JPS61189008A - Automatic gain control amplifier - Google Patents

Abstract

PURPOSE:To shorten the response time by connecting a rectifying element which conducts by a constant forward voltage, between a control terminal of an amplifier circuit and an input terminal of a comparing circuit, and holding a voltage difference between the terminals within a prescribed value. CONSTITUTION:A peak holding circuit 2 sets a crest value of an output signal Vout as a holding voltage V2. A comparing circuit 3 compares this holding voltage V2 and a reference voltage Vref, but its output V3 is delayed by a delay time of the comparing circuit 3 after the holding voltage V2 has risen. Also, a smoothing circuit 4 also generates an output voltage Vcont with a prescribed delay time. However, during this delay time, the holding voltage V2 of the peak holding circuit 2 and the output voltage Vcont of the smoothing circuit 4 exceeds a forward voltage of a diode 5, therefore, a current flows through the diode 5 to the smoothing circuit 4 from the peak holding circuit 2, and as a result, at the almost same time as a rise of the holding voltage V2 of the peak holding circuit 2, the output of the smoothing circuit 4, namely, the control voltage Vcont rises.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an amplifier that automatically controls amplification gain.

[Conventional technology]

FIG. 3 is a block diagram showing an example of a conventional automatic gain control amplifier. In the figure, 1 is an amplifier circuit whose gain can be controlled by a control voltage Vcont, and 2 is an output signal obtained by amplifying the input signal Vin in the amplifier circuit 1. A peak hold circuit that holds the peak value of Vout; 3 a comparison circuit that compares the holding voltage 2 held by the peak hold circuit 2 with a preset reference voltage Vref; 4, for example, a comparison circuit with capacitors C1 and C2; Comprising a resistor R, the comparison circuit 3
This is a smoothing circuit that smoothes the output V3 of the amplifier circuit 1 and generates a control voltage Vcont that controls the gain of the amplifier circuit 1.

Next, the operation will be explained. Note that FIG. 4 is a diagram of each signal waveform in this conventional example. If there is no input signal Vin to the amplifier circuit 1 for a long time, nothing will occur at the output Vout, and therefore the holding voltage V2 of the peak hold circuit 2 will decrease.
is near OV.

Since this holding voltage V2 is sufficiently higher than the reference voltage Vref, the output (3) of the comparator circuit 3 becomes the negative maximum voltage. The smoothing circuit 4 smoothes the output 3 of the comparison circuit 3, but in this case, since the output v3 of the comparison circuit 3 is the maximum voltage of the long eclipse, the output of the smoothing circuit 4, that is, the control voltage Vc
ont also becomes the maximum negative voltage, and as a result, the gain of the amplifier circuit 1 becomes maximum.

In this state, the input signal Vi with a certain amplitude to the amplifier circuit 1
When n is input, the amplifier circuit 1 receives the input signal V at maximum gain.
in and outputs an output signal Vout having a predetermined amplitude or more. The peak hold circuit 2 receives this output signal Vout
The comparator circuit 3 compares this held voltage (2) with the reference voltage Vref. At this time, since the output signal Vout of the amplifier circuit 1 has a larger amplitude than usual, the holding voltage 2 becomes higher than the reference voltage Vref, and the output 3 of the comparator circuit 3 becomes a higher voltage than usual.

The smoothing circuit 4 smoothes this output v3 and makes the control voltage Vco
nt. As a result, the gain of the amplifier circuit 1 decreases, and by repeating this, the holding voltage of the peak hold circuit 2
and the reference voltage Vref are approximately equal to each other.
As a result, the output signal Vo of the amplifier circuit 1 is controlled.
The amplitude of uL is approximately constant regardless of the amplitude of the input signal Vin.

[Problem that the invention seeks to solve]

However, since the conventional automatic gain control amplifier is configured as described above, the amplitude of the output signal Vout when changing from a no-signal input to a signal input is It takes a long response time to make the input signal Vin constant, and therefore there is a problem that it cannot be used until this response time has elapsed from the time when the input signal Vin changes.

This invention was made to solve the above-mentioned problems, and an object of the present invention is to provide an automatic gain control amplifier that has a short response time and can reduce unusable periods due to fluctuations in input signal amplitude. It is something.

[Means for solving problems]

The automatic gain control amplifier according to the present invention connects a rectifying element that conducts at a constant forward voltage between the control terminal of the amplifier circuit and the input terminal of the comparator circuit, and keeps the voltage difference between the terminals within a constant value. It was designed to be kept.

[Effect]

In this invention, when the voltage difference between the control terminal of the amplifier circuit and the input terminal of the comparator circuit exceeds a certain value, the rectifying element becomes conductive, thereby acting to compensate for the delay time with respect to changes in the input signal amplitude.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 1 is the control voltage V applied to the control terminal 1a.
2 is a peak hold circuit that holds the peak value of the output signal Vout of this amplifier circuit 1; 3 is a voltage V2 held by this peak hold circuit 2 and applied to the input terminal 3a; 4 is a smoothing circuit configured by connecting two capacitors CI and 02 and a resistor R in a π type; 5 is the output of peak hold circuit 2; In other words, the input terminal 3a of the comparator circuit 3
This is the most common diode as a rectifying element, with its anode connected to the output of the smoothing circuit 4, that is, the control terminal 1a of the amplifier circuit 1, and the holding voltage 2 is the control voltage V.
It becomes conductive when the forward voltage becomes higher than cont by a certain forward voltage.

Next, the operation will be explained. Note that FIG. 2 is a diagram of each signal waveform in this embodiment. If the input signal Vin is not input for a long period of time, nothing will occur at the output Vout of the amplifier circuit 1, and therefore the holding voltage V of the peak hold circuit 2 will decrease.
2 is almost 0 ■. Since this holding voltage V2 is sufficiently higher than the reference voltage Vref, the output of the comparator circuit 3 is
is the maximum negative voltage. At this time, peak hold circuit 2
Since the difference between the holding voltage (■2) and the output (■3) of the comparator circuit 3 is larger than the forward voltage of the diode 5, the output voltage of the smoothing circuit 4, that is, the control voltage Vcont, is smaller than the holding voltage (■2) of the peak hold circuit 2. The voltage is lowered by the forward voltage of 5.

In this state, when an input signal Vin having a normal amplitude is input, the amplifier circuit 1 amplifies it with a gain larger than normal and outputs an output signal Vout. The amplitude of the output signal Vout at this time is larger than the expected amplitude. The peak hold circuit 2 sets the peak value of the output signal Vout as a holding voltage (2). The comparator circuit 3 compares this holding voltage (2) with the reference voltage Vref, and its output (3) is the holding voltage V.
2 is delayed by the delay time of the comparison circuit 3. In addition, the smoothing circuit 4 also outputs a voltage C0 with a certain delay time.
Generate nt. However, during this delay time, the holding voltage 2 of the peak hold circuit 2 and the output voltage Vcont of the smoothing circuit 4 are higher than the forward voltage of the diode 5. A current flows through it, and as a result, the output of the smoothing circuit 4, that is, the control voltage Vcont, rises almost simultaneously with the rise of the holding voltage V2 of the peak hold circuit 2.

As a result, the gain of the amplifier circuit 1 approaches a stable state, and at the same time, charging of the capacitor C2 of the smoothing circuit 4 becomes faster.

Next, when the delay time of the comparator circuit 3 and the smoothing circuit 4 elapses from this state, the difference between the output voltage Vcont of the smoothing circuit 4 and the holding voltage V2 becomes less than the forward voltage of the diode 5, and the current flows through the diode 5. It stops flowing. After this, the circuit operation is similar to that of the conventional circuit.

Due to these effects, the response speed of the automatic gain control amplifier according to this embodiment is faster than that of the conventional one. −
.

In the above embodiment, the cathode of the diode 5 is connected to the output of the smoothing circuit 4, and the anode is connected to the output of the peak hold circuit 2. However, the relationship between the control voltage and the gain of the amplifier circuit 1 is different from the above embodiment. If they have opposite characteristics, the cathode and anode connections will be reversed.

〔Effect of the invention〕

As explained above, according to the present invention, a rectifying element that conducts at a constant forward voltage is connected between the control terminal of the amplifier circuit and the input terminal of the comparison circuit, and the voltage difference between the terminals is kept within a constant value. Since delay time can be compensated for by keeping the gain constant at .

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a diagram of each signal waveform in the above embodiment, Fig. 3 is a block diagram showing a conventional example, and Fig. 4 is a diagram of each signal waveform of the above embodiment. It is a diagram. DESCRIPTION OF SYMBOLS 1... Amplification circuit, la... Control terminal, 3... Comparison circuit, 3a... Input terminal, 5... Rectifying element. Note that the same reference numerals are used for the middle part of the figure or corresponding parts. Agent Masuo Oiwa (2 idiots) 1st meter!
FIG. 3 Vin 4 t Vin.

Claims (1)

[Claims] The amplifier circuit includes an amplifier circuit whose amplification gain can be controlled, and a comparison circuit that compares a preset reference voltage with a voltage corresponding to the output signal of the amplifier circuit, and calculates the gain of the amplifier circuit based on the output of the comparison circuit. In the automatic gain control amplifier, a rectifying element that conducts at a constant forward voltage is connected between the control terminal of the amplifier circuit and the input terminal of the comparison circuit, and the voltage difference between the terminals is kept constant. An automatic gain control amplifier characterized in that the gain is maintained within a certain value.