JPH0263308A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To improve the accuracy and stability of an input voltage to a comparator for producing a gain control voltage by adding outputs of a differential amplifier circuit so as to obtain a reference voltage of a comparator. CONSTITUTION:A DC potential of an output signal of a differential amplifier circuit and a minimum potential detected from the amplitude of a signal at a high potential side are brought to the same potential, the stable state. When the amplitude of the input signal is decreased, the amplitude of signal waveforms 201, 202 is decreased, a reference voltage 203 is unchanged and the amplitude of signal waveforms 204, 205 is decreased, then the minimum level in the amplitude is increased, showing a difference from the reference potential 203. Then difference is outputted at an output terminal 120 by a comparator 118 as a gain control voltage. Thus, the reference voltage is given from the differential amplifier and the control accuracy is improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an automatic gain control circuit used in a differential amplifier circuit composed of a bipolar integrated circuit, and in particular to an automatic gain control circuit that enables highly accurate and highly stable gain control. This invention relates to an automatic gain control circuit.

Conventionally, this type of automatic gain control circuit detects the maximum value of the output signal amplitude generated by the load resistor pair of the differential transistor pair constituting the differential amplifier circuit, and compares the detected voltage. In addition, a reference voltage was applied to the comparator from the outside, and the comparison output of the comparator was used as a control voltage for gain control.

FIG. 3 shows a conventional automatic gain control circuit. In FIG. 3, load resistor pairs 306 and 307 are connected between a differential transistor pair 303 and 304 and a power supply terminal 309 and a ground terminal 310, respectively, with 301 and 302 as long terminals and 315° and 317 as output terminals. and differential transistor pair 3
A current source 305 provided between the connection point of 03 and 304 and the ground terminal 308 constitutes a differential amplifier circuit.

The automatic gain control circuit includes a peak detector 312 that detects the maximum peak value of the signal amplitude generated at output terminals 315 and 317 through a load resistor pair 306 and 307, and a reference voltage terminal that receives the output of this peak detector 312 as input. 31.4 and a comparator 313 to which a reference voltage is applied, and the comparison result of this comparator 313 is output to a terminal 316 as a gain control output.

Figure 4 shows the operating waveforms. In Figure 4, 415.4
Reference numeral 17 indicates output signals generated at output terminals 315 and 317, respectively, in FIG. As an output signal, the peak detector 312 in FIG. 3 detects the maximum signal amplitude, and the potential 41
Get 2. 414 is the reference voltage terminal 314 in FIG.
Indicates the potential applied to The comparator 313 in FIG. 3 compares the potentials 412 and 414, and outputs the comparison result to the gain control output terminal 316 in FIG.

[Problems to be Solved by the Invention] However, the conventional automatic gain control circuit described above uses a comparator to compare a reference potential independent of the differential amplifier circuit with respect to the potential obtained as a result of detecting the maximum peak value of the signal amplitude. 313
Therefore, there is a drawback that the absolute accuracy between the maximum output amplitude value of the differential amplifier circuit and the reference voltage cannot be ensured.

The present invention has been made in view of such problems, and includes:
To provide an automatic gain control circuit that can improve accuracy and ensure stability of input voltage in a comparator for generating gain control voltage, thereby realizing high accuracy and high stability as a differential amplifier circuit. With the goal.

[Means for Solving the Problems] The automatic gain control circuit according to the present invention divides a pair of load resistors at the same ratio, adds voltages at specific opposing division points, and applies this added voltage to a comparator. The present invention is characterized in that the reference voltage is used as a reference voltage, the peak voltage at another opposing dividing point is used as an input to the comparator, and the output of the comparator is used as a gain control voltage.

[Operation] According to this configuration, by adding the voltages at specific opposing division points of the load resistor pair, a constant DC voltage corresponding to the division ratio can be obtained, so this can be used as the reference voltage. ,
Furthermore, since the peak voltage at the other opposing division points varies depending on the input voltage, this can be used as the input of the comparator.

Therefore, there is no need for a reference potential independent of the differential amplifier circuit, and the accuracy and stability of the input voltage of the comparator can be improved.

[Example] FIG. 1 shows an example of the present invention. In FIG. 1, the differential amplifier circuit has differential input terminals 101 and 102, a differential transistor pair 103 and 104, and a power supply terminal 113, respectively.
and 114, load resistors 107 and 1 divided into three, respectively.
08, 109 and load resistors 110, 111, 112 are connected, and a current source 105 is provided between the connection point of the differential transistor pair 103 and 104 and the ground terminal 106. The low potential sides P and P' of each load resistance dividing point are used as differential output terminals 119 and 121, respectively.

In the automatic gain control circuit, the low potential side P.

The voltage of P' is added by resistors 116 and 117 and is used as a reference input of comparator 118. In addition, a signal generated at a pair of points Q and Q' on the high potential side of the load resistance dividing point is input to the peak detector 115, and the peak value detector 115 detects the minimum amplitude value and inputs the signal to the other input of the comparator 118. give to The output of the comparator 118 is then outputted to the output terminal 120 as a gain control voltage.

Next, the operation will be explained using the example of operation waveforms shown in FIG.

201 and 202 indicate output signal waveforms generated at the output terminals 119 and 121 of the differential amplifier circuit shown in FIG. 1, respectively.

Further, 204 and 205 indicate signal waveforms generated at a pair of points Q and Q' on the high potential side of the load resistance dividing point in FIG. Furthermore,
Reference numeral 20B indicates a reference voltage input to the comparator 118, which is the sum of the minimum signal amplitude output of the peak detector 115 in FIG.

For this example of operation, the load resistances 107, 108.10
9 and 110, 111, 1. ．． 12 shows an example in which each is divided at a ratio of 1:1:2.

According to this, if the power supply voltage is ■, the voltages 201 and 202 at opposing dividing points P and P' are the potential (3/
4) Signal centered at V, voltages 204 and 205 at opposing dividing points Q and Q' are extracted as a signal centered at (7/8)■. In the illustrated example, signal waveforms 204, 20
The signal amplitude of No. 5 is half of the signal amplitude of the signal waveforms 201 and 202, and is shifted upward by half the amplitude of the half of the DC bias potential of the signal shown in the signal waveforms 201 and 202. It has a potential of

That is, the DC potential of the output signal of the differential amplifier circuit and the minimum value potential detected from the signal amplitude on the high potential side are at the same potential and are in a stable state. When the input signal amplitude becomes smaller, the reference voltage 203 does not change even if the amplitude of the signal waveforms 201 and 202 becomes smaller, and the signal waveform 204
, 205 becomes smaller, the level of the minimum value of the amplitude increases and becomes different from the reference potential 203, and this difference is transferred to the output terminal 120 by the comparator 118.
It performs the operation of outputting as a gain control voltage.

By doing so, the reference voltage can be applied by the differential amplifier, and control accuracy is improved.

In addition, in the present invention, the load resistance pair of the differential amplifier is divided at the same ratio, and the voltages at the opposing specific dividing points are added to obtain the reference voltage of the comparator, and the voltage at the other specific dividing points is obtained. Since the main point is to use the peak value as input to the comparator, the division ratio of the load resistance, the division point, whether the peak value is the minimum amplitude value or the maximum amplitude value, etc. should be determined in the above example. It is not limited.

[Effects of the Invention] As explained above, in the present invention, the reference voltage of the comparator is obtained by adding the outputs of the differential amplifier circuit, so that the reference potential independent of the differential amplifier circuit is This has the effect that the accuracy and stability of the comparator input voltage for generating the gain control voltage can be improved.

[Brief explanation of the drawing]

1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is an operational waveform diagram of FIG. 1, FIG. 3 is a circuit diagram of a conventional example, and FIG. 4 is an operational waveform diagram of FIG. 3.

Claims (1)

[Claims] (1) In an automatic gain control circuit that obtains a control voltage for gain control in a differential amplifier circuit consisting of a differential transistor pair, a load resistor pair, and a current source, each of the load resistor pairs is divided at the same ratio, and the The voltages at a specific dividing point are added, this added voltage is used as a reference voltage of a comparator, the peak voltage at another opposing dividing point is used as an input to the comparator, and the output of the comparator is used as a gain control voltage. An automatic gain control circuit characterized by: