JPS6257308A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To eliminate a defect of an AGC circuit that the gain of an amplifier is suppressed smaller and a substantial signal is decreased even when noise is restored by obtaining a difference between a memory value of a time slot and a memory value of a time slot just before said time slot so as to control the discharge time constant. CONSTITUTION:A control section 11 fetches a digital value being the A/D conversion of the input signal from a signal line 10, stores it to the 1st memory value to the 1st memory circuit 16, the 1st memory value and the 2nd memory value set in the time slot just before detected from a terminal 20 are compared by a comparison circuit 17. When the result is larger than the predetermined threshold value, the input signal at the existing time slot is discriminated to be an excessive input signal such as clock noise, and the discharge time constant of a time constant circuit 18 is set to a small value for a prescribed time. The discharge time constant of the 2nd memory value stored in the 2nd memory circuit is switched at the signal of the normal input level to apply the AGC operation corresponding to each signal.

Description

[Detailed Description of the Invention] (Technical Field of the Invention) The present invention relates to an automatic gain control (hereinafter referred to as AGC) circuit that operates stably even when an excessive signal such as click noise or noise is applied to an amplifier. .

(Prior art and its problems) In a conventional AGC circuit that does not have a calculation means such as a CPU, there is a means for converting an input signal into a DC signal,
It is equipped with a time constant circuit that gives a delay time to the converted DC signal, and a means for controlling the gain of the amplification system using the DC signal to which this delay time has been added, and depending on the magnitude of the input signal,
The gain of the amplification system was controlled to obtain the AGC effect.

In addition, in an AGC circuit equipped with arithmetic means such as a CPU, there is a means for converting an input signal to an amplification system into a DC signal, a means for A/D converting the DC signal, and a circuit for storing the converted digital value. a second memory that operates according to the first memory value and has a small charging time constant and a large discharging time constant; means for comparing the first memory value and the second memory value; means for controlling the gain of the amplification system based on the memory value, converting the input signal into a DC signal,
The digital value obtained by A/D converting this DC signal is input into the CPU, and the gain of the amplification system is controlled by the value (second memory value) obtained by adding a time constant to this value, thereby obtaining the AGC effect on the human input signal. was. Here, the time constant for controlling the gain of the amplification system is controlled based on the comparison result between the first memory value and the second memory value.

However, A
In a GC circuit, as in the conventional A'GC circuit which does not have a calculation means such as a CPU, when an excessive signal such as click noise or noise is added to an input signal of a normal signal level, the excessive signal level Even after the AGC functions and eliminates the excessive signal, the original input signal is suppressed to a low level, and the disadvantage that the necessary signal cannot be heard remains unresolved.

In order to avoid this drawback, it is possible to control the AGC recovery time to be short, but if the AGC recovery time is short,
This control cannot be applied to a practical AGC circuit in the case of an audio signal, since the signal level is compressed and there is no intonation, resulting in an unnatural speech sound.

(Objective of the Invention) The present invention distinguishes between a normal human power level and an excessive input level due to click noise or noise, and applies AGC determined by the excessive input level, thereby suppressing the original input level. An object of the present invention is to provide an automatic gain control circuit that eliminates the drawbacks of the circuit.

(Structure and operation of the invention) To achieve this objective, the automatic gain control circuit of the present invention:
a rectifying means for converting an input signal to the amplification system into a DC signal using a first discharge time constant; an A/D converting means for A/D converting the DC signal into a digital signal value; a first memory that stores the digital signal value as a first memory value every predetermined time slot period; and a first memory that stores the digital signal value as a first memory value every predetermined time slot period; a second memory for storing a second memory value using a second discharge time constant greater than a constant; the first memory value for a certain time slot and the second memory value for a time slot immediately preceding the time slot; and when the difference exceeds a predetermined threshold, the second discharge time constant is temporarily reduced by a longer time T than the time slot period. The apparatus includes constant switching means and gain control means for automatically controlling the gain of the amplification system based on the second memory value.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an example of the configuration of the present invention. In the figure, when an input signal is applied to line terminal 1, the input signal passes through side sound protection circuit 2 and receiver amplifiers 3 and 6, and is heard by speaker 7, and a part of the input signal is transmitted from terminal 4. The signal is detected, passes through the rectifying and smoothing circuit 8, becomes a DC signal, and is input to the A/D converter 9.

Furthermore, the control unit 11 takes in and stores the output signal of the A/D converter 9 from the signal line 10, and performs calculations using this input value. The amplifier control signal obtained as a result of the calculation is sent to signal line 1.
2 and input to the D/A converter 13, the D/A converter 13 sends the output signal to the signal line 14, and the gain control circuit 5 sets the gain of the amplifier 6 to a new gain.

In the above operation, how the control unit 11 distinguishes between a normal input level and an excessive input level such as click noise or noise will be specifically described.

The control unit 11 takes in a digital value obtained by A/D converting the input signal from the signal line 10 and stores it in the first memory circuit 16.
Store it as a memory value.

The first memory value and the second memory value set in the immediately previous time slot detected from the terminal 20 are compared in the comparison circuit 17, and the first memory value is larger than the second memory value and When the difference exceeds a predetermined threshold, it is determined that there is an excessive input such as click noise or noise, and a signal is sent to switch the discharge time constant of the time constant circuit 18 of the second memory 19 to be smaller for a certain period of time. The signal line 2
2 and switch the discharge time constant. Further, when the difference does not exceed a predetermined threshold value, the above-described process of switching the discharge time constant of the time constant circuit 18 is not performed. Also,
When the first memory value is greater than the second memory value, the first memory value is stored as a new second memory value in the second memory circuit 19 via the signal line 15.

On the other hand, as a result of the comparison by the comparison circuit 17 as described above, the first
When the memory value is smaller than the second memory value, the first memory value is not stored in the second memory circuit 19,
The second memory value is controlled by the discharge time constant set in the time constant circuit 18, and is stored in the second memory circuit 19 as a new second memory value.

The second memory value newly set in the second memory circuit 19 in this way is calculated by the AGC loss calculation circuit 21.
It is used to calculate the amount of GC loss, and the AGC loss amount calculation circuit 21 sends the calculation result to the signal line 12.

As described above, the input signal level in the current time slot stored in the first memory circuit, and the human input signal level up to that time slot processed in the immediately preceding time slot and stored in the second memory circuit. If the input signal level in the current time slot is higher than the previous input signal level by more than a predetermined threshold, the input signal in the current time slot is an excessive input due to click noise, noise, etc. The time constant circuit 18
Set the discharge time constant to a small value for a certain period of time,
Furthermore, when the threshold value has not been reached, the discharge time constant of the time constant circuit 18 is not switched to a smaller value.
Switch the discharge time constant of the second memory value stored in the second memory circuit when a signal with an excessive input level such as click noise or noise is input, and when a signal with a normal input level is input. AGC operation corresponding to the signal can be performed.

FIG. 2 is a diagram showing the state of signal waveforms and memory values at each part of (a) (bl (d)) (e) in FIG. 1.

(al is the waveform of the input signal, which is converted into a DC signal by the rectifying and smoothing circuit 8 in FIG. 1, resulting in the DC signal shown in FIG. 1B).

The DC signal of (bl is the first
It is converted into a digital value by the A/D converter 9 in the figure,
The first memo January 6 in FIG. 1 is stored as a first memory value as shown in (d). In addition, (e) shows the state of the second memory value under control of the discharge time constant, the part shown by the broken line is the second memory value when the control of the present invention is not performed, and the part shown by the solid line is the state of the second memory value when the control of the present invention is not performed. 6 shows a second memory value when a means for temporarily shortening the discharge time constant of the second memory of the present invention is taken.

FIG. 3 shows the operating procedure of the embodiment of the present invention as a flowchart. That is, the operation starts, and in step 100, a digital value obtained by A/D converting the input signal is read, and in step 101, it is stored in the first memory 16 as a first memory value. Next, in step 102, the first memory value and the second memory value are compared, and if the first memory value is larger than the second memory value, in step 103, the first memory value and the second memory value are compared. A charging process is performed in which the condition that the difference is equal to or greater than a certain value is YES. Furthermore, step 10
In Step 3, the first memory value and the second memory value are compared, and if the difference is, for example, 6 dB or more, the process branches to YES, and in Step 104, the discharge time constant of the second memory is switched to a smaller value by a predetermined time. Furthermore, in step 105, the first memory value is stored in the second memory as it is, and charging is performed. Further, in step 106, the AGC loss amount is calculated using the second memory value, and in step 107, the gain of the amplifier is controlled using the calculation result of step 106.

In step 103, if there is no difference greater than a predetermined constant value, step 104 is omitted and charging continues.

On the other hand, in step 102, when the first memory value is smaller than the second memory value, in order to perform the discharge process, step 108 determines whether the current discharge time constant is in a normal state or is temporarily reduced in step 104. Determine whether it is in the switched state, and return Y if it is in the normal state.
The process branches to ES, and in step 109, a minute value corresponding to a predetermined discharge time constant of the second memory is subtracted from the second memory value, and this is set as a new second memory value. If the discharge time constant of the second memory is temporarily changed to a smaller value, the process branches to NO, and in step 110, the second memory value is changed to correspond to the smaller value of the discharge time constant of the second memory. Subtract a certain value and use this as the new second
Let the memory value be Further, in step 111, the time during which the discharge time constant is small (determined by the number of passes x the processing cycle) is counted, and in step 112, it is determined whether a predetermined period of time has elapsed, and the period of time has been completed. If so, in step 113, the state in which the second discharge time constant is changed to a small value is returned to the original state, and the discharge time constant is returned to the normal state.

By setting this to a minute value (a constant value), it can be made to correspond to the magnitude of the discharge time constant.

Thereafter, the AGC loss amount is calculated in step 10G using the second memory value as in the case of charging, and the gain of the amplifier is controlled in step 107 to perform AGC control.

(Effects of the Invention) As explained above, according to the present invention, when an excessive signal such as click noise or noise is added, AGC is greatly applied, and even after the noise has subsided, the gain of the amplifier is kept small, and the original This has the advantage that the disadvantage of the AGC circuit that the signal becomes small is eliminated, and the AGC control corresponds to the actual operation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the invention, FIG. 2 is a waveform diagram for explaining the invention in detail, and FIG. 3 is a flowchart showing the operation of one embodiment of the invention.

Claims (1)

[Claims] rectifying means for converting an input signal to the amplification system into a DC signal using a first discharge time constant; A/D conversion means for A/D converting the DC signal into a digital signal value; a first memory storing a signal value as a first memory value every predetermined time slot period; and a first memory storing the digital signal value from the first discharge time constant every predetermined time slot period. a second memory for storing a second memory value using a larger second discharge time constant; and a second memory for storing the first memory value of a certain time slot and the second memory value of a time slot immediately before the time slot. and a time constant switch for temporarily reducing the second discharge time constant by a longer time T than the time slot period when the difference exceeds a predetermined threshold. and gain control means for automatically controlling the gain of the amplification system based on the second memory value.