JPH027708A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To control the gain instantly with respect to a change in input and output signal levels by controlling the gain of an amplifier depending on a detection output of an input signal level detector and a detection output of an output signal level detector. CONSTITUTION:Part of the signal entering an input terminal 1 is extracted by a directional coupler 3a and detected by a detector 4a. Moreover, part of the signal amplified by a Dual-Gate FET AMP 2 is extracted by a directional coupler 3b and detected by a detector 4b. Two signals being detected outputs detected by the detectors 4a, 4b are amplified into a signal of a required level by a differential amplifier 7, the result is fed to the 2nd gate of the AMP 2 thereby controlling the operating state of the AMP 2 and the gain. Thus, the gain is controlled instantly against the input level fluctuation and the gain is accurately controlled against the output level fluctuation.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an automatic gain control circuit for an amplifier that automatically controls the gain.

[Conventional technology]

Figure 3 shows, for example, "Microwave Journal J (M
This is a connection diagram showing a conventional automatic gain control circuit published in P2O5, September 1987. In the diagram, 1 is an input terminal, and 2 is a dual gate (2) that amplifies the signal input from input terminal 1. Dual-Gate) FET AMP (
Dual-GateF ETAMP), 3 is a directional coupler that extracts a part of the output level, 4 is a detector that detects the signal extracted from this directional coupler 3, and 5 is amplified the detection output of the detector 4. 6 is an output terminal. Next, the operation will be explained. The signal input to the input terminal 1 is amplified by the Dual-Gate FET AMP 2. A part of this amplified signal is taken out by a directional coupler 3, and this signal is detected by a detector 4. This detected signal is amplified to a signal of a required size by the video amplifier 5, and the Dual-Gate F ETAM
Added to the second gate of P2, Dual-GateF
Controls the operating state of E T A P 2 and controls the gain. Even if the level of the signal input to input terminal 1 changes, D
By changing the operating state of the ual-GateFETAMP 2 and controlling the gain, the signal level output to the output terminal 6 is always kept constant.

[Problem to be solved by the invention] Since the conventional automatic gain control circuit is configured as described above, it takes a long time from when the input level fluctuates to when the output level is notified and the gain is controlled. There are also problems in that it is difficult to precisely control the gain in response to fluctuations in the output level. This invention was made in order to solve the above-mentioned problems, and it is an automatic system that can instantly control the gain in response to input level fluctuations, as well as accurately control the gain in response to output level fluctuations. The purpose is to obtain a gain control circuit.

[Means to solve the problem]

The automatic gain control circuit according to the present invention uses two detection outputs of a detector for detecting an input signal level and a detector for detecting an output signal level as inputs of a differential amplifier, and uses the output of the differential amplifier as a control signal. That is.

[Effect]

A detector for detecting an input signal level in the present invention,
A differential amplifier that uses the two output signals of a detector that detects the output signal level as input signals immediately controls the gain in response to input level fluctuations, and also controls the gain in response to output level fluctuations.
Gain can be precisely controlled.

【Example】

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 1 is an input terminal, and 2 is a Dual-Gat amplifier that amplifies the signal input from this input terminal l.
eFET AMP, 3a is a directional coupler that takes out a part of the input level, 3b is a Dual-GateFET
A directional coupler that takes out a part of the output level of T AMP 2, 4a a detector that detects the signal taken out from the directional coupler 3a, and 4b a detector that detects the signal taken out from the directional coupler 3b. 6 is an output terminal, 7 is a Dual-Gate with two signals, the detection output of the input signal of the detector 4a and the detection output of the output signal of the detector 4b, as input signals.
This is a differential amplifier that performs differential amplification to control FET AMP2. Next, the operation will be explained. The signal input to the input terminal 1 is amplified by the Dual-Gate FET AMP 2. A part of the signal that has entered this input terminal 1 is taken out by a directional coupler 3a, and this signal is detected by a detector 4a. Also, Dual-Gate FET AM
A part of the signal amplified by P2 is taken out by a directional coupler 3b, and this signal is detected by a detector 4b. Two signals, the detection output detected by the detector 4a and the detection output detected by the detector 4b, are input to the differential amplifier 7,
Next, the differential amplifier 7 amplifies the signal to a required magnitude, and the signal is output to the Dual-Gate FET AM P2.
is added to the second gate of As a result, the mouthual-GateFET AM P
2 to control the operating state and control the gain. That is, when the signal level input to the input terminal 1 changes, the detection output of the detector 4a changes, the change is added to the differential amplifier 7, and the differential amplifier 7 outputs the required control signal. Created, Dual-Gate FET AM
Dual-Gate added to the second gate of P2
Changing the operating state of FET A M P 2,
By controlling the gain, the signal level output to the output terminal 6 is kept constant. Also, due to temperature fluctuations, Dual-Gate F E
When the gain of TAMP2 changes, the detection output of the detector 4b changes, and the amount of the change is added to the differential amplifier 7. Therefore, a required control signal is generated in the differential amplifier 7, and the Dual-Gate FETAM P2
Dual-Gate FET A
By changing the operating state of MP2 and controlling the gain, the signal level output to the output terminal 6 is kept constant. In addition, in the above embodiment, Dual-Gate FET
A MB2 showed how to control the gain, but the second
As shown in the figure, even if there are amplifiers 8a and 8b on the input and output sides, and a barrier pull attenuator 9 is located between the amplifiers 8a and 8b, the overall gain can be improved by controlling the amount of attenuation of the barrier pull attenuator 9. Since we control
The same effects as in the above embodiment are achieved. Further, in the above embodiment, Dual-Gate F E
Although the case where there is one TAMP2 is shown, a Dual-Gate F instead of the barrier pull attenuator 9 in FIG.
Even when a plurality of amplifiers are used, such as when E TAMP2 is used, the same effects as in the above embodiment can be obtained.

【Effect of the invention】

As described above, according to the present invention, the differential amplifier uses two signals, the detection output of the detector that detects the input signal level and the detection output of the detector that detects the output signal level.
By generating a control signal to control the gain of the amplifier, the gain can be accurately and instantly controlled in response to changes in signal levels on the input and output sides.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an automatic gain control circuit according to one embodiment of the present invention, Fig. 2 is a circuit diagram showing another embodiment of the invention, and Fig. 3 is a circuit diagram showing a conventional automatic gain control circuit. It is. 2 is Dual-GateFET AMP (amplifier)
, 4a and 4b are detectors, 7 is a differential amplifier, and 8a and 8b are amplifiers. In addition, in the figures, the same reference numerals refer to the same or equivalent parts.
DuJ-Gite FET AMP ("4'jS!'
)7 Mino? +4=! Figure 3 shows this. 8a, 8b 7) Bu (+'shitsushagi)

Claims (1)

[Claims] In an automatic gain control circuit for an amplifier that automatically controls the gain, a detector detects the input signal level, a detector detects the output signal level, and the detection outputs of the two detectors are used as input to generate a control signal. An automatic gain control circuit characterized by comprising a differential amplifier.