JP2012080298A - Nonlinear distortion compensation amplification device and nonlinear distortion compensation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonlinear distortion compensation amplification device capable of solving a problem of necessity of compensating for distortion generated at a feedback circuit because nonlinear distortion generated at a forward system and distortion generated at a frequency characteristic deviation of a feedback circuit system deteriorate characteristic after distortion compensation.SOLUTION: At testing, a test signal is generated and transmitted to a forward system, and branched to a feedback circuit and a detector circuit at a pre-amplification stage. Frequency characteristic deviations of both circuits are calculated from outputs of both the circuits. From a difference between them, a frequency characteristic deviation of the feedback circuit is calculated and the deviation of the feedback circuit is compensated for with an inverse characteristic of the calculated deviation for nonlinear distortion compensation.

Description

  The present invention relates to non-linear distortion compensation of a radio communication system transmitter, and more particularly to a non-linear distortion compensation amplifying apparatus and a feedback circuit frequency characteristic deviation compensating method for compensating for frequency characteristic variation of a feedback circuit.

  A non-linear distortion compensation amplifying apparatus is used in order to cope with non-linear distortion characteristics in a high-frequency amplifier constituting a transmitter of a wireless communication system, and to reduce power use efficiency and size due to the non-linear distortion characteristics. An adaptive predistortion compensation device is known as a nonlinear distortion compensation amplification device.

  FIG. 4 is a diagram showing a circuit configuration of a conventional nonlinear distortion compensation amplifying apparatus. The calculation unit 41, DAC 42, quadrature modulation unit 43, high frequency amplifier 44, directional coupler 45, antenna 46, and FB circuit (feedback circuit) 47 are included. The FB circuit 47 includes an ADC 51, a band pass filter 52, an amplifier 53, an amplitude equalizer 54, and a mixer 55.

  An input baseband signal is output from the calculation unit 41, converted into an analog signal by a digital-analog converter (DAC 42), and then orthogonally modulated by a quadrature modulation unit 43 into a high-frequency signal in a radio frequency band. The quadrature modulated wave is amplified by the high frequency amplifier 44 to a required transmission power, and then transmitted from the antenna 46 as a radio frequency transmission signal via the directional coupler 45.

  Non-linear distortion occurs in the transmission signal due to the non-linearity of the input / output power characteristics of the high-frequency amplifier 44.

  For this nonlinear distortion compensation, a part of the radio frequency transmission signal extracted by the directional coupler 45 is fed back to the arithmetic unit 41 by the FB circuit 47 to adaptively compensate the nonlinear distortion.

  In the FB circuit 47, the signal down-converted to the low frequency signal by the mixer 55 is amplified to a predetermined power by the amplifier, and after the unnecessary frequency signal is removed by the band pass filter 52, it is converted into a digital signal by the analog-digital converter (ADC 51). The result is converted and fed back to the calculation unit 41.

  The computing unit 41 extracts a distortion compensation component from the fed back signal, adds the distortion compensation component to the baseband signal of the transmission wave, and sends it out. By this operation, stable distortion compensation control is performed by adapting to nonlinear distortion generated in a high-frequency amplifier or the like. Such an adaptive nonlinear distortion compensation circuit can adapt to environmental changes and obtain stable characteristics. An adaptive nonlinear distortion compensation circuit is described in Patent Document 1, for example.

  Also, a method is known in which an equalizer is provided between the high-frequency amplifier and the adaptive nonlinear distortion compensator, and a filter coefficient that reduces the out-of-band radiation power is calculated and corrected (for example, Patent Document 2).

  In the following, the transmission path from the calculation unit 41 to the antenna 46 is represented as a forward system, the forward system signal is represented as a main signal, and the signal path branched from the directional coupler 45 is represented as a feedback system. (Depending on the case, it is expressed as a feedback circuit or an FB circuit).

JP 2002-141754 A Patent No. 4015455

  The analog filter (bandpass filter 52), the amplifier 53, the amplitude equalizer 54, and the ADC 51 constituting the FB circuit 47 of the conventional nonlinear distortion compensation amplifying apparatus have normal frequency characteristics. Therefore, distortion compensation is performed by detecting a distortion component, which is a factor that deteriorates nonlinear distortion compensation of a transmission signal.

  Specifically, due to the frequency characteristic variation of the FB circuit 47, the arithmetic unit detects an erroneous distortion component, and the distortion characteristic of the main signal after distortion compensation is, for example, one of the high frequency and the low frequency. Distortion worsens.

  As correction of this frequency characteristic, Patent Document 1 discloses a method of improving a frequency characteristic by providing a correction filter in a feedback circuit and correcting an inverse characteristic of the frequency characteristic of the entire loop.

  In this case, since the compensation including the frequency characteristic variation of the FB circuit 47 for detecting the nonlinear distortion component is performed, if there is a frequency characteristic variation in the feedback circuit, the transmission signal transmitted from the antenna As a result, distortion compensation that deteriorates the distortion characteristics is performed.

In other words, in the adaptive nonlinear distortion compensation circuit, the difference in frequency characteristics of the feedback circuit is confirmed in advance, and the distortion compensation is performed by correcting the difference in frequency characteristics.
The present invention relates to a nonlinear distortion compensation amplifying apparatus and a feedback circuit frequency characteristic deviation which can perform distortion compensation of nonlinear distortion generated in the main signal system by eliminating the influence of the frequency characteristic deviation of the feedback circuit. The purpose is to provide a compensation method.

  In order to solve the above problem, a test signal is generated at the time of testing the transmitter of the wireless communication system, and the test signal is branched and transmitted to the feedback circuit and the detection circuit before the high frequency amplification of the forward system. Calculate the frequency characteristic of the feedback circuit, calculate the frequency characteristic of the detection circuit from the output of the detection circuit, calculate the frequency characteristic deviation of the feedback circuit from the difference between the two frequency characteristic deviations, and calculate the frequency of the feedback circuit Nonlinear distortion compensation is performed by adding a reverse characteristic of the characteristic deviation to the transmission signal of the main signal system as a distortion compensation signal.

  According to the present invention, it is possible to perform distortion compensation of nonlinear distortion generated in the main signal system by eliminating the influence of the frequency characteristic deviation of the feedback circuit.

Block configuration of nonlinear distortion compensation amplifying apparatus of one embodiment of the present invention Calculation of amplitude difference in frequency characteristics of feedback circuit of the present invention Example of procedure for calculating frequency characteristic amplitude universal difference of feedback circuit of one embodiment of the present invention Block configuration of conventional nonlinear distortion compensation amplifier

Example 1
FIG. 1 is a diagram showing a block configuration of a nonlinear distortion compensation amplifying apparatus according to an embodiment of the present invention. Operation unit 1, adaptive nonlinear distortion compensation unit 2, DAC 3, quadrature modulation unit 4, demultiplexer 15, high frequency amplifier 6, directional coupler 7, antenna 8, FB circuit 9, demultiplexer 2 10, switch 11 The detector system circuit 12 is configured.

  The calculation unit 1 includes an equalizer (FIR filter) 21, a signal switching unit 22, a test signal generator 23, an out-of-band radiation power measurement / filter coefficient calculation unit 24, an FB circuit frequency characteristic calculation unit 25, a branching unit 26, and an FB circuit frequency. The characteristic calculation unit 27, the detector circuit frequency characteristic calculation unit 28, and the switching signal generation unit 29 are configured.

  The FB circuit 9 includes an ADC 1 30, a band pass filter 31, an amplifier 32, and a mixer 33, and the detector system circuit 12 includes an ADC 2 34 and a detector 35. Next, circuit operation will be described.

  In the forward circuit, the signal from the arithmetic unit 1 (test signal at the time of test, input baseband signal at the time of operation) is converted to an analog signal by the DAC 3 and then orthogonally modulated by the quadrature modulation unit 4 to a high-frequency signal in the radio frequency band. The

  In operation, this quadrature modulated wave is amplified to the required transmission power by the high frequency amplifier 6 via the demultiplexer 15, and then transmitted from the antenna 8 as a radio frequency transmission signal via the directional coupler 7. Is done. During the test, the demultiplexer 15 demultiplexes the transmission signal received from the quadrature modulation unit 4 to the switch 11.

  The switch 11 receives a test signal from the duplexer 15 at the time of the test by the switching control signal (for example, “ON” at the time of test and “OFF” at the time of operation) from the calculation unit 1, and the duplexer 2 10. Send to. During operation, the transmission signal from the directional coupler 7 is received and transmitted to the duplexer 210.

  The duplexer 210 receives the signal from the switch 11. At the time of the test, the test signal is branched and transmitted to the FB circuit 9 and the detector system circuit 12 on a one-to-one basis. During operation, a transmission signal from the switch 11 is transmitted to the FB circuit 9.

  In the FB circuit 9, the received signal is down-converted to a low frequency signal by the mixer 33, amplified to a predetermined power by the amplifier 32, unnecessary frequency components are removed by the band pass filter 31, and converted to a digital signal by the ADC 1 30. It is converted and fed back to the calculation unit 1.

  At the time of the test, in the detector system circuit 12, the power of the received test signal is converted into a DC voltage by the detector 35, converted into a digital signal by the ADC 234, and sent to the computing unit 1.

Next, the operation of the calculation unit 1 will be described separately during the test and during the operation.
1) During a test A test control signal is generated from the switching signal generator 29, and a test signal is transmitted from the test signal generator 23 to the forward circuit. The test signal is, for example, a modulated wave or a CW (Continuous Wave) signal. Processing of signals fed back to the FB circuit 9 and the detector system circuit 12 via the forward circuit will be described.

  The test signal received from the FB circuit 9 is input to the FB circuit frequency characteristic calculation unit 25 via the branch unit 26. The FB circuit frequency characteristic calculator 25 calculates the frequency characteristic of the feedback circuit. On the other hand, the test signal received from the detector system circuit 12 is transmitted to the detector system circuit frequency characteristic calculator 28.

The FB circuit frequency characteristic calculation unit 25 and the detector system circuit frequency characteristic calculation unit 28 calculate frequency characteristics, respectively. The FB circuit frequency characteristic unequal calculation unit 27 uses the detector system circuit frequency characteristic as a reference characteristic, and provides two paths. The frequency characteristic difference is calculated as the frequency characteristic universal difference of the FB circuit. FIG. 2 graphically explains that the difference between the frequency characteristics of the two paths is the FB circuit frequency characteristic difference.
2) During Operation The signal received from the FB circuit 9 is transmitted to the out-of-band radiation power measurement / filter coefficient calculation unit 25 and the adaptive nonlinear distortion compensation unit 2 via the branch unit 26.

  The out-of-band radiated power measurement / filter coefficient calculation unit 24 measures the out-of-band radiated power, determines the coefficient of the equalizer (FIR filter) so that the radiated power becomes small, and further determines this filter coefficient as the FB circuit frequency during the test. An equalizer filter coefficient adaptive process is performed by correcting the inverse characteristic of the frequency characteristic of the feedback circuit calculated by the characteristic difference calculation unit 27.

  On the other hand, the signal input to the adaptive nonlinear distortion compensator 2 is subjected to adaptive processing so that the difference from the input signal is reduced. The detailed operation of the adaptive nonlinear distortion compensator 2 will not be described.

Further, when a failure occurs in any of the forward circuit (DAC 3, quadrature modulation unit 4, demultiplexer 15 and high frequency amplifier 6) and the feedback circuit, the failure is caused by calculating the frequency characteristic of the feedback circuit and calculating the frequency characteristic of the detection circuit. It is possible to separate the points. For example,
A. When a test signal is transmitted to the forward circuit after a failure has occurred and the predetermined power cannot be detected as the FB circuit frequency characteristic calculation result, the detector circuit frequency characteristic calculation result is confirmed and the predetermined power can be detected Therefore, it can be determined that the FB circuit 9 is faulty.
A. After a failure occurs, a test signal is transmitted to the forward circuit, and when the predetermined power cannot be detected in both the FB circuit frequency characteristic calculation result and the detector system circuit frequency characteristic calculation result, it can be determined that the failure is in the forward circuit. Further, by switching the switch 11, it is possible to determine whether the failure is in the DAC 3, the quadrature modulation unit 4, or the high-frequency amplifier 6 in the forward circuit. If the switch 11 can detect the predetermined power when the signal from the demultiplexer 1 is selected, and cannot detect the predetermined power when the signal from the directional coupler is selected, then the high frequency amplifier 6 is faulty. It can be judged.

  On the contrary, when the switch 11 selects a signal from the duplexer 1, if the predetermined power cannot be detected, it can be determined that the DAC 3 and the quadrature modulation unit 4 are faulty.

  It should be noted that the blocks that do not require operation during operation of the detector system circuit 12, the FB circuit frequency characteristic deviation calculation unit 25, etc., which are operated during the test, can basically stop operating or processing.

FIG. 2 is a diagram showing an explanation of the calculation of the amplitude difference between the frequency characteristics of the feedback circuit of the present invention. The calculation of the frequency characteristic variation generated in the feedback circuit based on the frequency characteristics of the feedback circuit and the detector system circuit is described.
1) A test signal is generated by the test signal generator of the arithmetic unit and output to the forward circuit.
The generated test signal is a modulated wave or CW signal having an interval of Δf within the transmission band, and the level of the signal is set so as to match a predetermined level of the feedback circuit during operation, and N points from f ₁ to f _N (8 locations in the figure) are sequentially transmitted to the forward circuit for each wave.
2) When the test signal passes through each path, an uneven frequency characteristic occurs.
The transmitted test signal passes through the DAC 3 of the forward circuit, the quadrature modulation unit 4, the duplexer 15, the switch 11, and the duplexer 2 10, thereby generating an amplitude difference due to the frequency characteristics in the path.
3) Calculate the characteristics of the test signal that passes through the detector circuit.
The power of the test signal (ADC2 output) that passes through the detector is calculated by the calculation unit. Let P ₁ (f _i ).
4) Calculate the characteristics of the test signal via the feedback circuit.
The power of the test signal (output of ADC 1) that passes through the mixer 33, the amplifier 32, and the band pass filter 31 is calculated. Let P ₂ (f _i ).
5) Calculate the frequency characteristic homogeneity of the feedback circuit.
The power detection result P ₁ (f ₁ ) to P ₁ (f _N ) of the detector system circuit output is used as a reference signal, compared with the power calculation result of the feedback circuit output, and the frequency amplitude uniformity shown in Equation 1 is calculated. Since the characteristic deviation of the forward circuit described in 2) is common to the FB circuit and the detector circuit, this frequency amplitude difference is the frequency difference of the feedback circuit. Here, it is preferable that the detector 36 serving as the reference characteristic has no deviation in the frequency characteristic of the transmission band, and undergoes a primary change with respect to the power fluctuation. Alternatively, it is preferable that the characteristics can be complemented by the calculation unit 1.

  In addition, according to the present method, the frequency characteristic inhomogeneity of the feedback circuit can be calculated from a test signal that does not pass through the high frequency amplifier 6. That is, when the modulated wave or CW signal transmitted during the test is amplified, the high-frequency amplifier 6 may distort the signal or generate an unnecessary wave. There is.

FIG. 3 is a diagram showing an example of a frequency characteristic universal difference calculation procedure of the feedback circuit according to the embodiment of the present invention. FIG. 3 shows an example of a procedure for calculating frequency characteristic variation generated in the feedback circuit based on the description of calculating the frequency characteristic universal difference of the feedback circuit shown in FIG.
S1: The following is set as a test signal. Here, “i” = 1.
A. Initial value: f ₁
A. Frequency interval: Δf
C. Number of set frequencies: N
S2: transmitting a test signal of a frequency _{f i} to the forward circuit. Note that the level of the test signal is set to a predetermined level of the feedback circuit at the time of operation, the switching control signal is set to “ON”, and the signal of the duplexer 1 is output to the switch.
S3: signal power _P 1 _(f i) of the test signal feedback circuit output, calculates detector output signal power _P 2 a _{(f i).}
S4: The difference between both electric powers is calculated.

S5: i = i + 1
S6: Check if i> N. If i> N, go to S8, otherwise return to S2 via S7.
S7: f _i = f _i + Δf, i = i + 1
S8: Frequency characteristic amplitude deviation of feedback circuit (ΔP (f _i ) = P ₂ (f _i ) −P ₁ (f _i ) i = 1 to N) is added to the equalizer, and the frequency characteristic of the feedback circuit is added. Compensate for the inhomogeneity.

DESCRIPTION OF SYMBOLS 1 Computation part 2 Adaptive nonlinear distortion compensation part 3 Digital analog converter (DAC)
4 Quadrature modulation unit 5 Branching filter 1
6 High-frequency amplifier 7 Directional coupler 8 Antenna 9 FB circuit 10 Branching filter 2
DESCRIPTION OF SYMBOLS 11 Switcher 12 Detector system circuit 21 Equalizer 22 Signal switching part 23 Test signal generator 24 Out-of-band radiation power measurement and filter coefficient calculation part 25 FB circuit frequency characteristic calculation part 26 Branch part 27 FB circuit frequency characteristic inequality difference calculation part 28 Detection system circuit frequency characteristic calculation unit 29 Switching signal generator 30 Analog to digital converter (ADC1)
31 Band pass filter 32 Amplifier 33 Mixer 34 Analog to digital converter (ADC2)
35 Detector 41 Operation unit (conventional block diagram)
42 Digital-to-analog converter (DAC) (conventional block diagram)
43 Quadrature modulator (conventional block diagram)
44 High-frequency amplifier (conventional block diagram)
45 Directional coupler (conventional block diagram)
46 Antenna (conventional block diagram)
47 FB circuit (conventional block diagram)
51 Analog to Digital Converter (ADC) (Conventional Block Diagram)
52 Bandpass filter (conventional block diagram)
53 Amplifier (Conventional block diagram)
54 Amplitude equalizer (conventional block diagram)
55 Mixer (conventional block diagram)

Claims (3)

A part of the transmission signal is branched from the main signal system of a wireless communication system that modulates and amplifies the input signal to output a radio frequency transmission signal, and a distortion compensation signal is added to the input transmission signal based on the fed back signal. In addition, in a non-linear distortion compensator that compensates for distortion of the radio frequency transmission signal,
Means for generating a test signal during testing;
First branching means for branching the radio frequency transmission signal before amplification;
Switching means for switching one of the branch transmission signal branched before the amplification and the transmission signal of the radio frequency after amplification by a switching control signal;
At the time of the test, a first branching means branches a radio frequency test signal to the switching means, and a second branching means for branching the branched branch test signal to a feedback circuit and a detection circuit;
Feedback circuit frequency characteristic calculation means for calculating the frequency characteristic of the feedback circuit from the output of the branched feedback circuit, and detection circuit frequency characteristic calculation means for calculating the frequency characteristic of the detection circuit from the output of the branched detection circuit. And means for calculating the frequency characteristic deviation of the feedback circuit from the difference between the frequency characteristic of the feedback circuit calculated by the feedback circuit frequency characteristic calculation means and the frequency characteristic calculated by the detection circuit frequency characteristic calculation means; ,
Distortion compensation calculation means for adding the inverse characteristic of the calculated feedback circuit frequency characteristic deviation as a distortion compensation signal to the transmission signal of the main signal system during operation;
A non-linear distortion compensation amplifying apparatus comprising: A part of the transmission signal is branched from the main signal system of a wireless communication system that modulates and amplifies the input signal to output a radio frequency transmission signal, and a distortion compensation signal is added to the input transmission signal based on the fed back signal. In addition, a nonlinear distortion compensation method for a nonlinear distortion compensator that compensates for distortion of the transmission signal of the radio frequency,
Generate a test signal during the test,
The generated test signal is branched and transmitted to a feedback circuit and a detection circuit before the amplification of the forward system,
Calculate feedback circuit frequency characteristics from the output of the feedback circuit,
Calculate the detection circuit frequency characteristic from the output of the detection circuit,
The frequency characteristic deviation of the feedback circuit is calculated from the difference between the calculated feedback circuit frequency characteristic and the detection circuit frequency characteristic,
A nonlinear distortion compensation method for a nonlinear distortion compensation apparatus, wherein nonlinear distortion compensation is performed by adding an inverse characteristic of the calculated feedback circuit frequency characteristic deviation to a transmission signal of the main signal system as a distortion compensation signal during operation. The nonlinear distortion compensation method for a nonlinear distortion compensation apparatus according to claim 2,
3. The nonlinear distortion compensation of the nonlinear distortion compensator according to claim 2, wherein the failure location of the nonlinear distortion compensator is estimated by judging the power calculated from the path of the feedback circuit or the path of the detector circuit. Method.