JPS5824493Y2 - automatic volume adjustment device - Google Patents

Description

[Detailed description of the invention] This invention relates to an automatic volume adjustment device for audio equipment such as television receivers, which automatically adjusts the volume not only when the audio signal level is low but also when the audio signal level is high. This is intended to enable correct volume adjustment.

FIG. 1 is a block diagram of a conventional automatic volume adjustment device, in which the output of an audio intermediate frequency amplification circuit 1 of a television receiver is detected by a detection circuit 2, and the output is passed through a volume volume control device 3 to an audio output device. Join 4.

The output of the audio output device 4 passes through the speaker 5 and is output as a sound wave.

A microphone 7 is provided around the television receiver to detect ambient noise.

The detected noise is amplified by an amplifier 8 and enters a gate circuit 9.

As the gate signal of the gate circuit 9, a signal detected by the low level detector 6 in only the low level period of the output of the audio output device 4 is used.

Waveform a in FIG. 2 is the output waveform of the audio output device 4, and 11
Only the low level portion between *12 is detected by the low level detector 6, and the gate signal shown in FIG. 2 is generated.

The signal detected by the microphone I is the signal shown in FIG. 2C, and is gated by the gate circuit 9 using the gate signal to extract the signal shown in FIG. 2D.

Since this signal is a component only during the low level period of the audio signal, it may be considered to be almost exclusively an external noise component.

The output of the gate circuit 9 is applied to the integrator 10, as shown in FIG.
The control voltage shown in is obtained.

This control voltage is applied to the audio output device 4 to adjust the gain.

When there is a lot of ambient noise, the control voltage becomes high and the gain of the audio output device 4 becomes large.

The disadvantage of such a device is that when the signal has almost no low-level period, such as jazz, the control voltage drops during the high-level period of the signal, as shown in Figure 2e, and the control voltage drops as shown in Figure 2C. Even though there is external noise, the volume decreases.

The present invention aims to provide an automatic volume control device free from such drawbacks, and embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 shows an embodiment of the automatic volume adjustment device of the present invention, and the same parts as in FIG. 1 are given the same numbers and their explanation will be omitted.

The difference from the device shown in FIG. 1 is that a holding circuit is provided between the integrating circuit 10 and the audio output device 4.

The holding circuit connects the output terminal of the integrating circuit 9 to the base of the transistor 13, and connects the collector KB of the transistor 13 to the base of the transistor 13.
A voltage is applied, and the emitter is connected to the collector of the transistor 16 via the resistor 14, to the ground via the capacitor 15, and further to the audio output device 4.The emitter of the transistor 16 is grounded, and the base is connected to the low voltage. This is the sum of the output of the level detector 6.

Note that 11 and 12 are a resistor and a capacitor that constitute the integrating circuit 10.

Now, assuming that the audio signal is in a low level period, the output of the low level detector 6 is in a positive period as shown in Figure 2, and this voltage causes a short circuit between the collector and emitter of the transistor 16. , transistor 13 and resistor 14 form an emitter follower.

If the capacitor 15 is selected to have a smaller capacitance than the capacitor 12, during the low level period, most of the integrated output due to the time constant of the resistor 11 and capacitor 12 is given to the audio output circuit 4 as a control voltage.

Next, if the audio signal changes from a low level to a high level, the transistor 16 will be turned off, resulting in the same state as when the ground side of the resistor 14 is open.

Therefore, the transistor 13 only functions as a diode, and the capacitor 15 accumulated at low level
The charge is kept at that level.

Then, when the audio signal becomes low level again, capacitor 1
The charge that had been charged to 5 is discharged through resistor 14,
Transistor 13 again operates as an emitter follower.

By doing this, the emitter voltage of the transistor 13 becomes as shown in FIG. .

FIG. 4 shows another embodiment.

In this example, a holding circuit (MOS) transistor is used as a transfer gate, and during the low level period, the output of the low level detector 6 is passed through the inverter 18 to the M
In addition to the gate of the OS) transistor 17, this MOS) transistor 17 is turned on.

As a result, the integrated voltage of the integrating circuit 10 is applied to the base of the transistor 20.

Also, during the high level period of the audio signal, the output of the inverter 18 is 0, so the MOS transistor 17 is turned off, and the discharge path of the charge stored in the floating capacitor 19 becomes extremely high impedance, so the base of the transistor 20, That is, the emitter of the transistor 20 maintains the level it had before the MOS transistor 17 was turned off.

When this MOS transistor 17 is used, the MOS
) Since the impedance of the transistor 1T when it is off is much higher than that of a bipolar transistor, the holding capacitor 19 can be held with a stray capacitance or a capacitor with a fairly small capacitance.

As described above, according to the present invention, the voltage detected when the audio signal received by the audio equipment is at a low level is held when the audio signal changes from a low level to a high level. It is possible to automatically adjust the volume correctly even when the level is high, and the retention means is to prevent the voltage accumulated in the capacitor from discharging when the level is high, so it is easy to configure. It is something that can be done.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional automatic volume adjustment device;
Figures a, b, c, d, e, and f are conventional examples and waveform diagrams for explaining the present invention, Figure 3 is a circuit diagram of an automatic volume adjustment device according to an embodiment of the present invention, and Figure 4 is the same. FIG. 7 is a circuit diagram of an automatic volume adjustment device in another embodiment. 4...Audio output device, 5...Speaker,
6...Low level detector, 7...Microphone, 9...Gate circuit, 10...
・Integrator circuit, 13.16...transistor, 1
1, 14... Resistance, 12, 15... Con Answer.

Claims (1)

[Scope of utility model registration request] A microphone that detects the ambient sound of the audio equipment, a low level detector that detects only the low level period of the audio signal supplied to the speaker, and a gate signal corresponding to the low level period from this low level detector to detect the microphone. A gate circuit that passes the ambient sound detected by the audio signal, an integrating circuit that integrates the output of the gate circuit, and a holding circuit that holds the output of the integrating circuit for a period other than the low level period of the audio signal. The holding circuit includes a capacitor which is used to capacitate the output of the integrating circuit and whose value is smaller than the value of the capacitor in the integrating circuit, and a capacitor whose value is smaller than the value of the capacitor that receives the output gate signal of the low level detector. A switching transistor is provided to control the charging and discharging of the integrator and to cut off discharge from the small capacitance during periods other than the low level period, and the switching transistor is made conductive during the low level period to The output voltage is cut off during periods other than the low level period by cutting off the switching transistor to cut off the discharge loop, and the voltage of the small capacitance of the holding circuit is applied as a control voltage to the audio amplifier of the audio equipment to control its gain. Automatic volume adjustment device.