JP2007318297A - Distortion compensating circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distortion compensating circuit capable of accurately compensating distortion by evading a case wherein a vector adjuster becomes unable to adjust a pilot signal. <P>SOLUTION: The majority of basic constitution of the distortion compensating circuit is similar to a conventional feedforward type distortion compensating circuit. Namely, the distortion compensating circuit comprises a first divider (1), a first vector adjuster (2), a main amplifier (3), a first delay line (4), a second divider (5), a first synthesizer (6), a second delay line (7), a second vector adjuster (8), an error amplifier (9), a second synthesizer (10), a controller (11), a pilot signal generator (12), and a pilot signal detector (13). This distortion compensating circuit, however, is different from the conventional feedforward type distortion compensating circuit as to the pilot signal generator and the pilot signal detector, wherein the pilot signal generator varies the frequency of a pilot signal to be generated and the pilot signal detector synchronizes with the varied frequency. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a feedforward type distortion compensation circuit.

  As the distortion compensation circuit, a feed forward type is widely adopted. The feedforward distortion compensation circuit is for removing distortion components generated when an input signal is amplified by using a detour signal distributed from the input signal, and its basic configuration is as shown in FIG.

  In the feedforward distortion compensation circuit shown in FIG. 2, first, a high frequency signal is input from the input terminal 20, and is distributed to the initial main signal and the initial detour signal by the first distributor 1. (Hereinafter, the stage signal output from the first distributor is referred to as “initial”.) The initial main signal passes through the first vector adjuster 2 and is amplified by the main amplifier 3. The initial main signal amplified by the main amplifier 3 is added to the second distributor 5 while including the distortion component generated by the main amplifier 3, and a part of the initial main signal is used as the distortion detection signal. Added to 6. On the other hand, the initial detour signal is corrected by the delay time of the main amplifier 3 in the first delay line 4 and then added to the first combiner 6 and is combined with the distortion detection signal to make an intermediate detour. Output as a road signal. (Hereinafter, the detour signal output from the first synthesizer will be labeled “middle”.) In the first synthesizer 6, the detour signal includes a distortion component in the opposite phase. The distortion detection signal is synthesized, and only the distortion signal is extracted.

  The intermediate bypass signal passes through the second vector adjuster 8, is amplified by the error amplifier 9, and is added to the second combiner 10. On the other hand, the intermediate main signal including the distortion component that has passed through the second distributor 5 is corrected by the delay time of the error amplifier 9 in the second delay line 7 and added to the second combiner 10. (Hereinafter, the main signal distributed from the second synthesizer will be labeled “intermediate”.) In this second synthesizer 10, the distortion of the intermediate detour signal that is out of phase with each other. The component and the distortion component of the intermediate main signal are combined and canceled out, and the distortion component is removed from the main signal.

  However, if the characteristics of the main amplifier 3 change due to the influence of temperature and time, the distortion canceling characteristic of the distortion compensation circuit is deteriorated. In order to solve this problem, a method using a pilot signal is employed.

The pilot signal is a first pilot signal whose main purpose is adjustment of the first vector adjuster 2 (distortion detection circuit) and a second one whose main purpose is adjustment of the second vector adjuster 8 (distortion removal circuit). Two types of pilot signals are used. The first pilot signal is injected into the input signal from the first pilot signal generator 24 at the input end, and is detected by the first pilot signal detector 25 provided at the output end of the synthesizer 6. Then, the phase and gain are adjusted by the first vector adjuster 2 so that the first pilot signal is minimized. On the other hand, the second pilot signal is injected into the middle stage of the main amplifier 3 from the second pilot signal generator 22 and detected by the second pilot signal detector 23 provided at the output end. Then, the phase and gain are adjusted by the second vector adjuster 8 so that the second pilot signal is minimized. Thus, if the phase and gain are adjusted by the first and second vector adjusters 2 and 8 so that the first and second pilot signals are minimized, regardless of changes in the characteristics of the main amplifier 3, The characteristic of canceling the distortion of the distortion compensation circuit can be maintained. At this time, the outputs of the first pilot signal detector 25 and the second pilot signal detector 23 are taken in, and the control unit 21 for operating the first and second vector adjusters 2 and 8 is used, so that efficient operation is achieved. Adjustments can be made. For example, Japanese Patent Laid-Open No. 4-83406 discloses a document disclosing a feedforward type distortion compensation circuit using this pilot signal.
JP-A-4-83406

  However, in the feedforward distortion compensation circuit, a pilot signal having a predetermined frequency is used. For this reason, when an unexpected spurious is generated in the band, the influence becomes large, and there is a problem that adjustment of the pilot signal becomes impossible and accurate distortion compensation cannot be performed. In addition, even when an unexpected signal is input in the band, or when multiple signals are input intermittently in the band, the pilot signal cannot be detected due to the influence of spurious generated by the input signal. After all, there is a problem that adjustment of the pilot signal becomes impossible and accurate distortion compensation cannot be performed.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a distortion compensation circuit capable of accurately compensating for distortion while avoiding a situation in which adjustment of a pilot signal by a vector adjuster becomes impossible.

  The basic configuration of the first distortion compensation circuit according to the present invention is the same as that of the conventional feedforward distortion compensation circuit. That is, first distributor, first vector adjuster, main amplifier, first delay line, second distributor, first combiner, second delay line, second vector adjuster, error It comprises an amplifier, a second synthesizer, a control unit, a pilot signal generator, and a pilot signal detector. However, it differs from the conventional feedforward distortion compensation circuit in the pilot signal generator and the pilot signal detector, the pilot signal generator changes the frequency of the pilot signal to be generated, and the pilot signal detector It is characterized by synchronizing with the changed frequency.

  The frequency change may be performed by sweeping within a predetermined range.

  The change of the frequency may be executed by shifting to a predetermined specific value.

  The basic configuration of the second distortion compensation circuit according to the present invention is the same as that of the conventional feedforward distortion compensation circuit. That is, first distributor, first vector adjuster, main amplifier, first delay line, second distributor, first combiner, second delay line, second vector adjuster, error It comprises an amplifier, a second synthesizer, a control unit, a pilot signal generator, and a pilot signal detector. However, the pilot signal detector differs from the conventional feedforward distortion compensation circuit in that the pilot signal detector detects the pilot signal in a narrow band centered on the frequency of the pilot signal. To do.

  According to the first distortion compensation circuit of the present invention, the pilot signal generator changes the frequency of the pilot signal to be generated, and the pilot signal detector is synchronized with the changed frequency. A frequency that does not affect distortion compensation can be detected. Therefore, even if unexpected spurious signals generated in the band, unexpected input signals into the band, or multiple continuous signal inputs into the band occur, the pilot signal cannot be adjusted by the vector adjuster. The situation can be avoided and distortion can be compensated accurately.

  The frequency change may be executed by sweeping within a predetermined range, or may be executed by shifting to a predetermined specific value. The above-described change method may be unclear about the optimum frequency, and its application range is wide. However, there is a drawback that it takes time until the distortion compensation is executed. On the other hand, the later changing method is limited to a case where the optimum frequency is known in advance, but has an advantage that the distortion compensation is executed in a short time.

  According to the second distortion compensation circuit of the present invention, since the pilot signal detector detects the pilot signal in a narrow band centered on the frequency, the distortion in the vicinity of the input high-frequency signal can be detected, Further, when the input high-frequency signal is two or more waves, distortion between the signals can be detected.

  The width of the narrow band may be, for example, 1 kHz to 100 kHz. Particularly, if it is ± 15 kHz, it is suitable for applications such as AMP for terrestrial digital broadcasting. However, this narrow band width needs to be able to capture the modulated wave component of the signal to be detected.

  FIG. 1 shows a specific example of the present invention. FIG. 1 is a circuit diagram of a distortion compensation circuit. In addition, the same code | symbol as what was used for description of a prior art is attached | subjected to the part which employ | adopted the above-mentioned prior art as it is, and the description is abbreviate | omitted.

  The pilot signal generator 12 and pilot signal detector 13 of this distortion compensation circuit are first of the conventional feedforward type distortion compensation circuit (second pilot signal generator 22 and second pilot signal detector 23 of FIG. 2). It plays the same role as. That is, the pilot signal generator 12 injects the pilot signal into the middle stage of the main amplifier 3, and the pilot signal detector 13 provided at the output end detects this. And the control part 11 adjusts a phase and a gain with the 2nd vector adjuster 8 so that this pilot signal may become the minimum. In this way, the phase and gain are adjusted by the first and second vector adjusters 2 and 8 so that the pilot signal detected by the pilot signal detector 13 is minimized, regardless of changes in the characteristics of the main amplifier 3. Therefore, it is possible to maintain the characteristic of canceling the distortion of the distortion compensation circuit.

  On the other hand, if the detection level of the pilot signal detector 13 does not fall below the level set in advance in the control unit 11 even if the phase and gain of the first and second vector adjusters 2 and 8 are adjusted, the control unit 11 A control signal is supplied to the pilot generator 12 to sweep the frequency of the pilot signal generator 12. At the same time, a control signal is supplied from the control unit 11 to the pilot signal detector 13 to synchronize with the frequency of the pilot signal generator 12. Then, the phase and gain of the first and second vector adjusters 2 and 8 are adjusted at the frequency point at which the output of the pilot signal detector 13 is minimized, so that the pilot signal is minimized.

  When the cause of the inability to adjust the pilot signal is specified to some extent, and the optimal pilot signal frequency is known at that time, the frequency may be stored in the control unit 11 in advance. The change of the frequency of the pilot signal may be executed not by sweeping but by shifting to the stored value. The change of the frequency of the pilot signal may be executed not by sweeping but by shifting to the stored value. As a result, distortion compensation can be executed in a shorter time compared to the change by sweeping.

  The pilot signal detector 13 may detect the pilot signal in a narrow band centered on the frequency of the pilot signal. The band for detecting the pilot signal may be gradually narrowed. However, if the cause that makes the pilot signal adjustment impossible is specified to some extent and the optimum band is known at that time, the band is set in the control unit 11. It may be stored in advance. The band for detecting the pilot signal may be shifted to the stored band instead of gradually narrowing. In that case, the distortion compensation is performed in a shorter time than in the case of gradually narrowing. The width of the narrow band may be, for example, 1 kHz to 100 kHz. Particularly, if it is ± 15 kHz, it is suitable for applications such as AMP for terrestrial digital broadcasting. However, this narrow band width needs to be able to capture the modulated wave component of the signal to be detected.

It is a circuit diagram which shows the specific example of the distortion compensation circuit of this invention. It is a circuit diagram which shows the prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st divider | distributor 2 1st vector regulator 3 Main amplifier 4 1st delay line 5 2nd divider | distributor 6 1st synthesizer 7 2nd delay line 8 2nd vector regulator 9 Error amplifier 10 Second Synthesizer 11 Control Unit 12 Pilot Signal Generator 13 Pilot Signal Detector

Claims (4)

A first distributor (1) for distributing a high-frequency input signal to an initial main signal and an initial bypass signal;
A first vector adjuster (2) for phase control and gain adjustment of the initial main signal;
A main amplifier (3) for amplifying the initial main signal;
A first delay line (4) that matches the phase of the initial bypass signal with the phase of the initial main signal amplified by the main amplifier (3);
A second distributor (5) for distributing the initial main signal including a distortion component generated in the main amplifier to an intermediate main signal and a distortion detection signal;
A first combiner (6) for combining the distortion detection signal and the initial detour signal and outputting an intermediate detour signal;
A second delay line (7) for matching the phase of the intermediate main signal and the intermediate bypass signal;
A second vector adjuster (8) for phase control and gain adjustment of the intermediate detour signal;
Detour error amplifier (9),
A second combiner (10) for combining the intermediate bypass signal and the intermediate main signal and outputting the final main signal from which the distortion component has been removed;
A control unit (11) for performing phase control and gain adjustment; and
A pilot signal generator (12) for injecting a pilot signal into the middle stage of the main amplifier (3);
A pilot signal detector (13) for detecting the pilot signal at the output of the second combiner (10);
Consists of
The pilot signal generator (12) changes the frequency of a pilot signal to be generated, and the pilot signal detector (13) synchronizes with the changed frequency.   The distortion compensation circuit according to claim 1, wherein the frequency change is executed by sweeping within a predetermined range.   The distortion compensation circuit according to claim 1, wherein the frequency change is executed by shifting to a predetermined specific value. A first distributor (1) for distributing a high-frequency input signal to an initial main signal and an initial bypass signal;
A first vector adjuster (2) for phase control and gain adjustment of the initial main signal;
A main amplifier (3) for amplifying the initial main signal;
A first delay line (4) for matching the phase of the initial detour signal to the phase of the initial main signal amplified by the main amplifier (3);
A second distributor (5) for distributing the initial main signal including a distortion component generated in the main amplifier to an intermediate main signal and a distortion detection signal;
A first combiner (6) for combining the distortion detection signal and the initial detour signal and outputting an intermediate detour signal;
A second delay line (7) for matching the phase of the intermediate main signal and the intermediate bypass signal;
A second vector adjuster (8) for phase control and gain adjustment of the intermediate detour signal;
Detour error amplifier (9),
A second combiner (10) for combining the intermediate bypass signal and the intermediate main signal and outputting the final main signal from which the distortion component has been removed;
A control unit (11) for performing phase control and gain adjustment; and
A pilot signal generator (12) for injecting a pilot signal into the middle stage of the main amplifier (3);
A pilot signal detector (13) for detecting the pilot signal at the output of the second combiner (10);
Consists of
The distortion compensation circuit, wherein the pilot signal detector (13) detects the pilot signal in a narrow band centered on the frequency of the pilot signal.

Images