JPS6272211A - Transistor amplifier - Google Patents

Abstract

PURPOSE:To suppress generation of a gate current of a GaAs FET amplifier by providing a circuit detecting a gate current of an output stage transistor (TR) of an amplifier and a variable attenuator preventing excess input to the output stage TR, detecting the gate current so as to use the detection output thereby suppressing the gain. CONSTITUTION:A1, A2-An are n-set of amplifier stages and each has a GaAs FET 1. As a gate current detection circuit IGDET, a differential amplifier CA, for example, is used, a voltage at an output terminal B is fed to one input of the amplifier CA, a reference voltage is fed to the other input, and when the former exceeds the latter, the output is a gate current detection output of the outer stage TR An. A PIN diode is used for a variable attenuator ATT. The resistance of a PIN diode is changed depending on the current flowed thereto. Thus, when the gate current flows, the attenuation of the variable attenuator ATT is increased to lower the signal level, the input to the output stage TR An is decreased thereby bringing the gate curret into zero or minimizing it.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an amplifier constructed by connecting gallium arsenide field effect transistors in multiple stages, and to input protection of an output stage transistor.

[Conventional technology]

Field-effect transistors (FETs) using gallium arsenide (GaAs) as a semiconductor can operate at high speed, so a microwave band amplifier is constructed by connecting them in multiple stages. Unlike silicon, it is not easy to form a gate insulating film on GaAs, so CaAs FETs are usually of a diode gate type rather than an insulated gate type.

[Problem that the invention seeks to solve]

However, in the diode gate type, when the input becomes excessive (the input turns on a Schottky diode composed of a gate electrode and a GaAs substrate), a gate current flows. When gate current (rectified current) flows, GaAs
This is not preferable because it affects the reliability of the FET and shortens its life. However, since a large output can be obtained by increasing the input, QaAsFETs tend to operate not only in the linear range of small inputs but also in the large input saturation region. Therefore, in the present invention, the gate current of the output stage transistor through which the largest amount of gate current flows is detected, and the gain is suppressed using the detected output to provide over-input protection.

Means for Solving Problems] The present invention provides a high-output amplifier configured by connecting gallium arsenide field effect transistors in multiple stages. The variable attenuator is inserted into the amplifier and controls the amount of attenuation based on the output current of the gate current detection circuit to prevent excessive input to the output stage transistor.

[Effect]

By detecting the gate current of the output stage transistor and operating the variable attenuator to lower the signal level if there is a detected output, it is possible to suppress excessive input, extend the life of the GaAsFET amplifier, and improve reliability. can.

〔Example〕

To explain using FIG. 1, AI, A2. . . . An is n amplification stages, each including one GaAs FET. The number of stages to be configured is determined by the required gain. I.G.
DET is a circuit that detects the gate current of the output stage transistor An of this n-stage GaAs FET amplifier;
ATT is a variable attenuator inserted between the first stage transistor A1 and the second stage transistor A2, and CA is a control amplification stage, which amplifies the output of the gate current detection circuit IGDET and supplies it to the variable attenuator ATT. Change the signal attenuation of the device.

The gate current detection circuit IGDET is as shown in FIG.
It can be configured with a circuit that detects a voltage change at the output end B of a resistive voltage divider circuit RVD that supplies a gate bias voltage to the output stage transistor An. R+, R: are the resistances of the resistance voltage divider circuit, and L and C are the inductance and capacitor of the low-pass and high-cut filters. The voltage dividing circuit RDV passes through the low-pass filter to the gate G of the output stage transistor An, and applies a negative bias voltage (-〇, several V to
= 1, several V), but if the high frequency signal input becomes excessive and a gate current flows, the output terminal B of the voltage divider circuit RVD
voltage decreases (for example, what was -0, 8■ becomes -1,
2V etc.) Therefore, for example, a differential amplifier is used as the gate current detection circuit, and the voltage of the output terminal B is applied to one input terminal of the amplifier, and the reference voltage is applied to the other input terminal, so that when the former exceeds the latter, an output is generated. Then, the output becomes the gate current detection output of the output stage transistor An.

A PIN diode or dual gate transistor is used for the variable attenuator ATT. The resistance of the PIN diode changes depending on the current flowing, so the gate current detection circuit IGO
When the output of ET is amplified and added by amplifier CA, when the gate current flows, the amount of attenuation of variable attenuator ATT is increased to lower the signal level, and the input of output stage transistor An is lowered to reduce the gate current to 0 or a small amount. Can be made small.

A method of lowering the signal level by lowering the drain voltage of the transistor in the input stage according to the output of the gate current detection circuit IGOET can also be used as a variable attenuator.

Figure 3 is a diagram showing a specific example of a GaAs amplifier, with Ai, A
j is the first. The j-th amplification stage, RVD, and LC are a resistance voltage divider circuit and a low-pass filter for supplying bias voltage to each stage. Cc is the coupling capacitor of each stage, MO is the output side matching circuit, Mi is the input side matching circuit, Vd is the power supply, GRD
is ground.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to suppress the generation of gate current in a GaAsFET amplifier, which is effective in increasing the reliability and extending the life of the amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram of the main part thereof, and FIG. 3 is a circuit diagram showing details of a part of a GaAs FET amplifier. In the drawing, A1 to An are each amplification stage made of GaAs FET, An is an output stage transistor, IGDET is a gate current detection circuit, ATT is a variable attenuator, RVD is a resistive voltage divider circuit, and L and C are the inductance and capacitor of a low-pass filter. It is.

Claims (2)

[Claims] (1) In a high-output amplifier configured by connecting gallium arsenide field effect transistors in multiple stages, a circuit for detecting the gate current of the output stage transistor of the amplifier, and an output of the gate current detection circuit inserted into the amplifier. A transistor amplifier comprising: a variable attenuator that prevents excessive input to an output stage transistor by controlling an amount of attenuation using a current. (2) The gate current detection circuit is comprised of an output voltage detection circuit of a resistor voltage divider circuit that supplies a bias voltage to the gate of the output stage transistor via a low-pass filter. The transistor amplifier described.