JPS60201709A - Agc circuit - Google Patents

Abstract

PURPOSE:To obtain an AGC circuit which ensures a stable output amplitude with no effect of a temperature change by extracting not only signals but a reference potential out of an output stage of a main amplifier circuit. CONSTITUTION:A detection circuit 2 detects the output peak value of an amplifier circuit 31 which amplifies an input signal with the gain varying by a control signal. While only the DC component is extracted at a division point of a load resistance 32 of the circuit 31 through an LPF5. Then the output of the circuit 2 is compared with that of the LPF5, and a comparator delivers a control signal in response to the obtained difference of outputs. In such a constitution, the output signal of an AGC circuit is deflected in an amplitude of alphaRL.ILO centering on an output terminal potential VLO obtained in a no-signal mode. Thus the amplitude of a signal can be prescribed by a product of the resistance 32 and a current flowing to the resistance 32. Therefore the variation can be reduced effectively to the variance of the power supply voltage, temperatures, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an AGC (automatic gain control) circuit for waveform transmission used in pulse code transmission lines and the like.

[Prior art]

Conventionally, the AGC circuit Kb used in coaxial cable and original fiber cable transmission equipment, etc. is originally based on technology based on pulsed wave transmission, so it compensates for waveform deterioration and attenuation due to the transmission line and reproduces it. Repeaters for this purpose are installed on the transmission line at certain intervals. Therefore, the repeater uses an AGC circuit to compensate for waveform deterioration and attenuation that are affected by changes in environmental conditions, variations in relay distance, and the like.

Conventionally, the AGC circuit mainly includes a main amplifier circuit for amplifying the main signal, a peak detection circuit for detecting the peak value of the output signal of the main amplifier circuit, and a signal for controlling the amplification factor of the main amplifier circuit. It consists of a comparison circuit that generates

FIG. 1 shows a conventional AGC circuit. ] is the main amplifier circuit, and its amplification factor can be made variable by a control signal. , 2 is a peak detection circuit for detecting and holding the peak potential of the output signal of the main amplifier circuit. 3 is a comparison circuit that compares two input potentials. Reference numeral 4 denotes a reference potential generation circuit 91. In this example, the power supply voltage vs is divided by a resistor r so that a predetermined reference voltage can be obtained.

This AGC circuit detects the peak potential of the output signal obtained by amplifying the input signal, and uses the comparator circuit 3 to perform main amplification so that the peak potential becomes the same as the potential given from the reference potential generation circuit 4. It is a so-called negative feedback circuit in which circuit l is controlled.

FIG. 2 shows the relationship between the waveform of the output of the main amplifier circuit, the DC potential, and the set reference potential. FIG. 5A shows a case where the AGC circuit is in a steady state, and the peak potential of the waveform is the same as the set reference potential 10. FIG. 4B shows a transient state in which the peak potential of the waveform has not reached the reference potential 10. In this case, the output signal of the comparator circuit 3 operates to increase the gain of the main amplifier circuit and to increase the output amplitude of the output. FIG. 4(e) shows a transient state in which the peak potential of the waveform exceeds the reference potential 10.

In this case, the output signal of the comparator circuit 3 operates to reduce the gain of the main amplifier circuit and thus reduce the output amplitude. Therefore, in this AGC circuit, the gain of the main amplifier circuit changes until the output waveform peak potential matches the reference potential 10. A so-called AGC operation is performed.

In this conventional circuit, the circuit that determines the DC output potential of the main amplifier circuit and the circuit that generates the reference potential are independent.
There is a drawback that the difference between the two potentials changes in response to changes in power supply voltage and environmental temperature, and as a result, the amplitude of the output signal tends to change.

In addition, in order to maintain the same variation in the direct current potential of the two circuits with respect to temperature, etc., they must be combined into completely similar circuit configurations, resulting in an increase in the scale of one circuit.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an AGC circuit that eliminates the above drawbacks and provides stable output amplitude by extracting not only a signal but also a reference potential from the output stage of a main amplifier circuit.

[Structure of the invention]

The AGC circuit of the present invention includes an amplifier circuit that amplifies an input signal with a gain that is variable according to a control signal, and a detection circuit that detects the peak value of the output of the amplifier circuit.

an F-wave device that outputs a DC component from a signal at a distribution point of the load resistance of the amplifier circuit; a comparison circuit that compares the outputs of the detection circuit and the F-wave device and outputs the control signal according to the difference; It is characterized by having the following.

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the drawings.

Referring to FIG. 3, a first embodiment of the present invention is shown.

This configuration is such that the output stage of the main amplifier circuit 31 is emitter grounded. The output section has one end connected to a power source and the other end connected to a collector, and a predetermined distribution point of a collector load resistor 32 is input to the comparator circuit 3 via a low-frequency F wave generator 5. The other parts have the same configuration as the conventional circuit.

Its operation will be explained with reference to FIG. The output potential V when there is no signal (at equilibrium) is expressed using the power supply voltage vs, the lid load resistance RL, and the load current ILO when there is no signal.

V=V-RL・Work LOB. On the other hand, when the tap is taken out from the load resistor at the proportional division ratio α, the AC component is removed by the low-pass filter 5.

Its DC potential is V, -RL・"LO+αRL"1.0=V-(1-α
)・RLIIILO. However, in this AGC circuit, until the peak of the signal amplitude at the output section matches the potential of the above-mentioned tap.

It operates to change the gain of the main amplifier circuit. Therefore, signals such as codes and sine waves that do not have a DC component swing vertically symmetrically around the no-signal output terminal potential vLo, and their amplitude (0-P value).

zero to pea, k value) is vO-P
='P'LO'''' αRL・ILO.

In this way, the signal amplitude can be defined by the product of the load resistance and the current flowing through it, which is effective in reducing changes due to power supply voltage fluctuations, temperature changes, etc.

Furthermore, it is also very effective when implementing this AGC circuit with a semiconductor integrated circuit or the like. This is because in semiconductor integrated circuits, as the resistance value increases, the current flowing through it generally decreases, so the product of the resistance value and the current value remains approximately constant. A circuit configuration that is proportional to the product of resistance and load current (the proportionality constant α is one foot) is a very effective means.

Next, a second embodiment of the present invention is shown in FIG. This is a configuration in which the output section of the main amplifier circuit 41 is of a differential type. The basic operating principle is the same as that of the first embodiment, so the explanation will be omitted.

Although the above embodiment was explained using an NPN type bipolar transistor and a positive power supply voltage, it goes without saying that P
NP type bipolar transistor.

A field effect transistor (so-called MO8 type transistor) is used, and the operating principle is the same even with a negative power supply voltage. Furthermore, the same effect can be obtained by using the peak detection circuit to detect the lower peak (bottom) of the waveform in FIG. 4 instead of detecting the upper peak.

〔Effect of the invention〕

According to the present invention, as explained above, a stable AGC circuit can be realized by obtaining the DC reference voltage from the distribution point of the output load resistance.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a conventional AGC circuit, and Figure 2 (
a), (b), and (e) are waveform diagrams showing the operation of FIG. 1; FIG. 3 is a block diagram showing the first embodiment of the present invention, and FIG.
This figure is a waveform diagram showing the operation of FIG. 3, and FIG. 5 is a block diagram showing a second embodiment of the present invention. 1.31.41... Main amplifier circuit, 2...
・Peak detection circuit, 3... Comparison circuit, 4...
...Reference potential generation circuit, 5...Low AF wave device. Y1 priest v2 @ /ρ /θ -1111ryo $ 3 '7 Ju 4 - Father 1 family

Claims (1)

[Claims] The present invention includes an amplifier circuit that amplifies an input signal with a gain that is variable according to a control signal, a detection circuit that detects a peak value of the output of the amplifier circuit, and a comparison circuit that outputs a load resistance of the amplifier circuit. Features AGC circuit.