on the source of transistor 60.

The LO input terminals of the first and second mixer cores 51, 52 are connected to an LO signal generator. In one embodiment, the LO signal generator is a quadrature LO signal generating device. At large offset frequencies, e.g. above 20MHz in a GSM implementation, the phase noise of the LO signal must be very low, since the signal-to-out-of-band interference ratio is not improved by filtering before the input signal is supplied to the mixer arrangement 50 a. If the phase noise is too high, the intermixing of strong out-of-band interference can prevent reception of weak signals. In the GSM case, the phase noise requirement will be similar to that required in the transmitter. Thus, the same or similar oscillators may be used to generate the LO signal LO for the transmitter and radio receiver front-ends_I+、LO_I-、LO_Q+、LO_Q-. The low frequency local oscillator noise must also be low because it is passed directly to the IF output.

The signal generator may comprise an oscillator, such as a VCO (voltage controlled oscillator).

Fig. 4a illustrates one embodiment of a VCO (voltage controlled oscillator) that may be used to generate quadrature LO signals. A possibility to generate a low phase noise local oscillator signal substantially free of low frequency noise is to use an oscillator with an LC-tank. The LC-tank may be part of a transformer with secondary windings connected to the mixer cores 51, 52. In this case no local oscillator buffer is needed and the DC-level of the local oscillator signal feeding the mixer core can be easily set. The VCO comprises four pairs of transistors 71a, 71b, 72a, 72b, 73a, 73b, 74a, 74 b. The transistor may be provided by a FET or BJT transistor.

A source of the transistor 71a is connected to a drain of the transistor 71 b. The gate of transistor 71a is connected to the drain of transistor 73a and the drain of transistor 71a is connected to a first LC-tank comprising an inductor 75 connected in parallel with a capacitor 76. The center tap of inductor 75 is connected to the supply voltage. The value of capacitor 76 will set the frequency of the VCO. The gate of transistor 71b is connected to the drain of transistor 72a and to the gate of transistor 73 a. The source of transistor 71b is connected to the drain of bias transistor 79. The gate of bias transistor 79 will in operation receive a bias voltage V_bias3. The source of bias transistor 79 is connected to ground.

A drain of transistor 72a is connected to the second terminals of inductor 75 and capacitor 76, and to the gates of transistors 73a and 71 b. The gate of transistor 72a is connected to the drain of transistor 74 a. A source of transistor 72a is connected to a drain of transistor 72 b. The gate of transistor 72b is connected to the drain of transistor 71a and to the gate of transistor 74 a. The source of transistor 72b is connected to the drain of bias transistor 79.

A source of transistor 73a is connected to a drain of transistor 73 b. The gate of transistor 73a is connected to the drain of transistor 72a, and the drain of transistor 73a is connected to a second LC tank comprising an inductor 77 connected in parallel with a capacitor 78, and is connected toTo the gate of transistor 71 a. The center tap of inductor 77 is connected to the supply voltage. The value of capacitor 78 should track the value of capacitor 76 and it will set the frequency of the VCO. A gate of transistor 73b is connected to the drain of transistor 74a and to the gate of transistor 72 a. The source of transistor 73b is connected to the drain of bias transistor 80. The gate of bias transistor 79 will in operation receive a bias voltage V_bias3. The source of the bias transistor 80 is connected to ground.

A drain of transistor 74a is connected to the second terminals of inductor 77 and capacitor 78, and to the gates of transistors 72a and 73 b. The gate of transistor 74a is connected to the drain of transistor 71 a. The source of transistor 74a is connected to the drain of transistor 74 b. A gate of transistor 74b is connected to a gate of transistor 71a and to a drain of transistor 73 a. The source of transistor 74b is connected to the drain of bias transistor 80.

The VCO is magnetically coupled to the LO input terminals of the mixer cores 51, 52 through the first and second transformers. The first transformer includes an inductor 75 and an inductor 81 connected to the gate of the transistor 61a and the gate of the transistor 62 a. The primary winding of the first transformer is provided by inductor 75 and its secondary winding is provided by inductor 81. Likewise, the second transformer includes an inductor 77 and an inductor 82 connected to the gate of transistor 61b and the gate of transistor 62 b.

The LO signal LO is supplied to the mixer transistors 61a, 61b, 62a, 62b by means of a transformer arrangement_I+、LO_I-、LO_Q+、LO_Q-Meaning that low frequency noise will not be applied to the LO input terminals of the mixer cores 51, 52. Inductors 81 and 82 will short out any low frequency noise on the LO input terminals. Furthermore, the transformer will not consume any current, since it only comprises passive components, which is an advantage if low power consumption is important.

Fig. 4b illustrates an LO signal that may be generated by a VCO according to the embodiment of fig. 4. At each instant, the LO signal with the highest voltage level will dominate the other LO signals except at the intersection of the LO signals, due to the phase shift of the signals. This means that it is possible to interconnect the input terminals of the mixer cores 51, 52. The transistor receiving the LO signal having the highest voltage level will be conductive and therefore operable. Furthermore, the transistor receiving the LO signal having the highest voltage level will dominate the other transistors of the mixer arrangement, even if any other transistor is conducting to some extent.

Fig. 5a illustrates a method for generating an LO signal LO with sufficiently low phase noise and low frequency noise_I+、LO_I-、LO_Q+、LO_Q-In an alternative solution, the signals are phase shifted with respect to each other. The LO signals are phase shifted in this embodiment so that only one signal will be in a high state at substantially the same time. The high frequency oscillator 90 is connected to a digital frequency divider 91. In this embodiment, the frequency divider is arranged to generate quadrature LO signals, i.e. four LO signals LO, only one of which is active at a time_I+、LO_I-、LO_Q+、LO_Q-. The frequency of the high frequency oscillator should be at least twice the frequency of the output signal from the digital frequency divider 91. When more than one of the four local oscillator signals is high at the same time, it is important to avoid time overlap. By arranging for the frequency divider 91 to provide an approximately 1/N duty cycle to each of the output signals, i.e. 25% for quadrature signals, overlap can be avoided. If overlap exists, additional noise is generated and increases the sensitivity to matching inaccuracies of the mixer transistors. However, if the noise requirements are less stringent, some overlap may be allowed. An advantage of the high frequency oscillator 90 and the digital frequency divider 91 is that they provide a more compact design, despite the increased current consumption compared to the VCO implementation of fig. 4.

The frequency divider 91 may be provided by a Johnson counter with N flip-flops in series, wherein the output signal of the last flip-flop is fed back to the input terminal of the first flip-flop. All flip-flops should be clocked by the same clock signal with a frequency N times the frequency of the output signal. The flip-flop must be forced to a state where only one output is high at a time to avoid cycling of the error state. The N LO signals may then be extracted at the outputs of the N flip-flops.

Fig. 5b illustrates a phase shifted LO signal generated by the frequency divider 91, where N-4. The LO signals may be substantially non-overlapping square waves.

In the above description, the input signal RF_inIs single ended. However, the input signal may equally well be differential, wherein the LNA 50 would be arranged to amplify the differential signal and then supply the amplified signal to a double balanced mixer core instead of a single balanced mixer core as described above.

The radio receiver front-end as described above may be adapted for dual mode mobile communication, where it may process incoming signals from at least two mobile communication networks applying different communication standards, such as GSM and UMTS. A dual mode radio receiver front-end may be provided by arranging two radio receiver front-end circuits as disclosed in parallel, wherein each front-end is adapted according to a specific standard. The parallel connected circuits may be selectively activated by selectively biasing the LNA of each radio receiver front-end circuit. The controller may be arranged to control the biasing of the LNA of each circuit.

Alternatively, a dual mode radio receiver front end may be provided by varying the bandwidth of the frequency selective load, e.g. the current to voltage conversion means 53, 54. Thus, if the capacitors 64a, 64b, and 67a are variable capacitors having selectively variable capacitance values, the controller may be arranged to set a particular value of the capacitors 64a, 64b, and 67 a. The set value will be selected such that out-of-band interference of the input signal of different received signal bandwidths will be suppressed and the signal to be received will be substantially unaffected.

According to the invention a topology is selected that makes the LNA 50 and the mixer arrangement 50a sufficiently linear to handle out-of-band interference. If the LNA and the mixer arrangement are not sufficiently linear, the out-of-band interference will cause intermodulation distortion and compression of the input signal, since the band selection filter is removed according to the invention.

Fig. 6 is a circuit diagram of another embodiment of an N-phase radio receiver front-end according to the present invention. In the illustrated embodiment, N-4, i.e., it is a quadrature radio receiver front end. Components corresponding to those of the embodiment of fig. 3 are denoted by the same reference numerals and will not be described with respect to the embodiment of fig. 6. However, even if the components correspond, it should be noted that the values may be different, depending on the actual implementation.

The radio receiver front-end illustrated in fig. 6 comprises a double balanced mixer arrangement with a differential LNA. The differential amplifier comprises first and second amplifier means, for example provided by first and second amplifier transistors 160a, 160b, such as MOS or BJT transistors. The input port of the quadrature radio receiver front-end is connected to the input port of the LNA 50, which is directly connected to the input port to which the input signal RF may be applied_inThe source terminals of the transistors 160a, 160 b.

The gates of transistors 160a and 160b are connected to a bias voltage V_bias. Alternatively, the bias inputs (gates) of transistors 160a and 160b may be connected to a common mode feedback circuit (not shown) for controlling the bias of the transistors 160a, 160 b.

The first and second mixer cores 51, 52 according to the embodiment of fig. 6 each comprise four mixer transistors 161a, 161b, 161c, 161d, 162a, 162b, 162c, 162 d. The gates of transistors 161a and 162c are connected to receive the local oscillator signal LO_I+. The gates of transistors 161b and 162d are connected to receive the local oscillator signal LO_Q+. The gates of transistors 161c and 162a are connected to receive the local oscillator signal LO_Q-. The gates of the transistors 161d and 162b are connected to receive the local oscillator signal LOx.

The drains of transistors 161a and 162b are connected to a first terminal of capacitor 64a, resistor 63a, and capacitor 67 a. The drains of the transistors 161b and 162a are connected to a first terminal of the capacitor 64b, the resistor 63b, and the capacitor 67 b. The drains of the transistors 161c and 162d are connected to a first terminal of the capacitor 66b and the resistor 65b, and to a second terminal of the capacitor 67 b. The drains of the transistors 161d and 162c are connected to a first terminal of the capacitor 66a and the resistor 65a, and to a second terminal of the capacitor 67 a.

First output signal IF_IWill be generated between the output terminals connected to the terminals of the capacitor 67a during operation, and a second output signal IF_QWill be generated between the output terminals connected to the terminals of capacitor 67 b.

The local oscillator signal LO may be provided according to the principles as described with respect to fig. 4a-4b or fig. 5a-5b_I+、LO_I-、LO_Q+、LO_Q-。

Fig. 7 illustrates a method according to the invention. In a first step 100, an input signal comprising out-of-band interference is received at an input port of an N-phase radio receiver front-end. In step 101, an input signal including out-of-band interference is amplified in the LNA 50. The amplified input signal and the out-of-band interferer are then mixed with the phase-shifted LO signals to generate a mixed signal including the out-of-band interferer in step 102, as described above. Finally, in step 103, out-of-band interference of the mixed signal is suppressed, e.g. by applying the mixed signal to a frequency selective load, e.g. to a mixer load comprising a resistor and a capacitor, as described above. If the frequency selective load comprises a mixer load, the capacitors 64a, 66a, 64b, 66b, 67a, 67b of the mixer load may have values that are effective in suppressing out-of-band interference. If the capacitor is a variable capacitor, the method may comprise the step of setting the value of the capacitor. The method may further comprise the step of supplying the LO signal to the mixer cores 51, 52. Furthermore, if the capacitors 76, 78 of the LC-tank of the VCO are variable, the method may comprise the step of setting the values of said capacitors.

Reference is made below to an N-phase radio receiver front-end. The N-phase radio receiver may be a quadrature radio receiver front end. However, by arranging the front end appropriately, virtually any number of phases can be handled. For example, six phases may be handled by adding additional mixer cores to the mixer arrangement 50a according to the embodiment of fig. 4 a. The number of different LO signals to be generated will thus be 6. The appropriate number of LO signals may be generated by a frequency divider or by designing the VCO according to the principles of the embodiment of fig. 4 a. The number of phases processed may be represented by N. Thus, the number of different LO signals generated will be N. The LO signals will thus be phase shifted 360/N relative to each other.

The invention may be used, for example, to down-convert an RF signal to a zero IF or low IF signal without the use of a band selection filter. Thus, the front end according to the invention will have a compact design and be cheap to manufacture.

An advantage of embodiments of the present invention is that no band selection filter is required in the quadrature radio receiver front-end to suppress out-of-band interference. Thus, if the front-end is implemented using on-chip technology, the production costs can be reduced compared to conventional radio receiver front-ends with band selection filters arranged on-chip or off-chip.

The invention has been described above with reference to specific embodiments. However, other embodiments than the above described are equally possible within the scope of the invention. The different features of the invention may be combined in other combinations than those described. The invention is only limited by the patent claims.

Claims (36)

1. An N-phase radio receiver front-end for converting an input signal having a first frequency to an output signal having a second frequency, comprising: an input port; a low noise amplifier (50, 60) having an input port and an output port; a mixer arrangement (50a) having an input port and an output port; and a signal generator adapted to generate N local oscillator signals and operatively connected to the mixer arrangement, characterized by:

the input port of the N-phase radio receiver front-end is directly connected to the input port of a low noise amplifier (50, 60);

the mixer arrangement (50a) is a current mode mixer arrangement;

the output port of the low noise amplifier is directly connected to the input port of the mixer arrangement; and

the signal generator is adapted to generate N phase shifted local oscillator signals.

2. The N-phase radio receiver front-end according to claim 1, wherein the mixer arrangement (50a) comprises N/2 mixer cores (51, 52), each mixer core having an input terminal directly connected to an input port of the mixer arrangement.

3. The N-phase radio receiver front-end according to claim 2, wherein the mixer cores (51, 52) are single-balanced mixer cores or double-balanced mixer cores.

4. The N-phase radio receiver front-end according to any of the preceding claims, wherein the low noise amplifier is a differential amplifier (160a, 160b) or a single ended amplifier (60).

5. The N-phase radio receiver front-end according to claim 2 or 3, wherein each mixer core (51, 52) comprises two or four transistors (61a, 62a, 61b, 62b, 161a, 161b, 161c, 161c, 162a, 162b, 162c, 162d), the transistors of each mixer core being responsive to two different local oscillator signals.

6. The N-phase radio receiver front-end according to any of the preceding claims, wherein the signal generator is an oscillator for providing a local oscillator signal for driving the mixer arrangement (50 a).

7. The N-phase radio receiver front-end according to any of the preceding claims, wherein the signal generator is an oscillator operatively connected to the mixer arrangement (50a) with a transformer (75, 77, 81, 82) for providing a local oscillator signal at a local oscillator input terminal of said mixer arrangement (50 a).

8. The N-phase radio receiver front-end according to claim 7, wherein the oscillator is a quadrature oscillator for providing a quadrature local oscillator signal.

9. The N-phase radio receiver front-end according to claim 7 or 8, wherein the oscillator comprises LC-tanks, each LC-tank being provided by an inductor (75, 77) and a capacitor (76, 78).

10. The N-phase radio receiver front-end according to claim 9, wherein the inductor (75, 77) of the LC-tank provides a primary winding of a transformer, and wherein the inductor (81, 82) connected to the local oscillator input terminal of the mixer arrangement (50a) provides a secondary winding of said transformer.

11. The N-phase radio receiver front-end according to claim 9 or 10, wherein the capacitor (76, 78) of each LC-tank is a variable capacitor for adjusting the frequency of the local oscillator signal.

12. The N-phase radio receiver front-end according to any of claims 1 to 6, wherein the signal generator comprises a high-frequency oscillator (90) for providing a local oscillator signal and a frequency divider (91).

13. The N-phase radio receiver front-end according to claim 12, wherein the frequency divider (91) is arranged to provide N local oscillator signals each having a duty cycle of substantially 1/N, and only one signal of the local oscillator signals is in a high state at a time.

14. The N-phase radio receiver front-end according to any of the preceding claims, wherein the low noise amplifier (50) comprises at least one input transistor (60) connected in a common gate or common base configuration.

15. The N-phase radio receiver front-end according to any of the preceding claims, further comprising an active or passive frequency selective load connected to an output port of the mixer arrangement (50 a).

16. The N-phase radio receiver front-end according to claim 15, wherein the frequency selective load comprises current to voltage conversion means (53, 54, 63a, 64a, 65a, 66a, 63b, 64b, 65b, 66b, 67a, 67 b).

17. The N-phase radio receiver front-end according to claim 16, wherein an output port of a first mixer core (51) of the mixer arrangement (50a) is connected to the first current-to-voltage conversion arrangement and an output port of a second mixer core (52) of the mixer arrangement is connected to the second current-to-voltage conversion arrangement.

18. The N-phase radio receiver front-end according to claim 17, wherein each current-to-voltage conversion means (53, 54, 63a, 64a, 65a, 66a, 63b, 64b, 65b, 66b, 67a, 67b) comprises a mixer load connected to a respective output port of the mixer core and to the signal grounding means, respectively.

19. The N-phase radio receiver front-end according to claim 18, wherein each mixer load is a resistor (63a, 65a, 63b, 65b) connected in parallel with a capacitor (64a, 66a, 64b, 66b) and a capacitor (67a, 67b) connected between the output terminals of each mixer core.

20. The N-phase radio receiver of claim 19, wherein the capacitor (64a, 66a, 64b, 66b, 67a, 67b) of each mixer load has a value effective to suppress out-of-band interference of a signal input to the radio receiver front-end when the signal is mixed.

21. The N-phase radio receiver front-end according to claim 20, wherein the capacitance of each capacitor (64a, 66a, 64b, 66b, 67a, 67b) of each mixer load is variable for suppressing out-of-band interference of input signals of different received signal bandwidths.

22. The N-phase radio receiver front-end according to any of the preceding claims, further comprising a current device (68) connected to the input port of the low noise amplifier and to the grounding means.

23. The N-phase radio receiver front-end according to claim 22, wherein the current device (68) is an inductor, a resistor or a transistor connected as a current source.

24. The N-phase radio receiver front-end according to any of the preceding claims, wherein the N-phase radio receiver front-end is a quadrature radio receiver front-end.

25. Use of an N-phase radio receiver front-end as claimed in any of the preceding claims in a wireless electronic communication device (1) for converting an input signal having a first frequency to a signal having a second frequency.

26. A wireless electronic communication device (1) comprising an N-phase radio receiver front-end according to any of claims 1-24.

27. The wireless electronic communication device according to claim 23, wherein the wireless electronic communication device (1) is a mobile radio terminal, a pager, a communicator, an electronic organizer, or a smartphone.

28. The wireless electronic communication device according to claim 23, wherein the wireless electronic communication device is a mobile phone (1).

29. A method for converting an input signal having a first frequency to an output signal having a second frequency in an N-phase radio receiver front-end, said method comprising the step of receiving the input signal at an input port of the radio receiver front-end, characterized by the steps of:

amplifying an input signal comprising out-of-band interference in a low noise amplifier (50, 60);

the input signal and the out-of-band interference are mixed in a current mode mixer arrangement (50a) with a plurality of phase shifted local oscillator signals having a second frequency to generate a mixed signal having the second frequency.

30. The method of claim 29, wherein the mixed signal includes out-of-band interference; and the method further comprises suppressing out-of-band interference of the mixed signal with the frequency selective load.

31. The method according to claim 30, wherein the suppressing step comprises supplying the mixed signal comprising out-of-band interference to frequency selective loads (53, 54, 63a, 64a, 65a, 66a, 63b, 64b, 65b, 66b, 67a, 67b) connected to the output port of the mixer arrangement (50a) and to the signal grounding arrangement, respectively.

32. The method according to claim 31, wherein the step of suppressing comprises supplying the mixed signal comprising the out-of-band interference to a resistor (63a, 65a, 63b, 65b) connected in parallel with a capacitor (64a, 66a, 64b, 66b), and supplying the mixed signal comprising the out-of-band interference to a capacitor (67a, 67b) connected between the output terminals of the mixer arrangement.

33. The method of claim 32, wherein the suppressing step comprises suppressing with a capacitor (64a, 66a, 64b, 66b, 67a, 67b) having a value effective to suppress out-of-band interference of the mixed signal.

34. The method of claim 33, further comprising adjusting a capacitance of a capacitor (64a, 66a, 64b, 66b, 67a, 67b) of the frequency selective load for suppressing out-of-band interference of the mixed input signal of different received signal bandwidths, the capacitor being a variable capacitor.

35. A method according to any one of claims 29 to 34, further comprising the steps of generating a local oscillator signal, and supplying said generated local oscillator signal to first and second single-or double-balanced mixer cores (51, 52) of a mixer arrangement (50 a).

36. The method of claim 35, further comprising adjusting a capacitance of a capacitor (76, 78) of an oscillator connected to the mixer arrangement (50a) for adjusting the frequency of the local oscillator signal.