JPH0834449B2 - Automatic gain control device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain control device for compensating for a loss in a transmission system and a change in input signal level.

2. Description of the Related Art Conventionally, an automatic gain control device for keeping a constant output signal level has been emphasized when transmitting data or voice using a telephone line.

Hereinafter, the conventional automatic gain control device as described above will be described with reference to the drawings.

FIG. 5 shows the structure of a conventional automatic gain control device. In FIG. 5, 51 is an input terminal for inputting a signal,
52 is an output terminal that outputs a signal, 53 is a variable amplifier circuit that amplifies the input signal based on the gain setting value, 54 is an absolute value circuit that calculates the absolute value of the input signal, and 55 is the absolute value of the input signal within a fixed time A maximum value search circuit for searching for the maximum value of, and a gain control circuit 56 for setting the gain of the variable amplification circuit 53 based on the result obtained by the maximum value search circuit 55.

Regarding the automatic gain control device configured as described above,
The operation will be described below.

First, the input signal input from the input terminal 51 is amplified by the variable amplification circuit 53 based on the gain setting value from the gain control circuit 56 and output from the output terminal 52. The input signal input from the input terminal 51 is also sent to the absolute value circuit 54, converted into an absolute value, and output to the maximum value search circuit 55. The maximum value search circuit 55 finds the maximum value of the input signal that has been converted into an absolute value within a fixed time, and outputs the result to the gain control circuit 56. Here, it is appropriate that the length of the fixed time is about several hundred milliseconds to several seconds. The gain control circuit 56 keeps the past gain setting value when the maximum value is small and can be regarded as silence, but in other cases, when the maximum value is a large value near the maximum amplitude, the gain setting value is decreased and When the value is not silent but is small, the gain setting value is increased and the obtained gain setting value is output to the variable amplification circuit 53.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above-described configuration, the gain does not decrease until a certain time elapses even when an overflow occurs due to an excessive input signal. There is a problem that the signal becomes distorted and becomes difficult to demodulate, and in the case of a voice signal, it becomes a very audible sound.

In view of the above problems, the present invention provides an automatic gain control device capable of performing stable gain control even with an excessive input signal.

Means for Solving the Problems In order to achieve this object, an automatic gain control device of the present invention includes a variable amplification means for amplifying an input signal based on a set value to obtain an output signal, and the variable amplification means. The absolute value converting means for obtaining the absolute value of the output signal, the voice determining means for determining the presence / absence of the input signal based on the output signal of the absolute converting means, and the voice determining means are voiced. The time measuring means for accumulating the determined time length, the maximum value searching means for obtaining the maximum value of the output signal of the absolute value converting means while the time measuring means is accumulating, and the time measuring means for accumulating the fixed time. Upon completion, the gain control means for determining the set value of the gain based on the maximum value obtained by the maximum value searching means and outputting it to the variable amplifying means, and the variable amplifying means based on the output of the absolute value converting means Output signal is over Overflow detection means for sending a control signal to the timekeeping means when it is determined that the flow or overflow is likely to occur, and correcting the accumulated contents of the timekeeping means so that the timekeeping means finishes the accumulation earlier than a fixed time And a small signal detecting means for controlling to accelerate the total of the clocking means when the sound determining means determines that there is sound and the output signal of the absolute value converting means is smaller than a predetermined value. Is characterized by.

Action With this configuration, when the overflow detection means determines that it is overflowing or is about to overflow, the timekeeping means corrects the accumulated contents so that the accumulation of the fixed time is ended quickly, and thereby, an excessive input signal is generated. When an output signal is likely to overflow, it is immediately avoided, and even if the output signal overflows, it can be quickly cured. Also, the sound determination means and the time counting means accumulate only the time when there is sound,
By causing the maximum value searching means to find the maximum value each time a fixed time is reached, it is possible to prevent the gain control means from malfunctioning during silence or when pulse noise is input. Further, by controlling the small signal detecting means to speed up the accumulation of the time measuring means for a sound signal of a small level,
The start-up characteristics will be faster.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an automatic gain control device according to an embodiment of the present invention. In FIG. 1, 1 is an input terminal for inputting a signal, 2 is an output terminal for outputting a signal, 3 is a variable amplifier circuit for amplifying an input signal based on a gain setting value, 4 is an output signal of the variable amplifier circuit 3. An absolute value circuit for obtaining an absolute value, 5 is a maximum value search circuit for searching for the maximum absolute value, and 6 is a gain control circuit for setting the gain of the variable amplification circuit 3 based on the result obtained by the maximum value search circuit 5. , 7 is a voice determination circuit for determining whether the input signal is voiced or silent, 8 is a total of time lengths when the voice determination circuit 7 determines that the input signal is voiced, and the accumulated value is When the constant value is reached, the maximum value search circuit 5 is requested to obtain the maximum value, and 9 is a timer circuit of the timer circuit 8 when it is determined that the output signal of the variable amplifier circuit 3 is overflowing or is about to overflow. So that the cumulative value quickly becomes a constant value An overflow detection circuit for correcting the content of the accumulated value, and a small signal detection circuit 10 for controlling the accumulation of the time counting circuit 8 to be accelerated when the absolute value when the sound determination circuit 7 determines that there is sound is a small level. Is. FIG. 2 shows each threshold value of the automatic gain control device in one embodiment of the present invention. In FIG. 2, 21 is a zero level, 22 is the maximum amplitude level of the absolute value of the output signal, 23 is a voice determination threshold of the voice determination circuit 7, 24 is an undergain threshold of the gain control circuit 6, and 25 is gain control. An excessive gain threshold of the circuit 6, 26 is an overflow threshold of the overflow detection circuit 9, and 27 is a small signal threshold of the small signal detection circuit 10.

Regarding the automatic gain control device configured as described above,
The operation will be described below.

First, the input signal input from the input terminal 1 is amplified by the variable amplification circuit 3 based on the gain setting value from the gain control circuit 6 and output from the output terminal 2. The output signal of the variable amplification circuit 3 is also sent to the absolute value circuit 4 to be converted into an absolute value, and output to the maximum value search circuit 5, the sound determination circuit 7, the overflow detection circuit 9 and the small signal detection circuit 10. . The maximum value search circuit 5 obtains the maximum absolute value within the time period designated by the clock circuit 8 and outputs the result to the gain control circuit 6. The gain control circuit 5 determines that the gain is small if the maximum value is less than the excessive gain threshold 24 and increases the current gain setting value, and determines that the gain is large if the maximum value is greater than the excessive gain threshold 25 and presently. The gain setting value is reduced, and the obtained gain setting value is output to the variable amplifier circuit 3. If the absolute value is equal to or less than the half-sound threshold 23, the sound determination circuit 7 does nothing, and if the absolute value is equal to or greater than the sound determination threshold 23, the sound determination circuit 7 determines that there is sound. The time counting circuit 8 is controlled to advance the total. When the cumulative value reaches a constant value, the time counting circuit 8 controls the maximum value search circuit 5 to obtain the maximum absolute value from the start of the cumulative value until the constant value is reached. Here, it is appropriate that the constant value has a length of several hundred milliseconds to several seconds. The overflow detection circuit 9 detects if the absolute value exceeds the overflow threshold value 26.
The cumulative value of the clock circuit 8 is corrected so that the constant value is reached quickly. Here, the correction value of the cumulative value depends on the nature of the input signal, but it is suitable to set it so that the remaining time until a fixed value is from several milliseconds to several tens of milliseconds. In other words, if the remaining time to this fixed value is shortened, the overflow can be avoided immediately, but the gain may decrease too much. On the contrary, if it is made longer, the gain will not decrease too much, but it is possible to avoid the overflow. It may be slow, so it is necessary to adjust it appropriately. In the small signal detection circuit 10, when the sound determination circuit 7 determines that there is sound, and when the absolute value is less than the small signal detection threshold 27, control is performed so as to accelerate the cumulative total of the time counting circuit 8 so that the constant value is reached quickly. To

As described above, according to the present embodiment, when the overflow detection circuit 9 determines that the overflow has occurred or is about to overflow, the cumulative value of the time counting circuit 8 is corrected so that the fixed value is quickly reached. As a result, when an overflow is likely to occur, it can be immediately avoided, and even if an overflow should occur, it can be quickly controlled. In addition, the voice control circuit 7 and the timekeeping circuit 8 accumulate only voiced time, and the maximum value search circuit 5 is caused to obtain the maximum value each time the accumulated value reaches a certain value, whereby gain control is performed. Since the circuit 6 can perform gain control using information obtained from a meaningful signal, the gain is increased when there is no sound, and the gain is greatly decreased when pulse noise is input. Malfunctions can be prevented. Further, by providing the under-gain threshold 24 and the over-gain threshold 25 in the gain control circuit 6, the gain does not change when the maximum value is between the under-gain threshold 24 and the over-gain threshold 25, and the gain control is stabilized. Can be done Then, when the sound signal of a small level is present, the small signal detection circuit 10 controls so as to speed up the accumulation of the time counting circuit 8, whereby the rising characteristic for the small signal can be speeded up.

Another embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows the structure of an automatic gain control device according to another embodiment of the present invention. In the third, 31 is an input terminal, 32 is an output terminal, 33 is an analog / digital converter (hereinafter referred to as A / D converter), 34 is a micro-computer, and 35 is a digital / analog converter (hereinafter D / D converter). A converter).

Regarding the automatic gain control device configured as described above,
The operation will be described below.

First, the input signal input from the input terminal 31 is converted from an analog signal to a digital signal by the A / D converter 33 and input to the microcomputer 34. Then micro
The computer 34 processes the input signal and outputs it to the D / A converter 35. Then, the digital signal is sent to the D / A converter 3
It is converted into an analog signal by 5 and output from the output terminal 32.

FIG. 4 shows a flowchart of processing in the microcomputer 34. The threshold values used here are the same as those in FIG.

First, the digitized signal is input from the A / D converter 33 (step 401), amplified based on the gain setting value (step 402), and output to the D / A converter 35 (step 403). . The input signal is then absolute valued (step 40
4) Then, it is compared with the voice determination threshold 23 (step 405), and if it is determined that the voice determination threshold is less than 23, that is, no sound, the process ends (step 419). On the other hand, larger than the voice determination threshold 23,
In other words, if it is determined that there is sound, the timer is incremented (step 406), and the absolute value is further set to the small signal detection threshold 27.
(Step 419), if it is smaller than the small signal detection threshold value 27, it is judged to be a low level sound signal, the timer is incremented (step 420), the timer is compared with a constant value (step 407), and the constant value is maintained. If it is less than or equal to the value, the timer is still counting, so the absolute value is compared with the overflow threshold 26 (step 408), and if the absolute value is less than or equal to the overflow threshold 26, it is considered that no overflow occurs and the absolute value and the maximum value are exceeded. (Step 411). On the other hand, if the absolute value is larger than the overflow threshold value 26, it is determined that an overflow has occurred or is about to occur, and the timer is compared with the correction value (step 409). Is changed to the corrected value (step 410).
The absolute value is then compared to the maximum value (step 411),
If the absolute value is larger than the maximum value, the maximum value is changed to the absolute value (step 412), and the process ends (step 41).
9).

On the other hand, when comparing the timer with a fixed value (Step 40
9) If the timer is above a certain value, the timer has finished counting, so the maximum value found is the excessive gain threshold 25.
(Step 413), if the gain is over 25, it is judged that the gain is excessive, the gain setting value is lowered (step 418), and the maximum value is compared with the under-gain threshold 24 (step 413). 414) If it is below the under-gain threshold 24, it is judged that the gain is under-determined and the gain setting value is increased (step 417). Then the timer is cleared (Step 4
15), the maximum value is cleared (step 416), and the process ends (step 419). These series of operations are performed for each sampling frequency.

As described above, according to the present embodiment, by causing the microcomputer 34 to perform all signal processing, the circuit configuration becomes simpler and the cost can be reduced.

In the present embodiment, the signal processing was performed by the microcomputer 34, but the microcomputer 34
It may be a signal processor.

EFFECTS OF THE INVENTION The present invention, by providing the overflow detection means for controlling the timekeeping means, can be avoided immediately if an overflow is likely to occur, and can be quickly controlled even if an overflow should occur. By providing the clocking means for measuring the voiced time, it is possible to prevent the gain control means from malfunctioning when there is no sound or when pulse noise is input. Further, by providing a small signal detecting means for detecting a sound signal of a small level, it is possible to realize an excellent automatic gain control device capable of obtaining the effect of making the rising characteristic faster.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an automatic gain control device according to an embodiment of the present invention, FIG. 2 is a diagram showing respective threshold values thereof, and FIG. 3 is an automatic gain control device according to another embodiment of the present invention. Is a block diagram showing the configuration of FIG. 4, FIG. 4 is a flow chart of the microcomputer, and FIG. 5 is a block diagram showing the configuration of a conventional automatic gain control device. 3 ... Variable amplification circuit, 4 ... Absolute value circuit, 5 ... Maximum value search circuit, 6 ... Gain control circuit, 7 ... Voice determination circuit,
8 ... Clock circuit, 9 ... Overflow detection circuit, 10 ...
… Small signal detection circuit, 23 …… Voice judgment threshold, 24 …… Under-gain threshold, 25 …… Over-gain threshold, 26 …… Overflow threshold, 27 …… Small signal detection threshold.

Claims (2)

[Claims] 1. A variable amplifying means for amplifying an input signal based on a set value to obtain an output signal, an absolute value converting means for obtaining an absolute value of an output signal of the variable amplifying means, and an output of the absolute value converting means. The sound determination unit that determines the presence / absence of the input signal based on a signal, the time counting unit that accumulates the length of time that the sound determination unit determines that there is sound, and the time counting unit are cumulative. Between the maximum value searching means for finding the maximum value of the output signal of the absolute value converting means, and the set value of the gain based on the maximum value found by the maximum value searching means when the time counting means completes the accumulation of the fixed time. And a gain control means for outputting to the variable amplification means, and a control when it is determined that the output signal of the variable amplification means overflows or is likely to overflow based on the output of the absolute value conversion means. A signal is sent to the time measuring means, overflow detecting means for correcting the accumulated contents of the time measuring means so that the time measuring means completes the accumulation earlier than a fixed time, and the sound determining means determines that there is sound and An automatic gain control device, comprising: a small signal detecting means for controlling so as to speed up the accumulation of the time counting means when the output signal of the digitizing means is smaller than a predetermined value. 2. The first determination means for controlling the gain control means to increase the set value of the gain of the variable amplification means when it is determined that the maximum value obtained by the maximum value search means is smaller than the under-gain threshold. And a second judging means for controlling so as to decrease the current gain setting value of the variable amplifying means when it is judged that the maximum value is larger than the excessive gain threshold value. An automatic gain control device according to the paragraph.