JP2006174409A - Doherty high efficient amplifier for high frequency and signal processing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high efficient amplifier for high frequencies capable of providing accurate linearity and a signal processing method thereof. <P>SOLUTION: In a Doherty amplifier wherein an output of a main amplifier 1 is composed with an output of a peaking amplifier 2 and the composite output is outputted, a level comparator 8 measures a signal level of an input signal and a signal level of the output signal to check the linearity of the gain, and outputs a bias signal for controlling the gain to be constant even when the level of the input signal is changed to the peaking amplifier 2 via an amplitude limit unit 9. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a high-frequency Doherty high-efficiency amplifier used for microwave communication and the like, and a signal processing method thereof.

Conventionally, as a means to realize a highly efficient amplifier, a Doherty type high efficiency amplifier (hereinafter referred to as a combination of a main amplifier that performs linear amplification and a peaking amplifier that corrects the deterioration of the linearity of the main amplifier at high output) , Called Doherty amplifier). Doherty amplifiers have started to be used even in high frequency amplifiers such as microwaves in order to obtain a large output with low power (for example, Non-Patent Document 1).

FIG. 9 is a block diagram illustrating a functional configuration of a conventional Doherty amplifier, and FIG. 10 is a diagram illustrating input / output characteristics of the Doherty amplifier.
Hereinafter, the operation of the Doherty amplifier will be described with reference to FIGS.

In FIG. 9, the Doherty amplifier includes a main amplifier 100, a peaking amplifier 200, an output load 300, a distributor 400 that distributes a signal input to the Doherty amplifier to the main amplifier 100 and the peaking amplifier 200, and a bias controller 500. It consists of and.

In FIG. 10, an input-to-output operation line ML and an operation line PL of the main amplifier 100 and the peaking amplifier 200 are drawn. The peaking amplifier 200 starts output from the point S where the saturation of the output of the main amplifier 100 starts.

The bias controller 500 observes the input signal level of the Doherty amplifier, and outputs a bias control voltage to the peaking amplifier 200 when the input signal level exceeds the input level at the point S. Then, the peaking amplifier 200 compensates for a decrease in the output of the main amplifier 100 and outputs an amplified signal to the output load 300. As a result, a linear signal output combined with the output of the main amplifier 100 can be obtained at the output load 300 as indicated by the dotted line in FIG. 2 (for example, Patent Document 1).

However, even with this correction method, the input level S at which the peaking amplifier 200 starts operating is a preset level, and the input level at which the gain of the main amplifier and the peaking amplifier and the saturation of the main amplifier start is the temperature. Or the main amplifier 1
There was a problem that accurate linear correction was not possible due to individual differences of 00.
JP 2004-173231 A (page 8, FIG. 2) RJMcMorrow, DMVoton, and PRMalonney "The Doherty Microwave amplifier", 1994.IEEE MTTS Digest, TH3-E, 1994

Conventional high-frequency high-efficiency amplifiers adjust the voltage of the bias signal that controls the output of the peaking amplifier by monitoring the input signal level of the Doherty amplifier.
There was a problem that accurate linearity could not be obtained due to individual differences of amplifiers.

The present invention has been made to solve the above problems, and an object thereof is to realize a high-frequency high-efficiency amplifier capable of obtaining accurate linearity and a signal processing method thereof.

In order to achieve the above object, the high-frequency Doherty high-efficiency amplifier of the present invention has a main amplifier and a peaking amplifier, and is controlled by the output of the main amplifier that linearly amplifies the input signal and the bias signal. In the high-frequency Doherty type high-efficiency amplifier that outputs an output signal obtained by combining the output of the peaking amplifier that amplifies and outputs the signal distributed from the input signal, the input level generated by detecting the input signal A first detector for outputting a signal;
A second detector for outputting an output level signal generated by detecting the synthesized output signal;
The input level signal is input to one input terminal, the output level signal is input to the other input terminal, the input level signal and the output level signal are compared, and the gain of the output signal with respect to the input signal is predetermined. A level comparator that outputs to the amplitude limiter a bias signal that controls the gain to a predetermined value, and a maximum voltage of the bias signal that is input from the level comparator is set to a predetermined voltage. And an amplitude limiter for limiting and outputting to the peaking amplifier.

In addition, the main amplifier and the peaking amplifier of the present invention, the output of the main amplifier that linearly amplifies the input signal, and the peaking amplifier that amplifies and outputs the signal distributed from the input signal controlled by the bias signal In the signal processing method for a high-frequency Doherty-type high-efficiency amplifier that outputs an output signal obtained by synthesizing the output of A detector, a level comparator, and an amplitude limiter, wherein the first detector outputs an input level signal generated by detecting the input signal to one input terminal of the level comparator; The second detector outputs an output level signal generated by detecting the synthesized output signal to the other input terminal of the level comparator, and the input level signal is input to one input terminal. The level comparator, to which the output level signal is input to the other input terminal, compares the input level signal with the output level signal, and the gain of the output signal with respect to the input signal decreases from a predetermined value. A bias signal for controlling the gain to a predetermined value is output to an amplitude limiter, and the amplitude limiter to which the bias signal is input from the level comparator outputs the bias signal to be input. A signal processing method for a high-efficiency Doherty-type high-efficiency amplifier, wherein the signal is output to the peaking amplifier while being limited to a predetermined voltage.

According to the present invention, the input and output of the Doherty type high efficiency amplifier are compared, and the voltage of the bias signal of the peaking amplifier is controlled so that the gain is constant, so that the Doherty type high efficiency for high frequency with accurate linearity is achieved. An amplifier can be realized.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a functional configuration of a Doherty type high efficiency amplifier according to the first embodiment of the present invention, and FIG. 2 is a diagram for explaining input / output characteristics of the Doherty type high efficiency amplifier according to the first embodiment.
Hereinafter, the configuration and operation of a Doherty type high efficiency amplifier (hereinafter referred to as a Doherty amplifier) according to an embodiment of the present invention will be described with reference to FIGS.
In FIG. 1, a Doherty amplifier includes a main amplifier 1, a peaking amplifier 2, a distributor 3, 1
/ 4 wavelength impedance converter 4 a, ¼ wavelength impedance converter 4 b, bias controller 5, delay device 10, and temperature compensation attenuator 11. The bias controller 5
A detector 6, a detector 7, a level comparator 8, and an amplitude limiter 9 are provided. A coupler 21 and a coupler 22 are provided at the input and output to branch the signal to the level comparator 8, respectively.

In the Doherty amplifier according to the first embodiment, the level comparator 8 checks the gain of the Doherty amplifier by comparing the input and output signal levels. Then, a bias signal that keeps the gain constant, that is, the linearity constant, is output to the peaking amplifier. Hereinafter, the operation of each component will be described.

The main amplifier 1 is a high-output amplifier that operates with good linearity such as class AB. The peaking amplifier 2 is a high-output amplifier such as a class C or a class D, and includes a bias signal Vgg input terminal for controlling an operating point in addition to a signal input terminal.

A signal input to the Doherty amplifier is input to the distributor 3 through a temperature compensation attenuator 11 that compensates for a temperature change in the gain of the main amplifier 1 and the peaking amplifier 2. The input signal is divided into two by the distributor 3, one being input to the main amplifier 1 and the other being input to the peaking amplifier 2. The output terminal of the main amplifier 1 is connected to the output terminal of the peaking amplifier 2 via the quarter wavelength impedance converter 4a. The output terminal of the peaking amplifier 2 is further connected to
Another quarter wavelength impedance converter 4b is connected, and a signal amplified by the main amplifier 1 and the peaking amplifier 2 is synthesized and output to the outside of the Doherty amplifier.

In addition, a part of the input signal is branched out by the coupler 21 and output to the detector 6 of the bias controller 5 via the delay unit 10. The detector 6 detects the input signal, for example,
An input level signal Vi converted into a DC signal is generated and output to one input terminal of the level comparator 8. The combined output signal is branched by the output-side coupler 22, converted to the output level signal Vo in the same manner by the detector 7 of the bias controller 5, and output to the other terminal of the level comparator 8.

Here, since the main amplifier 1 performs a linear operation when the input is small, the peaking amplifier 2 is in a cutoff state. For example, if the peaking amplifier 2 is composed of an FET, a bias signal Vgg is applied from the bias control unit 5 to the gate of the FET of the peaking amplifier 2 so that the drain current of the FET becomes “0”. When the input becomes large and the output of the main amplifier 1 begins to saturate, the peaking amplifier 2 starts to operate, and the bias controller 5 starts the bias signal so that the output of the Doherty amplifier is linear, in other words, the gain is constant. Vgg is controlled.

The level comparator 8 measures the output level signal Vo and the input level signal Vi to check the linearity, and when a predetermined gain is deteriorated (corresponding to the S point at which the output in FIG. 2 starts to be saturated), the peaking amplifier. 2 outputs the bias signal Vgg via the amplitude limiter 9. In order to detect this deterioration, for example, an attenuator (not shown) or the like is used so that the input level signal Vi and the output level signal Vo previously supplied from the detector 7 and the detector 7 are equal to each other at a constant gain. It is adjusted by. If saturation occurs in the main amplifier 1, the output level signal Vo becomes a value lower than the input level signal Vi. And level comparator 8
Detects the difference and outputs the bias signal Vgg to the peaking amplifier 2 via the amplitude limiter 9 so that the output and input level signal Vo and the input level signal Vi are equal.

In the peaking amplifier 2, the bias signal Vgg is applied to the gate, and the output starts when the drain current that has been in the cutoff state so far flows to compensate for the saturated output of the main amplifier 1. The output is combined with the output of the main amplifier 1, and the linearity of the Doherty amplifier is secured by outputting the voltage of the bias signal Vgg so that the level comparator 8 has a constant gain.

In the above description, in order to make the gain constant, the level comparator 8 controls the bias signal so that the input voltages of the level signals to both terminals of the level comparator 8 are equal. Method, for example, the level comparator 8 calculates the ratio of both level signals inputted to both terminals and calculates the ratio to obtain the gain of the Doherty amplifier, and controls the bias voltage so that the gain becomes constant. There may be.

The control performed by the conventional Doherty-type high-efficiency amplifier measures only the input signal level, and outputs a bias signal for performing a preset compensation operation to the peaking amplifier 2 when the input signal level is assumed to be saturated. Therefore, when the operation of the main amplifier 1 or peaking amplifier is different from the set condition, accurate linearity cannot be secured.

In the first embodiment, an amplitude limiter 9 is further added to monitor the voltage of the bias signal Vgg and to prevent the peaking amplifier 2 from outputting an output that is not rated when there is an excessive input. The maximum value of is limited. As a result, the peaking amplifier 2 is protected and the operating range is accurately set, and the linearity of the Doherty amplifier is accurately maintained within the operating range. In Embodiment 1 of the present invention, if the maximum output of the main amplifier is M watts and the maximum output of the peaking amplifier is P watts, (M + P) watts is the maximum output of the Doherty amplifier.

The temperature compensation attenuator 11 is installed on the input side of the distributor 3 in order to compensate for fluctuations in operation with respect to temperature changes such as the gain of the main amplifier 1 and the peaking amplifier 2. as a result,
Since the load on the peaking amplifier 2 can be reduced by suppressing the magnitude of the gain change and the temperature fluctuation at the point where the output saturation starts, unnecessary power consumption is prevented and the stability of the Doherty amplifier is improved.

FIG. 3 is a block diagram showing a functional configuration of a high-efficiency amplifier (Doherty amplifier) according to Embodiment 2 of the present invention, and FIG. 4 is a diagram showing a relationship between input and output characteristics of the Doherty amplifier according to Embodiment 2 of the present invention. is there.
In FIG. 3, the Doherty amplifier has peaking amplifiers 2a and 2b, and the bias control unit 5 includes level comparators 8a and 8b, amplitude limiters 9a and 9b, and a quarter wavelength impedance converter 4c. The same as in the first embodiment.

When the number of peaking amplifiers 2 is two, the peaking amplifier 2b is connected to the output 1
The / 4 wavelength impedance converter 4c is further added to the output of the quarter wavelength impedance converter 4b of the peaking amplifier 2a, and the output of the Doherty amplifier is a combined output of the main amplifier 1 and the two peaking amplifiers 2a, 2b. .

In the second embodiment, the combined output is input to the level comparator 8b via the detector 7. When the main amplifier 1 is saturated, the level comparator 8b outputs the gate voltage Vggb to the peaking amplifier 2b and one input terminal of the level comparator 8a via the amplitude limiter 9b.

The amplitude limiter 9b outputs the bias signal Vggb so as to compensate for the output drop of the main amplifier 1 until the input voltage reaches the point A in FIG. However, if the output of the peaking amplifier 2b at point A (here, P watts) is the rated output of the peaking amplifier 2b, the peaking amplifier 2 will be saturated and useless power if the output exceeds that. Consumes or even breaks down.

Therefore, as in the first embodiment, the amplitude limiter 9b includes the bias signal V of the peaking amplifier 2b.
A constant voltage of X volts is output so that ggb does not exceed an allowable voltage (for example, X volts), and the output of the peaking amplifier 2b is also maintained at P watts.

However, the second embodiment of the present invention is provided with a peaking amplifier 2a for parallel output so that the output can be further increased even if the point A is exceeded in preparation for further output.

That is, in the level comparator 8a, for example, the output of Y volts from the level comparator 8b is input to one input terminal, and the output of the amplitude limiter 9b and the bias signal of maximum X volts are input to the other input terminal. Vggb is input as a comparison input. If the peaking amplifier 2b operates within the rated range, the voltage of each level signal input to the two terminals of the level comparator 8b is equal to X = Y. When the output of the Doherty amplifier increases and the output Y volt from the level comparator 8b exceeds X volt, a difference occurs between the two input voltages, so the level comparator 8a A bias signal Vgga is output to the peaking amplifier 2a through the amplitude limiter 9a so that the voltages are equal.

If the peaking amplifiers 2a and 2b have the same specifications, the bias signals Vgga and Vg
The maximum voltage of gb is the same X volt, and the maximum output voltage of the amplitude limiter 9a is also X volt. The peaking amplifier 2a outputs a maximum of P watts in the same manner as the peaking amplifier 2b. The total output of the main amplifier 1 and the peaking amplifiers 2a and 2b is (M + 2P
) Watts.

In general, a high-power semiconductor device has a drawback that a response speed is slowed against an allowable output. In the second embodiment, there is an effect that the maximum output can be increased without reducing the response speed by using the small output peaking amplifier 2 of the same specification in parallel.

Although the case where two peaking amplifiers 2 are connected in parallel has been described here, the number of peaking amplifiers 2, level comparators 8, and amplitude limiters 9 is the same even when a plurality of peaking amplifiers 2 are connected in parallel. May be increased in the same manner as in the second embodiment, and the configuration and operation thereof can be easily estimated, so that the description thereof is omitted.

As described above, in each embodiment of the present invention, a high-efficiency amplifier having excellent amplitude linearity can be realized. In the second embodiment, a Doherty type high-efficiency amplifier capable of maintaining a high response speed is realized by using a small-output peaking amplifier 2 in parallel.

By the way, at high frequencies such as microwaves, it is important that the phase characteristics are constant not only according to the response speed but also according to the output. Therefore, in the present invention, not only the amplitude characteristic but also the output having the same phase characteristic can be obtained even when the output amplitude changes (in other words, the input amplitude changes).

FIG. 5 is a functional block diagram of a Doherty type high efficiency amplifier according to Embodiment 3 of the present invention.
In FIG. 5, the Doherty amplifier is the same except that a variable phase shifter 12, a delay unit 13, a detector 14, and a coupler 23 are added to the Doherty amplifier of the first embodiment shown in FIG.

The input signal is input to the variable phase shifter 12 via the delay unit 13, and the output of the variable phase shifter 12 is input to the Doherty amplifier similar to that of the first embodiment. The input signal is branched and input to the detector 14 by the coupler 23. The detector 14 generates a DC phase bias signal or an input level signal corresponding to the input signal level and outputs it to the variable phase shifter 12.

FIG. 6 is a block diagram showing an internal functional configuration of the variable phase shifter 12.
In FIG. 6, the variable phase shifter 12 includes an operation amplifier 121, a reference voltage device 122, and a phase adjuster 123. The phase adjuster 123 is known in advance with respect to the phase characteristic with respect to the bias adjustment signal, and is also known in advance with respect to the phase characteristic between the input signal level and the output of the Doherty amplifier, and the phase to be corrected from this input signal level. The applied bias adjustment signal is phase adjuster 1
23.

  In the variable phase shifter 12, the input signal is input to the signal input terminal of the phase adjuster 123.

The phase bias signal (input level signal) from the detector 23 is input to one input terminal of the operational amplifier 121. Then, the reference voltage set by the reference voltage device 122 necessary to give a predetermined phase difference to the phase adjuster 123 is input to the other input terminal. This set phase is, for example, aligned with the phase characteristics of the Doherty amplifier at the maximum input signal level.

The operational amplifier 121 outputs a bias adjustment signal to the phase adjuster 123 so that the difference between the reference voltage and the input phase bias signal is minimized, so that the output of the Doherty amplifier is independent of the level of the input signal. It has a certain phase characteristic.

FIG. 7 is a block diagram of a functional configuration when the Doherty amplifier that performs phase adjustment is realized with a smaller configuration.

In FIG. 5, a phase bias signal or an input level signal is output from the detector 14 provided exclusively for phase adjustment to the variable phase shifter 12, but the Doherty amplifier in FIG.
An input level signal output from the detector 6 is used as the phase bias signal supplied to the variable phase shifter 12.

FIG. 8 is a block diagram of a functional configuration according to the fourth embodiment of the Doherty type high efficiency amplifier of the present invention.
In FIG. 8, in order to align the phase characteristics of the Doherty amplifier, feedback control is performed in which a phase detector 15 is connected to the combined output and the phase signal is connected to the variable phase shifter 12 as a phase bias signal. In the Doherty amplifier of Example 3 shown in FIG. 5 and FIG.
The input signal is measured, and an open loop phase correction is performed in which a bias for phase correction corresponding to the level of the input signal is applied to the phase adjuster 123. On the other hand, in the fourth embodiment, the level of the input signal is not measured, and the phase characteristic of the output of the Doherty amplifier is changed to the phase detector 15.
The error signal between the reference phase and a preset reference phase is output to the variable phase shifter 123 as a DC phase bias signal for feedback.

By feedback control, it is possible to realize a Doherty amplifier in which the phase characteristic is not affected by the input signal level as well as the linearity of the amplitude characteristic.

The phase compensation method of the Doherty amplifier in the third and fourth embodiments can be similarly applied to the case of using a plurality of peaking amplifiers as in the second embodiment.

As described above, a Doherty type high efficiency amplifier with good gain linearity can be realized according to the present invention. As in the third and fourth embodiments, not only the gain characteristic but also the output of the output signal is changed not only with respect to the level change of the input signal. A Doherty-type high-efficiency amplifier whose phase characteristics do not change can be realized.

1 is a block diagram showing a functional configuration of a Doherty type high efficiency amplifier according to Embodiment 1 of the present invention. FIG. FIG. 3 is a diagram illustrating input / output characteristics of the Doherty amplifier according to the first embodiment of the present invention. The block diagram which shows the function structure of the Doherty type | mold high efficiency amplifier concerning Example 2 of this invention. The figure explaining the input-output characteristic of the Doherty type | mold high efficiency amplifier concerning Example 2 of this invention. The block diagram which shows the function structure of the Doherty type | mold high efficiency amplifier concerning Example 3 of this invention. The block diagram which shows the function structure of a variable phase shifter. The block diagram which shows the 2nd example of a function structure of the Doherty type | mold high efficiency amplifier concerning Example 3 of this invention. The block diagram which shows the function structure of the Doherty type | mold high efficiency amplifier concerning Example 4 of this invention. The block diagram which shows the function structure of the conventional Doherty type | mold high efficiency amplifier. The figure explaining the input-output characteristic of the conventional Doherty type high efficiency amplifier.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main amplifiers 10 and 13 Delay device 11 Temperature compensation attenuator 12 Variable phase shifter 121 Differential amplifier 122 Reference voltage device 123 Phase adjuster 15 Phase detector 2 Peaking amplifiers 21, 22, and 23 Coupler 3 Dividers 4a, 4b, and 4c 1/4 wavelength impedance converter 5 Bias control unit 6, 7, 14 Detector 8, 8a, 8b Level comparator 9, 9a, 9b Amplitude limiter

Claims (6)

It has a main amplifier and a peaking amplifier, and combines the output of the main amplifier that linearly amplifies the input signal and the output of the peaking amplifier that amplifies and outputs the signal distributed from the input signal under the control of the bias signal. In high-frequency Doherty type high-efficiency amplifier that outputs the output signal
A first detector for outputting an input level signal generated by detecting the input signal;
A second detector for outputting an output level signal generated by detecting the synthesized output signal;
The input level signal is input to one input terminal, the output level signal is input to the other input terminal, the input level signal and the output level signal are compared, and the gain of the output signal with respect to the input signal is predetermined. A level comparator that outputs a bias signal to the amplitude limiter for controlling the gain to a predetermined value when the value drops from the value;
A Doherty-type high-efficiency amplifier for high frequency, comprising: an amplitude limiter that limits a maximum voltage of the bias signal input from the level comparator to a predetermined voltage and outputs the same to the peaking amplifier. A plurality of main amplifiers and peaking amplifiers that amplify the input signal linearly and amplify and output the signals distributed from the input signal by controlling each of them with a bias signal In the high-frequency Doherty type high-efficiency amplifier that outputs an output signal that is synthesized with each output of the peaking amplifier of
A first detector for outputting an input level signal generated by detecting the input signal;
A second detector for outputting an output level signal generated by detecting the synthesized output signal;
The input level signal is input to one input terminal, the output level signal is input to the other input terminal, the input level signal and the output level signal are compared, and the gain of the output signal with respect to the input signal is predetermined. A first level comparison that outputs a first bias signal for controlling the gain to a predetermined value to one input terminal of the second level comparator and the first amplitude limiter when the gain decreases from the value; And
The highest voltage of the first bias signal input from the first level comparator is limited to a predetermined voltage and output to the first peaking amplifier and the other input terminal of the second level comparator. Said first amplitude limiter;
Input to the first one input terminal output from the first level comparator;
The first bias signal is input to the other input terminal via the amplitude limiter, and the voltages of the bias signals input to the two input terminals are compared, and control is performed so that the voltages of the bias signals are equal. A second level comparator that outputs a second bias signal to the second amplitude limiter;
And a second amplitude limiter for limiting the input second bias signal to a predetermined maximum voltage and outputting the second bias signal to a second peaking amplifier. Efficiency amplifier. A temperature compensation attenuator having an attenuation characteristic for compensating a temperature vs. gain characteristic of the main amplifier and the peaking amplifier set in advance;
The high-efficiency amplifier according to claim 1, wherein the input signal is input to the main amplifier and the peaking amplifier via the temperature compensator. Variation in phase characteristics with respect to input signal levels of the main amplifier and the peaking amplifier by an input level signal output from the first detector or a third detector provided before the first detector Further comprising a variable phase shifter for compensating
The high-efficiency amplifier according to claim 1, wherein the input signal is input to the main amplifier and the peaking amplifier via the variable phase shifter. The high efficiency amplifier further includes a phase detector and a variable phase shifter,
The main amplifier and the peaking amplifier receive the input signal via the variable phase shifter,
The phase detector measures the phase of the combined output signal and outputs an error voltage indicating a difference from a reference phase to the variable phase shifter as a phase bias signal,
The variable phase shifter is
3. The high efficiency amplifier according to claim 1, wherein feedback control is performed to adjust a phase of the output signal to a predetermined phase by the phase bias signal. It has a main amplifier and a peaking amplifier, and combines the output of the main amplifier that linearly amplifies the input signal and the output of the peaking amplifier that amplifies and outputs the signal distributed from the input signal under the control of the bias signal. In a signal processing method for a high-efficiency Doherty-type high-efficiency amplifier that outputs the output signal,
The high efficiency amplifier includes a main amplifier, a peaking amplifier, a first detector, a second detector, a level comparator, and an amplitude limiter.
The first detector outputs an input level signal generated by detecting the input signal to one input terminal of the level comparator,
The second detector outputs an output level signal generated by detecting the synthesized output signal to the other input terminal of the level comparator,
The level comparator in which the input level signal is input to one input terminal and the output level signal is input to the other input terminal,
The input level signal and the output level signal are compared, and when the gain of the output signal with respect to the input signal decreases from a predetermined value, a bias signal for controlling the gain to a predetermined value is output to the amplitude limiter. ,
The amplitude limiter to which the bias signal is input from the level comparator,
A signal processing method for a high-frequency Doherty type high-efficiency amplifier, characterized in that the input bias signal is limited to a predetermined voltage and output to the peaking amplifier.

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