JPH02260809A - Automatic gain stabilizing circuit - Google Patents

Abstract

PURPOSE:To keep the gain of an modulator stably by comparing a gain of a 2nd fixed gain amplifier with a gain after a modulator and controlling a variable power attenuator so that the both are coincident. CONSTITUTION:An input signal is branched at first into two; one is amplified by a 2nd fixed gain amplifier 2 to be compared as a reference gain, its output is detected by a 2nd detector 6 to obtain a reference detection voltage. The other branched input signal is amplified by a 1st fixed gain amplifier 1 and attenuated by the attenuation depending on an AGS control voltage being an output of an AGS control circuit 8 by a variable power attenuator 3 and modulated by a modulator 4. The modulation output is detected by the 1st detector 5 and the detection voltage and the reference voltage are compared to obtain a difference voltage by a differential amplifier 7 and the error voltage of the gain controls the AGS control voltage of the variable power attenuator 3 at the AGS control circuit 8. Thus, the fluctuation of the gain in the modulator is absorbed to keep the gain stably.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit for stabilizing the gain in a phase modulator or a frequency modulator.

[Conventional technology]

For example, it is used when there are multiple input signals and the signal that has passed through the modulator and another signal are to be synthesized or compared under the same conditions in terms of amplitude, such as in the in-phase synthesis space diversity method. A phase modulator or frequency modulator requires the same gain from its input to the combiner or comparator.

Conventionally, in this type of phase modulator or frequency modulator, an amplitude limiter (limiter) or an automatic gain control (AGC) is used.
The amplifier circuit made it possible to obtain a constant level of modulated wave output. Furthermore, when the gain or conversion loss in the modulator must be kept constant, the modulation signal is controlled so that the deviation in the gain of the modulator itself with respect to the modulation signal is reduced.

[Problem to be solved by the invention]

The above-described conventional modulator with a constant output level is not suitable when constant gain is required. In addition, in a modulator that controls the modulation signal to reduce the gain deviation with respect to the modulation signal, a correction circuit is required to correct the gain deviation with the modulation signal, which makes this circuit complex and requires a continuous There is a problem in that it cannot handle modulated signals.

An object of the present invention is to provide an automatic gain stabilization circuit that solves these problems and makes it possible to stably maintain the gain of a modulator.

[Means to solve the problem]

The automatic gain stabilization circuit of the present invention includes first and second fixed gain amplifiers that branch and amplify input signals, a variable power attenuator that varies the output of the first fixed gain amplifier, and a variable power attenuator that varies the output of the first fixed gain amplifier. a modulator that modulates the output of the attenuator; a first detector that detects the output of the modulator; a second detector that detects the output of the second fixed gain amplifier; The present invention includes a differential amplifier that compares the outputs of two wave detectors, and an automatic gain stabilization (AGS) control circuit that controls the variable power attenuator based on the comparison output of the differential amplifier.

[Operation] In the configuration described above, the gain of the second fixed gain amplifier and the gain after passing through the modulator are compared and the variable power attenuator is controlled so that the two match, thereby adjusting the gain in the modulator. This allows the gain to be kept stable regardless of the characteristics of the modulator with respect to the modulated signal.

〔Example] Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a bronc diagram of one embodiment of the present invention.

In the same figure, 1.2 is the 1st. 3 is a variable power attenuator, 4 is a modulator whose gain is varied with respect to a modulation signal or a control signal, 5 and 6 are respectively second fixed gain amplifiers; In each of the second detectors, 7 is a differential amplifier, and 8 is an AGS control circuit.

The input signal (modulated signal) is first branched into two, one is amplified with a constant gain by a second fixed gain amplifier 2 for comparison as a reference gain, and its output is amplified by a second detector 6. The reference detection voltage is obtained by detection.

The other branched input signal is amplified by the first fixed gain amplifier 1, and the AGS control circuit 8 is amplified by the variable power attenuator 3.
After being attenuated by an amount determined by the AGS control voltage output from the AGS control voltage, the signal is modulated by the modulator 4. This modulated output is detected by a first detector 5, this detected voltage is compared with the reference detected voltage, and a differential voltage is obtained by a differential amplifier 7.
The AGS IJ control circuit 8 controls the AGS control voltage of the variable power attenuator using this gain error voltage.

Therefore, as a result of controlling the loop so that the error voltage becomes 0, the gain seen in the input/output signal is stabilized, and the gain is always equal to the gain of the second fixed gain amplifier 2 as the reference gain.

[Effects of the Invention] As explained above, the present invention compares the gain of the second fixed gain amplifier and the gain after passing through the modulator, and controls the variable power attenuator so that the two match. This has the effect of absorbing gain fluctuations in the modulator and stably maintaining the gain.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... First fixed gain amplifier, 2... Second fixed gain amplifier, 3... Variable power attenuator, 4... Modulator,
5...First detector, 6...Second detector, 7...
-Differential amplifier, 8...AGS control circuit.

Claims (1)

[Claims] 1. First and second fixed gain amplifiers that branch and amplify input signals, a variable power attenuator that varies the output of the first fixed gain amplifier, and modulation that modulates the output of the variable power attenuator. a first detector for detecting the output of the modulator, and a second detector for detecting the output of the second fixed gain amplifier.
a differential amplifier that compares the outputs of the first and second detectors, and an automatic gain stabilization control circuit that controls the variable power attenuator using the comparison output of the differential amplifier. Features an automatic gain stabilization circuit.