JPH10209770A - Power amplifier and radio telephone device using the same power amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve power addition efficiency of a power amplifier at the time of small-signal operation by individually varying and controlling a drain voltage generated by a drain voltage generator and a gate voltage generated by a gate voltage generator corresponding to an input signal level and applying them to the power amplifier. SOLUTION: A power amplifier 2 selectively inputs input signals of a digital modulation system and an analog modulation system from an input terminal 1 for operation. A drain voltage generator 4 inputs a positive voltage, outputted by a power source 5 for drain voltage generation and varies and controls the positive voltage under the control of a control part 8, thereby applying the voltage as a drain voltage to the power amplifier 2. Further, a gate voltage generator 6 inputs negative voltage outputted by a power source 7 for gate voltage generation and varies and controls the negative voltage under the control of the control part 8, thereby applying the voltage as a gate voltage to the power amplifier 2. Consequently, the power addition efficiency of the power amplifier 2 at the time of small-signal operation is improved, under the control of the control part 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power amplifier for a radio transmitter operating in both a digital modulation system and an analog modulation system, and more particularly, to a power amplifier in which the power addition efficiency of a power amplifier during small signal operation is improved. .

[0002]

2. Description of the Related Art Conventionally, for example, as in North American cellular,
2. Description of the Related Art A wireless transmitter equipped with a power amplifier that operates in both a digital modulation scheme and an analog modulation scheme is known.

FIG. 7 is a circuit diagram showing an example of a power amplifier of a radio transmitter operating in both the digital modulation system and the analog modulation system.

In FIG. 7, a power amplifier 2 power-amplifies an input signal input from a power amplifier input terminal 1 and outputs the amplified signal from a power amplifier output terminal 3, and uses a field effect transistor (FET) as a circuit element. It is configured to operate using a positive drain voltage generated from the drain voltage generating power supply 5 and a negative gate voltage generated from the gate voltage generating power supply 7 as bias voltages.

In the North American cellular system described above, the specifications are set such that the output level of the analog modulation system is larger than the output signal level of the digital modulation system. Therefore, as shown in FIG. 8, in a power amplifier used in such a system, the power added efficiency is set to be maximum when used in an analog modulation method. The power added efficiency, as is well known, is the output power of the power amplifier minus the input power (corresponding to the AC power consumed by the power amplifier) divided by the DC power used to operate this power amplifier. Value. In other words, it is shown that if the power addition efficiency is high, the required power can be obtained with low power consumption.

Therefore, in the above-described power amplifier, when the input signal modulated by the digital modulation method is input and amplified, the power addition efficiency is poor because the signal is deteriorated as compared with the analog modulation method. There is a problem that wasteful power consumption occurs.

In order to solve this problem, FIG.
As shown in FIG. 1, a drain voltage generator 4 for inputting a positive voltage generated from a drain voltage generating power supply 5 to generate a drain voltage is provided, and the drain voltage generated from the drain voltage generator 4 is supplied to a power amplifier 2. , And the drain voltage generated from the drain voltage generator 4 is switched by a control unit 8 including a microcomputer or the like between a digital modulation method and an analog modulation method. Such a configuration has been proposed.

According to such a configuration, as shown in FIG. 10, the output signal saturation point of the power amplifier 2 is set lower in the case of operating in the digital modulation system than in the case of operating in the analog modulation system. can do. By doing so, it is possible to improve the power addition efficiency operating in the digital modulation system, and it is possible to suppress waste of power consumption to some extent.

However, according to the conventional method, although the power addition efficiency is improved at the time of operating a large signal when operating by the digital modulation method, it is hardly effective when operating at the time of small signal. Since the actual power amplifier 2 does not always operate with a large signal but performs a small signal operation regardless of whether it is a digital modulation system or an analog modulation system, it has been desired to improve the power added efficiency during the small signal operation.

[0010]

As described above, in a power amplifier of a radio transmitter operating in both the conventional digital modulation scheme and the analog modulation scheme, the power added efficiency is reduced when used in the digital modulation scheme. There is a problem of deterioration. In order to improve this problem, a configuration has been proposed in which the drain voltage applied to the power amplifier is switched between a case where the drain voltage is operated by the digital modulation system and a case where the drain voltage is operated by the analog modulation system. According to the configuration, there is a problem that the power added efficiency can hardly be improved when performing the small signal operation.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a power amplifier which operates in both a digital modulation system and an analog modulation system and has improved power addition efficiency during small signal operation, and a radio telephone device using this power amplifier. With the goal.

[0012]

To achieve the above object, the present invention provides a power amplifier control circuit which operates by selectively inputting an input signal modulated by a digital modulation method or an analog modulation method. A drain voltage generating means for generating a drain voltage to be applied to the power amplifier; a gate voltage generating means for generating a gate voltage to be applied to the power amplifier; a drain voltage generated from the drain voltage generating means; Control means for individually and variably controlling the gate voltage generated from the means in accordance with the level of the input signal.

Here, a plurality of gate voltages are applied, and the control means variably controls the plurality of gate voltages.

Here, the control means individually variably controls the plurality of gate voltages.

According to the present invention, a radio telephone apparatus using a power amplifier which operates by selectively inputting an input signal modulated by a digital modulation method or an analog modulation method receives a signal transmitted from a base station. Receiving means, a receiving level detecting means for detecting a level of a received signal, a drain voltage generating means for generating a drain voltage applied to the power amplifier, and a gate voltage for generating a gate voltage to be applied to the power amplifier And a control means for variably controlling a drain voltage generated by the drain voltage generating means and a gate voltage generated by the gate voltage generating means according to the reception level.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the power amplifier according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a first embodiment of a power amplifier according to the present invention. In FIG. 1, portions that perform the same functions as those of the conventional circuit shown in FIG. 9 are denoted by the same reference numerals used in FIG. 9 for convenience of explanation.

In FIG. 1, the control circuit of the power amplifier according to the present embodiment has the same structure as that of the conventional circuit shown in FIG. 9 except that the power supply 7 for generating gate voltage is used instead of the power supply 7 for generating gate voltage. A gate voltage generator 6 for inputting a voltage to generate a gate voltage is provided, and the gate voltage generated from the gate voltage generator 6 is variably controlled by a control unit 8 including a microcomputer or the like. You.

That is, in FIG. 1, 1 is a power amplifier input terminal, 2 is a power amplifier, 3 is a power amplifier output terminal,
4 is a drain voltage generator, 5 is a power supply for drain voltage generation, 6 is a gate voltage generator, and 7 is a power supply for gate voltage generation.

Here, the power amplifier 2 power-amplifies the input signal input from the power amplifier input terminal 1 and outputs it from the power amplifier output terminal 3.

The drain voltage generator 4 receives the positive voltage output from the drain voltage generating power supply 5 and variably controls the positive voltage under the control of the control unit 8 to apply the positive voltage to the power amplifier 2 as a drain voltage. I do.

The gate voltage generator 6 receives a negative voltage output from the power supply 7 for generating a gate voltage, and variably controls the negative voltage under the control of the control unit 8 to apply the negative voltage to the power amplifier 2 as a gate voltage. I do.

FIG. 2 shows a specific configuration of the power amplifier 2 shown in FIG. In FIG. 2, the power amplifier 2 includes a first power amplifier 2a and a second power amplifier 2b connected in series.

Here, the first power amplifier 2a and the second power amplifier 2a
Although the detailed configuration of the power amplifier 2b of FIG.
Power amplifier 2a and second power amplifier 2b each have a field effect transistor (FET) as its circuit element.
And a well-known circuit configuration that operates by inputting the applied drain voltage and gate voltage as bias voltages can be employed.

A drain voltage generated from the drain voltage generator 4 shown in FIG. 1 is applied to the drain voltage input terminal 9. This drain voltage is applied to the first power amplifier 2
a and the second power amplifier 2b.

That is, the drain voltage applied to the drain voltage input terminal 9 is applied as a drain bias to the FETs constituting the first power amplifier 2a and the second power amplifier 2b.

The gate voltage input terminal 10 is
The gate voltage generated from the gate voltage generator 6 shown in FIG. This gate voltage is applied to the first power amplifier 2
a and the second power amplifier 2b.

That is, the gate voltage applied to the gate voltage input terminal 10 is applied to the first power amplifier 2a and the second power amplifier 2a.
Are applied as gate biases to the FETs constituting the power amplifier 2b.

In general, the first power amplifier 2a
And the voltage of the FET constituting the second power amplifier 2b−
As shown in FIG. 11, the current characteristic is smaller than that of the voltage between the drain and the source (drain bias).
Varying the voltage between the sources (gate bias) can greatly change (decrease) the drain current (consumption current).

Therefore, in this embodiment, under the control of the control unit 8, not only the drain voltage (drain bias) generated from the drain voltage generator 4 but also the gate voltage (gate bias) generated from the gate voltage generator 6 is controlled. ) Is also variably controlled according to the input signal. In this way, the value of the drain current can be controlled (limited), and this control acts in the direction of improving the power added efficiency during small signal operation.

FIG. 3 shows the input / output characteristics of the power amplifier 2 and the power addition efficiency realized by the control of the control unit 8 of this embodiment.

In FIG. 3, the input / output characteristics and power added efficiency of the power amplifier 2 when the input signal level is equal to or higher than A are indicated by solid lines, and the input / output characteristics of the power amplifier 2 when the input signal level is equal to or lower than A. The power addition efficiency is indicated by a dashed line.

The input / output characteristics and the power addition efficiency are determined by controlling the drain voltage generated by the drain voltage generator 4 and the gate voltage generated by the gate voltage generator 6 by the control unit 8 to determine whether the level of the input signal is A or more. It can be realized by performing switching control in accordance with the above.

As is apparent from FIG. 3, according to such a configuration, the power addition efficiency in the case of performing a small signal operation can be improved. The input signal level for switching the drain voltage generated from the drain voltage generator 4 and the gate voltage generated from the gate voltage generator 6 is divided not only at one point A shown in FIG. 3 but also at two or more points. You may comprise so that it may be divided and controlled.

FIG. 4 is a block diagram showing a schematic configuration of a portable telephone device using the power amplifier of the present invention. Hereinafter, an application example of the power amplifier of the present invention in a mobile phone device will be described with reference to this drawing.

This portable telephone device is used as a mobile station of a so-called dual-mode cellular radio communication system used in the North American cellular system. The Dewar mode is a method that uses both an analog mode using an analog modulation method and a digital mode using a digital modulation method.

First, the part relating to the digital mode is constituted as follows.

That is, the radio frequency signals transmitted from the base stations BS1, BS2,... Via the digital communication channel are received by the antenna 101 and then received by the receiving circuit (RX) 103 via the antenna duplexer (DUP) 102. Is input to In the receiving circuit 103, the radio frequency signal is mixed with a receiving local oscillation signal output from a frequency synthesizer (SYN) 104 and converted into an intermediate frequency. Note that the frequency of the reception local oscillation signal generated from the frequency synthesizer 104 is specified by the channel specification data SYC output from the control circuit 200.

The reception circuit 103 has a function of detecting a received signal level (reception electric field strength), and the detected reception level is input to the control circuit 200. This reception level detection function is the same in the analog mode described later.

The received intermediate frequency signal is supplied to the A / D converter 1
After being converted into a digital signal at 06, it is input to a digital demodulation circuit (DEM) 107. In the digital demodulation circuit 107, the received intermediate frequency signal is digitally demodulated and converted into a digital baseband signal. The digital baseband signal output from the digital demodulation circuit 107 includes a digital communication signal and a digital control signal. Among them, the digital control signal is taken into the control circuit 200 and identified.

On the other hand, the digital speech signal is input to an error correction code composite circuit (CH-CODEC) 108 after the demodulated waveform signal is equalized by an equalizer (not shown).
The error correction code compound circuit 108 performs error correction compound processing of the digital speech signal supplied from the equalizer, and the error-corrected compound digital communication signal is sent to a speech code compound circuit (SP-CODEC) 109. Is entered. In the voice code composite circuit 109, voice digitalization processing of the digital call signal is performed. The speech signal output from the voice code composite circuit 109 is transmitted to the D / A converter 11
After being converted into an analog call signal by 0, the signal is input to the analog switch 111.

The analog switch 111 is connected to the control circuit 20
In a state where the digital mode is set by the switching control signal output from the audio code composite circuit 10
The switching is controlled so as to selectively output the analog call signal output from the switch 9. Therefore, the analog call signal output from the D / A converter 110 is supplied to the speaker 112 via the analog switch 111, and is output from the speaker 112.

On the other hand, the transmission signal output from the microphone 113 is input to the analog switch 114. At this time, switching of the analog switch 114 is controlled by a switching control signal output from the control circuit 200 so that the transmission signal is output to the speech code composite circuit 109 when the digital mode is set.
Therefore, the transmission signal is transmitted to the analog switch 11.
The signal is converted into a digital transmission signal by the A / D converter 115 via the A / D converter 4, and then input to the speech code composite circuit 109. In the voice code composite circuit 109, voice coding processing of the digital transmission signal is performed. The digital transmission signal output from the audio code composite circuit 109 is input to the error correction code composite circuit 108. The error correction code composite circuit 108 performs the error correction coding process on the digital transmission signal. The encoded digital transmission signal is added with a digital control signal generated by the control circuit 200, and then a digital modulation circuit (MOD) 116 is added.
Is input to

In the digital modulation circuit 116, π / 4 shift DQPSK (π
/ 4 Shifted, differentially
encoded quadrature phase
A modulated signal modulated by a shift keying method is generated, and the modulated signal is converted by the D / A converter 117.
After being converted to an analog signal by the transmission circuit (TX)
105 is input. Then, in the frequency conversion circuit, the modulated signal is combined with a transmission local oscillation signal corresponding to the radio frequency of the digital communication channel output from the frequency synthesizer 104 and converted into a radio frequency signal. Further, the power is amplified to a predetermined power level in a power amplifier (PA) 2 at a high frequency. Then, the power amplifier (P
A) The radio frequency signal output from 2 is an antenna duplexer 1
The signal is supplied to the antenna 101 via the antenna 02 and transmitted from the antenna 101 to a base station (not shown).

On the other hand, the part relating to the analog mode is constituted as follows.

That is, a radio frequency signal transmitted from a base station via an analog communication channel is received by an antenna 101 and then input to a receiving circuit 103 via an antenna duplexer 102. Downconverted to a signal. The reception intermediate frequency transmitted from the reception circuit 103 is converted into an analog audio circuit (ANA
LOG AUDIO) 118. In the analog audio circuit 118, the received intermediate frequency signal is FM-demodulated and then audio-amplified. This analog audio circuit 1
The analog call signal output from 18 is input to analog switch 111. At this time, the analog switch 1
Reference numeral 11 denotes a state in which the analog communication signal output from the analog audio circuit 118 by the switching control signal output from the control circuit 200 is set to the speaker 1 via the analog switch 111 when the analog mode is set.
12 and output from the speaker 112. On the other hand, the transmission signal output from the microphone 113 is input to the analog switch 114. At this time, the switching of the analog switch 114 is controlled by the switching control signal output from the control circuit 200 so that the transmission signal is input to the analog audio circuit 118 when the analog mode is set. Therefore, the transmission signal is input to the analog audio circuit 118 via the analog switch 114. The analog audio circuit 118 generates a modulation signal that is FM-modulated according to the transmission signal, and the modulation signal is transmitted to the transmission circuit 10.
5 is input. In the transmitting circuit 105, the modulated signal is mixed with the transmitting station oscillation signal in accordance with the radio frequency of the analog communication channel generated from the frequency synthesizer 104, up-converted into a radio frequency signal, and output from the transmitting circuit 105. The RF signal is amplified to a predetermined output power by a power amplifier (PA) 2 and supplied to an antenna 101 to be transmitted to a base station (not shown).

Reference numeral 301 denotes a key switch group, and 302 denotes a display.

Reference numeral 304 denotes a power supply circuit. The power supply circuit 304 generates a desired operating voltage Vcc based on the output voltage of the battery 303 and supplies it to the circuit.

In the above configuration, the control circuit 200 outputs the reception circuit control signal RXC and the transmission circuit control signal TXC for controlling the transmission and reception timings and the like. The control signal PAC is output. This power amplifier control signal PA
C is generated by the control circuit 200 in accordance with the received electric field strength of a signal received by the receiving circuit 103 via the antenna 101. The control unit 8 shown in FIG. This corresponds to the output signal. For example,
The level of the reception electric field strength is from about -25 dBm to about -10 dBm.
It is assumed that it fluctuates between 0 dBm. In this case, when the received electric field strength indicates a value of -80 dBm, the input signal level shown in FIG. When the received electric field strength is equal to or less than -80 dBm, that is, when the mobile phone device is located relatively far from the base station or in a place where radio waves are relatively hard to reach, the control circuit 200 performs the one-point operation shown in FIG. The power amplifier (PA) 2 is controlled by outputting a power amplifier control signal PAC such that the power added efficiency indicated by a chain line is obtained. Thus, the power amplifier control signal PAC can be said to be a signal for setting the output level of the power amplifier (PA) 2 according to the reception level.

FIG. 5 is a block diagram showing a second embodiment of the control circuit of the power amplifier according to the present invention.

In the embodiment shown in FIG. 5, two drain voltages and two gate voltages are applied to the power amplifier 2 as bias signals. In FIG. 5, portions that perform the same functions as those of the circuit shown in FIG. 1 are denoted by the same reference numerals as those used in FIG. 1 for convenience of description.

That is, in FIG. 5, 1 is a power amplifier input terminal, 2 is a power amplifier, 3 is a power amplifier output terminal,
4 is a drain voltage generator, 5 is a power supply for drain voltage generation, 6a is a first gate voltage generator, 6b is a second gate voltage generator, and 7 is a power supply for gate voltage generation.

Here, the power amplifier 2 amplifies the power of the input signal input from the power amplifier input terminal 1 and outputs it from the power amplifier output terminal 3.

The drain voltage generator 4 receives a positive voltage output from the power supply 5 for generating a drain voltage, variably controls the positive voltage under the control of the control unit 8, and applies the positive voltage to the power amplifier 2 as a drain voltage. I do.

The first gate voltage generator 6a receives the negative voltage output from the power supply 7 for gate voltage generation,
This negative voltage is variably controlled by the control of the control unit 8 and applied to the power amplifier 2 as a first gate voltage.

The second gate voltage generator 6b receives the negative voltage output from the power supply 7 for gate voltage generation,
This negative voltage is variably controlled by the control of the control unit 8 and applied to the power amplifier 2 as a second gate voltage.

FIG. 6 shows a specific configuration of the power amplifier 2 shown in FIG. In FIG. 6, the power amplifier 2 includes a first power amplifier 2a and a second power amplifier 2b connected in series.

Here, the first power amplifier 2a and the second power amplifier 2a
Although the detailed configuration of the power amplifier 2b of FIG.
Power amplifier 2a and the second power amplifier 2b also have a field effect transistor (FET) as their circuit elements, respectively.
And a well-known circuit configuration that operates by inputting the applied drain voltage and gate voltage as bias voltages can be employed.

The drain voltage generated from the drain voltage generator 4 shown in FIG. 5 is applied to the drain voltage input terminal 9. This drain voltage is applied to the first power amplifier 2
a and the second power amplifier 2b.

That is, the drain voltage applied to the drain voltage input terminal 9 is applied as a drain bias to the FETs constituting the first power amplifier 2a and the second power amplifier 2b.

The first gate voltage generated from the first gate voltage generator 6a shown in FIG. 5 is applied to the first gate voltage input terminal 10a. This first gate voltage is input to the first power amplifier 2a.

That is, the first gate voltage applied to the gate voltage input terminal 10a is applied as a gate bias to the FET constituting the first power amplifier 2a.

The second gate voltage generated from the second gate voltage generator 6b shown in FIG. 5 is applied to the second gate voltage input terminal 10b. This second gate voltage is input to the second power amplifier 2b.

That is, the second gate voltage input terminal 10
The second gate voltage applied to b is applied as a gate bias to the FET constituting the second power amplifier 2b.

Incidentally, also in this embodiment, under the control of the control unit 8, not only the drain voltage (drain bias) generated from the drain voltage generator 4 but also the first gate voltage generator 6a and the second gate Voltage generator 6
By controlling the switching of the first gate voltage (first gate bias) and the second gate voltage (first gate bias) generated from b according to the input signal,
It is configured to improve the power addition efficiency at the time of small signal operation at the time of small signal operation.

With such a configuration, as in the embodiment of FIG. 1, the input / output characteristics and the power added efficiency as shown in FIG. 3 can be realized, and the power added efficiency when performing a small signal operation is improved. can do.

In the embodiment shown in FIG. 5,
First gate voltage (first gate bias) and second gate voltage
Gate voltage (first gate bias) can be individually controlled. As shown in FIG. 6, the power amplifier 2 is generally composed of a plurality of FETs. Therefore, individual FETs vary in performance such as impedance characteristics and power consumption. In the present invention, these F
Since the ET can be individually controlled, it is possible to perform control in accordance with the characteristics of each FET, so that it is possible to further improve the power added efficiency during small signal operation.

In this case, control unit 8 also controls the drain voltage generated from drain voltage generator 4 and the first and second gate voltage generators 6a and 6b generated from first gate voltage generator 6a. FIG. 3 shows the division of the input signal level for switching the second gate voltage generated from FIG.
It is also possible to adopt a configuration in which control is performed not only at one location A, but also at two or more locations.

[0069]

As described above, according to the present invention,
Since the drain voltage generated by the drain voltage generating means and the gate voltage generated by the gate voltage generating means are individually variably controlled according to the level of the input signal and applied to the power amplifier, the digital modulation method is used. Alternatively, it is possible to significantly improve the power adding efficiency of a power amplifier that operates by selectively inputting an input signal modulated by an analog modulation method during a small signal operation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a power amplifier according to the present invention.

FIG. 2 is a circuit diagram showing a specific configuration of the power amplifier of the first embodiment shown in FIG.

FIG. 3 is a graph showing input / output characteristics and power added efficiency of the power amplifier according to the present invention.

FIG. 4 is a block diagram showing a schematic configuration of a mobile phone device using the power amplifier of the present invention.

FIG. 5 is a block diagram showing a second embodiment of the power amplifier according to the present invention.

FIG. 6 is a circuit diagram showing a specific configuration of the power amplifier according to the second embodiment shown in FIG. 5;

FIG. 7 is a block diagram showing a conventional power amplifier.

8 is a graph showing input / output characteristics and power added efficiency of the conventional power amplifier shown in FIG.

FIG. 9 is a block diagram showing another configuration of a conventional power amplifier.

10 is a graph showing input / output characteristics and power added efficiency of the conventional power amplifier shown in FIG.

FIG. 11 is a graph showing voltage-current characteristics of a field effect transistor (FET) included in a power amplifier.

[Explanation of symbols]

 Reference Signs List 1 power amplifier input terminal 2 power amplifier 2a first power amplifier 2b second power amplifier 3 power amplifier output terminal 4 drain voltage generator 5 drain voltage generation power supply 6 gate voltage generator 6a first gate voltage generator 6b Second gate voltage generator 7 Power supply for gate voltage generation 8 Control unit 9 Drain voltage input terminal 10 Gate voltage input terminal 10a First gate voltage input terminal 10b Second gate voltage input terminal 101 Antenna 102 Antenna common unit 103 Reception Circuit 104 Frequency synthesizer 105 Transmission circuit 106 A / D converter 107 Digital demodulation circuit 108 Error correction code composite circuit 109 Audio code composite circuit 110 D / A converter 111 Analog switch 112 Speaker 113 Microphone 114 Analog switch 115 A / D conversion Device 116 digital modulation circuit 117 D / A converter 118 analog audio circuit 200 control circuit 301 key switch 302 display 303 battery 304 power supply circuit

Claims (4)

[Claims] 1. A power amplifier which operates by selectively inputting an input signal modulated by a digital modulation method or an analog modulation method, comprising: a drain voltage generating means for generating a drain voltage to be applied to the power amplifier; A gate voltage generating means for generating a gate voltage to be applied to the amplifier; and a drain voltage generated from the drain voltage generating means and a gate voltage generated from the gate voltage generating means, individually corresponding to the level of the input signal. A power amplifier, comprising: control means for variably controlling. 2. The power amplifier according to claim 1, wherein a plurality of gate voltages are applied, and said control means variably controls said plurality of gate voltages. 3. The power amplifier according to claim 1, wherein the control unit individually variably controls the plurality of gate voltages. 4. A radio telephone apparatus using a power amplifier which operates by selectively inputting an input signal modulated by a digital modulation method or an analog modulation method, a receiving means for receiving a signal transmitted from a base station. Receiving level detection means for detecting a level of a received signal; drain voltage generation means for generating a drain voltage to be applied to the power amplifier; gate voltage generation means for generating a gate voltage to be applied to the power amplifier; Control means for variably controlling a drain voltage generated from said drain voltage generating means and a gate voltage generated from said gate voltage generating means in accordance with said reception level. Telephone equipment.