JPH0927719A - Amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the size and cost of the amplifier circuit by constituting a variable gain amplifier circuit as the main part of a high-frequency amplifier circuit with AGC on one GaAs substrate. SOLUTION: An equivalent variable resistance circuit in which a pin diode is conventionally used is composed of an FET 1 of the same kind with an FET 2 which is used for amplification. Consequently, the whole variable gain amplifier circuit can be constituted on one GaAs substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit, and particularly to A
The present invention relates to a high frequency amplifier circuit with a GC.

[0002]

2. Description of the Related Art In recent years, with the development of CATV and satellite communications, the receiver market for them has been expanding rapidly.

In these receivers, it is unavoidable that the input signal level greatly changes depending on the usage situation. On the other hand, for the frequency selection circuit, the demodulation circuit, and the frequency conversion circuit, distortion is generated and the SN ratio is deteriorated even if the input signal level is excessive or excessive, which is not preferable. Therefore, a high frequency amplifier circuit with an AGC (automatic gain adjustment circuit) which has a small distortion, a good SN ratio and a wide output level constant range is desired.

An example of a conventional high frequency amplifier circuit with an AGC is disclosed in Japanese Patent Laid-Open No. 62-73807. FIG. 4 shows the circuit diagram thereof. In FIG. 4, the input high frequency signal (IN) is supplied to the gate of the FET3 which is an amplifying transistor through the coupling capacitor C4. A bias voltage E4 is applied to the gate of the FET3 via an isolation resistor R.
A power supply voltage E is applied to the drain of the FET3 through a load resistor R.
6 will be supplied. The high frequency signal amplified by the FET3 is output (OUT) through the coupling capacitor C7.

Partial coupling capacitors C5 and C6 of the high frequency signal amplified by FET3 and pin diode D1
Is fed back to the input gate of FET3). In this case, the pin diode D1 operates equivalently as a variable resistance element, and by controlling the resistance value, the feedback amount can be controlled to control the gain of the amplifier circuit centered on the FET3.

A control voltage (bias voltage) is applied to the pin diode D1 through the isolation coils L1 and L2, and the equivalent resistance value of the pin diode D is controlled by the control voltage E5. It is used as the control voltage E5.

[0007]

In FIG. 4, the FET is
3 and the pin diode D1 have different diffusion steps, so F
It is difficult to fabricate ET and pin diode on a single GaAs substrate. Not impossible, but too costly to make sense. Therefore, the internal circuit 10 centered on the FET 3 and the external control unit 20 including the pin diode D3 are packaged separately.

However, the use of another package is extremely disadvantageous in terms of cost and miniaturization.

It is an object of the present invention to provide an amplifier circuit which can combine these amplifier section and control section in one package.

[0010]

According to the present invention, an amplifier including an amplifying transistor and a feedback circuit provided between an input and an output of the amplifying transistor and having a feedback resistance variable according to an external control signal. An amplifier circuit is obtained in which the feedback resistor is composed of a transistor of the same type as the amplifying transistor.

[0011]

[Function] By using the FET instead of the pin diode in the variable resistance circuit inserted in the feedback circuit, the amplification FET and the variable resistance element of the control unit (FET in this case) are formed on one GaAs substrate. It was realized to be summarized in.

[0012]

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

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIGS. 2 and 3 are graphs showing simulation results of frequency characteristics during gain control.

In FIG. 1, the input high frequency signal (IN) is applied to the gate of the amplifying FET 2 via the coupling capacitor C1. A bias voltage E1 is applied to the gate of the FET2 through an isolation resistor R1. FE
The power supply voltage E3 is applied to the drain of T2 through the negative resistance R2. The amplified high frequency signal is output (OUT) from the drain of FET2 through the coupling capacitor C3.
Is done.

On the other hand, a part of the amplified high frequency signal is fed back to the input side (gate) of FET2 via the coupling capacitor C2 and FET1. A control voltage E2 is applied to the gate of the FET1. The FT1 equivalently operates as a variable resistance element and controls the feedback amount. Therefore, by controlling the control voltage E2 as an AGC signal, a variable gain high frequency increasing circuit with an AGC function is constructed including the FET2.

The portion surrounded by the dotted line in FIG. 1 is all integrated on one GaAs substrate.

FIG. 2 shows the computer simulation result of the frequency characteristic of the variable gain amplifier circuit when the feedback amount is maximum (when the gain is minimum). Similarly, the characteristics when the feedback amount is minimum (when the gain is maximum) are shown in FIG.
Shown in

In the above embodiment, the FE is used as the amplifying element.
Although T is used, other unipolar type transistors and bipolar type transistors can be used,
Accordingly, the transistors, which are variable resistance elements, are of the same type, and the substrate for the integrated circuit is appropriately selected.

[0019]

According to the present invention, the amplifying circuit and the equivalent variable resistance circuit for controlling the feedback amount can be constituted by the same type of transistors, and the variable gain amplifying circuit including the peripheral circuits can be constructed on one substrate. The effect is that you can do it.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a simulation graph of frequency characteristics when the feedback amount is maximum according to the embodiment of this invention.

FIG. 3 is a simulation graph of frequency characteristics when the feedback amount is minimum according to the embodiment of this invention.

FIG. 4 is a circuit diagram showing an example of a conventional variable gain high frequency amplifier circuit.

[Explanation of symbols]

 1,2 FET

Claims (3)

[Claims] 1. An amplifier circuit including an amplifying transistor and a feedback circuit provided between the input and output of the amplifying transistor and having a variable equivalent feedback resistance variable by an external control signal. Is constituted by a transistor of the same kind as the amplifying transistor. 2. The amplifier circuit according to claim 1, wherein at least the transistor of the equivalent feedback resistor and the amplifying transistor are formed on one GaAs substrate. 3. The amplifier circuit according to claim 1, wherein the amplifier circuit is an amplifier circuit with an AGC function, and the external control signal is an AGC signal.