JP6665500B2 - Characteristic detecting device and characteristic detecting method - Google Patents

Description

  The present invention relates to a characteristic detecting device and a characteristic detecting method, and more particularly to a technique for detecting a characteristic change of a power amplifier.

  AM (Amplitude Modulation) / AM characteristics and AM / PM (Phase Modulation) characteristics are known as indices indicating input / output characteristics of a power amplifier (PA) provided in a transmitter. The AM / AM characteristic indicates a relationship between the amplitude of the input signal to the PA and the amplitude of the output signal. The AM / PM characteristic indicates a relationship between the amplitude of the input signal to the PA and the amount of phase change of the output signal. The AM / AM characteristic of an ideal PA having no distortion indicates that the amplitude of the output signal changes linearly with the change in the amplitude of the input signal. Further, the ideal AM / PM characteristics of the PA indicate that the phase of the output signal does not change with respect to the change in the amplitude of the input signal and is constant.

  As a distortion compensation technique for a transmitter, digital pre-distortion (DPD) is known. The measurement results of the AM / AM and AM / PM characteristics and their dispersion include distortion that can be sufficiently compensated by DPD and other distortion that cannot be sufficiently compensated by DPD. Hereinafter, “distortion that can be sufficiently compensated by DPD” is referred to as “compensable distortion”, and “distortion that cannot be sufficiently compensated by DPD” is referred to as “uncompensable distortion”. The compensable distortion includes distortion caused by a change in linear characteristics and memory distortion. Memory distortion is distortion that occurs when an output signal of an amplifier is affected by a past input signal. The non-compensable distortion includes a distortion caused by aging of the entire PA.

  Regarding the distortion measurement and distortion compensation of PA, Patent Literature 1 describes a technique for performing distortion compensation of PA based on AM / AM characteristics and AM / PM characteristics. Patent Literature 2 describes a technique for estimating a characteristic change due to aging of PA. Further, Non-Patent Document 1 describes a technique for generating a signal that compensates for distortion.

JP 2014-103540 A JP 2012-178740 A

J. Jeong et al., "Wideband Envelope Tracking Power Amplifiers With Reduced Bandwidth Power Supply Waveforms and Adaptive Digital Predistortion Techniques", IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, Vol. 57, No. 12, pp. 3307-3314, December 2009 , USA

  The uncompensable distortion includes distortion that does not include memory distortion and the like and that occurs due to aging. Therefore, by extracting only the uncompensable distortion included in the output of the PA and measuring the secular change of the distortion, it can be used as a guide for maintenance and replacement of the PA. However, in general, the operating modulated wave input to the PA includes a random signal. Therefore, in order to completely compensate for the compensable distortion included in the operating modulated wave and extract only the uncompensable distortion, a large-scale operation is required. Circuit is required. Therefore, it is difficult to extract only the uncompensable distortion from the output of the PA.

(Object of the invention)
An object of the present invention is to provide a technique capable of extracting distortion (uncompensable distortion) that cannot be sufficiently compensated by DPD.

  The characteristic detection device of the present invention includes a first signal generation unit configured to generate a first signal, and the first signal generation unit configured to generate the first signal and the second signal obtained by amplifying the first signal by an amplifier. Second signal generating means for generating a third signal in which a signal in which distortion that can be removed by a predistortion compensation (DPD: Digital Pre-Distortion) process is suppressed by amplification by an amplifier is output as a fourth signal; A first switch that outputs one of the first signal and the third signal to the amplifier, and a distortion added in the amplifier based on the first signal and the fourth signal. Measuring means for measuring.

  The characteristic detecting method according to the present invention generates a first signal, and performs predistortion by amplification by the amplifier based on the first signal and a second signal obtained by amplifying the first signal by the amplifier. A signal in which distortion that can be removed by compensation (DPD: Digital Pre-Distortion) processing is suppressed is generated as a fourth signal to generate a third signal, and one of the first signal and the third signal is generated. To the amplifier, and measuring distortion added in the amplifier based on the first signal and the fourth signal.

  The present invention makes it possible to extract distortion that cannot be sufficiently compensated by DPD.

FIG. 2 is a block diagram illustrating a configuration example of a transmitter 100 according to the first embodiment. 5 is a flowchart illustrating an operation example of the transmitter 100. FIG. 9 is a diagram illustrating an example of AM / AM characteristics when compensable distortion and uncompensable distortion are not separated. FIG. 9 is a diagram illustrating an example of AM / AM characteristics when the uncompensable distortion is relatively small. FIG. 7 is a diagram illustrating an example of AM / AM characteristics when distortion that cannot be compensated is relatively large. It is a block diagram showing the example of composition of transmitter 100A of a 2nd embodiment. 6 is a flowchart illustrating an operation example of the transmitter 100A.

  Detects changes in PA characteristics by measuring dispersion of AM / AM characteristics and dispersion of AM / PM characteristics (that is, dispersion of output amplitude and dispersion of input / output phase difference when a signal of a certain constant amplitude is given). it can. In the embodiment described below, the compensable distortion generated in the PA is compensated by a simple mechanism by using a test signal independent of the main signal, and only the uncompensated distortion generated in the PA is extracted. Further, an embodiment in which the time for replacing or repairing the PA is determined based on the amount of uncompensable distortion will be described.

(First embodiment)
FIG. 1 is a block diagram illustrating a configuration example of a transmitter 100 according to the first embodiment of the present invention. The transmitter 100 includes a modulator 1, a power amplifier (PA) 2, and a distributor 3. As the distributor 3, for example, a directional coupler can be used. The transmitter 100 is used, for example, for transmitting a television signal. The modulator 1 modulates input digital data and converts the digital data into a radio frequency (RF) signal. PA 2 amplifies the RF signal output from modulator 1 to a predetermined power. A distributor 3 is arranged at the output of PA2. The distributor 3 branches the output of the PA 2 into two. Divider 3 outputs a part of the branched output of PA 2 to modulator 1, and outputs the other to antenna 4. The antenna 4 radiates the output of the PA 2 input from the distributor 3 as a radio wave.

  The modulator 1 includes a modulation unit 10, a DPD unit 11, switches 12 and 15, a test signal generation unit 13, a compensation test signal generation unit 14, and a measurement unit 16. The output signal of PA2 input from distributor 3 is input to DPD unit 11 and compensation test signal generation unit 14.

  The modulation unit 10 modulates digital data such as a video signal into a signal specified by ISDB-T or the like. ISDB stands for “Integrated Services Digital Broadcasting”, and ISDB-T stands for “ISDB for Terrestrial Television Broadcasting”.

  The DPD unit 11 has a digital predistortion compensation function. That is, the DPD unit 11 adds a distortion having a characteristic opposite to the distortion generated in the PA 2 to the signal modulated by the modulation unit 10. As a result, the compensable distortion included in the output signal of PA2 is suppressed.

  The switches 12 and 15 switch the path of the electric signal. As the switches 12 and 15, one-input two-output switches can be used. The switch 12 outputs one of the main signal output from the DPD unit 11 and a diagnostic signal for diagnosing the state of PA2 to PA2. The switch 15 outputs one of the test signal and the compensation test signal to the switch 12 as a diagnostic signal. The measurement unit 16 measures the AM / AM characteristics, the AM / PM characteristics of the PA2, and their dispersion based on the signal input from the distributor 3 and the test signal.

  The test signal generator 13 generates and outputs a test signal. The test signal is a known repetitive modulation signal. As the test signal, a signal defined by ISDB-T and recording a part of the signal generated by the modulator 1 may be used. Compensation test signal generating section 14 generates a compensation test signal based on the test signal and the signal obtained by amplifying test signal in PA2. The compensation test signal is a signal in which “compensable distortion” included in the test signal is sufficiently compensated by being amplified by the PA2. The compensation test signal is obtained by calculating the inverse characteristic of PA2 for all sample data of the test signal for each sample data. That is, the compensation test signal is easily generated from the test signal and the output signal of PA2 without preparing a dedicated device.

  When the compensation test signal is amplified by PA2, PA2 outputs a signal in which compensable distortion including memory distortion and linear characteristics is sufficiently compensated. In other words, it can be considered that the distortion of the signal obtained by amplifying the compensation test signal by PA2 hardly includes compensable distortion, but includes only uncompensable distortion. Therefore, from the AM / AM characteristics and AM / PM characteristics of the signal and their variances, it is possible to extract only uncompensable distortion, that is, distortion that cannot be compensated by DPD.

(Explanation of Operation of First Embodiment)
FIG. 2 is a flowchart showing an operation example of the transmitter 100 shown in FIG. Normally, the switch 12 is set so that the output of the DPD unit 11 is amplified by PA2 ("normal mode"). In the normal mode, a part of the output of the PA 2 is input to the DPD unit 11 via the distributor 3. The DPD unit 11 performs a process for DPD on the signal output from the modulation unit 10 based on the signal input from the distributor 3.

  The flowchart of FIG. 2 is started when the modulator 1 is changed from the “normal mode” to the “PA diagnostic mode”. First, the modulator 1 is set to the “PA diagnostic mode”. The instruction to set the PA diagnostic mode may be issued by a maintenance person from outside the modulator 1. In the PA diagnostic mode, first, the switches 12 and 15 are set so that the test signal output from the test signal generator 13 is amplified by the PA2 (step S1 in FIG. 2).

  Next, the compensation test signal generation unit 14 generates a compensation test signal Xc (t) based on the test signal and the output signal of PA2 (Step S2). Assuming that the test signal is X (t) and the output signal of PA2 is Y (t), the compensation test signal Xc (t) can be easily obtained using the following equation (1).

  Subsequently, the switches 12 and 15 are set so that the compensation test signal is amplified by PA2 (step S3). In the transition from step S2 to step S3, the input of the switch 15 is switched from the test signal generator 13 to the compensation test signal generator 14. When the compensation test signal is amplified by PA2, PA2 outputs a signal in which the compensable distortion is sufficiently compensated but the uncompensable distortion remains. The measurement unit 16 measures the AM / AM characteristics and the AM / PM characteristics of the PA2 based on the test signal and the output signal of the PA2, and further measures their variance (Step S4). Among the distortions included in the output signal of PA2, the compensable distortion has been compensated in advance by the procedure of step S2. Therefore, the larger the variance measured by the measuring unit 16 is, the larger the distortion that cannot be compensated by the DPD is.

  FIG. 3 is a diagram illustrating an example of the AM / AM characteristic when the compensable distortion and the uncompensable distortion are not separated in the output of PA2. The horizontal axis of FIG. 3 is the amplitude P0 of the test signal, and the vertical axis is the amplitude P1 of the output signal of PA2. P0 and P1 are arbitrary scales. The greater the variation of the AM / AM characteristic in the vertical axis direction, that is, the greater the variance of the output power with respect to the same input power, the greater the distortion of the output signal. However, since the dispersion in FIG. 3 includes the compensable distortion and the uncompensable distortion, it is not possible to determine only the magnitude of the uncompensable distortion from the measurement result in FIG.

  4 and 5 are diagrams showing examples of the AM / AM characteristics of PA2 measured according to the procedure of FIG. FIG. 4 shows an example where the uncompensable distortion is relatively small, and FIG. 5 shows an example where the uncompensable distortion is large as compared with FIG. 4 and 5, the horizontal axis is the test signal amplitude P0, and the vertical axis is the output signal amplitude P2 of PA2. 4 and 5 show examples of characteristics when the compensation test signal is input to PA2. According to the procedure of FIG. 2, the compensable distortion is removed from the compensation test signal amplified by PA2. As a result, in FIGS. 4 and 5, the amount of uncompensable distortion can be extracted from the dispersion of the AM / AM characteristics. Also, by measuring the AM / AM characteristics using the compensation test signal at appropriate time intervals and determining the variation with time of the dispersion, the variation with time of the uncompensable distortion can be known. According to such a procedure, the amount of deterioration of the PA can be more accurately and quantitatively detected based on the change over time of the uncompensable distortion as compared with the case where the compensable distortion and the uncompensable distortion are not separated.

  In the present embodiment, the procedure for extracting the amount or change of the uncompensable distortion based on the measurement result of the variance of the AM / AM characteristic has been described. However, the amount or change of the uncompensable distortion can also be obtained based on the measurement result of the dispersion of AM / PM. In the AM / PM characteristic, the change in the phase of the output signal with respect to the change in the amplitude of the input signal to PA2 is measured. By measuring the variance of the AM / PM characteristic, that is, the magnitude of the variance of the phase change, the amount or change of the uncompensable distortion can be extracted. Further, the amount or change of the uncompensable distortion may be obtained from only the variance value of the AM / AM characteristic, only the variance value of the AM / PM characteristic, or a value obtained by weighting these variances.

  The procedure for obtaining the amount of distortion from the variance value is not particularly limited. For example, in FIG. 4 or 5, the variance of the output amplitude of the PA2 of the test signal at a specific amplitude may be defined as the amount of distortion. Alternatively, the variance of the output amplitude of PA2 with respect to the amplitudes of a plurality of test signals may be obtained, and the average value thereof may be defined as the amount of distortion.

  As described above, the transmitter 100 according to the first embodiment can extract the distortion that cannot be compensated for by the DPD (uncompensable distortion) generated in the PA2, and can determine the amount of the PA degradation based on the amount of the distortion that cannot be compensated for by the DPD. Can be detected more accurately and quantitatively.

  Note that the test signal generated by the test signal generation unit 13 is not limited to a signal generated from a modulated signal (for example, an ISDB-T signal) output from the modulator 1. For example, another signal having the same signal distribution (amplitude probability distribution) or occupied bandwidth as the modulation signal may be used as the test signal. The test signal may be a repetitive signal that can be transmitted as a broadcast signal, such as a repetitive video signal such as a “color bar”.

(Second embodiment)
FIG. 6 is a block diagram illustrating a configuration example of a transmitter 100A according to the second embodiment of the present invention. The transmitter 100A includes a modulator 1A, a PA 2, and a distributor 3. As the distributor 3, for example, a directional coupler can be used. The modulator 1A of the second embodiment is different from the modulator 1 of the first embodiment in that a modulator 17 is provided. The measurement result of the amount of uncompensable distortion by the measurement unit 16 is input to the detection unit 17. Since the configuration and operation of a portion other than the detection unit 17 of the transmitter 100A are the same as those of the transmitter 100 of the first embodiment, elements having the same functions are denoted by the same reference numerals, and description thereof will be omitted. I do.

  The detection unit 17 detects the deterioration of the PA based on the measurement result of the AM / AM characteristic or the dispersion of the AM / PM characteristic in the measurement unit 16. For example, when at least one of the variance of the AM / AM characteristic and the variance of the AM / PM characteristic is equal to or greater than a certain value, the detection unit 17 determines that PA2 has deteriorated. When the deterioration of PA2 is detected, the detection unit 17 may output an alarm prompting maintenance of PA2 to the outside.

  FIG. 7 is a flowchart showing an operation example of the transmitter 100A shown in FIG. The flowchart of FIG. 7 is different from the flowchart of FIG. 2 in that step S5 is added. The procedure of steps S1 to S4 in FIG. 7 is the same as that in FIG. As described above, if at least one of the variance of the AM / AM characteristic and the variance of the AM / PM characteristic is equal to or more than a certain value, the detection unit 17 determines that PA2 has deteriorated (step S5 in FIG. 7). .

  The transmitter 100A of the second embodiment incorporates a diagnostic function based on the measurement result of distortion that cannot be suppressed even by using the DPD into the modulator 1A as the detection unit 17. Thereby, in addition to the effect of the transmitter 100 of the first embodiment, the transmitter 100A of the second embodiment has the effect of judging the deterioration of PA2 and notifying the judgment result to the maintenance person quickly. . The transmitter 100A according to the second embodiment can realize a function of diagnosing the deterioration of the PA with a simple configuration without requiring a dedicated device.

(Third embodiment)
The configuration having the effects described in the first embodiment is also realized in a characteristic detecting device according to the third embodiment described below. Hereinafter, the description will be given with the parentheses added to the names and reference numerals of the elements corresponding to FIG. 1 of the first embodiment.

  The characteristic detection device includes a first signal generation unit (13), a second signal generation unit (14), a first switch (15), and a measurement unit (16). The first signal generator (13) generates a first signal (test signal). A second signal generator configured to generate a third signal (compensation test signal) based on the first signal and a second signal obtained by amplifying the first signal by the amplifier (2); I do. The third signal (compensation test signal) is amplified by the amplifier (2) and output as a fourth signal.

  Here, when the third signal is amplified by the amplifier (2), the signal whose distortion that can be removed by the DPD processing is suppressed is output from the amplifier (2) as a fourth signal. Is generated as follows.

  The switch (15) outputs one of the first signal (test signal) and the third signal (compensation test signal) to the amplifier (2). The measuring unit (16) is added in the amplifier (2) based on the fourth signal obtained by amplifying the third signal (compensation test signal) by the amplifier (2) and the first signal (test signal). Measure distortion.

  In the characteristic detecting device having such a configuration, distortion that can be removed by the DPD process is suppressed in the fourth signal obtained by amplifying the third signal by the amplifier. Therefore, only the distortion that cannot be removed by the DPD process can be extracted from the distortion measured based on the first signal and the fourth signal. As a result, the characteristic detection device according to the third embodiment can detect the deterioration of the amplifier more accurately and quantitatively.

  The measurement unit of each embodiment may include a central processing unit (Central Processing Unit, CPU) and a storage device. The CPU and the storage device can be included in any element of the modulator 1 or 1A. The CPU implements the functions of the modulator of each embodiment by executing a program stored in the storage device. The storage device is a fixed non-transitory recording medium. As the recording medium, a semiconductor memory or a fixed magnetic disk device is used, but is not limited thereto. Each unit other than the measurement unit may be controlled by an instruction from the measurement unit.

  Embodiments of the present invention may be described as the following supplementary notes, but are not limited thereto.

(Appendix 1)
First signal generating means for generating a first signal;
Based on the first signal and the second signal obtained by amplifying the first signal by an amplifier, distortion that can be removed by a predistortion compensation (DPD: Digital Pre-Distortion) process by amplification by the amplifier is provided. Second signal generation means for generating a third signal from which the suppressed signal is output as a fourth signal;
A first switch that outputs one of the first signal and the third signal to the amplifier;
Measuring means for measuring distortion added in the amplifier based on the first signal and the fourth signal;
A characteristic detecting device comprising:

(Appendix 2)
Assuming that the third signal is Xc (t), the first signal is X (t), and the second signal is Y (t), Xc (t) is X (t) × X (t) / The characteristic detecting device according to Supplementary Note 1, which satisfies Y (t).

(Appendix 3)
The measuring means is added to the amplifier based on at least one of variance of AM (Amplitude Modulation) / AM characteristics and variance of AM / PM (Phase Modulation) characteristics of the fourth signal with respect to the first signal. 3. The characteristic detecting device according to claim 1 or 2, wherein the characteristic detecting device measures distortion.

(Appendix 4)
The characteristic detecting device according to any one of supplementary notes 1 to 3, wherein the first signal is a signal based on ISDB-T (Integrated Services Digital Broadcasting for Terrestrial Television Broadcasting).

(Appendix 5)
Modulating means for modulating the input data and outputting a fifth signal;
A distortion compensator that outputs a signal obtained by performing a DPD process on the fifth signal based on an output of the amplifier as a sixth signal;
A second switch that outputs one of the output of the first switch and the sixth signal to the amplifier;
The characteristic detection device according to any one of supplementary notes 1 to 4, further comprising:

(Appendix 6)
The characteristic detecting device according to claim 5, wherein the first signal has the same amplitude probability distribution and occupied bandwidth as the fifth signal.

(Appendix 7)
7. The characteristic detecting device according to claim 5, wherein the first signal is a repetitive signal included in the fifth signal.

(Appendix 8)
8. The characteristic detection device according to any one of supplementary notes 5 to 7, further comprising a detection unit that detects deterioration of the amplifier based on a measurement result of the measurement unit.

(Appendix 9)
A characteristic detection device according to any one of supplementary notes 5 to 8,
An amplifier that amplifies the first signal, the third signal, and the sixth signal output from the characteristic detection device;
A distributor that outputs a part of the output of the amplifier to the second signal generation unit and the distortion compensator of the characteristic detection device;
Transmitter.

(Appendix 10)
Generating a first signal;
Based on the first signal and the second signal obtained by amplifying the first signal by an amplifier, distortion that can be removed by a predistortion compensation (DPD: Digital Pre-Distortion) process by amplification by the amplifier is provided. Generating a third signal in which the suppressed signal is output as a fourth signal;
Outputting one of the first signal and the third signal to the amplifier;
Measuring distortion added in the amplifier based on the first signal and the fourth signal;
Characteristics detection method.

(Appendix 11)
In the computer of the characteristic detection device,
Generating a first signal;
Based on the first signal and the second signal obtained by amplifying the first signal by an amplifier, distortion that can be removed by a predistortion compensation (DPD: Digital Pre-Distortion) process by amplification by the amplifier is provided. A procedure for generating a third signal in which the suppressed signal is output as a fourth signal;
Outputting one of the first signal and the third signal to the amplifier;
Measuring a distortion added in the amplifier based on the first signal and the fourth signal;
Characteristic detection program for executing

  Each embodiment of the present invention can be applied to a wireless transmitter such as a television transmitter, a radio transmitter, and a mobile phone transmitter, and a wired transmission device such as a cable television.

1, 1A modulator 2 power amplifier (PA)
Reference Signs List 3 splitter 4 antenna 10 modulation unit 11 DPD unit 12, 15 switch 13 test signal generation unit 14 compensation test signal generation unit 16 measurement unit 17 detection unit 100, 100A transmitter

Claims (10)

First signal generating means for generating a first signal;
Based on the first signal and the second signal obtained by amplifying the first signal by an amplifier, distortion that can be removed by a predistortion compensation (DPD: Digital Pre-Distortion) process by amplification by the amplifier is provided. Second signal generation means for generating a third signal from which the suppressed signal is output as a fourth signal;
A first switch that outputs one of the first signal and the third signal to the amplifier;
Measuring means for measuring distortion added in the amplifier based on the first signal and the fourth signal;
A characteristic detecting device comprising:   Assuming that the third signal is Xc (t), the first signal is X (t), and the second signal is Y (t), Xc (t) is X (t) × X (t) / The characteristic detection device according to claim 1, wherein Y (t) is satisfied.   The measuring means is added to the amplifier based on at least one of variance of AM (Amplitude Modulation) / AM characteristics and variance of AM / PM (Phase Modulation) characteristics of the fourth signal with respect to the first signal. The characteristic detecting device according to claim 1, wherein the characteristic detecting device measures distortion.   4. The characteristic detection device according to claim 1, wherein the first signal is a signal based on ISDB-T (Integrated Services Digital Broadcasting for Terrestrial Television Broadcasting). 5. Modulating means for modulating the input data and outputting a fifth signal;
A distortion compensator that outputs a signal obtained by performing a DPD process on the fifth signal based on an output of the amplifier as a sixth signal;
A second switch that outputs one of the output of the first switch and the sixth signal to the amplifier;
The characteristic detecting device according to any one of claims 1 to 4, further comprising:   The characteristic detection device according to claim 5, wherein the first signal has the same probability distribution and occupied bandwidth of amplitude as the fifth signal.   The characteristic detecting device according to claim 5, wherein the first signal is a repetitive signal included in the fifth signal.   8. The characteristic detecting device according to claim 5, further comprising a detecting unit configured to detect deterioration of the amplifier based on a measurement result of the measuring unit. A characteristic detection device according to any one of claims 5 to 8,
An amplifier that amplifies the first signal, the third signal, and the sixth signal output from the characteristic detection device;
A distributor that outputs a part of the output of the amplifier to the second signal generation unit and the distortion compensator of the characteristic detection device;
Transmitter. Generating a first signal;
Based on the first signal and the second signal obtained by amplifying the first signal by an amplifier, distortion that can be removed by a predistortion compensation (DPD: Digital Pre-Distortion) process by amplification by the amplifier is provided. Generating a third signal in which the suppressed signal is output as a fourth signal;
Outputting one of the first signal and the third signal to the amplifier;
Measuring distortion added in the amplifier based on the first signal and the fourth signal;
Characteristics detection method.

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