JPS6142966B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic gain control amplification circuit for audio signals, which is particularly useful for use in speech recognition devices.

Speech recognition devices have developed rapidly in recent years, and are now being applied to consumer devices.
A voice recognition device amplifies the voice input from a microphone using an amplifier circuit, extracts voice characteristics from the voice signal using various methods, and uses a computer to recognize the voice.

By the way, it is ideal that the audio signal amplifier in the speech recognition device selectively amplifies only the voice of the person to be recognized. But this is not possible. This is because it is not possible to distinguish between a human voice and external noise, including voices of people other than the person who is trying to be recognized. Therefore, noise-canceling microphones or highly directional microphones are used to capture the voice of the person speaking. Furthermore, the audio signal level varies greatly depending on the distance between the mouth and the microphone, which adversely affects recognition results. Therefore, automatic gain control amplifier circuit (Automatic Gain Control amplifier circuit)
Amp. (abbreviated as AGC Amp.) is often used.
However, when using this AGC Amp., small sounds are amplified with a large amplification degree, and loud sounds are amplified with a small amplification degree, so that the magnitude of the input level does not have a large effect on the output level, so the sound cannot be uttered. When there is no such thing, the amplification degree of AGC Amp. will be on standby at a very large value. In such a state, even if a small external noise enters, it will be amplified with a large degree of amplification, resulting in the external noise being picked up.

For reference, FIG. 1 shows an example of an existing automatic gain control amplifier circuit. In the figure, 1 is a microphone that converts audio into an audio signal, and 2 is an operational amplifier (hereinafter abbreviated as Operation Amp) to which the audio signal from the microphone 1 is connected to one input terminal.
OPe Amp.), whose output terminal constitutes an output terminal 3 as an amplifier circuit and is applied to an LED 5 via a diode 4. This LED5 is above
A photocoupler 7 is constituted by a photosensitive element 6 made of CdS or the like connected between the output terminal of the OPe Amp 2 and one input terminal. The resistance value of this photosensitive element 6 changes depending on the amount of light emitted from the LED 5, and as the amount of light increases, the resistance value decreases, and as a result, OPe
The amplification degree of Amp.2 decreases and its output level decreases. Then, the amount of light emitted from LED5 decreases, and OPe
Increase the amplification degree of Amp2 and perform automatic gain control as an amplifier circuit. Incidentally, a capacitor 8 inserted and connected in parallel with the LED 5 is for smoothing the output level of the OPe Amp 2.

According to the amplifier circuit with such a configuration, when the audio signal from microphone 1 disappears, the output of OPe Amp 2 disappears, and after the audio signal disappears,
After 10 milliseconds have passed, the charge in the capacitor 8 disappears, the LED 5 turns off completely, the resistance value of the photosensitive element 6 reaches its maximum, and the amplification degree of the OPe Amp 2 also reaches its maximum state. As mentioned above, in this state, even a small noise input will be greatly amplified.

The present invention has been made in view of these problems, and will be described in detail with reference to FIG. 2. In Fig. 2, 1, 2, 3, 4, 5, 6, 7, and 8 are microphones and OPe Amp, respectively, as in Fig. 1.
The output terminal, diode, LED, photosensitive element, photocoupler, and capacitor are shown. Furthermore, in this figure, 10 is the first auxiliary OPe Amp.11 whose one input terminal is connected to the output terminal of OPe Amp2. An analog switch 12 that is controlled to open and close according to the output of the first auxiliary OPe Amp 10 connects one input terminal to the above analog switch 11 via this analog switch 11.
The second auxiliary connected to the output terminal of OPe Amp2
OPe Amp, whose output terminal is the first OPe mentioned above.
It is connected to the LED 14 which is connected to the other input terminal of the amplifier 10 and constitutes the second photocoupler 13. The photosensitive element 15 of this second photocoupler 13 is connected between the input and output terminals of the OPe Amp 2, as in the case of the photocoupler 7 shown above. Reference numeral 16 denotes a charge storage capacitor connected to the input terminal of the second OPe Amp 12, which has the function of storing and holding the output level of the OPe Amp 2 obtained via the analog switch 11 for a predetermined period of time ranging from several seconds to several minutes. . 17 is this capacitor 16
A reset switch is provided in parallel with the capacitor 16 and is turned on when discharging the charge in the capacitor 16.

When a large audio signal is obtained from microphone 1, a high-level output signal is obtained at the output terminal of OPe Amp 2, and as in the previous case, the automatic gain is set by the function of diode 4 and photocoupler 7. controlled. At the same time, the high level output signal is applied to the first auxiliary OPe Amp 10, and the analog switch 11 is turned on to store the high level in the charge storage capacitor 16 and store it. is applied to the second photocoupler 13 via OPe
The degree of amplification caused by Amp2 is reduced in cooperation with photocoupler 7. On the other hand, the second auxiliary OPe Amp1
When the output level of 2 increases, the 1st auxiliary OPe
Amp10 output disappears and analog switch 1
1 is turned off, the discharge of the charge storage capacitor 16 is cut off, and this capacitor 1
The charge of No. 6 is maintained for a long period of time ranging from several seconds to several minutes. As a result, the output of the second auxiliary OPe Amp 12 maintains a high level over this long period of time, suppressing the amplification degree of the OPe Amp 2 caused by the second photocoupler 13. In other words, Microphone 1
Even if the audio signal from the device disappears and the device goes into standby mode,
During the high level memory retention time by the charge storage capacitor 16, the optimum amplification at the time of voice arrival is maintained without exhibiting a high amplification. That is, the photocoupler 7 is used to determine the optimum degree of amplification for short-term sound fluctuations of several tens of milliseconds, and the second photocoupler 13 is used for long-term amplification control of several seconds to several minutes.

As is clear from the above description, in the present invention, the output level of the OPe Amp that amplifies the audio signal is stored and held for a predetermined period of time using the holding means, so even if the audio signal disappears, the output level of the OPe Amp that amplifies the audio signal can be amplified for a predetermined period of time. The amplification degree of the circuit can be maintained at the optimal state when the voice arrives, and the possibility of picking up noise other than the desired voice is significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing the configuration of an existing amplifier circuit, and FIG. 2 is an electric circuit diagram showing the configuration of the automatic gain control circuit of the present invention.
13 is a photocoupler, 10 and 12 are auxiliary OPe
amp, 11 is an analog switch, and 16 is a charge storage capacitor.

Claims (1)

[Claims] 1 An operational amplifier to which an audio signal from a microphone is applied to one input terminal, an LED that emits light in response to the output signal of the amplifier, and an amplification level of the operational amplifier that receives the light from the LED. an automatic gain control amplifier circuit comprising: a control element for controlling the operational amplifier; The output of the second auxiliary operational amplifier constitutes the other input of the first auxiliary operational amplifier, and the output of the second auxiliary operational amplifier constitutes the other input of the first auxiliary operational amplifier. The voltage is applied to a second LED that irradiates light to a second control element that controls the amplification degree, and the voltage of the operational amplifier obtained through the switch means is applied to the input terminal of the second auxiliary operational amplifier. An automatic gain control amplifier circuit comprising a retaining means for storing and retaining an output level for a predetermined period of time.