JP2003318661A - Distortion compensating circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain superior distortion compensation accuracy, and at the same time to reduce the number of quantization bits in an A/D converter, in a distortion compensating circuit for compensating distortion in a nonlinear circuit. <P>SOLUTION: A synthesizer 41 obtains the difference between an analog output signal, outputted from the nonlinear circuit and an analog input signal where a digital signal inputted from an input terminal 31 is D/A-converted into the output of an analog synthesized signal. In the A/D converter 43, the analog synthesis signal is A/D-converted as a digital synthesis signal. At an adaptive distortion compensating section 11, distortion is given to the digital input signal according to the digital synthesis signal to generate a predistortion signal. Then, the predistortion signal is D/A-converted and is given as an input signal to the nonlinear circuit as the analog distortion signal. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distortion compensating circuit for compensating for distortion in a non-linear circuit, and more particularly to a distortion compensating circuit for compensating for distortion (non-linearity) in a non-linear amplifier which is a non-linear circuit. .

[0002]

2. Description of the Related Art Generally, an amplifier (nonlinear circuit) used in various communication systems such as a satellite communication system, a terrestrial microwave communication system, a mobile communication system, etc. has an unavoidable nonlinearity. The output signal (amplified signal) from will be distorted.
Therefore, conventionally, the distortion of the amplified signal is compensated by using a distortion compensation circuit for compensating the distortion of the amplified signal.

As such a distortion compensation circuit, for example, Y. Nagata, Proc. ofthe 39 Ve
hic. Tech. Conf. , Pages 159-16
The distortion compensation circuit described in May 4, 1989 is known. FIG. 9 is a diagram showing a configuration of a conventional distortion compensation circuit. In the figure, 11 is an adaptive distortion compensator, 12 is D /
A (digital-analog) converter, 13 is an A / D (analog-digital) converter, and 14 is a combiner. Here, these adaptive distortion compensators 11, D / A converters 12,
A distortion compensation circuit is configured by the A / D converter 13 and the combiner 14.

As shown in the figure, the distortion compensating circuit is arranged before the non-linear circuit (for example, the non-linear amplifier) 21. Then, a digital input signal is given from the input terminal 31, and an analog output signal (for example, an analog amplified signal) is output from the nonlinear circuit 21 as described later (this analog output signal is, for example, a high frequency signal). is there). The analog output signal is output from the output terminal 33 via the directional coupler 32, and the A / D converter 13
And is A / D converted here, and is converted into a digital output signal (hereinafter, referred to as a digital feedback signal) to the combiner 1
Feedback to 4.

Further, a digital input signal is given to the synthesizer 14, and the synthesizer 14 generates a digital synthesized signal according to the digital output signal and the digital input signal as described later. Then, the adaptive distortion compensator 11
Then, the digital input signal is converted into a pre-distortion signal (hereinafter referred to as a predistortion signal) according to the digital composite signal.

Next, the operation will be described. As described above, the analog output signal output from the nonlinear circuit 21 inevitably has distortion. The combiner 14 obtains the difference between the digital input signal and the digital feedback signal, and outputs this difference as a digital combined signal. A parameter (distortion parameter) that defines, for example, the amount of distortion is set in the adaptive distortion compensator 11. When the adaptive distortion compensator 11 receives a digital composite signal, that is, a difference, the adaptive distortion compensator 11 distorts the digital input signal based on the distortion parameter corresponding to the difference to generate a predistortion signal. In other words, the adaptive distortion compensator 11 updates the distortion parameter according to the difference and distorts the digital input signal according to the distortion parameter so as to cancel the distortion component generated in the non-linear circuit 21 to obtain the predistortion signal. To do.

This predistortion signal is converted into an analog predistortion signal by the D / A converter 12 and given to the non-linear circuit 21. Then, the non-linear circuit 21 outputs an analog output signal according to the analog predistortion signal. This analog output signal is given to the combiner 14 again as a digital feedback signal via the directional coupler 32 and the A / D converter 13. Synthesizer 1
In 4, the digital composite signal representing the difference is generated and applied to the adaptive distortion compensator 11, as described above.

By thus updating the distortion parameter according to the difference and generating the predistortion signal, the distortion is removed from the analog output signal finally output from the nonlinear circuit 21. (Ie, the analog output signal will have linearity).

By the way, in the above distortion compensation circuit,
It is necessary to consider the number of quantization bits as one of the factors that determine the distortion compensation accuracy. Now, it is assumed that the analog output signal shown in FIG. 10 is given to the A / D converter 13. A /
When the dynamic range of the analog output signal given to the D converter 13 increases, the resolution for detecting the distortion component improves as the number of quantization bits in the A / D converter 13 increases. As a result, distortion compensation accuracy is improved.

[0010]

Since the conventional distortion compensating circuit is configured as described above, the analog output signal output from the non-linear circuit 21 has an input signal component and a distortion component whose levels are greatly different from each other. Considering that (non-linear distortion component) and are included (input signal level>
> Distortion component level), the dynamic range of the analog output signal (output signal from the nonlinear circuit 21) given to the A / D converter 13 inevitably increases. Therefore, in order to quantize the distortion component with a desired resolution, an extremely large number of quantization bits are required, and there is a problem that the A / D converter itself becomes expensive.

The present invention has been made to solve the above problems, and provides a distortion compensation circuit which can obtain a high distortion compensation accuracy and can reduce the number of quantization bits of an A / D converter. The purpose is to get.

[0012]

A distortion compensating circuit according to the present invention is a distortion compensating circuit for compensating for a distortion component contained in an analog output signal output from a non-linear circuit, by D / A converting a digital input signal. An analog input signal, a combiner that outputs an analog composite signal by obtaining a difference between the analog input signal and the analog output signal, and a digital composite signal obtained by A / D converting the analog composite signal,
An adaptive distortion compensator for adding distortion to a digital input signal to generate a predistortion signal, and a D / A for outputting an analog predistortion signal obtained by D / A converting the predistortion signal as an input signal of a non-linear circuit.
And a converter.

The distortion compensating circuit according to the present invention is a distortion compensating circuit for compensating for a distortion component contained in an analog output signal output from a non-linear circuit, and calculates a difference between an analog input signal and an analog output signal to obtain an analog composite signal. The analog input signal is A / D according to the synthesizer which outputs the signal and the digital synthesized signal obtained by A / D converting the analog synthesized signal.
An adaptive distortion compensator for generating a predistortion signal by adding distortion to the converted digital signal, and a D for outputting an analog predistortion signal obtained by D / A converting the predistortion signal as an input signal of a non-linear circuit.
/ A converter.

The distortion compensating circuit according to the present invention comprises adjusting means for adjusting the amplitude and phase of the input signal according to the amplitude and phase of the analog predistortion signal.

The distortion compensating circuit according to the present invention comprises adjusting means for adjusting the amplitude and phase of the analog output signal or the analog predistortion signal.

The distortion compensating circuit according to the present invention comprises control means for controlling the adjusting means according to at least the characteristics of the non-linear circuit to adjust the amplitude and phase of the analog output signal or the analog predistortion signal.

The distortion compensating circuit according to the present invention detects the level of the analog composite signal and outputs the level detection signal, and the adjusting means based on the level detection signal to control the analog output signal or the analog predistortion. And a control means for adjusting the amplitude and phase of the signal.

In the distortion compensating circuit according to the present invention, the control means controls the adjusting means to adjust the amplitude and phase of the analog output signal or the analog predistortion signal so that the level value indicated by the level detection signal is minimized. Is.

In the distortion compensating circuit according to the present invention, the signal passing characteristic in the first path until the analog output signal obtained from the input signal via the adaptive distortion compensating section and the non-linear circuit is given to the combiner, The adjusting means is provided for adjusting the amplitude and phase of the analog output signal or the analog predistortion signal so that the signal passing characteristics in the second path until the input signal is given to the combiner match.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below. Embodiment 1. 1 is a diagram showing a configuration of a distortion compensation circuit according to a first embodiment of the present invention. The same components as those in FIG. 9 are designated by the same reference numerals. In the figure, 41 is a synthesizer (analog synthesizer), 42 is a D / A converter, and 43 is an A / D converter. In the illustrated example, the output (analog output signal) from the nonlinear circuit 21 is given to the combiner 41 as an analog feedback signal via the directional coupler 32. On the other hand, the digital input signal is the D / A converter 4
It is D / A converted in 2 and given to the combiner 41 as an analog input signal. Then, the combiner 41 obtains the difference between the analog feedback signal and the analog input signal and outputs it as an analog combined signal. This analog composite signal is A / D converted by the A / D converter 43 and is given to the adaptive distortion compensating section 11 as a digital composite signal.

Next, the operation will be described. As described above, the combiner 41 obtains the difference between the analog input signal and the analog feedback signal (difference signal = analog feedback signal−analog input signal), and outputs this difference as an analog composite signal. Then, the analog composite signal is converted into a digital composite signal by the A / D converter 43. As described above, the parameter (distortion parameter) that defines the amount of distortion is set in the adaptive distortion compensator 11. Further, when the adaptive distortion compensator 11 receives the digital composite signal related to the difference, the adaptive distortion compensator 11 distorts the digital input signal based on the distortion parameter corresponding to the difference to generate the predistortion signal. That is, the adaptive distortion compensator 11 updates the distortion parameter according to the difference, and distorts the digital input signal according to the distortion parameter so as to cancel the distortion component generated in the non-linear circuit 21 to obtain a predistortion signal. .

The predistortion signal is converted into an analog predistortion signal by the D / A converter 12 and given to the non-linear circuit 21. Then, the non-linear circuit 21 outputs an analog output signal according to the analog predistortion signal. This analog output signal is given to the combiner 41 again as an analog feedback signal via the directional coupler 32. The combiner 41 generates an analog combined signal representing the difference between the analog feedback signal and the analog input signal as described above. This analog composite signal (analog difference signal) is A / D converted by the A / D converter 43,
It is provided to the adaptive distortion compensator 11 as a digital composite signal (digital difference signal).

By thus updating the distortion parameter according to the difference and generating the predistortion signal, the distortion is finally removed from the analog output signal output from the nonlinear circuit 21. (Ie, the analog output signal will have linearity).

By the way, the analog feedback signal includes an input signal component resulting from the digital input signal and a distortion component generated in the non-linear circuit 21. On the other hand, in the synthesizer 41, the analog feedback signal and the analog input signal are included. Find the difference with (input component due to digital input signal),
Since the analog composite signal (analog difference signal) is generated, the input signal component resulting from the digital input signal is removed (canceled) from this analog difference signal. That is, the analog composite signal includes only the distortion component.

In other words, as shown in FIG. 2, the dynamic range of the analog composite signal is smaller than the dynamic range of the analog feedback signal by the amount of the input signal component resulting from the digital input signal. As a result, A /
In the D converter 43, the distortion component is set to a predetermined (desired)
The number of quantization bits for quantizing with resolution is small. This makes it possible to reduce the number of quantization bits of the A / D converter with high distortion compensation accuracy.

In the example shown in FIG. 1, an example in which a digital input signal is applied from the input terminal 31 has been described. However, even when an analog input signal is applied from the input terminal 31, distortion generated in the nonlinear circuit 21 is similarly caused. The component can be compensated. In this case, as shown in FIG. 3, between the adaptive distortion compensator 11 and the input terminal 31, A /
The D converter 44 will be arranged. Then, the analog input signal is directly given to the synthesizer 41, the analog input signal is A / D converted by the A / D converter 44, and given to the adaptive distortion compensating section 11 as a digital input signal.

As described above, according to the first embodiment, an analog combiner (analog differencer) is used as a combiner to obtain the difference signal between the analog input signal and the analog feedback signal, and then the difference signal is calculated. Since the signal is A / D-converted and the predistortion signal is generated by the adaptive distortion compensator in accordance with the difference signal, the distortion component may be A / D-converted, and as a result, the A / D converter may perform predetermined conversion. Therefore, the number of quantization bits for quantizing with the resolution of is small. That is, it is possible to reduce the number of quantization bits of the A / D converter with high distortion compensation accuracy.

Embodiment 2. FIG. 4 is a diagram showing the configuration of the distortion compensation circuit according to the second embodiment of the present invention. In addition,
The same components as those in FIG. 3 are designated by the same reference numerals. In the figure, 45 is a vector adjuster (adjusting means),
A D / A converter 46 receives an analog input signal from the input terminal 31.

Next, the operation will be described. As described with reference to FIG. 3, the adaptive distortion compensator 11 generates a digital predistortion signal. This digital predistortion signal is D / A converted by the D / A converter 46 and is given to the vector adjuster 45 as an analog predistortion signal. The vector adjuster 45 adjusts the vector amount of the analog input signal according to the vector amount (amplitude and phase) of the analog predistortion signal. That is, in the vector adjuster 45, the signal passing characteristic (vector amount) of the path to the non-linear circuit 21, the directional coupler 32, and the combiner 41 is made equal to the vector amount of the analog input signal. The vector amount (amplitude and phase) of the analog input signal is adjusted according to the vector amount (amplitude and phase).

As described above, according to the second embodiment, after the vector amount of the analog input signal is adjusted according to the vector amount of the analog predistortion signal, the non-linear circuit 21 is subjected to the vector amount adjusted analog predistortion signal. If it is given as
The vector amount of the analog output signal output from 1 can be matched with the vector amount of the analog input signal.
As a result, the distortion component generated in the nonlinear circuit 21 can be accurately compensated.

Embodiment 3. 5 is a block diagram showing a configuration of a distortion compensation circuit according to a third embodiment of the present invention. The same components as those in FIG. 1 are designated by the same reference numerals. In the figure, 51 is a vector adjuster (adjusting means), which is arranged between the directional coupler 32 and the combiner 41. Further, the vector adjuster 51 is provided with an analog feedback signal (analog output signal) via the directional coupler 32. Then, the vector adjuster 51 adjusts the vector amount (amplitude and phase) of the analog feedback signal, and then the synthesizer 4 outputs the vector adjusted analog feedback signal.
Give to one.

Next, the operation will be described. The vector adjuster 51 adjusts the vector amount of the analog feedback signal in advance so that the input signal component included in the analog feedback signal can be favorably canceled in the combiner 41. That is,
Signal pass characteristic in the first path from the input terminal 31 to the combiner 41 through the adaptive distortion compensator 11, the D / A converter 12, the nonlinear circuit 21, the directional coupler 32, and the vector adjuster 51. (First pass characteristic) and input terminal 3
2 from 1 to the combiner 41 via the D / A converter 42
The vector adjuster 51 adjusts the vector amount of the analog feedback signal so that the signal passing characteristic (second passing characteristic) in the path of (1) matches. The vector adjustment amount for the analog feedback signal is set in the vector adjuster 51 according to the first and second passage characteristics measured in advance.

By thus configuring the vector amount of the analog feedback signal so that it matches the vector amount of the analog input signal, it is possible to accurately cancel the input signal component in the combiner. As a result, only the distortion component can be accurately extracted, and the distortion component can be accurately compensated.

As shown in FIG. 6, the vector adjuster 51 may be arranged between the D / A converter 12 and the nonlinear circuit 21. In this case, the analog adjuster 5 is adjusted so that the passage characteristics in the first and second paths match.
1 adjusts the vector amount of the analog predistortion signal.

As described above, according to the third embodiment, the vector adjuster 5 is arranged so that the vector amounts of the analog input signal and the analog feedback signal supplied to the combiner are the same.
Since the vector amount of the analog feedback signal (or analog predistortion signal) is adjusted by 1, it is possible to accurately extract only the distortion component in the combiner,
Further, it is possible to accurately compensate the distortion component.

Fourth Embodiment 7 is a block diagram showing a configuration of a distortion compensation circuit according to a fourth embodiment of the present invention. The same components as those in FIG. 5 are designated by the same reference numerals. In the figure, reference numeral 52 is a control circuit, which controls the vector adjuster 51 as described later.
Control the vector adjustment amount of.

Next, the operation will be described. As described with reference to FIG. 5, the vector adjuster 51 adjusts the vector amount of the analog feedback signal in order to match the first pass characteristic and the second pass characteristic. By the way, the ambient temperature, the signal level (the level of the signal passing through the first or second path), and other external factors (hereinafter, simply referred to as fluctuation factors) for both the first and second passage characteristics. Fluctuates depending on. In particular, in the non-linear circuit 21, its pass characteristic greatly varies depending on the ambient temperature, the signal level, and other external factors.

Therefore, the first and second pass characteristics, in particular, the characteristics of the non-linear circuit 21 are measured in advance according to the fluctuation factors to obtain the measurement result. Then, the control circuit 52 gives the vector adjuster 51 an amount of vector adjustment according to the measurement result as a vector control command. The vector adjuster 51 adjusts the vector amount of the analog feedback signal based on the vector control command. In other words, the vector adjustment amount is set in the control circuit 52 as a vector adjustment parameter according to the variation factor, and the control circuit 52 generates a vector control command based on the vector adjustment parameter according to the variation factor, It will be given to the adjuster 51.

In this way, if the vector adjuster is controlled on the basis of the variation factor to adjust the vector amount of the analog feedback signal, only the distortion component can be accurately extracted even if the variation factor changes. Therefore, the distortion component can be compensated with high accuracy.

In the distortion compensation circuit shown in FIG. 6,
The vector adjuster 51 may be controlled by the control circuit 52.

As described above, according to the fourth embodiment, the vector adjuster is controlled based on the variation factor to adjust the vector amount of the analog feedback signal (or the analog predistortion signal). Even if it changes, only the distortion component can be accurately extracted, and the distortion component can be accurately compensated.

Embodiment 5. FIG. 8 is a block diagram showing the configuration of the distortion compensation circuit according to the fifth embodiment of the present invention. The same components as those in FIG. 5 are designated by the same reference numerals. In the figure, 61 is a control circuit, 62 is a detector (level detector), 63 is a directional coupler, and the directional coupler 63 is arranged between the combiner 41 and the A / D converter 43. Output from synthesizer 41 (analog synthesized signal)
To the A / D converter 43 and the detector 62. The detector 62 detects the level of the analog composite signal and supplies the level detection signal to the control circuit 61. Then, the control circuit 61 controls the vector adjuster 51 as described later.

Next, the operation will be described. As described above, in the detector 62, the analog composite signal (difference signal and
The level of the distortion component) is detected and the level detection signal is continuously given to the control circuit 61. As described above, the first and second passage characteristics change due to the fluctuation factors, and
Also, due to the variation of the second pass characteristic, it becomes difficult for the combiner 41 to accurately extract the distortion component. Then, if the first and second pass characteristics change, it becomes difficult to extract only the distortion component with high accuracy, and as a result, the level of the analog composite signal inevitably increases.

In the example shown in FIG. 8, the level of the analog composite signal is monitored, and the control circuit 61 controls the vector adjuster 51 so that the value of the level detection signal becomes small. That is, since the level detection signal is continuously supplied to the control circuit 61, the control circuit 61 controls the vector adjuster 51 to reduce the vector of the analog feedback signal in the direction in which the level value indicated by the level detection signal decreases. The amount will be adjusted. Then, the vector amount of the analog feedback signal is adjusted in this way, and the vector amount of the analog feedback signal is adjusted by the vector adjustment amount that minimizes the level value indicated by the level detection signal.

In this way, if the vector adjuster is controlled based on the level of the analog composite signal to adjust the vector amount of the analog feedback signal, only the distortion component is accurately measured even if the variation factor changes. Since it can be extracted, the distortion component can be more accurately compensated.

In the distortion compensation circuit shown in FIG. 6,
The vector adjuster 51 may be controlled by the control circuit 61.

As described above, according to the fifth embodiment, the vector adjuster is controlled based on the level of the analog composite signal to adjust the vector amount of the analog feedback signal (or analog predistortion signal). Even if the variation factor changes, only the distortion component can be accurately extracted, and the distortion component can be compensated with high accuracy.

[0048]

As described above, according to the present invention, the difference between the analog input signal (or the analog input signal obtained by D / A converting the digital input signal) and the analog output signal output from the non-linear circuit is obtained. To obtain an analog composite signal, A / D convert the analog composite signal, and distort the digital input signal (or the digital input signal obtained by A / D converting the analog input signal) according to the digital composite signal. Since the predistortion signal is generated and the predistortion signal is D / A converted and given to the non-linear circuit as the analog predistortion signal, only the distortion component is included in the analog composite signal, and therefore the analog composite signal is A / D converted. At this time, the number of quantization bits for quantizing with a predetermined (desired) resolution is small, which results in high distortion. There is an effect that it is possible with the compensation accuracy yet reducing the number of quantization bits of the A / D converter.

According to the present invention, the amplitude and phase of the analog input signal are adjusted based on the amplitude and phase of the analog output signal or analog predistortion signal output from the non-linear circuit. There is an effect that it can be extracted well and the distortion component can be accurately compensated.

According to the present invention, since the amplitude and the phase of the analog output signal or the analog predistortion signal are adjusted according to at least the characteristic of the non-linear circuit, only the distortion component is accurately extracted even if the characteristic of the non-linear circuit changes. Therefore, there is an effect that the distortion component can be accurately compensated.

According to the present invention, the level of the analog composite signal indicating the difference between the analog input signal and the analog output signal output from the non-linear circuit is detected, and the analog output signal or the analog predistortion is detected based on this level value. Since the amplitude and phase of the signal are adjusted, there is an effect that only the distortion component can be accurately extracted in the combiner, and the distortion component can be accurately compensated.

According to the present invention, the level of the analog composite signal indicating the difference between the analog input signal and the analog output signal output from the non-linear circuit is detected, and the analog output signal or the analog output signal is minimized so that the level value becomes minimum. Since the amplitude and phase of the analog predistortion signal are adjusted,
In the synthesizer, there is an effect that only the distortion component can be accurately extracted.

According to the present invention, the signal passing characteristic in the first path until the analog output signal obtained through the adaptive distortion compensator and the non-linear circuit is given to the synthesizer, and the input signal is Since the amplitude and phase of the analog output signal or the analog predistortion signal are adjusted so that the signal passing characteristics in the second path until they are given to the combiner are adjusted, only the distortion component is accurately extracted in the combiner. There is an effect that can be done.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a configuration of a distortion compensation circuit according to a first embodiment of the present invention.

FIG. 2 is an A / D used in the distortion compensation circuit shown in FIG.
It is a figure which shows the relationship between the quantization bit width of a converter, and a dynamic range.

FIG. 3 is a diagram showing another example of the configuration of the distortion compensation circuit according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a distortion compensation circuit according to a second embodiment of the present invention.

FIG. 5 is a diagram showing an example of a configuration of a distortion compensation circuit according to a third embodiment of the present invention.

FIG. 6 is a diagram showing another example of the configuration of the distortion compensation circuit according to the third embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of a distortion compensation circuit according to a fourth embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of a distortion compensation circuit according to a fifth embodiment of the present invention.

FIG. 9 is a diagram showing a configuration of a conventional distortion compensation circuit.

10 is a diagram illustrating an A / A used in the distortion compensation circuit shown in FIG.
It is a figure which shows the relationship between the quantization bit width of a D converter, and a dynamic range.

[Explanation of symbols]

11 Adaptive distortion compensator, 12, 42, 46 D / A converter, 21 Non-linear circuit, 31 Input terminal, 32, 63
Directional coupler, 33 output terminals, 41 combiner (analog combiner), 43,44 A / D converter, 45,51
Vector adjuster (adjusting means), 52, 61 control circuit, 62 detector (level detector).

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masatoshi Nakayama             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Yoshinori Yasunaga             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. F-term (reference) 5J090 AA01 CA22 CA26 FA08 GN03                       HN03 KA00 KA26 KA34 MA14                       SA13 TA01 TA06                 5J500 AA01 AC22 AC26 AF08 AK00                       AK26 AK34 AM14 AS13 AT01                       AT06 NH03

Claims (8)

[Claims] 1. A distortion compensating circuit for compensating for a distortion component included in an analog output signal output from a non-linear circuit, wherein a digital input signal is D / A converted into an analog input signal, and the analog input signal and the analog output are provided. A combiner that obtains a difference from the signal and outputs an analog composite signal, and an adaptive that distorts the digital input signal to generate a predistortion signal according to a digital composite signal obtained by A / D converting the analog composite signal. A distortion compensating circuit comprising: a type distortion compensating section; and a D / A converter which outputs an analog predistortion signal obtained by D / A converting the predistortion signal as an input signal of the nonlinear circuit. 2. A distortion compensating circuit for compensating for a distortion component included in an analog output signal output from a non-linear circuit, comprising: a combiner for obtaining a difference between an analog input signal and the analog output signal and outputting an analog combined signal. An adaptive distortion compensator for generating a pre-distortion signal by distorting the digital signal obtained by A / D converting the analog input signal according to the digital combined signal obtained by A / D converting the analog combined signal, A distortion compensating circuit comprising: a D / A converter that outputs an analog pre-distortion signal obtained by D / A converting the distortion signal as an input signal of the nonlinear circuit. 3. The distortion compensating circuit according to claim 1, further comprising adjusting means for adjusting the amplitude and phase of the input signal according to the amplitude and phase of the analog predistortion signal. 4. The distortion compensating circuit according to claim 1, further comprising adjusting means for adjusting the amplitude and phase of the analog output signal or the analog predistortion signal. 5. The distortion according to claim 4, further comprising control means for controlling the adjusting means according to at least the characteristic of the non-linear circuit to adjust the amplitude and phase of the analog output signal or the analog predistortion signal. Compensation circuit. 6. A detection means for detecting the level of the analog composite signal and outputting the level detection signal, and an adjusting means for controlling the amplitude and phase of the analog output signal or the analog predistortion signal based on the level detection signal. 5. The distortion compensating circuit according to claim 4, further comprising a control means for adjusting. 7. The control means controls the adjusting means to adjust the amplitude and phase of the analog output signal or the analog predistortion signal so that the level value indicated by the level detection signal is minimized. Item 4. The distortion compensation circuit according to item 4. 8. A signal passing characteristic in a first path until an analog output signal obtained through an adaptive distortion compensator and a non-linear circuit is given to a synthesizer, and the input signal is the synthesizer. 2. The adjusting means for adjusting the amplitude and the phase of the analog output signal or the analog predistortion signal is provided so that the signal passing characteristics in the second path until being given to the same are matched. The distortion compensation circuit according to claim 3.