JP2006086928A - Nonlinear distortion compensation circuit for power amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power amplifier which facilitates a method of controlling a gain of a forward side RF unit circuit of a Cartesian type negative feedback amplifier and employs the Cartesian type negative feedback amplifier for making the gain of the forward side RF unit circuit be predetermined gain at all the time. <P>SOLUTION: A first detector 23 is provided in an output of a power amplifier 12, a second detector 28 is provided in an output of a modulator 21, a first variable attenuator 26 is provided between the modulator 21 and the power amplifier 12, and a second variable attenuator 27 is provided between a feedback path for extracting, as a feedback modulation signal, a part of an output signal of the power amplifier 12, and a demodulator 22. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a non-linear distortion compensation circuit that compensates for non-linear distortion of a power amplifier by a negative feedback method, and more particularly to improvement of a non-linear distortion compensation circuit of a power amplifier in a radio device.

  Generally, in a digitizing radio using a linear modulation system such as QPSK or multi-level QAM, particularly for mobile communication, strict adjacent channel leakage power is defined from the viewpoint of effective frequency utilization. For this reason, it is necessary to compensate for the interference to the adjacent channel caused by the nonlinear distortion of the power amplifier.

  FIG. 3 shows a circuit block diagram of a transmitter of a radio device using orthogonal modulation using a nonlinear compensation circuit of a conventional power amplifier, and the prior art will be described.

  FIG. 3 shows an example in which a Cartesian negative feedback amplifier that performs feedback to the amplifier using an in-phase signal and a quadrature signal is used (not related to a known document).

  In FIG. 3, 1 and 2 are signal input terminals, 3 and 4 are adders, 5 and 6 are amplifiers, 7 and 8 are modulators, 9 is a 90 ° phase shifter, and 10 is a modulation from the modulators 7 and 8. An adder for adding signals, 21 is a quadrature modulator comprising modulators 7 and 8, 90 ° phase shifter 9 and adder 10, 25 is a connector with a switch, 26 and 27 are variable attenuators, and 11 is an unnecessary component. , 12 is a power amplifier, and 13 is an antenna.

  Further, 14 is a directional coupler for extracting a feedback signal from the output of the power amplifier 12, 15 and 16 are demodulators, 17 is a 90 ° phase shifter, and 22 is a demodulator 15, 16 and 90 ° phase shifter. 17 is a quadrature demodulator, 18 is a carrier wave oscillator (local oscillator), 20 is a phase difference detector that detects the phase difference between the input signal and the feedback signal, and 19 is a phase shift of the carrier wave output from the carrier wave oscillator 18. A variable phase shifter that shifts the phase according to the detection output of the phase difference detector 20, 23 is a detector, and 24 is a CPU.

  The quadrature component signal (Q) applied from the signal input terminal 1 is input to the adder 3 and the phase difference detector 20, and the in-phase component signal (I) applied from the signal input terminal 2 is compared with the adder 4. It is input to the phase difference detector 20.

  The quadrature component signal input to the adder 3 is defined as a feedback quadrature component signal (0) when the optimum phase difference value for the quadrature component signal (Q) of the feedback quadrature component signal (Qr) separately input to the adder 3 is 0 °. A quadrature component signal obtained by subtracting Qr) is output to the amplifier 5, amplified to a required level by the amplifier 5, and then output to the modulator 7 of the quadrature modulator 21.

  The in-phase component signal input to the adder 4 becomes an in-phase component signal obtained by subtracting the feedback in-phase component signal (Ir) separately input to the adder 4, is output to the amplifier 6, and is amplified to a required level by the amplifier 6. Then, the signal is output to the modulator 8 of the quadrature modulator 21.

  On the other hand, the carrier wave oscillator 18 oscillates a carrier wave having a required frequency, and is output to the modulator 8 of the quadrature modulator 21, the 90 ° phase shifter 9, and the variable phase shifter 19. The carrier wave inputted to the 90 ° phase shifter 9 is phase-shifted by 90 ° and inputted to the modulator 7 of the quadrature modulator 21.

  The carrier wave input to the variable phase shifter 19 is input to the demodulator 16 and the 90 ° phase shifter 17 of the quadrature demodulator 22, and the carrier wave input to the 90 ° phase shifter 17 is shifted in phase by 90 °. And input to the demodulator 15 of the quadrature demodulator 22.

  The quadrature component signal input to the modulator 7 modulates the carrier wave output from the 90 ° phase shifter 9. Then, the modulator 7 outputs a modulated signal based on the quadrature component signal to the adder 10. The in-phase component signal input to the modulator 8 modulates a carrier wave separately input to the modulator 8. Then, the modulator 8 outputs a modulation signal based on the in-phase component signal to the adder 10.

  The modulation signal based on the quadrature component signal and the modulation signal based on the in-phase component signal are added by the adder 10, output to the connector 25 with switch, pass through the variable attenuator 26, and output to the filter 11.

  The quadrature modulation signal input to the filter 11 is output to the power amplifier 12 after unnecessary components are removed. The quadrature modulation signal input to the power amplifier 12 is amplified to the required power, compensated for with non-linear distortion of the power amplifier 12, and a quadrature modulation signal without distortion is transmitted from the antenna 13.

  Part of the transmission output amplified to the required power by the power amplifier 12 is extracted by the directional coupler 14, passes through the variable attenuator 27, and is fed back to the demodulators 15 and 16 of the quadrature demodulator 22.

  The feedback signal fed back to the demodulator 15 demodulates the feedback quadrature component signal (Qr) by the carrier wave of the required frequency that is phase shifted by 90 ° by the 90 ° phase shifter 17 separately input to the demodulator 15. Then, the demodulator 15 outputs the demodulated feedback quadrature component signal to the adder 3 and the phase difference detector 20.

  The feedback signal fed back to the demodulator 16 demodulates the feedback in-phase component signal (Ir) by the carrier wave having the required frequency separately inputted to the demodulator 16. Then, the demodulator 16 outputs the demodulated feedback in-phase component signal to the adder 4 and the phase difference detector 20.

  The carrier wave input to the quadrature demodulator 22 is corrected for the phase difference φ by the variable phase shifter 19 so that the feedback signals Ir and Qr have an optimum phase. This phase amount detection control is performed by the phase difference detector 20. The phase difference φ is a value determined by a delay time by the connector 25 with a switch from the quadrature modulator 21 to the quadrature demodulator 22, the variable attenuator 26, the filter 11, the power amplifier 12, the directional coupler 14, the variable attenuator 27, and the like. The input quadrature component signal (Q) and in-phase component signal (I), and the feedback quadrature component signal (Qr) and feedback in-phase component signal (Ir) are obtained. Feedback is constituted by this feedback loop, and nonlinear distortion generated by the power amplifier 12 or the like can be compensated.

  The transmission output level is controlled by varying the attenuation amount of the variable attenuator 27. The CPU 24 reads the detection voltage of the detector 23 connected to the output of the power amplifier 12, and the CPU 24 controls the amount of deduction of the variable attenuator 27 so that it becomes the detection voltage when the specified transmission output level is output. Thus, a prescribed transmission output level can be obtained.

  Next, a method for adjusting the gain of the forward-side RF unit circuit of the Cartesian negative feedback amplifier, which has been conventionally performed, will be described with reference to FIG. The signal generator 30 is connected to the connector 25 with a switch. At this time, the switch of the switch-equipped connector 25 is switched, and the signal output from the signal generator 30 is not input to the quadrature modulator 21 but is input only to the variable attenuator 26.

  A predetermined output level signal is input from the signal generator 30 to the connector 25 with switch, and the signal level that has passed through the variable attenuator 26, the filter 11, and the power amplifier 12 is measured by a wattmeter 31 connected to the power amplifier 12. . The gain of the forward side RF unit circuit is adjusted by adjusting the attenuation amount of the variable attenuator 26 so that the signal level measured by the wattmeter 31 becomes a prescribed transmission output level.

  In the conventional method of adjusting the gain of the forward side RF unit circuit of the Cartesian negative feedback amplifier, a signal generator is required at the time of adjustment, and it is troublesome and the adjustment cannot be automated. In addition, after adjustment, when the gains of the filter 11 and the power amplifier 12 change due to temperature changes, there is a disadvantage that the gain of the forward side RF unit circuit changes.

  An object of the present invention is to facilitate a method of adjusting the gain of a forward side RF unit circuit of a Cartesian type negative feedback amplifier, and to provide a power amplifier using a Cartesian type negative feedback amplifier which always has a predetermined gain of the forward side RF unit circuit. It is to provide.

  In order to achieve the above object, the present invention provides a carrier oscillator that generates a carrier wave having a predetermined frequency, a modulator that modulates the carrier wave by an input signal and outputs a modulated signal, and a power amplifier that amplifies the modulated signal to a required power. A feedback path that extracts a part of the output signal of the power amplifier as a feedback modulation signal; and a demodulator that demodulates the feedback modulation signal from the feedback path using the carrier wave and outputs a feedback demodulation signal; In a nonlinear distortion compensation circuit for a power amplifier that compensates for nonlinear distortion of the power amplifier that feeds back a demodulated signal to the input signal, a first detector is provided at the output of the power amplifier, and the output of the modulator is A second detector is provided, a first variable attenuator is provided between the modulator and the power amplifier, and a part of the output signal of the power amplifier is taken as a feedback modulation signal. Providing the second variable attenuator between the to return path of the demodulator and said.

  According to the present invention, in a nonlinear distortion compensation circuit of a power amplifier, a transmission operation is performed with the attenuation amount of the second variable attenuator as a predetermined amount, and the detected voltage value of the first detector and the second detector The gain of the forward side RF section circuit is adjusted by adjusting the attenuation amount of the first variable attenuator according to the detected voltage value.

  Further, according to the present invention, in the nonlinear distortion compensation circuit of the power amplifier, the abnormality detection operation of the backward side circuit is performed by the detection voltage value of the first detector and the third detector provided at the input of the demodulator. It is characterized by that.

  According to the present invention, a method of adjusting the gain of the forward side RF unit circuit of the Cartesian type negative feedback amplifier is facilitated, and a power amplifier using a Cartesian type negative feedback amplifier that always sets the gain of the forward side RF unit circuit to a predetermined value is provided. Obtainable.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a circuit block diagram showing a transmitter of a radio using a nonlinear compensation circuit for a power amplifier according to an embodiment of the present invention.

  In FIG. 1, 1 is a quadrature component signal input terminal, 2 is an in-phase component signal input terminal, 3 is an adder for adding an input quadrature component signal and a feedback quadrature component signal, and 4 is an input in-phase component signal and a feedback in-phase component signal. 5 is an amplifier that amplifies the addition-corrected quadrature component signal, 6 is an amplifier that amplifies the addition-corrected in-phase component signal, 7 is a modulator that modulates a carrier wave with the quadrature component signal, and 8 is an in-phase modulator. A modulator that modulates a carrier wave with a component signal, 9 is a 90 ° phase shifter that shifts the phase of the carrier by 90 °, 10 is an adder that adds modulation signals from the modulators 7 and 8, and 21 is a modulator 7, 8 is a quadrature modulator comprising a 90 ° phase shifter 9 and an adder 10, 11 is a filter for removing unnecessary components of the quadrature modulation signal, 12 is a power amplifier for amplifying the quadrature modulation signal to the required power, and 13 is an antenna. is there.

  Further, 14 is a directional coupler for extracting a feedback signal from the output of the power amplifier 12, 15 is a demodulator that demodulates a quadrature component signal from the feedback quadrature modulation signal, and 16 is a demodulator of the in-phase component signal from the feedback quadrature modulation signal. A demodulator, 17 is a 90 ° phase shifter that shifts the phase of the carrier by 90 °, 22 is a quadrature demodulator comprising the demodulators 15, 16 and 90 ° phase shifter 17, 18 is a carrier wave oscillator (local oscillator), Reference numeral 20 denotes a phase difference detector that detects the phase difference between the input signal and the feedback signal.

  23 is a detector connected to the output of the power amplifier 12, 28 is a detector connected to the output of the quadrature modulator 21, 29 is a detector connected to the input of the quadrature demodulator 22, 24 is a CPU, and 26 is a quadrature. A variable attenuator 27 is connected between the modulator 21 and the power amplifier 12, and 27 is a variable attenuator connected between the quadrature demodulator 22 and a feedback path for extracting a part of the output signal of the power amplifier 12 as a feedback modulation signal. .

  The quadrature component signal (Q) applied from the signal input terminal 1 is input to the adder 3 and the phase difference detector 20, and the in-phase component signal (I) applied from the signal input terminal 2 is compared with the adder 4. It is input to the phase difference detector 20.

  The quadrature component signal input to the adder 3 is defined as a feedback quadrature component signal (0) when the optimum phase difference value for the quadrature component signal (Q) of the feedback quadrature component signal (Qr) separately input to the adder 3 is 0 °. A quadrature component signal obtained by subtracting Qr) is output to the amplifier 5, amplified to a required level by the amplifier 5, and then output to the modulator 7 of the quadrature modulator 21.

  The in-phase component signal input to the adder 4 becomes an in-phase component signal obtained by subtracting the feedback in-phase component signal (Ir) separately input to the adder 4, is output to the amplifier 6, and is amplified to a required level by the amplifier 6. Then, the signal is output to the modulator 8 of the quadrature modulator 21.

  On the other hand, the carrier wave oscillator 18 oscillates a carrier wave having a required frequency, and is output to the modulator 8 of the quadrature modulator 21, the 90 ° phase shifter 9, and the variable phase shifter 19. The carrier wave inputted to the 90 ° phase shifter 9 is phase-shifted by 90 ° and inputted to the modulator 7 of the quadrature modulator 21.

  The carrier wave input to the variable phase shifter 19 is input to the demodulator 16 and the 90 ° phase shifter 17 of the quadrature demodulator 22, and the carrier wave input to the 90 ° phase shifter 17 is shifted in phase by 90 °. And input to the demodulator 15 of the quadrature demodulator 22.

  The quadrature component signal input to the modulator 7 modulates the carrier wave output from the 90 ° phase shifter 9. Then, the modulator 7 outputs a modulated signal based on the quadrature component signal to the adder 10. The in-phase component signal input to the modulator 8 modulates a carrier wave input separately to the modulator 8. Then, the modulator 8 outputs a modulation signal based on the in-phase component signal to the adder 10.

  The modulation signal based on the quadrature component signal and the modulation signal based on the in-phase component signal are added by the adder 10, pass through the variable attenuator 26, and output to the filter 11.

  The quadrature modulation signal input to the filter 11 is output to the power amplifier 12 after unnecessary components are removed. The quadrature modulation signal input to the power amplifier 12 is amplified to the required power, compensated for with non-linear distortion of the power amplifier 12, and a quadrature modulation signal without distortion is transmitted from the antenna 13.

  Part of the transmission output amplified to the required power by the power amplifier 12 is extracted by the directional coupler 14, passes through the variable attenuator 27, and is fed back to the demodulators 15 and 16 of the quadrature demodulator 22.

  The feedback signal fed back to the demodulator 15 demodulates the feedback quadrature component signal (Qr) by the carrier wave of the required frequency that is phase shifted by 90 ° by the 90 ° phase shifter 17 separately input to the demodulator 15. Then, the demodulator 15 outputs the demodulated feedback quadrature component signal to the adder 3 and the phase difference detector 20.

  The feedback signal fed back to the demodulator 16 demodulates the feedback in-phase component signal (Ir) by the carrier wave having the required frequency separately inputted to the demodulator 16. Then, the demodulator 16 outputs the demodulated feedback in-phase component signal to the adder 4 and the phase difference detector 20.

  The carrier wave input to the quadrature demodulator 22 is corrected for the phase difference φ by the variable phase shifter 19 so that the feedback signals Ir and Qr have an optimum phase. This phase amount detection control is performed by the phase difference detector 20. The phase difference φ is a value determined by the delay time of the variable attenuator 26, the filter 11, the power amplifier 12, the directional coupler 14, the variable attenuator 27, etc. from the quadrature modulator 21 to the quadrature demodulator 22, and the input quadrature It is obtained from the component signal (Q) and the in-phase component signal (I), the feedback quadrature component signal (Qr) and the feedback in-phase component signal (Ir). Feedback is constituted by this feedback loop, and nonlinear distortion generated by the power amplifier 12 or the like can be compensated.

  The transmission output level is controlled by varying the attenuation amount of the variable attenuator 27. The CPU 24 reads the detection voltage V1 of the detector 23 connected to the output of the power amplifier 12, and the CPU 24 sets the attenuation amount of the variable attenuator 27 so that it becomes the detection voltage V1 when the specified transmission output level is output. By controlling, a prescribed transmission output level can be obtained.

  The amount of attenuation of the variable attenuator 27 at this time is G1. At this time, the CPU 24 reads the detection voltage V2 of the detector 29 connected to the input of the quadrature demodulator 22 and the detection voltage V3 of the detector 28 connected to the output of the quadrature modulator 21, and the prescribed transmission output The detection voltages V1, V2, and V3 of each detector when the level is output are set as reference voltages.

  Next, a method for adjusting the gain of the forward side RF unit circuit of the Cartesian negative feedback amplifier will be described with reference to FIG. A power meter 31 is connected to the output of the power amplifier 12, and the variable attenuator 27 is set to G1 for transmission operation. At this time, the specified transmission output level is output, the detection voltage of the detector 23 is V1, and the detection voltage of the detector 29 is V2. Then, the CPU 24 adjusts the gain of the forward side RF unit circuit by varying the attenuation amount of the variable attenuator 26 so that the detection voltage of the detector 28 becomes the predetermined value V3.

  After the adjustment, when the gains of the filter 11 and the power amplifier 12 change due to temperature changes during operation, the CPU 24 varies the attenuation amount of the variable attenuator 26 so that the detection voltage of the detector 28 becomes V3. The gain of the RF circuit is adjusted as needed.

  When the detection voltage of the detector 23 is V1 and the specified transmission output level is transmitted, the total gain of the backward circuit is a specified value. At that time, the detection voltage of the detector 29 is V2. If not, the gains of the RF circuit and baseband circuit of the backward circuit are different from the specified values. As a result, the input / output characteristics (distortion characteristics, noise characteristics) of the backward-side components are a predetermined design. Since it changes with respect to the value, degradation of transmission performance such as adjacent channel leakage power occurs.

  Therefore, the CPU 24 reads and monitors the detection voltage value of the detector 23 connected to the output of the power amplifier 12 and the detection voltage value of the detector 29 connected to the input of the quadrature demodulator 22, so that an abnormality in the backward side circuit is detected. To detect.

It is a circuit block diagram which shows the transmission part of the radio | wireless machine using the nonlinear compensation circuit of the power amplifier by embodiment of this invention. It is a circuit block diagram which shows the adjustment method of the gain of the forward side RF part circuit of the nonlinear compensation circuit of the power amplifier by embodiment of this invention, and the detection method of the abnormality of a backward side circuit. It is a circuit block diagram which shows the transmission part of the radio | wireless machine using the nonlinear compensation circuit of the conventional power amplifier. It is a circuit block diagram which shows the adjustment method of the gain of the forward side RF part circuit of the nonlinear compensation circuit of the conventional power amplifier.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 2 ... Signal input terminal 3, 4 ... Adder, 5, 6 ... Amplifier, 7, 8 ... Modulator, 9, 17 ... 90 degree phase shifter, 10 ... Adder, 11 ... Filter, 12 ... Electric power Amplifier, 13 ... Antenna, 14 ... Directional coupler, 15, 16 ... Demodulator, 18 ... Carrier wave oscillator, 19 ... Variable phase shifter, 20 ... Phase difference detector, 21 ... Quadrature modulator, 22 ... Quadrature demodulator, 23, 28, 29 ... detector, 24 ... CPU, 25 ... connector with switch, 26, 27 ... variable attenuator, 30 ... signal generator, 31 ... wattmeter.

Claims (1)

  A carrier oscillator that generates a carrier wave of a predetermined frequency, a modulator that modulates the carrier wave by an input signal and outputs a modulated signal, a power amplifier that amplifies the modulated signal to a required power, and a part of an output signal of the power amplifier And a demodulator that demodulates the feedback modulation signal from the feedback path with the carrier and outputs a feedback demodulated signal, and feeds back the feedback demodulated signal to the input signal. In a nonlinear distortion compensation circuit for a power amplifier configured to compensate for nonlinear distortion of the amplifier, a first detector is provided at the output of the power amplifier, a second detector is provided at the output of the modulator, and the modulator A first variable attenuator is provided between the power amplifier and the power amplifier, and a second variable attenuator is provided between the demodulator and a feedback path for extracting a part of the output signal of the power amplifier as a feedback modulation signal. Nonlinear distortion compensating circuit of a power amplifier, characterized in that a variable attenuator.

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