JPH05267945A - Amplifier provided with overload control circuit - Google Patents

Abstract

PURPOSE:To provide the amplifier with an overload control circuit for detecting an excessive signal input from a supply current to an FET. CONSTITUTION:A variable attenuator 1 for receiving an input signal from an input terminal 11 increases the attenuation quantity by an input of a control signal S3 from a comparator 3, and avoids an excessive signal input of an amplifier 2 having an FET. The amplifier 2 for outputting an amplifying signal to an output terminal 12 receives a positive drain voltage from a terminal 15 by a terminal 14, and receives a negative gate voltage from a terminal 16 by a terminal 13. In an overload state of the amplifier 2, in which a voltage S1 of the terminal 14 is lower than a reference voltage from a reference voltage input terminal 17, a comparator 3 outputs a control signal S3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an excessive signal input (overload).
The present invention relates to an amplifier with an overload control circuit capable of preventing the above.

[0002]

2. Description of the Related Art A conventional amplifier with an overload control circuit of this type is an amplifier having an FET (field effect transistor) as an amplifying element and is connected to the preceding stage of this amplifier to increase the attenuation amount by inputting a control signal. The variable attenuator for detecting the input signal level of the amplifier connected to the preceding stage of the amplifier, and comparing the detector output with a preset overload level, the detector output And a variable attenuator control means for generating the control signal when the load level is higher than the overload level. When an excessive input to the amplifier is detected, the attenuation amount of the variable attenuator is increased to eliminate the overload state of the amplifier.

[0003]

The above-mentioned conventional amplifier with an overload control circuit requires a detector for detecting the overload state of the amplifier in the signal transmission line, and thus it is difficult to reduce the size and weight. There was a drawback. This drawback is particularly serious in the satellite-mounted amplifier which requires extremely small size and light weight.

[0004]

An amplifier with an overload control circuit according to the present invention comprises an amplifier having an FET as an amplifying element, and a variable attenuator connected to the preceding stage of the amplifier for increasing an attenuation amount by inputting a control signal. A drain current detecting means for detecting a drain current of the FET, and a first control signal generating means for generating the control signal when the detected drain current is equal to or more than a predetermined first reference value. There is.

Further, instead of detecting the drain current of the FET, the gate current detecting means for detecting the gate current of the FET and the detected gate current instead of the first control signal generating means are predetermined. A second control signal generating means for generating the control signal when the second reference value or more is obtained may be provided.

[0006]

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

FIG. 1 is a circuit diagram of a first embodiment of the present invention. A signal input from the input terminal 11 of the amplifier with the overload control circuit passes through the variable attenuator 1 and is input to the amplifier 2 having the FET as an amplification element. The output signal from the amplifier 2 is output to the output terminal 12. FE in amplifier 2
The drain (D) of T has a positive voltage (+
The drain voltage S1 which is the voltage V) supplied via the resistor R4 is supplied from the drain power supply terminal 14. Further, the gate (G) of the FET is divided from the negative voltage (-V) of the negative power supply terminal 16 by the resistors R2 and R3, and further, the gate voltage which is the voltage passing through the resistor R1 is supplied from the gate power supply terminal 13. Supplied. The voltage S1 at the terminal 14 is applied to one input terminal of the comparator 3, and the reference voltage input terminal 1 is applied to the other input terminal of the comparator 3.
A first reference voltage S2 from 7 is applied.

Here, when the voltage S1 at the terminal 14 is lower than the first reference voltage S2 which is the reference for judging the overload of the amplifier 2, the amplifier 2 is judged to be overloaded. That is, as the input power to the amplifier 2 increases, the drain current supplied to the terminal 14 increases, and therefore the voltage of the terminal 14 decreases due to the voltage drop due to the resistance value R4. The above determination can be made by measuring in advance and setting the first reference voltage S2 to the voltage S01.

In the comparator 3, the voltage S1 is the first voltage
When the voltage is lower than the reference voltage S2, the control signal S3 is generated to increase the attenuation amount of the variable attenuator 1. Therefore, the input level of the amplifier 2 is lowered, and the overloaded state of the amplifier 2 can be avoided.

FIG. 2 is a circuit diagram of the second embodiment of the present invention. This amplifier with an overload control circuit is almost the same as the circuit of the embodiment shown in FIG. 1, except that the voltage S4 from the connection point (point P) of the resistors R1 and R2 is applied to one input terminal of the comparator 3.
Then, the second reference voltage S5 is applied from the reference voltage input terminal 17 to the other input terminal of the comparator 3.

In the embodiment shown in FIG. 2, the amplifier 2 is judged to be overloaded when the voltage S4 at the point P is lower than the second reference voltage S5, which is the reference for judging the overload of the amplifier 2. That is, as the input power to the amplifier 2 increases, the terminal 1
3, the gate current supplied to 3 increases, and thus the resistance value R1
Although the voltage of the terminal 13 drops due to the voltage drop due to, the voltage S02 of the terminal 13 in the overloaded state is measured in advance,
The determination can be made by setting the first reference voltage S5 to the voltage S02.

In the comparator 3, the voltage S4 is the second voltage.
When the voltage is lower than the reference voltage S5, the control signal S3 is generated to increase the attenuation amount of the variable attenuator 1. Therefore, the input level of the amplifier 2 is lowered, and the overloaded state of the amplifier 2 can be avoided.

[0013]

As described above, according to the present invention, the supply current to the FET of the amplifier is detected to detect the overload state of the amplifier. Therefore, the detection for detecting the overload state of the amplifier in the signal transmission line is performed. There is an effect that it is possible to easily reduce the size and weight without using a vessel. This is particularly effective for an on-board amplifier that requires extremely small size and light weight.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment according to the present invention.

FIG. 2 is a circuit diagram of a second embodiment according to the present invention.

[Explanation of symbols]

 1 Variable Attenuator 2 Amplifier 3 Comparator 11 Input Terminal 12 Output Terminal 13 Gate Power Supply Terminal 14 Drain Power Supply Terminal 15 Positive Power Supply Terminal 16 Negative Power Supply Terminal 17 Reference Voltage Input Terminal

Claims (2)

[Claims] 1. An amplifier using an FET as an amplifying element, a variable attenuator connected to the preceding stage of the amplifier to increase an attenuation amount by inputting a control signal, and a drain current detecting means for detecting a drain current of the FET. An amplifier with an overload control circuit, comprising: a control signal generating means for generating the control signal when the detected drain current is equal to or higher than a predetermined reference value. 2. An amplifier using an FET as an amplifying element, a variable attenuator connected to a preceding stage of the amplifier for increasing an attenuation amount by inputting a control signal, and a gate current detecting means for detecting a gate current of the FET. An amplifier with an overload control circuit, comprising: a control signal generating means for generating the control signal when the detected drain current is equal to or higher than a predetermined reference value.