JPH0613816A - Bias circuit for transistor power amplifier - Google Patents

Abstract

PURPOSE:To provide a bias circuit for transistor power amplifier which reduces the ripple type impact given to a power line when the output is discontinued for maintenance, etc. CONSTITUTION:A transistor power amplifier 1 contains a transistor power amplifier 5 and a bias circuit 11. The circuit 11 contains a bias changeover switch 13 which selectively outputs the bias voltage that cuts off the amplifier 5 or the bias voltage that secures the normal operation of the amplifier 5 and a time constant circuit 15 which smoothly changes the output signal received from the switch 13 and supplies it to the amplifier 5. When the output of the amplifier 5 is going to be discontinued for maintenance, etc., the bias voltage is gradually changed by the circuit 15 even if the transmission/cut-off changeover is carried out by the switch 13. Thus the output of the amplifier 5 is also gradually changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bias circuit for a transistor power amplifier which applies a bias voltage to a power amplifier composed of transistors.

[0002]

2. Description of the Related Art This type of transistor power amplifier is used, for example, in a transmission output section of a radio transmitter / receiver, and recently, a FET power amplifier is provided.

FIG. 4 is a block diagram showing an example of a conventional transmission output unit. As shown in this figure, the transmission output unit 101 of the wireless transmission / reception device includes a signal input terminal 103, a transistor power amplifier 105 including an FET, a signal output terminal 107, a power input terminal 109, a bias circuit 111, and a power disconnect switch 113. Is equipped with.

The signal input to the signal input terminal 103 is
It is amplified to the transmission output level by the transistor power amplifier 105 and supplied to the signal output terminal 107. The transistor power amplifier 105 performs power amplification operation with the bias voltage from the bias circuit 111.

In such a transmission output unit 101, when the transmission output is stopped for maintenance work of the device or the like, the power supply of the transistor power amplifier 105 is turned off by a switch 113.
I was shut off directly.

[0006]

In such a conventional transmission output unit 101, when the power supply disconnection switch 113 is turned on or off, the current value flowing in the power supply line of the device is sharp and large. Due to the change, a large ripple is generated in the power supply line, which seriously affects the operation of other circuits in the device.

In order to reduce such an influence, it is necessary to strengthen the load fluctuation resistance of the power supply device or to use a strong smoothing circuit for each power supply input part of other circuits in the device. Therefore, whichever treatment is performed, the number of parts is increased, and there are drawbacks that expensive and large-sized parts must be used.

An object of the present invention is to provide a bias circuit for a transistor power amplifier which eliminates the above-mentioned drawbacks and alleviates a ripple-like impact on a power supply line when the output is stopped for maintenance or the like.

[0009]

In order to achieve the above object, a bias circuit for a transistor power amplifier according to the present invention cuts off the transistor power amplifier in a bias circuit that applies a bias voltage to the transistor power amplifier formed of transistors. The present invention is characterized by comprising a bias changeover switch capable of switching and outputting a bias voltage for normal operation or a bias voltage for normal operation, and a time constant circuit capable of smoothly changing an output signal of the switch and supplying the same to a transistor power amplifier. .

According to the present invention, when the output from the transistor power amplifier is to be stopped for maintenance or the like, the bias voltage is gradually changed by the time constant circuit at the change point even if the transmission or interruption is switched by the bias switch. Since the output of the transistor power amplifier is gradually changed by changing the output power to 1, the power supply line is not abruptly changed.

[0011]

EXAMPLES The present invention will be described in detail below with reference to examples.

FIG. 1 is a block diagram showing an embodiment of a bias circuit of a transistor power amplifier according to the present invention.

In FIG. 1, for example, a transmission output unit 1 of a radio transmitter / receiver includes a signal input terminal 3, a transistor power amplifier 5 composed of an FET, a signal output terminal 7, a power supply input terminal 9, and a bias circuit 11. It has and. Further, the bias circuit 11 changes the bias voltage applied to the transistor power amplifier 5 to a normal value or an output cutoff value, and a change in rising or falling of the bias voltage switched by the bias switching switch 13. And a time constant circuit 15 which supplies the power to the gate of the FET for power amplification of the transistor power amplifier 5 and the like.

The signal input to the signal input terminal 3 is introduced to the transistor power amplifier 5. The transistor power amplifier 5 amplifies the signal to a transmission output level and then supplies it to the signal output terminal 7. The transistor power amplifier 5 is adapted to perform power amplification operation with the bias voltage from the bias circuit 11 or to cut off the transmission output.

FIG. 2 is a circuit diagram showing a specific example of the bias circuit 11 used in the embodiment of the present invention.

In FIG. 2, a series body of a resistor Ra, a variable resistor VR, and a resistor Rb is connected between the power supply line V _DD and the ground. The bias voltage extracted from the variable terminal of the variable resistor VR is connected to one end of the bias changeover switch 13. The other end of the bias changeover switch 13 is connected to the ground. The output terminal of the bias changeover switch 13 is connected to the input terminal of the time constant circuit 15. The time constant circuit 15 is composed of an integrating circuit including a resistor Rc and a capacitor C. The input terminal is connected to one end of the capacitor C via the resistor Rc, and the output bias voltage is obtained from one end of the capacitor C and applied to the gate of the FET for power amplification of the transistor power amplifier 5.

The operation of such an embodiment will be described below.

3A and 3B are time charts for explaining the operation of the embodiment of the present invention. FIG. 3A shows a change in the gate voltage Vg, and FIG. 3B shows a change in the transmission output Po. They are shown respectively.

When the bias changeover switch 13 is off, as shown in FIG. 3, when the transistor power amplifier 5 is operating normally (before time t ₁ ), the resistor R
The bias voltage Vg of the transistor power amplifier 5 is set to the optimum value Vbs by a, the variable resistor VR, and the resistor Rb.
The transmission output Po is also the normal value Ps.

Here, as shown in FIG. 3, in order to stop the transmission from the transistor power amplifier 5, the bias changeover switch 13 is turned on (time t ₁ ). As a result, the bias voltage output from the bias changeover switch 13 immediately drops to the transmission output cutoff value (ground potential). However, the bias voltage Vg output from the time constant circuit 15 becomes a voltage that gradually decreases toward the transmission output disconnection voltage Vct from time t _{1 to} time t ₂ . Therefore, the transmission output Po of the transistor power amplifier 5 also gradually decreases from the normal value Ps. Then, until a time t ₂ ~t ₃ transmission output Po is the output cut-off state CT.

When the bias changeover switch 13 is turned off at time t ₃ , the bias voltage output from the bias changeover switch 13 immediately returns to the normal value.
However, when this bias voltage is input to the time constant circuit 15, the bias voltage Vg output from the time constant circuit 15 gradually increases from time t _{3 to} t ₄ and approaches the normal value Vbs. Become. Therefore, the transmission output Po of the transistor power amplifier 5 also gradually approaches the normal value Ps from the output cutoff state CT. Then, time t ₄
After that, the normal value Ps is transmitted and output.

As described above, in the above-described embodiment, even if the bias changeover switch 13 switches between transmission and interruption, the bias voltage V is changed by the time constant circuit 15 at the change point.
Since g is gradually changed, no sudden change is given to the power supply line. Therefore,
According to the present embodiment, it is possible to reduce the influence on the power supply line without increasing the number of parts, using expensive parts having large dimensions.

[0023]

As described above, according to the present invention, when a bias voltage for cutting off the output power of the transistor power amplifier or a bias voltage for outputting the power is applied, the change of the voltage is changed to a time constant circuit. By smoothing with, there is an effect that the transistor power amplifier can be smoothly turned on and off in the maintenance of the device and the like, and the influence on the power supply line can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a transistor power amplifier of the present invention.

FIG. 2 is a circuit diagram showing a configuration example of a bias circuit used in an embodiment of the present invention.

FIG. 3 is a time chart for explaining an example of the present invention.

FIG. 4 is a block diagram showing an example of a conventional transistor power amplifier.

[Explanation of symbols]

 1 Transmission Output Section 3 Signal Input Terminal 5 Transistor Power Amplifier 7 Signal Output Terminal 9 Power Supply Input Terminal 11 Bias Circuit 13 Bias Change Switch 15 Time Constant Circuit

Claims (1)

[Claims] 1. A bias circuit for applying a bias voltage to a transistor power amplifier composed of transistors, and a bias changeover switch capable of switching and outputting a bias voltage for shutting off the transistor power amplifier or a bias voltage for normal operation, and an output of the switch. A bias circuit for a transistor power amplifier, comprising: a time constant circuit capable of smoothly changing a signal and supplying the signal to the transistor power amplifier.