JP2901899B2 - Automatic gain control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system or a voice system, which controls a gain of a variable gain amplifying circuit in accordance with an amplitude of an input signal so as to keep the amplitude of the output signal constant. The present invention relates to an automatic gain control device for suppressing.

[0002]

2. Description of the Related Art A conventional automatic gain control device capable of extracting a constant output signal while suppressing fluctuations of an input signal will be described below with reference to the drawings.

FIG. 11 is a block diagram of a conventional automatic gain control device. In FIG. 11, reference numeral 1 denotes a variable gain amplifying circuit for amplifying an input signal voltage according to a gain controlled by a control voltage, 2 denotes a peak detection circuit for detecting and holding a peak of an output voltage of the variable gain amplifying circuit 1, 21 Is a rectifier circuit for rectifying the input signal voltage, 22 is a hold circuit for holding the peak value of the rectified voltage rectified by the rectifier circuit 21, 3 is a DC amplifier circuit for outputting a voltage proportional to the difference between the input voltages, 4 Is a low-pass filter that removes high-frequency components of the output voltage of the DC amplifier circuit 3 and outputs an effective voltage; 51 is a resistor voltage dividing circuit that generates an appropriate reference voltage from the power supply potential Vcc; A first resistor, R
2 is a second resistor for dividing the power supply potential Vcc, 61 is a switching buffer circuit with a control terminal for switching between a state where the input signal passes through the variable gain amplifier circuit 1 and a state where it does not pass, 6
1A is an input terminal to which an input signal is directly input, 61B is an input terminal to which an output signal of the variable gain amplifier circuit 1 is input, and Y is an input terminal.
Is an output terminal of the automatic gain control device, Vref is a reference voltage output from the resistance voltage dividing circuit 51, Vx is a peak voltage output from the peak detection circuit 2, and Vc is a difference between the peak voltage Vx and the reference voltage Vref. DC amplifier circuit 3
A control voltage, which controls the variable gain amplifying circuit 1 by removing the ripple component by the low-pass filter 4
cc is a power supply voltage for driving the device.

The operation of the automatic gain control device configured as described above will be described below with reference to the drawings.

FIG. 12 shows an AGC of a conventional automatic gain control device.
FIG. 4 is a diagram showing (= Automatic Gain Control) characteristics. FIG. 12A is a correlation diagram between a control voltage Vc and a gain (= Gain) of a conventional automatic gain control device. In FIG. 12A, G0 is the maximum gain, and G9 is the minimum gain.

FIG. 12B is a correlation diagram between the peak voltage Vx of the DC amplifier circuit and the control voltage Vc when the reference voltage is kept constant. In FIG. 12B, Vx1 corresponds to FIG.
(A) is a peak voltage having a gain of 0 dB at the time of the reference voltage Vr1, and Vc1 is a control voltage for setting the gain of the variable gain amplifier circuit 1 to 0 dB at the time of the peak voltage Vx1.

FIG. 12C is a correlation diagram in which the voltage of the input signal and the voltage of the output signal of the conventional automatic gain control device are logarithmic values. In FIG. 12C, vin0 is the minimum value at which the AGC of the input signal voltage is valid, vin1 is the input signal voltage having a gain of 0 dB at the reference voltage Vr1 shown in FIG. 10, and vin9 is the AGC of the input signal voltage is valid. G0 is the maximum gain, and G9 is the minimum gain. v
Since the gain decreases as the input signal voltage increases with reference to in1, and the gain increases as the input signal voltage decreases, the amplitude of the output signal voltage can be kept constant.

Further, a control voltage Vc shown in FIG.
When it is 1, the gain is 0 dB as shown in FIG. When the reference voltage Vref input to the DC amplifier circuit 3 is changed from the standard reference voltage Vr1 shown in FIG. 10A to a reference voltage Vr3 higher than the standard, the peak voltage Vx1 for outputting the control voltage Vc1 becomes standard. , The input signal voltage is also shifted to the standard vin.
The gain becomes 0 dB from 1 to higher vin3. Conversely, the reference voltage Vref is changed to the reference voltage Vref shown in FIG.
When the voltage is changed to r2, the peak voltage Vx1 for outputting the control voltage Vc1 shifts to a lower side, so that the input signal voltage also has a gain of 0 dB at vin2 lower than the standard vin1. Therefore, the AGC characteristic of the automatic gain control device can be changed by changing the reference voltage Vref input to the DC amplifier circuit 3.

Next, a conventional automatic gain control device for audio will be described with reference to the drawings.

FIG. 13 is a circuit diagram of a conventional automatic gain control device for audio. 13, only the members newly added to the conventional automatic gain control device shown in FIG. 11 will be described. Reference numeral 7 denotes a clamp circuit that holds a constant voltage when the output voltage of the minute voltage detection circuit exceeds a predetermined value, 72 denotes a PNP transistor that conducts when the output voltage of the minute voltage detection circuit exceeds a predetermined value, and 73 denotes a clamp voltage value. The constant voltage power supply 8 to be determined is a minute voltage detecting circuit for increasing the output voltage and rectifying the output voltage as the input voltage decreases.

The operation of the automatic gain control apparatus for audio constructed as described above will be described below with reference to the drawings.

FIG. 14 is a diagram showing AGC characteristics of a conventional automatic gain control device for voice. FIG. 14A is a correlation diagram between an input signal voltage and a control voltage Vc of the conventional automatic gain control device for audio. FIG. 14B is a correlation diagram between an input signal voltage and an output signal voltage of the conventional automatic gain control device. FIG.
4 (a), L1 is the output voltage of the rectifier circuit 21 shown in FIG. 13, L2 is the output voltage of the minute voltage detection circuit 8 shown in FIG. 13, L3 is the output voltage of the clamp circuit 7 shown in FIG. 13, and vin1 is the figure. An input signal voltage having a gain of 0 dB at the time of the reference voltage Vr1 shown in FIG. 10, vin5 is an input signal voltage at which the output voltages of the minute voltage detecting circuit 8 and the rectifying circuit 21 shown in FIG. An input signal voltage Vc1 at which the output voltages of the voltage detection circuit 8 and the clamp circuit 7 are equal to each other is a control voltage at the time of the peak voltage Vx1, and is a control voltage corresponding to the input signal voltages vin1 and vin6 having a gain of 0 dB. . FIG.
In FIG. 4 (b), G0 is the maximum gain and G9 is the minimum gain.

When the input signal voltage is smaller than vin1, the gain approaches the maximum value G0 and eventually saturates. Even when the input signal voltage is extremely small, the gain remains maximum without the small voltage detection circuit 8, and noise increases. This small voltage detection circuit 8 generates a higher voltage than the DC amplifier circuit 3 shown in FIG. 13 when the input signal voltage is vin5 or less, so that the gain is reduced as shown in FIG. 14B. Further, in the case of only the minute voltage detection circuit 8, the clamp circuit 7 has a negative gain when the input signal voltage becomes smaller than vin6. Therefore, the clamp circuit 7 forcibly applies the control voltage to Vc1 at which the gain becomes 0 dB. Is provided.

According to the automatic gain control apparatus for audio having the above-mentioned AGC characteristic, a loud sound is moderated and a small sound is reduced to S / S.
The N ratio is improved and reproduced clearly.

[0015]

However, in the conventional automatic gain control device, since the change of the gain by the function of changing the reference voltage and the AGC on / off function are separated, control is not performed by a plurality of terminals. The first problem is that the gain must not be maintained at a constant value with respect to a change in the AGC characteristic when the reference voltage is variable, and the second problem is that the input signal level cannot be changed. The third problem is that the AGC characteristics cannot be set or stored freely, and the AGC on / off switching cannot be performed at high speed because it takes time to charge the capacitance of the low-pass filter. Had the problem of

The present invention solves the above-mentioned conventional problems, and includes a method of changing an AGC characteristic by modifying a reference voltage and an AGC characteristic.
A first object is to make it easy to control on / off switching, and a second object is to make the lower limit gain of the AGC characteristic constant, so that the AGC characteristic can be set and stored. A third object is to make AGC on / off switching at a high speed.

[0017]

According to the first aspect of the present invention, there is provided an automatic gain control apparatus comprising:
A variable gain amplifier circuit for amplifying or attenuating an input signal according to a gain controlled by a control voltage, a rectifier circuit for rectifying an output signal of the variable gain amplifier circuit, and a peak voltage of a rectified voltage rectified by the rectifier circuit , A reference voltage circuit that outputs a reference voltage that changes based on an external voltage, a DC amplification circuit that outputs the control voltage according to a difference between the peak voltage and the reference voltage, And a switching circuit for switching between the output signal of the variable gain amplifier circuit and the input signal based on the above.

According to the above configuration, since the reference voltage circuit includes the resistance voltage dividing circuit and the voltage control switch such as the MOS transistor, the AGC characteristic is changed by modifying the reference voltage and the AGC on / off switching is performed by one terminal. Can be performed.

According to a second aspect of the present invention, the configuration of the first aspect further includes a configuration further including a low-pass filter for removing a high-frequency component of the DC voltage from the control voltage output from the DC amplifier circuit. It is.

According to the above configuration, since the low-pass filter removes the high-frequency component of the control voltage for controlling the variable gain amplifier, the operation of the variable gain amplifier is stabilized.

According to a third aspect of the present invention, there is provided an automatic gain control device comprising: a variable gain amplifying circuit for amplifying or attenuating an input signal according to a gain controlled by a control voltage; A rectifier circuit for rectifying an output signal of the variable gain amplifier circuit, a low-pass filter for outputting an effective voltage of the rectified voltage rectified by the rectifier circuit, and a reference voltage circuit for outputting a reference voltage that changes based on an external voltage A DC amplifier circuit that outputs the control voltage according to the difference between the effective voltage and the reference voltage, and a switching circuit that switches between the output signal of the variable gain amplifier circuit and the input signal based on the reference voltage. Is provided.

According to the above configuration, since the reference voltage circuit is composed of a resistor voltage dividing circuit and a voltage control switch such as a MOS transistor, the change of the AGC characteristic by the correction of the reference voltage and the switching of the AGC on / off are performed at one terminal. Can be performed.

Further, since the low-pass filter also serves as a hold circuit, the number of elements can be reduced.

According to a fourth aspect of the present invention, there is provided an automatic gain control apparatus comprising: a variable gain amplifier circuit for amplifying or attenuating an input signal according to a gain controlled by a control voltage; A rectifier circuit for rectifying an output signal of the variable gain amplifier circuit to output a first rectified voltage; and a rectifier for reversing and rectifying a voltage of an input signal of the variable gain amplifier circuit to form a second rectified voltage. An output minute voltage detection circuit;
A clamp circuit that suppresses a second rectified voltage output from the minute voltage detection circuit to a predetermined value or less in accordance with the value of the reference voltage; a first rectified voltage output from the rectifier circuit and the minute voltage detection A hold circuit that outputs a peak voltage of a higher rectified voltage of the second rectified voltage output from the circuit and that is suppressed by the clamp circuit, a reference voltage circuit that supplies an appropriate reference voltage, A DC amplifier circuit that outputs the control voltage in accordance with a difference between the peak voltage output from the hold circuit and the reference voltage.

With the above configuration, the clamp circuit changes the voltage for clamping the output voltage of the minute voltage detection circuit according to the value of the reference voltage, so that the AGC gain becomes 0 dB when a minute signal is input. Can be corrected.

According to a fifth aspect of the present invention, in addition to the configuration of the fourth aspect, a configuration further comprising a low-pass filter for removing a high-frequency component of the DC voltage from the control voltage output by the DC amplifier circuit is added. It is.

With the above configuration, the low-pass filter removes the high-frequency component of the control voltage for controlling the variable gain amplifier circuit, so that the operation of the variable gain amplifier circuit is stabilized.

According to a sixth aspect of the present invention, in the configuration of the fourth or fifth aspect, a configuration is provided in which the clamp circuit has a DC amplifier circuit for amplifying the reference voltage.

With the above configuration, since the clamp circuit has the DC amplifier circuit, an appropriate clamp voltage can be generated.

According to a seventh aspect of the present invention, there is provided an automatic gain control apparatus comprising: a variable gain amplifying circuit for amplifying or attenuating an input signal according to a gain controlled by a control voltage; A rectifier circuit for rectifying an output signal of the variable gain amplifier circuit to output a first rectified voltage; and a rectifier for reversing and rectifying a voltage of an input signal of the variable gain amplifier circuit to form a second rectified voltage. An output minute voltage detection circuit;
A clamp circuit that suppresses a second rectified voltage output from the minute voltage detection circuit to a predetermined value or less in accordance with the value of the reference voltage; a first rectified voltage output from the rectifier circuit and the minute voltage detection A low-pass filter that outputs an effective voltage of the higher rectified voltage of the second rectified voltage output from the circuit and that is suppressed by the clamp circuit; a reference voltage circuit that supplies an appropriate reference voltage; A DC amplification circuit that outputs the control voltage in accordance with a difference between an effective voltage output from the low-pass filter and the reference voltage.

According to the above configuration, the clamp circuit changes the voltage for clamping the output voltage of the minute voltage detection circuit according to the value of the reference voltage, so that the AGC gain becomes 0 dB when a minute signal is input. Can be corrected.

Further, since the low-pass filter also serves as a hold circuit, the number of elements can be reduced.

According to an eighth aspect of the present invention, in the configuration of the seventh aspect, a configuration is provided in which the clamp circuit has a DC amplifier circuit for amplifying the reference voltage.

According to the above configuration, since the clamp circuit has the DC amplifier circuit, an appropriate clamp voltage can be generated.

According to a ninth aspect of the present invention, there is provided an automatic gain control device comprising: a variable gain amplifying circuit for amplifying or attenuating an input signal according to a gain controlled by a control voltage; A switching circuit that switches and outputs an input signal and an output signal of the variable gain amplifier circuit, a rectifying circuit that rectifies the output signal of the switching circuit, and a switching circuit that opens and closes a rectified voltage rectified by the rectifying circuit, A hold circuit that outputs the peak voltage of the rectified voltage via the switching circuit; an analog / digital conversion circuit that converts the peak voltage into a digital signal; and a storage circuit that stores output data of the analog / digital conversion circuit. A digital / analog conversion circuit for converting data read from the storage circuit into an analog signal; It is an arrangement and a DC amplifying circuit for outputting the control voltage according to a difference between the output voltage of the converter circuit.

With the above configuration, the analog / digital conversion circuit digitizes the peak voltage output from the hold circuit, the storage circuit stores the digitized peak voltage, and the digital / analog conversion circuit digitizes and stores the digitized peak voltage. Since the peak voltage is returned to analog and a reference voltage is generated, the set value of the reference voltage can be stored and reproduced at any time.

According to a tenth aspect of the present invention, the fourth object is achieved. According to the ninth aspect of the present invention, the output of the digital / analog conversion circuit is provided while the switching circuit is outputting the input signal. This configuration adds a configuration further including a charging circuit that charges the hold circuit with a voltage.

With the above configuration, while the variable gain amplifying circuit is not operating, the hold circuit is charged by the charging circuit, and thus is activated as soon as the variable gain amplifying circuit starts operating.

According to an eleventh aspect of the present invention, in addition to the configuration of the ninth or tenth aspect, a configuration further comprising a low-pass filter for removing a high-frequency component of the DC voltage from the control voltage output by the DC amplifier circuit is added. Is what you do.

With the above configuration, the low-pass filter removes the high-frequency component of the control voltage for controlling the variable gain amplifier circuit, so that the operation of the variable gain amplifier circuit is stabilized.

According to a twelfth aspect of the present invention, in the configuration of any of the ninth to eleventh aspects, the storage circuit is a nonvolatile memory.

According to a thirteenth aspect of the present invention, in the configuration according to any one of the ninth to eleventh aspects, the storage circuit includes a volatile memory and a backup circuit for holding the contents of the volatile memory. It is assumed that.

[0043]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of the automatic gain control device according to the first embodiment of the present invention. FIG. 2 is a circuit diagram of the automatic gain control device according to the first embodiment of the present invention. 1 and 2, the same members as those in the configuration diagram of the conventional automatic gain control device shown in FIG. 1 and 2, reference numeral 5 denotes a reference voltage circuit for generating a reference voltage Vref for generating a control voltage Vc based on a difference from a peak voltage Vx;
Is a switching circuit for switching between a state of passing through the variable gain amplifier circuit 1 and a state of not passing therethrough, and Vctl is an external voltage applied to the reference voltage circuit 5 and controlling the switching circuit 6. FIG.
, 52 is an n-channel MOS transistor that controls the switching circuit 6, and 62 is controlled by the reference voltage Vref generated by the reference voltage circuit 5 and the switching voltage Vsw of the switching circuit 6, and the reference voltage Vref is higher than the switching voltage Vsw. In this case, the voltage comparator circuit outputs the voltage “H”, and otherwise outputs the voltage “L”.

A feature of the first embodiment shown in FIG. 1 is that the AGC characteristic can be changed by changing the reference voltage Vref and AGC on / off switching can be performed by one external terminal.

The switching operation of the automatic gain control device configured as described above will be described below.

As the external voltage Vctl for performing AGC on / off switching, for example, a voltage “H” or a voltage “L” is input digitally under the control of a microcomputer or the like from outside the automatic gain control device.

First, when the external voltage Vctl is "L",
Since the n-channel MOS transistor 52 is shut off,
The reference voltage Vref has a value determined by the formula Vcc × R2 / (R1 + R2), and the reference voltage Vref can be changed by changing the value of the first resistor R1 or the second resistor R2. Further, the voltage comparator circuit 62 compares the reference voltage Vref with the switching voltage Vsw. When the switching voltage Vsw is determined so that the reference voltage Vref becomes higher than the switching voltage Vsw, the voltage comparator circuit 62 outputs the voltage “H”. Therefore, the input terminal 61B of the switching buffer circuit with control terminal 61 is selected, and the output signal from the automatic gain control device is output.

Next, when the external voltage Vctl is "H",
Since the n-channel MOS transistor 52 conducts, the reference voltage Vref becomes lower than the switching voltage Vsw,
Since the output of the voltage comparator circuit 62 becomes the voltage “L”, the input terminal 61A of the switching buffer circuit with control terminal 61 is selected, and the input signal is directly output.

As a feature of this embodiment, the reference voltage Vre
The setting of the AGC characteristic by the control of f and the AGC on / off function can be performed by one terminal. When the present automatic gain control device is integrated into an IC, the external voltage Vctl or the reference voltage Vref may be used as an external terminal.

The reference voltage circuit 5 has a switching voltage Vs
Any circuit configuration is possible as long as the circuit configuration can switch and control a voltage equal to or lower than w and a DC voltage higher than w. The same effect can be obtained by a method of supplying Vref, or by replacing the n-channel MOS transistor 52 with an npn bipolar transistor or an electromagnetic relay.
In the above, the reference voltage Vref is the switching voltage V
Although the description has been made assuming that the variable gain amplifier circuit 1 is turned off when the voltage is lower than sw, the combination of the polarities of the n-channel MOS transistor 52, the voltage comparator circuit 62, and the switching buffer circuit 61 causes the reference voltage Vre
It is obviously possible to operate the variable gain amplifier circuit 1 to be turned off when f is higher than the switching voltage Vsw.

Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a circuit diagram of the automatic gain control device according to the second embodiment of the present invention. In FIG. 3, FIG.
The same members as those in the circuit diagram of the automatic gain control device according to the first embodiment shown in FIG. FIG.
, The low-pass filter 4 is connected in series between the rectifier circuit 21 and the DC amplifier circuit 3 and
And outputs an effective voltage Vx2 of the input rectified voltage. The DC amplifier 3 amplifies the difference between the reference voltage Vref of the reference voltage circuit 5 and the effective voltage Vx2 to generate a control voltage Vc. In this embodiment, the variable gain amplifier circuit 1, the rectifier circuit 2, the low-pass filter 4, and the switching circuit 6 are added, and the DC amplifier circuit 4 has the highest voltage or average voltage among the multi-input execution voltages Vx2. A configuration in which a plurality of variable gain amplifier circuits 1 to which values are input can be controlled can also be supported.

As a feature of this embodiment, similarly to the first embodiment, the setting of the AGC characteristic by controlling the reference voltage Vref and the AGC on / off function can be performed by one terminal.

Further, since the hold circuit 22 is also used by the low-pass filter 4, the configuration of the device is simplified.

Hereinafter, a third embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a configuration diagram of the automatic gain control device according to the third embodiment of the present invention. FIG. 5 shows a third embodiment of the present invention.
FIG. 3 is a circuit diagram of an automatic gain control device according to the embodiment. In FIGS. 4 and 5, the same members as those in the circuit diagram of the conventional automatic gain control device for audio shown in FIG. In FIG. 4, the variable gain amplifying circuit 1 has the gain characteristic of FIG. 12 (a). Therefore, when the input signal is a very small voltage, as shown by the characteristic of L1 in FIG. The output drops. Also,
As shown by the characteristic of L2 in FIG. 14A, the output voltage of the minute voltage detection circuit 8 which outputs a higher voltage as the input signal voltage becomes lower than the predetermined voltage is combined with the output voltage of the rectifier circuit 21. Thus, the peak voltage Vx, which is the output voltage of the hold circuit 22, is the higher of the two output voltages. As the peak voltage Vx increases, the control voltage Vc via the DC voltage circuit 3 and the low-pass filter 4 increases, and the gain of the variable gain amplifier circuit 1 decreases. Further, in order to prevent a gain below a predetermined input level from excessively decreasing, a minute voltage detecting circuit 8 is provided.
As shown by the characteristic of L3 in FIG.
It is limited by the clamp circuit 7. Next, when the AGC characteristic is changed by changing the reference voltage Vref, the clamp circuit 7 changes the clamp voltage in accordance with the reference voltage Vref, and the lower limit gain at the time of inputting a predetermined minute signal changes the reference voltage Vref. Can be corrected so as to be constant according to.

As a feature of the third embodiment shown in FIG.
In order to prevent the deterioration of the S / N ratio due to an increase in the gain of the AGC characteristic when a small signal is input, a small voltage detection circuit 8 and a clamp circuit 7 are provided to reduce the gain of the AGC characteristic.

Further, by changing the reference voltage Vref, A
The GC characteristics are changed, and the clamp voltage is changed to the reference voltage Vr.
AGC at the time of inputting a small signal to change according to ef
Correction can be performed so that the lower limit gain of the characteristic becomes constant.

In FIG. 5, reference numeral 71 denotes a clamp DC amplifier circuit which amplifies the reference voltage Vref to generate a clamp voltage. The clamp circuit 7 includes a clamp DC amplifier circuit 71 to which the reference voltage Vref is input, and a PNP transistor 72 to which the amplified reference voltage Vref is applied to the base electrode.

The operation of the automatic gain control device configured as described above will be described below with reference to the drawings. FIG. 10 is an AGC characteristic diagram of the automatic gain control device according to the third embodiment of the present invention. FIG. 10A shows a reference voltage Vref and a gain of 0d of the automatic gain control device according to the third embodiment of the present invention.
FIG. 6 is a correlation diagram with a voltage of an input signal that becomes B. FIG.
(B) is a correlation diagram between the voltage of the input signal and the voltage of the output signal of the automatic gain control device according to the third embodiment of the present invention. In FIG. 10A, Vr1 is a standard reference voltage,
Vr2 is a reference voltage lower than the standard, Vr3 is a reference voltage higher than the standard, and vin1 is 0d at the reference voltage Vr1.
An input signal voltage having a gain of B, vin2 is a reference voltage Vr
2, the input signal voltage that results in a gain of 0 dB,
Is an input signal voltage having a gain of 0 dB at the reference voltage Vr3. In FIG. 10B, vin1, vin
2 and vin3 are the same as above. vin5 is an input signal voltage at which the output voltages of the minute voltage detection circuit 8 and the rectifier circuit 21 are equal, vin6 is an input signal voltage at which the output voltages of the minute voltage detection circuit 8 and the clamp circuit 7 are equal, G0
Is the maximum gain and G9 is the minimum gain.

First, when the reference voltage Vref is the standard reference voltage Vr1 shown in FIG. 10A, the output voltage of the rectifier circuit 21 is applied to an input signal larger than the input signal voltage Vin5 shown in FIG. Is higher than the output voltage of the minute voltage detection circuit 8, and this output voltage is output and coupled by the emitter follower. The output of the rectifier circuit 2 is output via the hold circuit 22 as the peak voltage Vx.

Next, for an input signal whose input signal voltage is lower than the input signal voltage Vin5 shown in FIG. 14A, the output of the minute voltage detection circuit 8 becomes higher than the output of the rectifier circuit 21. The peak voltage Vx via the circuit 22
Therefore, the output voltage of the minute voltage detection circuit 8 increases as the input signal voltage decreases. Therefore, the peak voltage Vx and the control voltage Vc increase, and the gain attenuates as shown in FIG. When the output voltage of the clamp circuit 7 is added to the output voltage of the minute voltage detection circuit 8, the excessive output voltage of the minute voltage detection circuit 8 is clamped at the output voltage of the clamp circuit 7. Therefore, when the voltage of the input signal is lower than the input signal voltage Vin6 shown in FIG. 14A, the gain becomes 0 dB even if a very small signal voltage is input, and the AGC characteristic is kept constant regardless of the amplitude of the input signal. can do.

Next, in the case where the reference voltage Vref is set to Vr3 shown in FIG. 10A, which is higher than the standard voltage, if the input signal voltage is vin1, the DC voltage is passed through the DC amplification circuit 3 and the low-pass filter 4. Since the control voltage Vc is low, AG
Although the gain of the C characteristic increases, if the clamp voltage has the same value as described above, the gain at the time of minute input also increases. In order to prevent this phenomenon, the clamp voltage is set higher than the case of the standard reference voltage Vr1 through the clamp DC amplifying circuit 71 having the reference voltage Vref as an input value and the pnp bipolar transistor 72, so that the predetermined voltage vin6 The lower limit gain at the time of the following minute signal input is V
The gain of 0 dB can be maintained as in the case where ref is the standard reference voltage Vr1.

Next, when the reference voltage Vref is set to Vr2, which is lower than the standard, the operations and voltage changes of the respective parts are the reverse of the above, and the clamp voltage is set lower than that in the case of the standard reference Vr1. The lower limit gain can be maintained at the same gain of 0 dB as in the standard case.

By adding the variable gain amplifying circuit 1 and the peak detecting circuit 2, a plurality of variable gains to which the highest voltage or the average value of the multi-input peak voltage Vx is input to the DC amplifying circuit 3 A configuration that can control the amplifier circuit 1 can also be supported.

Hereinafter, a fourth embodiment of the present invention will be described with reference to the drawings. FIG. 6 is a circuit diagram of an automatic gain control device according to a fourth embodiment of the present invention. In FIG. 6, FIG.
The same members as those in the circuit diagram of the automatic gain control device according to the third embodiment of the present invention shown in FIG. In FIG. 6, only differences from the third embodiment will be described. As in the second embodiment, the low-pass filter 4 is connected in series between the rectifier circuit 21 and the DC amplifier circuit 3. , A rectified voltage output by the rectifier circuit 21 is input, and an effective voltage Vx of the input rectified voltage is input.
2 is output. The DC amplifier circuit 3 is configured to amplify the difference between the effective voltage Vx2 and the reference voltage Vref by DC to generate a control voltage Vc.

As a feature of this embodiment, the reference voltage Vre
Even if f is changed, the lower limit gain at the time of inputting a small signal of a predetermined value or less can be maintained at a constant value by changing both of the clamp voltages.

Further, since the hold circuit 22 is also used by the low-pass filter 4, the configuration of the device is simplified.

The variable gain amplifying circuit 1 and the rectifying circuit 2
1. By adding the low-pass filter 4 and the switching circuit 6, the multi-input effective voltage Vx
It is possible to cope with a configuration in which the highest voltage or the average value of the two is input and the plurality of variable gain amplifier circuits 1 can be controlled.

Hereinafter, a fifth embodiment of the present invention will be described with reference to the drawings. FIG. 7 is a configuration diagram of an automatic gain control device according to a fifth embodiment of the present invention. FIG. 8 shows a fifth embodiment of the present invention.
FIG. 3 is a circuit diagram of an automatic gain control device according to the embodiment. 7 and 8, only members newly added to the automatic gain control device according to the first embodiment of the present invention shown in FIG. 1 will be described. 7 and 8, reference numeral 9 denotes an A / D conversion circuit that digitizes the peak voltage Vx output from the hold circuit 22, and 10A denotes a storage circuit that stores the peak voltage Vx digitized by the A / D conversion circuit 9. , 10
B is a semiconductor memory such as an SRAM, and 11 is a storage circuit 10A.
Digitized peak voltage Vx stored by
, A charging circuit for charging the capacity of the hold circuit 22, a switching circuit 13 for opening and closing the hold circuit 22, a reference numeral 14 for the A / D conversion circuit 9, a storage circuit 10A, A control circuit 15 controls the D / A conversion circuit 11, the charging circuit 12, the switching circuit 13, and the switching circuit 6, and a backup circuit 15 for a storage circuit such as an SRAM that requires a backup power supply. In addition,
When a non-volatile memory such as an EEPROM is used as the semiconductor memory 10B, the backup circuit 15 is not required. The operation of the automatic gain control device configured as described above will be described below.

First, the switching circuit 6 is controlled by the control circuit 14.
When the input terminal 6A is selected and the switching circuit 13 is closed, the input signal is supplied to the rectifier circuit 21 and the hold circuit 2
2, a peak voltage Vx is generated and an A / D conversion circuit 9
, And the digitized data Vx is stored in the storage circuit 10A including the backup circuit 15.

Next, the data Vx of the storage circuit 10A is set to D /
The restored voltage is restored by the A conversion circuit 11, and the restored voltage is input to the DC amplifier circuit 4 as the reference voltage Vref.
Input voltage Vx of A / D conversion circuit 9 and D / A conversion circuit 11
Has an always equal relationship with the output voltage Vref of
The number of bits is ensured so that the quantization error of the / D conversion circuit 9 can be ignored.

Next, the switching circuit 6 is controlled by the control circuit 14.
Is selected as the input terminal 6B, and an input signal is input to the DC amplifier circuit 3 via the variable gain amplifier circuit 1, the rectifier circuit 21, and the hold circuit 22. When the peak voltage Vx is equal to the reference voltage Vref, the peak voltage Vx, the reference voltages Vref and Vc, or the gain of the variable gain amplifier circuit 1 is adjusted so that the gain of the variable gain amplifier circuit 1 becomes 0 dB with respect to the control voltage Vc. If the relationship with
The gain converges to 0 dB due to the operating characteristics of the GC. In addition,
When the peak voltage Vx is equal to the reference voltage Vref,
The gain of the variable gain amplifier circuit 1 is 0 d with respect to the control voltage Vc.
B, the relationship of the gain of the variable gain amplifier circuit 1 is assumed, but the gain of the variable gain amplifier circuit 1 is arbitrary NdB.
(Where N indicates a real number), it is possible to obtain N by the same standard input signal by using the same procedure as described above.
AGC characteristics having a gain of dB can be realized.

Therefore, the reference voltage Vref can be stored, and the AGC characteristic can be set for an arbitrary input signal.

Next, the switching circuit 6 is controlled by the control circuit 14.
Is selected as the input terminal 6A, the switching circuit 13 is opened, and AG
When the state is turned off, the capacitance of the hold circuit 22 is charged through the charging circuit 12 so that the peak voltage Vx becomes equal to the reference voltage Vref. When the switching circuit 6 switches from off to on, the charging circuit 12
Since the output is brought into a high impedance state by the control circuit 14 and the switching circuit 13 is closed, the peak voltage Vx is switched to the driving by the rectifier circuit 21 again.

Since the time for charging the hold circuit 22 via the rectifier circuit 21 at the time of switching the AGC from off to on can be omitted, the automatic gain control device can instantaneously stabilize and perform high-speed switching. Since the charge of the hold circuit 22 occupying most of the switching time has been completed in advance, the rise time until the AGC characteristics are stabilized can be shortened, so that high-speed switching from AGC off to on can be realized. Note that switching from AGC on to off is sufficiently fast that no countermeasure is required.

Hereinafter, a sixth embodiment of the present invention will be described with reference to the drawings. FIG. 9 is a circuit diagram of the automatic gain control device according to the sixth embodiment of the present invention. In FIG. 9, FIG.
Only the members newly added to the automatic gain control device according to the fifth embodiment of the present invention will be described. In FIG. 9, reference numeral 16 denotes a reference voltage circuit for setting a reference gain, and Vref2 denotes a second control voltage for setting a reference gain. Switching buffer circuit 61 with control terminal
The second control voltage Vref2, which is the output voltage of the reference voltage circuit 16, and the control voltage Vc, which is the output voltage of the low-pass filter, are input to the variable gain amplifier circuit 1, and the second control voltage Vref2 or the control voltage Vc is input.

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

First, the input terminal of the switching buffer circuit 61 is selected to 61A, and the gain of the variable gain control circuit 1 is set to 0 dB by the second control voltage Vref2.

Next, a standard input signal for setting the AGC characteristic to 0 dB is input, and the peak voltage Vx via the rectifier circuit 21 and the hold circuit 22 is converted into data Vx by the A / D converter 9. It is stored in the semiconductor memory 10B.

Next, the data Vx is read out and the D / A conversion circuit 11 generates the reference voltage Vref. The peak voltage Vx and the reference voltage Vref are always equal, and it is necessary to secure a data length such that a quantization error due to digitization is sufficiently small.

Next, when the switching buffer circuit 61 with a control terminal is selected as the input terminal 61B and the standard input signal is input, the peak voltage Vx and the reference voltage Vref have the same relationship, so that the variable gain control circuit Since the relationship between the control voltage Vc and the gain is determined so that the gain of 1 becomes 0 dB, the peak voltage Vx via the rectifier circuit 21 and the hold circuit 22 becomes the reference voltage Vc as the operation characteristic of the AGC.
It converges to a voltage equal to ref. When a semiconductor memory 10B having a large storage capacity is used, a plurality of standard signals can be set, and a standard signal can be read out from the standard signals to change the control characteristic of the AGC gain.

As a feature of this embodiment, as in the fifth embodiment, the reference voltage Vref can be stored, and the AGC characteristics can be set for an arbitrary input signal.

Further, since the reference voltage circuit 16 having a smaller number of elements than the switching circuit 13 is used, the structure is simplified.

[0083]

As described above, according to the automatic gain control device according to the first aspect of the present invention, the change of the reference voltage and the automatic gain control
Since the C on / off function can be realized by one terminal, control for changing the reference voltage and switching the operation of the automatic gain control device becomes easy.

Further, since the number of terminals can be reduced when an IC is formed, the package cost can be reduced.

According to the automatic gain control device according to the second aspect of the present invention, the effect of the automatic gain control device according to the first aspect of the present invention is obtained, and the operation of the variable gain amplifying circuit is stabilized, so that the AGC characteristic is improved. It will be even better.

According to the automatic gain control device according to the third aspect of the present invention, the effect of the automatic gain control device according to the first aspect of the present invention can be obtained, and the device can be easily manufactured because the number of elements is reduced.

According to the automatic gain control device of the fourth aspect, when a small signal is input, the AGC gain becomes 0d.
B can be corrected so that a stable A
GC characteristics can be realized.

According to the automatic gain control device according to the fifth aspect of the present invention, the effect of the automatic gain control device according to the fourth aspect of the present invention can be obtained, and the operation of the variable gain amplifier circuit is stabilized. It will be even better.

According to the automatic gain control device according to the sixth aspect of the present invention, not only the effect of the automatic gain control device according to the fourth or fifth aspect of the invention can be obtained, but also an appropriate clamp voltage can be generated. AGC characteristics are further improved.

According to the automatic gain control device according to the seventh aspect of the present invention, the effect of the automatic gain control device according to the fourth aspect of the present invention can be obtained, and the number of elements is reduced, so that the device can be easily manufactured.

According to the automatic gain control device according to the eighth aspect of the present invention, the effect of the automatic gain control device according to the seventh aspect of the invention can be obtained, and an appropriate clamp voltage can be generated. The characteristics are further improved.

According to the automatic gain control device of the ninth aspect, the set value of the reference voltage can be stored and reproduced, so that the AGC characteristic according to the purpose of use can be set.

Further, when the IC is formed, the variation in the manufacturing process can be suppressed and the uniform AG can be suppressed by programming with a standard waveform by, for example, an IC tester in the inspection process.
C characteristics can be obtained.

According to the automatic gain control device of the tenth aspect of the present invention, the effect of the automatic gain control device of the ninth aspect of the present invention can be obtained, and in addition, the AGC operates immediately after the start of the variable gain amplifying circuit. High-speed on / off switching can be performed.

According to the automatic gain control device according to the eleventh aspect, the effect of the automatic gain control device according to the ninth or tenth aspect can be obtained, and the operation of the variable gain amplifier circuit is stabilized. The characteristics are further improved.

According to the automatic gain control device according to the twelfth aspect, the effects of the automatic gain control device according to any one of the ninth to eleventh aspects can be obtained, and even if the power is turned off. Since the stored data is retained, it can be easily reset.

Further, since the memory is nonvolatile, a backup circuit is not required.

According to the automatic gain control device according to the thirteenth aspect, the effect of the automatic gain control device according to any one of the ninth to eleventh aspects can be obtained, and further, data is written to the storage circuit. The time and the time for reading data from the storage circuit are shortened.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an automatic gain control device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of the automatic gain control device according to the first embodiment of the present invention.

FIG. 3 is a circuit diagram of an automatic gain control device according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram of an automatic gain control device according to a third embodiment of the present invention.

FIG. 5 is a circuit diagram of an automatic gain control device according to a third embodiment of the present invention.

FIG. 6 is a circuit diagram of an automatic gain control device according to a fourth embodiment of the present invention.

FIG. 7 is a configuration diagram of an automatic gain control device according to a fifth embodiment of the present invention.

FIG. 8 is a circuit diagram of an automatic gain control device according to a fifth embodiment of the present invention.

FIG. 9 is a circuit diagram of an automatic gain control device according to a sixth embodiment of the present invention.

FIG. 10 is a diagram showing AGC characteristics of the automatic gain control devices according to the third embodiment and the fourth embodiment of the present invention.
(A) shows the reference voltage Vref and the gain of 0d of the automatic gain control devices according to the third and fourth embodiments of the present invention.
6 is a correlation diagram with an input signal voltage B. FIG. (B) is a correlation diagram showing the input signal voltage and the output signal voltage of the automatic gain control device according to the third embodiment and the fourth embodiment of the present invention as logarithmic values.

FIG. 11 is a circuit diagram of a conventional automatic gain control device.

FIG. 12 is a diagram showing AGC characteristics of a conventional automatic gain control device. (A) is a correlation diagram between the control voltage Vc and the gain of the conventional automatic gain control device. (B) is a correlation diagram between the peak voltage Vx of the DC amplifier circuit and the control voltage Vc when the reference voltage is kept constant. (C) is a correlation diagram showing the input signal voltage and the output signal voltage of the conventional automatic gain control device as logarithmic values.

FIG. 13 is a circuit diagram of a conventional automatic gain control device for audio.

FIG. 14 is a diagram showing AGC characteristics of a conventional automatic gain control device for audio. (A) is a correlation diagram between an input signal voltage and a control voltage Vc of the conventional automatic gain control device for audio.
(B) is a correlation diagram showing the input signal voltage and the output signal voltage of the conventional automatic gain control device for voice as logarithmic values.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 variable gain increase circuit 2 peak detection circuit 21 rectifier circuit 22 hold circuit 3 DC amplifier circuit 4 low-pass filter 5 reference voltage circuit 51 resistance voltage divider circuit 52 n-channel MOS transistor R1 first resistor R2 second resistor Reference Signs List 6 switching circuit 61 switching buffer circuit with control terminal 6A input terminal 6B input terminal 61A input terminal 61B input terminal 62 voltage comparator circuit Y output terminal 7 clamp circuit 71 clamp DC amplifier circuit 72 PNP transistor 73 constant voltage power supply 8 micro voltage detection circuit 9 A / D conversion circuit 10A storage circuit 10B semiconductor memory 11 D / A conversion circuit 12 charging circuit 13 switching circuit 14 control circuit 15 backup circuit 16 reference voltage circuit Vc control voltage Vx peak voltage Vx2 effective voltage Vref reference voltage Vre 2 Control voltage Vctl External voltage Vcc Power supply voltage Vsw Switching voltage Vr1 Standard reference voltage Vr2 Reference voltage lower than standard Vr3 Reference voltage higher than standard vin0 Minimum value at which AGC of input signal voltage is valid vin1 0 dB at reference voltage Vr1 The input signal voltage vin2 having a gain of 0 dB at the time of the reference voltage Vr2 vin3 The input signal voltage vin5 having a gain of 0 dB at the time of the reference voltage Vr3 Vin5 The output voltage of the minute voltage detecting circuit 8 and the rectifying circuit 21 is Equal input signal voltage vin6 Input signal voltage vin9 at which the output voltages of the minute voltage detection circuit 8 and the clamp circuit 7 become equal Maximum value at which the AGC of the input signal voltage is valid G0 Maximum gain G9 Minimum gain Vx1 0 dB at the time of the reference voltage Vr1 The peak of the gain Voltage Vc1 Control voltage at peak voltage Vx1 L1 Output voltage of rectifier circuit 21 L2 Output voltage of minute voltage detection circuit 8 L3 Output voltage of clamp circuit 7

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-56-140714 (JP, A) JP-A-5-191180 (JP, A) JP-A-4-150523 (JP, A) JP-A-60-140 152137 (JP, A) JP-A-5-14089 (JP, A) JP-A-61-161010 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H03G 3/30

Claims (13)

(57) [Claims] A variable gain amplifier for amplifying or attenuating an input signal according to a gain controlled by a control voltage; a rectifier circuit for rectifying an output signal of the variable gain amplifier circuit; A hold circuit that outputs a peak voltage of a rectified voltage; a reference voltage circuit that outputs a reference voltage that changes based on an external voltage; and a DC amplifier circuit that outputs the control voltage according to a difference between the peak voltage and the reference voltage. An automatic gain control device comprising: a switching circuit that switches between an output signal of the variable gain amplifier circuit and the input signal based on the reference voltage. 2. The automatic gain control device according to claim 1, further comprising a low-pass filter that removes a high-frequency component of the DC voltage from the control voltage output by the DC amplifier circuit. 3. A variable gain amplifying circuit for amplifying or attenuating an input signal according to a gain controlled by a control voltage; a rectifying circuit for rectifying an output signal of the variable gain amplifying circuit; A low-pass filter that outputs an effective voltage of a rectified voltage; a reference voltage circuit that outputs a reference voltage that changes based on an external voltage; and a DC that outputs the control voltage according to a difference between the effective voltage and the reference voltage. An automatic gain control device comprising: an amplifier circuit; and a switching circuit that switches between an output signal of the variable gain amplifier circuit and the input signal based on the reference voltage. 4. A variable gain amplifying circuit for amplifying or attenuating an input signal according to a gain controlled by a control voltage, and a rectifying circuit for rectifying an output signal of the variable gain amplifying circuit and outputting a first rectified voltage. A minute voltage detection circuit that reverses and rectifies the voltage of the input signal of the variable gain amplifier circuit and outputs a second rectified voltage; and a second rectified voltage output from the minute voltage detection circuit. A first rectified voltage output from the rectifier circuit and a second rectified voltage output from the minute voltage detection circuit and suppressed by the clamp circuit. A hold circuit that outputs a peak voltage of the higher one of the rectified voltages, a reference voltage circuit that supplies an appropriate reference voltage, and a peak voltage that is output from the hold circuit. An automatic gain control device, comprising: a DC amplifier circuit that outputs the control voltage according to a difference from the reference voltage. 5. The automatic gain control device according to claim 4, further comprising a low-pass filter that removes a high-frequency component of the DC voltage from the control voltage output by the DC amplification circuit. 6. The automatic gain control device according to claim 4, wherein the clamp circuit has a DC amplifier circuit that amplifies the reference voltage. 7. A variable gain amplifier circuit for amplifying or attenuating an input signal according to a gain controlled by a control voltage, and a rectifier circuit for rectifying an output signal of the variable gain amplifier circuit and outputting a first rectified voltage. A minute voltage detection circuit that reverses and rectifies the voltage of the input signal of the variable gain amplifier circuit and outputs a second rectified voltage; and a second rectified voltage output from the minute voltage detection circuit. A first rectified voltage output from the rectifier circuit and a second rectified voltage output from the minute voltage detection circuit and suppressed by the clamp circuit. A low-pass filter that outputs an effective voltage of the higher one of the rectified voltages, a reference voltage circuit that supplies an appropriate reference voltage, and an effective voltage that is output from the low-pass filter. An automatic gain control device comprising: a DC amplifier circuit that outputs the control voltage in accordance with a difference between a voltage and the reference voltage. 8. The automatic gain control device according to claim 7, wherein said clamp circuit has a DC amplifier circuit for amplifying said reference voltage. 9. A variable gain amplifying circuit for amplifying or attenuating an input signal according to a gain controlled by a control voltage, a switching circuit for switching and outputting an input signal and an output signal of the variable gain amplifying circuit, A rectifier circuit for rectifying an output signal of the switching circuit; an open / close circuit for opening / closing a rectified voltage rectified by the rectifier circuit; a hold circuit for outputting a peak voltage of the rectified voltage via the open / close circuit; And an analog / digital conversion circuit that converts the digital signal into a digital signal, and while the switching circuit outputs the input signal,
A storage circuit for storing the output data of the analog / digital converter, a digital / analog converter circuit for converting the data read from the storage circuit to an analog signal, the output of the peak voltage and the digital / analog converter circuit An automatic gain control device, comprising: a DC amplifier circuit that outputs the control voltage according to a difference from a voltage. 10. The charging circuit according to claim 9, further comprising a charging circuit that charges the output voltage of the digital / analog conversion circuit to the hold circuit while the switching circuit outputs the input signal. 3. The automatic gain control device according to claim 1. 11. The automatic gain control device according to claim 9, further comprising a low-pass filter that removes a high-frequency component of a DC voltage from the control voltage output by the DC amplifier circuit. . 12. The automatic gain control device according to claim 9, wherein said storage circuit is a nonvolatile memory. 13. The storage circuit according to claim 9, wherein the storage circuit includes a volatile memory and a backup circuit for retaining the contents of the volatile memory.
The automatic gain control device according to the paragraph.