JPH0595238A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To realize the automatic gain control circuit with configuration offering ease of assembling and adjustment and high general-purpose performance. CONSTITUTION:When an amplifier circuit 1 amplifies an input signal I and outputs a resulting output signal J, a reference voltage V whose voltage is selected in response to a selection signal S given externally and the output signal J are compared and a gain control signal G controlling an amplification factor in the amplifier circuit 1 is generated. Thus, the amplitude of the output signal J is set again in response to the selection signal S. As a result, an excess externally mounted component, replacement and adjustment or the like are not required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain control circuit, and more specifically, the amplitude of an output signal used in an audio device having a recording / reproducing function, a video processing device, a device having a signal transmitting function or the like can be selected. Automatic gain control circuit.

[0002]

2. Description of the Related Art An automatic gain control circuit is a signal recording means,
In order to prevent the adverse effect of the amplitude level of the input signal received by the processing circuit being changed undesirably due to variations in the recording state, the reproducing means, the reproducing state, or the device characteristics, the input signal is amplified and the output signal is amplified. Upon generation, the gain is controlled, that is, the amplification factor is changed, and the amplitude value of the output signal is automatically controlled so as to be within a predetermined value or a predetermined range. FIG. 4 shows a block diagram of an automatic gain control circuit having a conventional configuration. The detailed configuration and operation will be described below with reference to this figure.

Here, 1 is an amplification circuit, 2 is a gain signal generation circuit, 3 is a comparison circuit, and 4 is a reference voltage generation circuit. The reference voltage generation circuit 4 generates the reference voltage V by resistance voltage division between the power supply Vcc and the ground. The comparison circuit 3 has a reference voltage V
And the output signal J, the magnitudes of these signal values are compared, and a binary comparison signal is output according to the comparison result.

The gain control signal generating circuit 2 is a smoothing circuit 2a.
And receives the comparison signal from the comparison circuit 3 and smoothes the binary information of this signal by the smoothing circuit 2a to generate a gain control signal G having an analog value, which is output to the amplification circuit 1. The amplifier circuit 1 receives an input signal I, amplifies it, and outputs an output signal J.
At this time, the gain control signal G is also received, and the amplification factor for the input signal I is changed according to the value of the gain control signal G, so that the amplitude of the output signal J corresponds to the reference voltage V. Hold at a predetermined value. That is, the amplitude of the output signal J is controlled by the duty ratio control according to the signal of the amplitude of the output signal J that exceeds the reference signal V.

With such a configuration, the amplitude of the output signal J is constantly monitored and controlled so as to reach a predetermined value.
Even if the amplitude level of the input signal I changes undesirably, the influence thereof is exerted on the output signal J for only a short period. Therefore, the output signal J can maintain a substantially constant amplitude irrespective of fluctuation factors such as signal recording / reproducing means, state and device characteristic variations. Since it has such a function, this automatic gain control circuit is often used in the front stage portion of various signal processing circuits.

[0006]

However, in the automatic gain control circuit having such a conventional structure, only one reference voltage can be generated, and therefore only one amplitude level of the output signal can be set. Therefore, for example, when this automatic gain control circuit is adopted in a video tape recorder, a television or the like, a plurality of systems such as the NTSC system and the PAL system are switched and operated, and an input signal from a tuner and a microphone input signal are switched. When it is necessary to reset the level of the output signal of this circuit, such as switching, it is necessary to replace the resistance of the reference voltage generating circuit, which is inconvenient because the assembly adjustment man-hours are wasted.

Particularly, when circuits other than the smoothing circuit are integrated in one IC, it is impossible to reset the level of the output signal, which is not versatile, and the resistance of the reference voltage generating circuit is also increased. In the case of integration except the above, it is possible to reset the level of the output signal, but since there are many external parts, extra assembly and adjustment man-hours are required, which is a problem.
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide an automatic gain control circuit having a structure with easy assembly and adjustment and high versatility.

[0008]

The structure of the automatic gain control circuit of the present invention which achieves the above object is an automatic gain control circuit which generates an output signal having an amplitude corresponding to a reference voltage with respect to an input signal. A reference voltage generating circuit that generates a plurality of voltages by resistance voltage division, selects one of the plurality of voltages according to the value of a selection signal received from the outside, and outputs the reference voltage as the reference voltage; A comparison circuit that receives the reference voltage and the output signal, compares the magnitudes of these signal values, and outputs a binary comparison signal according to the comparison result; and a comparison circuit that receives the comparison signal and generates a smoothed signal according to this signal A gain control signal generating circuit for outputting a gain control signal having an analog value and an input signal, and changing the amplification factor for the input signal according to the value of the gain control signal so that the output signal corresponds to the reference voltage. The predetermined amplitude, and an amplifier circuit for outputting an output signal, but with a.

Another structure of the automatic gain control circuit according to the present invention is an automatic gain control circuit for generating an output signal having an amplitude corresponding to a reference voltage with respect to an input signal, wherein a plurality of voltages are obtained by resistance voltage division. And a reference voltage generating circuit that selects any one of the plurality of voltages corresponding to a predetermined value of a selection signal received from the outside and a value other than the predetermined value and outputs the selected voltage as the reference voltage. Receiving the reference voltage and the output signal, selected by the predetermined value of the selection signal, comparing the value of the reference voltage and the value of the output signal, the comparison result as a binary comparison signal 1st to output
Comparing circuit, receiving the reference voltage and the output signal,
Selected by a value other than the predetermined value of the selection signal,
Comparing the value of the reference voltage and the value of the output signal,
A second comparison circuit that outputs a comparison result as the comparison signal; a gain control signal generation circuit that receives the comparison signal, generates a smoothed signal corresponding to the comparison signal, and outputs the smoothed signal as an analog gain control signal; and an input signal Receiving the input signal, the amplification factor for the input signal is changed according to the value of the gain control signal, and the output signal has a predetermined amplitude corresponding to the reference voltage,
And an amplifier circuit that outputs this output signal.

Still another configuration of the automatic gain control circuit of the present invention is that the remaining circuit portion excluding the circuit for smoothing described above is integrated in a one-chip IC from the circuit having the above configuration. ..

[0011]

In the automatic gain control circuit of the present invention having such a structure, according to the value of the selection signal received from the outside,
The reference voltage is switched, or the reference voltage is switched, and the comparison circuit that outputs the comparison result is also switched.
On the other hand, the amplitude level of the output signal is determined to correspond to the reference voltage via the gain control signal obtained by smoothing the comparison signal. Therefore, the amplitude level of the output signal is
It is set to one of a plurality of predetermined values according to the value of the selection signal.

As a result, when resetting the level of the output signal of this circuit, it is not necessary to replace the resistance of the reference voltage generating circuit, so that the assembly and adjustment are facilitated. Particularly, when integrated in a one-chip IC, the amplitude level of the output signal can be reset without using external parts such as resistors, so that versatility is increased and assembly and adjustment are facilitated.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the automatic gain control circuit having the structure of the present invention will be described below. FIG. 1 is a block diagram showing the circuit configuration of this embodiment, in which 1 is an amplifier circuit, 2 is a gain signal generation circuit, 3 is a comparison circuit, and 14 is a reference voltage generation circuit. The reference voltage generation circuit 14 generates a plurality of voltages by resistance voltage division between the power supply Vcc and the ground, selects one voltage from these voltages according to the value of the selection signal S, and uses it as a reference. Output as voltage V. The selection signal S is given, for example, by a signal externally input to a certain terminal of the IC. The comparison circuit 3 receives the reference voltage V and the output signal J, compares the magnitudes of these signal values, and outputs a binary comparison signal according to the comparison result.

The gain control signal generating circuit 2 includes a smoothing circuit 2a.
And receives the comparison signal from the comparison circuit 3 and smoothes the binary information of this signal by the smoothing circuit 2a to generate a gain control signal G having an analog value, which is output to the amplification circuit 1. The amplifier circuit 1 receives an input signal I, amplifies it, and outputs an output signal J.
At this time, the output signal J is also fed back to receive the gain control signal G generated, and the amplification factor for the input signal I is changed according to the value of the gain control signal G, that is, The amplitude of the output signal J is held at a predetermined value corresponding to the reference voltage V by the duty ratio control according to the signal of the amplitude of the output signal J that exceeds the reference signal V.

With such a configuration, the fluctuation of the amplitude value of the output signal J with respect to the reference voltage V is fed back to the amplification factor in the amplifier circuit 1, and the amplitude of the output signal J is changed to the reference voltage V.
Is controlled to a predetermined value corresponding to. Therefore, the amplitude level of the output signal J of the automatic gain control circuit is reset only by switching the value of the selection signal S, so that the circuit can be easily adjusted.

Another embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram showing a circuit configuration in the case of having a plurality of comparison circuits. 1 is an amplification circuit, 2 is a gain signal generation circuit, 14 is a reference voltage generation circuit, and 15 and 16
Is a comparison circuit. The amplifier circuit 1, the gain control signal generating circuit 2, and the reference voltage generating circuit 14 have the same configurations as those of the above-described embodiments with the same reference numerals.

The comparator circuit 15 has a comparator 15a and a switch circuit 15b, and when the switch circuit 15b is selected and operated by a predetermined value of the selection signal S, the switch circuit 1
The comparator 15a also operates by receiving the current supply via 5b, compares the reference voltage V with the signal value of the output signal J,
A binary comparison signal is output according to the comparison result. The comparator circuit 16 has a comparator 16a and a switch circuit 16b, and when the switch circuit 16b is selected and operated by a value other than the predetermined value of the selection signal S, the switch circuit 16b.
The comparator 16a also operates by receiving the supply of a current via the reference voltage V, compares the reference voltage V with the signal value of the output signal J, and outputs a binary comparison signal according to the comparison result.

Thus, the comparison circuit 15 and the comparison circuit 16
Corresponds to different values of the selection signal S, either one outputs a comparison signal. Therefore, similarly to the above-described embodiment, in the circuit having the configuration of this embodiment, the amplitude level of the output signal J of the automatic gain control circuit is reset only by switching the value of the selection signal S, so that the circuit is assembled. It is easy to make adjustments.

As a final example, FIG. 3 shows a specific example in which the circuit having the above-mentioned configuration having a plurality of comparison circuits is integrated in one chip IC except the smoothing circuit 2a. The configuration and operation of this circuit are the same as those of the above-mentioned embodiment, and the versatility and productivity are improved.

[0020]

As can be understood from the above description, in the automatic gain control circuit of the present invention, the level of the output signal is reset to a predetermined value simply by switching the value of the selection signal given from the outside. So extra external parts or replacement,
No adjustment is required. Therefore, there is an effect that an assembly and adjustment are easy and a highly versatile automatic gain control circuit configuration can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic gain control circuit having a configuration of the present invention.

FIG. 2 is a block diagram of an embodiment of another configuration of the automatic gain control circuit of the present invention.

FIG. 3 is a block diagram of an embodiment in which the automatic gain control circuit of the present invention is integrated in a one-chip IC.

FIG. 4 is a block diagram of an automatic gain control circuit having a conventional configuration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Amplifier circuit 2 ... Gain signal generation circuit 2a ... Smoothing circuit 3 ... Comparison circuit 4 ... Reference voltage generation circuit 14 ... Reference voltage generation circuit 15, 16 ... Comparison circuit 15a, 16a ... Comparator 15b, 16b ... Switch circuit

Claims (3)

[Claims] 1. An automatic gain control circuit for generating an output signal having an amplitude corresponding to a reference voltage with respect to an input signal, wherein a plurality of voltages are generated by resistance voltage division, and a plurality of voltages are generated according to a value of a selection signal received from the outside. A reference voltage generation circuit that selects any one of the plurality of voltages and outputs the reference voltage, receives the reference voltage and the output signal, compares the magnitudes of these signal values, and outputs two values according to the comparison result. A comparison circuit that outputs a comparison signal of a value; a gain control signal generation circuit that receives the comparison signal, generates a smoothed signal according to the comparison signal, and outputs the smoothed signal as a gain control signal of an analog value; An amplification circuit that changes the amplification factor for the signal according to the value of the gain control signal to make the output signal have a predetermined amplitude corresponding to the reference voltage, and outputs the output signal. Automatic gain control circuit that. 2. An automatic gain control circuit for generating an output signal having an amplitude corresponding to a reference voltage with respect to an input signal, wherein a plurality of voltages are generated by resistance voltage division and a predetermined value of a selection signal received from the outside and this A reference voltage generating circuit that selects any one of the plurality of voltages corresponding to a value other than a predetermined value and outputs the reference voltage as the reference voltage, receives the reference voltage and the output signal, and selects the selection signal. A first comparison circuit which is selected by the predetermined value, compares the value of the reference voltage with the magnitude of the value of the output signal, and outputs the comparison result as a binary comparison signal; A second comparison circuit that receives a signal and selects a value other than the predetermined value of the selection signal, compares the value of the reference voltage with the value of the output signal, and outputs the comparison result as the comparison signal. Circuit and the ratio A gain control signal generation circuit that receives a comparison signal, generates a smoothed signal according to this signal, and outputs it as a gain control signal of an analog value, and an input signal that receives an amplification factor for this input signal according to the value of the gain control signal. An automatic gain control circuit, further comprising: an amplifier circuit that outputs the output signal by setting the output signal to a predetermined amplitude corresponding to the reference voltage. 3. The automatic gain control circuit according to claim 1, wherein the circuits other than the smoothing circuit are integrated in a one-chip IC. An automatic gain control circuit characterized by the above.