JP2000151294A - Feedforward distortion compensating amplifier and distortion compensating and amplifying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To actualize a feedforward distortion compensating amplifier which can suppress malfunction even if the balance between the distortion control quantities of a distortion detection loop and a distortion compensation loop is lost owing to the input of instantaneous peak electric power. SOLUTION: In the distortion detection loop, an RF input signal is branched by a distributor 9 and one input signal is amplified by a main amplifier 1; and the amplifier output signal is branched by a directional coupler 11 and a branched amplifier output signal and the other branched input signal are put together in opposite-phase relation to make a detecting detector 2 detect a distortion component signal generated by the amplifier. When the amplitude of a distortion component signal is larger than a specific threshold, a control circuit 4 varies the distortion component signal into an alternate signal having an amplitude smaller than the specific prepared threshold and a vector adjuster 3 is controlled according to the amplitudes of the detected distortion component signal and alternate signal so that the amplitude of the detected distortion component signal becomes small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feed-forward distortion compensating amplifier and a distortion compensating amplification method used for, for example, a relay device for high-frequency wireless communication, and more particularly to a distortion detecting loop and a distortion compensating circuit when an instantaneous peak power is input. The present invention relates to a feedforward distortion compensation amplifier and a distortion compensation amplification method that can suppress malfunction even when the balance of distortion control amounts in a loop is lost.

[0002]

2. Description of the Related Art In a relay device used in a mobile radio system such as a portable telephone system, a radio wave from a base station is amplified and transmitted to a mobile station. In this case, in order to simultaneously amplify multi-channel radio waves, the amplifier of the repeater is required to have considerable linearity, but this is limited. Therefore, when an excessive input due to an instantaneous peak is input to the amplifier, a nonlinear distortion compensating circuit, that is, a self-adjustment type feed forward (SAFF: Self) is used as a circuit method for canceling distortion generation due to the nonlinear operation of the amplifier.
An apparatus mounted with a distortion compensating amplifier called an Adjusting Feed Forward circuit is used.

Conventionally, such a feedforward distortion compensating amplifier has been disclosed in, for example, Japanese Patent Application Laid-Open No. 5-315847.
What is described in a gazette and what is described in JP-A-8-78965 are known. Such a feedforward distortion compensation amplifier has a rough configuration as follows.
A distortion detection loop and a distortion compensation loop are arranged in series. In the distortion detection loop, the input signal is branched, one of the input signals is amplified by an amplifier, the amplifier output signal is branched, and the branch is performed. A distortion component signal generated in the amplifier is extracted by inverting and synthesizing the amplifier output signal and the other input signal that has been branched, and the distortion compensation signal includes a distortion component signal output from the distortion detection loop. By inverting and synthesizing the amplifier output signal with each other, an amplifier output signal from which a distortion component generated in the amplifier is removed is obtained.

In such a feedforward distortion compensating amplifier, for example, a CD having a signal envelope as shown in FIG.
MA signal (Code Division Multiple)
leAccess: code division multiple access) is input,
If the input signal includes the instantaneous peaks P1 and P1 'as a desired wave, the peak power reaches near or above the saturation level, and becomes extremely high due to amplification in the distortion detection loop. Distortion occurs. This is shown in FIG. 9, which shows the input / output characteristics of a general main amplifier used in the distortion detection loop of the feedforward amplifier. If the slope of the actual performance line deviates from the ideal line, , Reaches the saturation level and suppresses the output voltage, causing distortion in the main amplifier.

For example, when a signal having an instantaneous peak as shown in FIG.
As shown in (b), the output signal from the main amplifier is suppressed by 1 dB, and the distortion cancellation amount is approximately 1
8 dB. If it is assumed that the operation is always performed with the distortion cancellation amount of 30 dB or more, the distortion cancellation level is degraded by the instantaneous peak power as shown in FIG. Is input to

According to the above example, it is known that the cancellation amount is expressed by the following equation.

[Equation 1] Cancellation amount = 10 log (1 + 10 ^{d / 10} −2)
× 10 ^{d / 20} × COSp) d is amplitude deviation (dB), p is phase deviation (deg)

[0007]

In a conventional feed-forward distortion compensating amplifier, if an input signal has an instantaneous peak, normal amplification processing cannot be performed due to the instantaneous peak. Has a problem that the quality of wireless communication is deteriorated. FIG. 1 shows the configuration of a feedforward distortion compensation amplifier according to the present invention, as will be described later. The above situation will be specifically described with reference to FIG.

In the distortion detection loop, the vector adjustment in the distortion detection loop is performed so that the output of the detection detector 2 is minimized, that is, the distortion component signal of the main amplifier 1 extracted by the cancellation processing in the distortion detection loop is minimized. The vessel 3 is controlled. However, when the detection detector 2 detects the peak power, the control operation starts to change the vector adjuster 3 in order to maintain the balance of the distortion detection loop, but the output level of the detection detector 2 is reduced due to the peak input. Because of the sudden increase, it takes a long time to return to the normal control even if the change is automatically controlled to converge, or the loop control is lost (thus causing a malfunction).

Such a problem is caused by a feedforward distortion compensating amplifier (FIG. 7) that uses a pilot signal as an input signal for distortion detection so that distortion detection control can always be performed even when there is no input. The same applies to the case of an embodiment of the present invention). When an input signal (communication signal) such as an RF signal to be amplified has an instantaneous peak, distortion compensation control for the input signal is performed. It is not performed normally, and as a result, distortion is caused in amplification of a desired wave.

The present invention has been made in view of the above-mentioned conventional circumstances, and has as its object to stably perform appropriate distortion compensation control using a feedforward distortion compensation amplifier. Also,
SUMMARY OF THE INVENTION It is an object of the present invention to prevent a distortion detection loop from taking a long time for malfunction or recovery even if the main amplifier operates near saturation due to instantaneous peak power.

[0011]

According to the present invention, a distortion detection loop and a distortion compensation loop are arranged in series. In the distortion detection loop, an input signal is branched and one of the input signals is amplified by an amplifier. Branching the amplifier output signal, extracting the distortion component signal generated by the amplifier by inverting and combining the branched amplifier output signal and the other of the branched input signals with each other, and in the distortion compensation loop, The present invention is applied to a feed-forward distortion compensation amplifier that obtains an amplifier output signal from which a distortion component generated in an amplifier is removed by inverting and combining a distortion component signal output from a distortion detection loop and an amplifier output signal with each other.

According to the present invention, the split amplifier output signal and the other input signal are adjusted to mutually inverted amplitudes and phases by adjusting means provided in the distortion detection loop, and are adjusted by the amplifier as described above. The generated distortion component signal is extracted, but the distortion component signal is detected by the detection means, and when the amplitude of the detected distortion component signal is larger than a predetermined threshold, the distortion component signal is prepared in advance. The replacement signal is changed to an alternative signal having an amplitude smaller than a predetermined threshold, and the adjustment control unit adjusts based on the detected distortion component signal and the amplitude of the alternative signal so that the amplitude of the distortion component signal detected by the detection unit becomes small. Control means.

That is, when an instantaneous peak is included in the input signal, an extremely large amplification distortion is generated by the instantaneous peak, and when the adjusting means is controlled based on the distortion, the malfunction as described above occurs. And a situation that takes a long time for recovery occurs. On the other hand, in the present invention, when an extremely large amplification distortion exceeding a predetermined threshold occurs, using an alternative signal having an amplitude smaller than a predetermined threshold prepared in advance without using the distortion signal component, Based on this, the adjusting means is controlled to stabilize the adjusting process.

The present invention is also embodied as a feed-forward distortion compensating amplifier for detecting distortion of a communication signal itself as an input signal to the amplifier and compensating for the distortion, but a means for generating a pilot signal of a specific frequency. The pilot signal is input as an input signal to a distortion detection loop, and is implemented as a feedforward distortion compensation amplifier that detects distortion of the pilot signal and performs distortion compensation.

In the present invention, the changing means samples the detected distortion component signal and, if the sampling value is larger than a predetermined amplitude threshold value, sets the sampling value to a predetermined amplitude threshold value prepared in advance. The value is changed to the alternative sampling value having a small amplitude, and the adjustment control unit controls the adjustment unit based on the detected sampling value and the alternative sampling value. Here, as the alternative sampling value, a sampling value whose amplitude is smaller than a predetermined amplitude threshold obtained in the past at a sampling point where the sampling value is larger than a predetermined amplitude threshold, or a predetermined amplitude obtained in the past at the sampling point. It is preferable to use an average sampling value of a sampling value smaller than the threshold value. In this way, by using the past history of the same sampling point as an alternative signal value, a different alternative signal value having no consistency with before and after , And more appropriate adjustment control can be performed.

Further, in the present invention, the sampling values in the vicinity including the above-mentioned sampling values are also changed to alternative sampling values, and the adjusting means is controlled based on this. In this way, by using the past history as an alternative signal value without using the sampling value near the sampling point where the instantaneous peak occurs, it is possible to perform the stable adjustment control by eliminating the influence of the instantaneous peak as much as possible. it can.

Further, according to the present invention, the distortion detection loop includes a second pilot signal generating means for mixing a second pilot signal into an input signal to the amplifier, and the distortion compensation loop includes:
Second adjusting means for adjusting the amplitude and phase of the amplifier output signal and the distortion component signal from the distortion detection loop to mutually inverted amplitudes and phases, an auxiliary amplifier for amplifying the distortion component signal extracted by the distortion detection loop, and a distortion component signal And a second detection means for detecting a distortion component signal of the second pilot signal from the amplifier output signal from which the distortion component obtained by inverting and combining the output signal and the amplifier output signal is removed. . When the amplitude of the detected distortion component signal of the second pilot signal is larger than a predetermined threshold, the changing unit changes the distortion component signal to an alternative signal having an amplitude smaller than a predetermined threshold prepared in advance. , The adjustment control means, the detection means and the second
The adjusting means and the second adjusting means are controlled based on the detected distortion component signal and the amplitude of the substitute signal so that the amplitude of the distortion component signal detected by the detecting means becomes smaller.

In the feedforward distortion compensation amplifier, for example, when a signal level including the instantaneous peak power as shown in FIG. 6A is input, the output level of the main amplifier (amplifier 1 in FIG. 1) of the distortion detection loop is output. Assume that as shown in FIG. 6B, the instantaneous peak power of the input signal level is suppressed by 1 dB in the main amplifier. At this time, the balance of the distortion detection loop is broken by 1 dB, and the cancellation amount is degraded by 18 dB according to the above equation (1). Therefore, 3 to the average power
When the operation is performed with the cancellation amount of 0 dB, the detection voltage waveform of the detection means (the detection detector 2 in FIG. 1) is as shown in FIG.
It becomes as shown in.

In the present invention, for example, the detected value is taken in by an A / D converter in a control unit (control circuit 4 in FIG. 1) constituting the changing means and the adjustment control means, and is sampled at a certain timing to obtain an instantaneous peak. Control of the adjusting means (the vector adjuster 3 in FIG. 1) is performed without using a sampling value. In this case, for example, instead of operating the control by one sampling, normal averaging processing is performed. At this time, averaging is performed excluding the instantaneous peak power. In the case of a cycle in which a plurality of samplings are performed in the time width of the peak power of the signal, a plurality of sampling values near the instantaneous peak value may be discarded and an alternative value may be used.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described with reference to the embodiments shown in the drawings. FIG. 1 shows a configuration of a feedforward distortion compensation amplifier according to one embodiment of the present invention. This feed-forward distortion compensation amplifier is roughly composed of a distortion detection loop and a distortion compensation loop. Broadly speaking, in the distortion detection loop, an input signal is branched and one of the input signals is amplified by the amplifier. Performing a process of branching the amplifier output signal and extracting a distortion component signal generated in the amplifier by inverting and combining the branched amplifier output signal and the other branched input signal with each other; In the loop, the distortion component signal output from the distortion detection loop and the amplifier output signal are inverted and combined to obtain an amplifier output signal from which the distortion component generated in the amplifier has been removed.

In the distortion detection loop, the RF signal to be amplified is input to the distributor 9, and the RF input flows through the vector adjuster 3 and the main amplifier 1 and is input to the first directional coupler 11. And the signal that flows through the delay line 13 and is input to the first directional coupler 11. Vector adjuster 3
As shown in FIG. 2, the vector adjuster 7 described later has a variable attenuator 31 and a variable phase shifter 32 so as to be able to change the amplitude component and the phase component of the signal. Adjust the amplitude and phase of the signal. In this embodiment, since the vector adjustment is controlled in accordance with the detection by the distortion compensation loop, the pilot signal of the specific frequency generated by the pilot signal generator 10 is applied to the input of the main amplifier 1 by the coupler 17. I try to combine them.

In the first directional coupler 11, the main amplifier 1
Is output as one output, and the output from the main amplifier 1 is branched and subjected to antiphase synthesis with the RF signal from the delay line 13 to obtain the other output. That is, according to the first directional coupler 11, the RF signal and the pilot signal amplified by the main amplifier 1 are input to the delay line 14 of the distortion compensation loop, and the delay equal to the delay due to the vector adjustment and the amplification is provided. The result obtained by inverting the phases of the RF input signal provided by the delay line 13 and the amplified RF signal and pilot signal by inverting the phase of the RF input signal and performing reverse phase synthesis (that is,
The amplified pilot signal and the distortion component signal of the RF input signal generated by the main amplifier 1) are input to the vector adjuster 7 and the auxiliary amplifier 5 of the distortion compensation loop.

Here, a DC component is detected by the detection detector 2 from the signals input to the vector adjuster 7 and the auxiliary amplifier 5 via the coupler 15, whereby the amplitude value of the signal is detected and the control circuit is operated. Enter 4 That is, the amplitude value of the distortion component signal included in the signal is input to the control circuit 4. The control circuit 4 controls the vector adjuster 3 based on the amplitude value of the distortion component signal as described later, and the distortion component signal detected by the detection detector 2 is minimum (ie, the amount of cancellation by the loop is maximum). The amount of amplitude and phase adjustment by the vector adjuster 3 is controlled so that

In the distortion compensation loop, the first directional coupler 1
1 to the vector adjuster 7 and the auxiliary amplifier 5 are phase- and amplitude-adjusted and further amplified. The signal and the signal given a delay equal to the delay due to the vector adjustment and amplification by the delay line 14 are converted to the second signal. And outputs a signal (amplified RF signal and pilot signal) from which the distortion component signal is canceled and removed by the directional coupler 12. As described above, the feedforward distortion compensation amplifier detects a distortion component other than the input signal by reverse-phase synthesis in the distortion detection loop including the main amplifier 1 which is the amplifier to be compensated, and converts the detected distortion component to the distortion compensation loop. After inputting and performing necessary amplification and phase adjustment of the distortion component, the signal amplified by the main amplifier 1 is subjected to reverse phase synthesis to cancel the distortion component, thereby performing distortion compensation.

Here, the pilot signal component is detected by the pilot detector 6 from the output signal of the second directional coupler 12 via the coupler 16, whereby the amplitude value of the signal is detected and the control circuit 4 To enter. That is, the amplitude value of the amplified distortion component signal included in the pilot signal is input to the control circuit 4. The control circuit 4 controls the vector adjuster 7 based on the amplitude value of the distortion component signal in the same manner as described above, and controls the vector adjuster 7 so that the distortion component signal detected by the pilot detector 6 is minimized. And the amount of phase adjustment.

The control circuit 4 has a configuration as shown in FIG. 3, and converts the detection signal input from the detection detector 2 and the detection signal input from the pilot detector 6 into A / D converters 41 and 42. And converts the control signal by the CPU 45 based on the detection signal into the D / A converters 43 and 4.
In step 4, the signal is converted into an analog signal and output to the vector adjusters 3 and 7. Note that a control program by the CPU 45 is stored in the ROM 46, and by executing the program, a vector adjustment control and the like using a sampling value and an alternative value described later are executed.

A memory table having the contents as shown in FIG. 4 is formed in the RAM 47 of the control circuit 4, and stores information on the amplitude values obtained by sampling the detection signals from the detectors 2 and 6. As will be described later with reference to FIG. 5, the control circuit 4 performs adjustment control of the vector adjusters 3 and 7 using the average power value of the amplitude value stored and managed in the memory table. Control is performed excluding a certain detection value (that is, an extremely large amplitude value). The contents stored in the memory table will be specifically described by taking a signal detected by the detection detector 2 (a distortion component signal of an RF signal by the main amplifier 1 and a pilot signal) as an example.

If the signal detected by the detection detector 2 is a signal as shown in FIG. 6C as described above, it is input to the control circuit 4 and is sampled at a fixed time interval by A / D conversion. Then, a sampling value as shown in FIG. 6D is obtained. The control circuit 4 stores the amplitude value of each sampling point in the memory table of the RAM 47 while repeating the operation on this sampling value. That is, the memory table shown in FIG.
The amplitude value at each sampling point S1, S2, S3,... Sn, the difference (pre-amplitude difference) between the previously input amplitude value and the currently input amplitude value at the same sampling point,
Average value of amplitude value at each sampling point (output average power)
Is stored.

Then, the control circuit 4 outputs a control signal based on the amplitude average value (output average power) of the memory table to the vector adjuster, and performs control excluding the detection value affected by the instantaneous peak. Here, in the calculation of the amplitude average value (output average power), the control circuit 4 compares the amplitude of the detection signal with a predetermined threshold value (limit value) to avoid vector adjustment control by a distortion component signal having an excessive amplitude. ing.

The control processing by the control circuit 4 will be specifically described with reference to FIG. For the sake of simplicity, the signal detected by the above-described detection detector 2 (a distortion component signal of an RF signal by the main amplifier 1 and a pilot signal) will be described as an example.
The same applies to the control based on the signal detected by.

In this example, the limit value of the amplitude (the threshold value of the amount changed compared with the previous sampling) is set to “2.0 points” in advance, and the A / D conversion (step S
1) Read the amplitude value of the signal sampled and sampled this time (step S2). Next, the difference between the amplitude value and the amplitude value at the same sampling point obtained in the previous sampling (that is, the difference before amplitude) is obtained, and the difference before amplitude is compared with the limit value (step S3).

As a result, if the previous difference value does not exceed the limit value, the output average power (amplitude value) of the past sampling amplitude value including the current sampling amplitude value at the same sampling point is calculated (step S4). ), The calculated output average power value is stored in a memory table (step S5), and the vector averager 3
Output to perform adjustment control (step S6). On the other hand, if the previous difference value exceeds the limit value, the output average power already stored in the memory table is used as it is as the current output average power (step S7), and the same processing as above is performed (step S5). , S6).

That is, when the amplitude value sampled this time is larger than the previous time by more than the threshold value, the current sampling value can be considered to be affected by the instantaneous peak, and therefore, the past sampling value excluding the current sampling value is used. Vector adjustment is controlled based on the average value. Specifically, in the example shown in FIG. 4, the difference before the amplitude (5.0) of the sampling point S7 exceeds the limit value (2.0) due to the influence of the peak power.
In, vector adjustment control is performed using an average value excluding the current sampling value (8.5). At other sampling points, vector adjustment control is performed using an average value including the current sampling value. Therefore, according to the present example, even if an instantaneous peak occurs in the input signal, the vector adjustment can be performed without the influence of the instantaneous peak, and a control malfunction of the distortion detection loop can be prevented to achieve stable distortion compensation amplification. It can be carried out.

FIG. 7 shows the configuration of a feedforward distortion compensating amplifier according to another embodiment of the present invention. In this example, a pilot signal of a specific frequency (different from the signal from pilot signal generator 10) of pilot signal generator 20 is input via combiner 19, and the pilot signal is input to distributor 9 together with an RF input signal. You are typing. Also, instead of the detection detector 2 of the embodiment of FIG.
Detector 2 for detecting a pilot signal via
2, a distortion component signal of a pilot signal generated in the main amplifier 1 due to the input of the instantaneous peak is detected and input to the control circuit 4. In this example, the RF input signal is not directly controlled, and the control circuit 4 performs the same control as above to perform distortion compensation on the main amplifier 1 based on the distortion component signal generated in the pilot signal. I have.

In the above embodiment, when the detected signal amplitude value (sampling value) is larger than the predetermined threshold value, the average value of the past sampling values not including the present time is used as a substitute value, thereby obtaining the amplitude threshold value. Performed vector adjustment control based on alternative values of smaller amplitude values,
The substitute value is not limited to this, and for example, the following various values can be used. The point is that the adjustment process by the adjuster can be controlled as a value excluding the influence of the instantaneous peak.

That is, instead of the past average value, a certain amplitude value smaller than the amplitude threshold value is prepared in advance as a substitute value, or a certain sample value smaller than the amplitude threshold value in the past sampled values is used as a substitute value. If the current sampling value is larger than the threshold value, adjustment control may be performed using the substitute value. Further, in the above embodiment, when the detected sampling value is larger than the predetermined threshold value, the value of the sampling point is set as the substitute value. However, for the neighboring sampling points including the sampling point, the substitute value prepared in advance is used. May be changed. As a result, a value in a certain sampling range centered on the instantaneous peak is substituted, and control excluding the influence of the instantaneous peak can be realized.

[0037]

As described above, according to the present invention,
When a signal including instantaneous peak power is input, it is possible to control the distortion detection loop by removing the influence due to non-linearity such as saturation of the main amplifier. A stable feed-forward distortion compensation amplifier capable of performing the recovery control can be realized. In addition, the present invention is particularly suitable for application to CDMA communication, and realizes stable distortion compensation operation even when a signal having a large peak power is input even if the signal is a desired signal such as a CDMA signal. be able to.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a feedforward distortion compensation amplifier according to one embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration example of a vector adjuster.

FIG. 3 is a diagram illustrating a configuration example of a control circuit.

FIG. 4 is a diagram illustrating a memory table of a control circuit.

FIG. 5 is a flowchart illustrating a processing procedure performed by a control circuit.

FIG. 6 is a diagram showing a waveform of an input / output level of a main amplifier, a detected voltage waveform obtained by detecting the waveform, and a sampling waveform thereof.

FIG. 7 is a configuration diagram of a feedforward distortion compensation amplifier according to another embodiment of the present invention.

FIG. 8 is a diagram showing a waveform in which peak power such as CDMA is superimposed on an envelope of an input signal.

FIG. 9 is a diagram illustrating output characteristics of a main amplifier.

[Explanation of symbols]

1 ... Main amplifier, 2 ... Detection detector, 3, 7, ...
・ Vector adjuster, 4 ・ ・ ・ Control circuit, 5 ・ ・ ・ Auxiliary amplifier, 6, 22 ・ ・ ・ Pilot detector, 9 ・ ・ ・
Distributors, 10, 20 ... pilot signal generators, 1
1, 12 ... directional coupler, 13, 14 ... delay line, 15, 16, 17, 19 ... coupler, S1, S
2, S3, Sn ... sampling points, P1, P1 '
..Peak power,

Claims (8)

[Claims] A distortion detection loop and a distortion compensation loop are arranged in series. In the distortion detection loop, an input signal is branched, one input signal is amplified by an amplifier, and an amplifier output signal is branched. By inverting and synthesizing the branched amplifier output signal and the other branched input signal with each other to extract a distortion component signal generated in the amplifier, the distortion compensation loop outputs the distortion component signal. In a feedforward distortion compensation amplifier for obtaining an amplifier output signal in which a distortion component generated in an amplifier is removed by inverting and combining a distortion component signal and an amplifier output signal with each other, an amplifier provided in a distortion detection loop and branched Adjusting means for adjusting the output signal and the other input signal to an inverted amplitude and phase, and detecting means for detecting a distortion component signal extracted by a distortion detection loop. Changing means for changing the detected distortion component signal to an alternative signal having an amplitude smaller than a predetermined threshold value when the amplitude of the detected distortion component signal is larger than a predetermined threshold; and a distortion component detected by the detection means. A feed-forward distortion compensation amplifier, comprising: an adjustment control unit that controls the adjustment unit based on the amplitude of the detected distortion component signal and the amplitude of the substitute signal so that the amplitude of the signal is reduced. 2. The distortion compensation amplifier according to claim 1, further comprising means for generating a pilot signal of a specific frequency, wherein the pilot signal is input to the distortion detection loop as the input signal. Feedforward distortion compensation amplifier. 3. The feedforward distortion compensating amplifier according to claim 1, wherein the changing means samples the detected distortion component signal and, when the sampling value is larger than a predetermined amplitude threshold,
The sampling value is changed to an alternative sampling value having an amplitude smaller than a predetermined amplitude threshold prepared in advance, and the adjustment control means controls the adjustment means based on the detected sampling value and the alternative sampling value. Forward distortion compensation amplifier. 4. The feedforward distortion compensating amplifier according to claim 3, wherein the alternative sampling value has an amplitude smaller than a predetermined amplitude threshold obtained in the past at a sampling point at which the sampling value becomes larger than the predetermined amplitude threshold. A feedforward distortion compensation amplifier characterized by being a sampling value. 5. The feedforward distortion compensation amplifier according to claim 3, wherein the substitute sampling value is a sampling value smaller than a predetermined amplitude threshold obtained in the past at a sampling point where the sampling value has become larger than the predetermined amplitude threshold. A feed-forward distortion compensation amplifier, characterized in that it is an average sampling value. 6. The feedforward distortion compensating amplifier according to claim 3, wherein the changing unit includes a sampling point having a sampling value larger than a predetermined amplitude threshold and a sampling point near the sampling point. A feed-forward distortion compensation amplifier, wherein a sampling value is also changed to an alternative sampling value. 7. The feedforward distortion compensation amplifier according to claim 1, wherein the distortion detection loop includes a second pilot signal for mixing a second pilot signal into an input signal to the amplifier. The distortion compensation loop includes pilot signal generation means, a distortion compensation loop, an amplifier output signal and a distortion component signal from the distortion detection loop, and a second adjustment means for adjusting the amplitude and phase of the distortion component signal to mutually inverted amplitudes and phases. An auxiliary amplifier for amplifying the distortion component signal; and a distortion component signal of the second pilot signal from the amplifier output signal from which the distortion component has been removed by inverting and combining the distortion component signal and the amplifier output signal. And a second detecting means for detecting, when the amplitude of the detected distortion component signal of the second pilot signal is larger than a predetermined threshold value, the changing means comprises: An adjustment signal is changed to an alternative signal having an amplitude smaller than a predetermined threshold value prepared in advance, and the adjustment control means adjusts the detected distortion component signal so that the amplitude of the distortion component signal detected by the detection means and the second detection means becomes small. And a control means for controlling the adjusting means and the second adjusting means based on the amplitude of the alternative signal. 8. In a distortion detection loop, an input signal is branched, one input signal is amplified by an amplifier, an amplifier output signal is branched, and the branched amplifier output signal and the other input signal are branched. And the signal is inverted by a vector adjuster and then combined to extract the distortion component signal generated by the amplifier. In the distortion compensation loop, the distortion component signal output from the distortion detection loop and the amplifier output signal are inverted with respect to each other. In the feed-forward distortion compensation amplification method of obtaining an amplifier output signal from which the distortion component generated by the amplifier is removed by combining the signals, the amplitude value of the distortion component signal extracted by the distortion detection loop is sampled and detected. If the amplitude value is larger than the predetermined amplitude threshold, the sampling value is changed to another alternative sampling value, and the alternative sampling value is changed. Feedforward distortion compensation amplification method by controlling the vector adjuster and performs adjustment of the amplitude and phase by using a tag value.