JPS63160404A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To prevent malfunction of a gain control circuit in response to an offset control circuit by adding a band limit circuit to the gain control circuit. CONSTITUTION:An input signal is inputted to a variable gain amplifier 1 and outputted from an output signal terminal 8. The variable gain amplifier 1 is added with the offset control circuit 2 to compensate the deviation of the operating point due to the input offset fluctuation and the DC fluctuation caused equivalently at the output signal terminal 8 is fed back to the input side to apply offset control. A clamp circuit 3 clamps high or low level of the output signal and since the offset fluctuation by the operation of the offset control circuit 2 is added to the signal, then the fluctuation component is eliminated by a band limit circuit 4. Then the signal peak value by a peak value detection circuit 5 is detected, it is compared with a reference signal amplitude by the gain control circuit 6, the difference signal is amplified and integrated and inputted to the variable gain amplifier 1 as the gain control signal. Thus, the gain control circuit does not receive the effect due to offset fluctuation and no malfunction takes place.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an automatic gain side # that controls the output amplitude of an electrical signal to be constant. The present invention relates to an automatic gain control circuit having characteristics suitable for variations in input signal mark rate.

[Conventional technology]

The present invention provides a gain of 47! when a variable gain amplifier used in an automatic gain control circuit has an offset control function. llJ#
This relates to the configuration of the circuit. A conventional gain control circuit is disclosed in Japanese Patent Laid-Open No. 138208/1983. In the case of this prior art, gain control is performed by determining the received power, but the gain control circuit does not take into account the band of the signal when it is superior to the control signal.

[Problem that the invention seeks to solve]

A gain control circuit originally attempts to control the signal output to a constant value regardless of the magnitude of the input signal, but if this control signal is superior to the % variable gain amplifier and an offset control circuit is added. It is necessary to consider this response when the mark rate of the input signal (indicates the ratio of '1' to the whole for a signal string consisting of 'o1.J#) changes.

The gain control circuit changes to d14 due to the response of the offset control circuit.
There was a problem with MIJ production.

An object of the present invention is to provide an automatic gain control circuit that is stable in the operation of an offset control circuit.

[Means for solving problems]

The above purpose is to add a band-limiting circuit to the gain control circuit, so that the gain control circuit does not respond to offset fluctuations of the variable gain amplifier due to the operation of the offset control circuit caused by fluctuations in the mark rate of the input signal. If you do this, K will be more achieved.

[Effect]

The automatic gain control circuit according to the invention operates as follows.

The input signal is input to a variable gain enhancer.

Variable gain amplifiers are used to compensate for operating point shifts due to input offset fluctuations when the amplification degree is large.

An offset control circuit is added. This offset control circuit performs control using differential output signals of the variable gain amplifier. That is, the average value of both of the differential outputs of the variable gain amplifier is used as a reference value, and the difference from the average value of one of the variable gain amplifiers is taken as an error signal. After amplifying and integrating this error signal, feedback is applied to the input signal terminal, and 1rlJ control is performed so that the error signal becomes zero. The offset control circuit in this format depends on the mark rate of the input signal.
The optimal operating point will vary. This offset fluctuation frequency is determined by the integration time constant of the error signal. Various configurations other than those described here are conceivable for controlling offset fluctuations, but the present invention can be applied to other configurations as long as the offset fluctuations are basically controlled in the low frequency range including direct current. can be applied.

A part of the variable gain amplifier output is clamped at high level or low level by a clamp circuit in order to maintain the output amplitude at a constant value. At this time, band limitation is applied so as not to follow offset fluctuations of the variable gain amplifier. Offset control is basically DC control, but the band limiting circuit not only cuts off DC but also cuts off low frequencies up to a band corresponding to the integral time constant of the offset control circuit. This method takes advantage of the fact that the input signal component has no variable frequency component due to the offset system.In other words, it is a feature and condition of the present invention that frequency can be completely separated.

The peak value of this signal is detected, compared with the reference signal amplitude, and the difference signal is amplified and divided by S, and then input as a gain control signal to the gain control terminal of the variable gain amplifier.

With this circuit configuration, this circuit operates as an automatic gain control circuit. In the 2-amp circuit, it is important to limit the bandwidth.
Therefore, the gain control circuit is not affected by offset fluctuations and does not malfunction.

〔Example〕

Hereinafter, one embodiment of the present invention will be explained with reference to Figure 'm1. An input signal is inputted to a variable gain amplifier 1 whose gain can be varied through an input signal terminal 7 and outputted from an output signal terminal 8.

The oT variable gain amplifier 1 is used to compensate for shifts in the operating point due to input offset fluctuations.

offsera)? ff1j# circuit 2 is added, and the DC fluctuation generated isometrically at the output 1B terminal 8 is input to the input 1gI.
Returns to JK and performs offset control.

2 amplifier circuit 3. Firefly area limiting circuit 4/peak value detection circuit 5
．． gain? The ffIIa1 circuit 6 receives the signal m at the output signal terminal 8.
It performs an operation to control l@ to a constant value. The clamp circuit 3 clamps the high level or low level of the output signal. This signal includes an offset control circuit 2
Since the offset fluctuation due to the operation is also added, this fluctuation is removed by the band limiting circuit 4. Furthermore, since this gain control system only requires signal components, it may be necessary to remove signals such as unnecessary high frequency out-of-band noise in order to perform stable gain control. Konori 2
There is no problem even if the signal processing of the amplifier circuit 3 and the band limiting circuit 4 is reversed.

Flang circuit 5. A peak value detection circuit 5 detects the peak value of the signal that has passed through the band limit circuit 4, and a gain control circuit 6 compares it with the reference signal amplitude, amplifies and integrates the difference signal, and outputs it as a gain control signal. The automatic gain control loop is formed by inputting K to the gain control terminal of the variable gain amplifier 1.

The averaging circuit 3 and the peak value detection circuit 5 are circuits for determining the signal amplitude, and when determining the signal amplitude as an average value, an average value detection circuit may be used.

In this case as well, if the band limiting circuit 4 is inserted before detecting the average value, the same effect as that of the present invention can be obtained.

[@Ming effect]

As described above, according to the present invention, the band limiting circuit 4
In order not to follow the offset fluctuation of the a7 variable gain amplifier 1, the low frequency band is adjusted to a band corresponding to the integral time constant of the offset control circuit.JPt! By using fr, the gain-side # circuit does not malfunction due to offset fluctuations, so a stable intransitive 41tllll@J circuit can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an automatic profit control circuit according to an embodiment of the present invention.

Claims (1)

[Claims] In an automatic gain control circuit consisting of a variable gain amplifier having an offset control circuit and a gain control circuit that controls the amplitude of the output signal to a constant value, a band limiting circuit is added to the gain control circuit to control the response of the offset control circuit. An automatic gain control circuit characterized in that the automatic gain control circuit is configured such that the response of the gain control circuit does not follow the response of the gain control circuit.