JPH07162241A - Automatic control circuit for microwave band output level - Google Patents

Abstract

PURPOSE:To hold the output level of a microwave band power amplifier constant irrelevantly to temperature with simple constitution by detecting a drain current and holding its current value constant. CONSTITUTION:A microwave signal is inputted to the gate of an FET 1 for microwave band power amplification from an input terminal through an isolator 9. The output signal of the FET 1 is outputted through an isolator 10. Choke coils 11 and 12 stop high frequencies when supplying the gate voltage to the FET 1. A drain voltage is inputted to the drain of the FET 1 from a power supply circuit 13 through a resistance 2 for drain current detection and the choke coil 12. Further, a gate voltage is supplied from a gate voltage control circuit 3 through the coil 11. The gate voltage control circuit 3 controls the gate voltage so that the potential difference across a resistance 2 becomes invariably constant, and consequently the gain of an FET amplifier is held constant and further the output level is automatically controlled to a constant level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave band output level automatic control circuit.

[0002]

2. Description of the Related Art In a conventional microwave band output level automatic control circuit, as shown in FIG. 2, in a microwave band amplifier 4 using an FET, a FET amplifier 5 and a variable attenuation provided in an intermediate stage or a preceding stage thereof. Vessel 6, temperature sensitive element 7,
And an operational amplifier 8 (for example, Japanese Patent Laid-Open No.
-99503 publication). In the figure, the output level deviation due to the temperature-dependent power gain deviation is detected by the temperature sensing element 7, and the detection result is fed back to the variable attenuator 6 via the operational amplifier 8 to keep the attenuation amount constant. Came.

[0003]

This conventional microwave band output level automatic control circuit has a problem in that the circuit is complicated because the variable attenuator is provided in the preceding stage or in the middle and the amplifier structure becomes large in scale. there were.

[0004]

According to the present invention, there is provided a gate voltage control for controlling a gate voltage of a FET by detecting a potential difference between both ends of a microwave band power amplification FET, a drain current detection resistor, and a drain current detection resistor. And a circuit.

[0005]

The present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of the present invention, in which a microwave signal is input from an input end to a gate of a microwave band power amplification FET 1 via an isolator 9. FET
The output signal of 1 is output via the isolator 10. FETs 11 and 12 are gate voltage and drain voltage
1 is a choke coil for blocking high frequency when supplying to 1.
The drain voltage is FET from the power supply circuit 13 through the drain current detection resistor 2 and the high frequency blocking choke coil 12.
1 is supplied to the drain. The gate voltage is supplied from the gate voltage control circuit 3 through the high frequency blocking choke coil 11.

In general, the FET amplifier has a large temperature dependency, and when the temperature rises, the drain current also decreases and the gain decreases, so that the output level also decreases.

Therefore, when the drain current decreases due to temperature or the like, the potential difference across the resistor 2 also decreases. In the present invention, the gate voltage control circuit 3 controls the gate voltage so that the potential difference between both ends of the resistor 2 is always constant, so that the gain is kept constant and the output level is automatically controlled to be constant. It will be possible.

[0008]

As described above, according to the present invention, by detecting the drain current and keeping the current value constant, the output level of the microwave power amplifier is kept constant regardless of temperature with a simple structure. Have an effect.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a microwave band FET amplifier according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional microwave band output level automatic control circuit.

[Explanation of symbols]

 1 FET for microwave power amplifier 2 Resistor for detecting drain current 3 Gate voltage control circuit 4 Microwave amplifier using FET 5 FET amplifier 6 Variable attenuator 7 Temperature sensing element 8 Operational amplifier 9,10 Isolator 11,12 High frequency blocking Choke coil for power supply 13

Claims (2)

[Claims] 1. A FET for microwave power amplifier, and F
And a gate voltage control circuit for detecting a potential difference between both ends of the drain current detection resistor of ET, comparing the difference with a reference voltage, and controlling the gate voltage of the FET based on the comparison result. Characteristic microwave band output level automatic control circuit. 2. The microwave band output level automatic control circuit according to claim 1, wherein the gate voltage control circuit is provided with a varying means for varying a reference voltage.