JP2003168928A - Voice mute circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voice mute circuit easily realized in simple circuit arrangement even for stereos. <P>SOLUTION: When a transient current flows out from an amplifier circuit 11, a voice mute circuit 17 is set off to block the transient current from flowing to speakers 13R, 13L, resulting in no pop noise out of the speakers 13R, 13L. Only inserting one voice mute circuit 17 between the grounding terminal of each speaker 13R, 13L and a ground point prevents enough the pop noise out of the two speakers 13R, 13L. This realizes the simplification of the circuit arrangement and the cost reduction. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio mute circuit attached to an audio reproducing device such as a portable information terminal, a portable music player and a personal computer.

[0002]

2. Description of the Related Art As a conventional audio reproducing apparatus, there is one having a structure as shown in FIG. 5, for example (Japanese Patent Laid-Open No. 8-33168).
No. 8 and Japanese Unexamined Patent Publication No. 9-46149).
In FIG. 5, the amplifier circuit 101 inputs and amplifies the left and right audio signals for stereo, and applies the amplified left and right audio signals to the speakers 103R and 103L through the respective lines 102R and 102L. Each speaker 103
The R and 103L convert left and right audio signals into respective sounds and reproduce and output these sounds. The microcomputer 104 controls the power supply control circuit 105 and turns on the power supply control circuit 105 to start power supply to the amplification circuit 101, or turns off the power supply control circuit 105 to supply power to the amplification circuit 101. The power supply is stopped. At the time of starting and stopping the power supply to the amplifier circuit 101, a transient current is output from the amplifier circuit 101 to the respective lines 102R and 102L. Therefore, the microcomputer 104 causes each audio mute circuit 106 to start and stop the power supply to the amplifier circuit 101.
R and 106L are turned on, and each line 102R and 102L
L is grounded and the transient current is applied to each of the lines 102R, 102R.
It flows from 2L to the grounding point through each of the audio mute circuits 106R and 106L. If each audio mute circuit 1
When 06R and 106L are turned off, the transient current is transmitted to each speaker 10 through each line 102R and 102L.
3R, 103L flow to each speaker 103R, 103
A large pop noise is output from L.

Further, as another conventional audio reproducing apparatus, there is one having a structure as shown in FIG. 6 (Japanese Patent Laid-Open No. 9-98039).
(See No. Here, each audio mute circuit 10
6R and 106L to the respective lines 102R and 102L
Is being inserted in the middle of. Microcomputer 104
At the time of starting and stopping the power supply to the amplifier circuit 101, turns off the audio mute circuits 106R and 106L, disconnects the lines 102R and 102L in the middle thereof, and changes the transient current from the amplifier circuit 101. Each line 10
It is cut off on 2R and 102L. As a result, large pop noises are not output from the speakers 103R and 103L.

[0004]

However, in any of the above-described conventional audio reproducing apparatuses, since the audio mute circuits 106R and 106L are attached to the lines 102R and 102L for transmitting the left and right audio signals, respectively. One audio mute circuit is required, which leads to a complicated circuit configuration.

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide an audio mute circuit having a simple circuit configuration even in stereo.

[0006]

In order to solve the above problems, the present invention includes a mute switch inserted between the speaker and the ground point.

According to the present invention having such a configuration, the mute switch is inserted between the speaker and the ground point. When the mute switch is turned on, the audio signal flows to the grounding point through the speaker, so the audio signal is converted into the audio by the speaker, and the audio is reproduced and output from the speaker. Further, when the mute switch is turned off, the audio signal does not flow through the speaker to the ground point, and audio is not reproduced and output from the speaker. Even when the left and right speakers are provided for stereo, the grounding points of these speakers are common, and it is only necessary to insert one mute switch between each speaker and the grounding point. Therefore, compared with the conventional circuit, the number of mute switches can be reduced, and the circuit configuration can be simplified and the cost can be reduced.

Further, the present invention is provided with control means for turning off the mute switch when the power supply to the amplifier circuit for amplifying the audio signal and applying it to the speaker is turned on. Alternatively, there is provided control means for turning off the mute switch when the power supply to the amplifier circuit for amplifying the audio signal and applying it to the speaker is turned off.

When the power supply to the amplifier circuit is turned on and off, a transient current is output from the amplifier circuit.
The mute switch is turned off to block the path through which the transient current flows to the ground point through the speaker, thereby preventing a large pop noise from being output.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a sound reproducing apparatus to which an embodiment of a sound mute circuit of the present invention is applied. In FIG. 1, an amplifier circuit 11 inputs and amplifies left and right audio signals for stereo, and applies the amplified left and right audio signals to respective speakers 13R and 13L through respective lines 12R and 12L. Each speaker 13R, 13
L converts left and right audio signals into respective sounds and reproduces and outputs these sounds. Microcomputer 14
Switches on and off the power supply control circuit 15 by switching the control signal Va to either a high level or a low level. When the control signal Va is at high level, the power supply control circuit 15 is turned on and the power supply control circuit 1
When the power supply to the amplifier circuit 11 is started from 5 and the control signal Va is at the low level, the power supply control circuit 15 is turned off and the power supply to the amplifier circuit 11 is stopped.

On the other hand, the ground side terminals of the speakers 13R and 13L are commonly connected, and an audio mute circuit 17 is inserted between the common connection point 16 and the ground point. The microcomputer 14 controls the audio mute circuit 17 to turn on / off by switching the control signal Vb to either a high level or a low level. When the control signal Vb is at the high level, the audio mute circuit 17 is turned on, and the ground side terminals of the speakers 13R and 13L are grounded. In this state, the left and right audio signals from the amplifier circuit 11 flow to the ground point through the speakers 13R and 13L, and the left and right audios are reproduced and output from the speakers 13R and 13L. Further, when the control signal Vb is at the low level, the audio mute circuit 17 is turned off, and each speaker 1
The ground side terminals of 3R and 13L are separated from the ground point. In this state, the left and right audio signals from the amplifier circuit 11 do not flow to the ground point through the speakers 13R and 13L, and the audio is not reproduced and output from the speakers 13R and 13L.

When starting and stopping the power supply to the amplifier circuit 11, a transient current is output from the amplifier circuit 11 to the lines 12R and 12L. what if,
When this transient current flows through the speakers 13R and 13L, large pop noises are output from the speakers 13R and 13L.

Therefore, the microcomputer 14 is
At the time of starting and stopping the power supply to the amplifier circuit 11, the audio mute circuit 17 is turned off, and each speaker 13R, 1
The 3L grounding side terminal is separated from the grounding point, and the amplifier circuit 11
This prevents the transient current of (3) from flowing through the speakers 13R and 13L. Specifically, immediately before the control signal Va is switched from the low level to the high level, that is, immediately before the power supply control circuit 15 is turned on, the control signal Vb is turned off and the audio mute circuit 17 is turned off. In this state, the control signal Va is switched to the high level to turn on the power supply control circuit 15 and then the control signal Vb to turn on the audio mute circuit 17. Further, immediately before the control signal Va is switched from the high level to the low level, that is, immediately before the power supply control circuit 15 is turned off, the control signal Vb is turned off and the audio mute circuit 17 is turned off. The signal Va is switched to the low level to turn off the power supply control circuit 15, and then the control signal Vb is turned on to turn on the audio mute circuit 17. As a result, when the transient current is output from the amplifier circuit 11, the audio mute circuit 17 is turned off, and the transient current does not flow to the speakers 13R and 13L.

FIG. 2 shows a more specific structure of the audio reproducing apparatus of FIG. Here, each operational amplifier 11-1,
11-2 and respective capacitors 11-3 and 11 for removing DC components
-4 corresponds to the amplifier circuit 11 in FIG. 1, and the left and right audio signals for stereo are the respective operational amplifiers 11-1 and 11-2.
These audio signals are amplified by the respective speakers 13R and 13L through the capacitors 11-3 and 11-4, respectively.
Added to. The voltage regulator 15-1 corresponds to the power supply control circuit 15 in FIG. 1, and when the control signal Va is at a high level, the voltage regulator 15-1 is turned on, and when the control signal Va is at a low level. The voltage regulator 15-1 is turned off. Further, the field effect transistor 17-1 corresponds to the audio mute circuit 17 of FIG. 1, and when the control signal Vb is at a high level, the field effect transistor 17-1 is turned on and each speaker 13R, 1 is turned on.
The ground side terminal of 3L is grounded, the left and right audio signals flow to the ground point through the respective speakers 13R and 13L,
Further, when the control signal Vb is at the low level, the field effect transistor 17-1 is turned off, and each speaker 13R, 1
The ground side terminal of 3L is separated from the ground point, and the left and right audio signals do not flow to the ground point through the respective speakers 13R and 13L.

In FIG. 3A, the control signal Vb is maintained at a high level, the field effect transistor 17-1 is turned on, and the ground side terminals of the speakers 13R and 13L are grounded. The control signal Va is switched from the low level to the high level to output the transient current from the voltage regulator 15-1. At this time, the voltage Vc on each of the lines 12R and 12L and the voltage Vd of the ground side terminal of each of the speakers 13R and 13L. Is measured and shown with reference to the ground potential.
Further, in FIG. 3B, in the same state, the control signal Va is switched to output the transient current, and each line 1 at this time is output.
The voltage Vc on 2R and 12L is applied to each speaker 13R and 13L.
The voltage Vd of the ground side terminal is measured and shown. Since the ground side terminals of the speakers 13R and 13L are kept grounded, the voltage Vd of the ground side terminals is at the ground potential.

As is apparent from FIGS. 3A and 3B, when the transient current is output from the voltage regulator 15-1, the voltage Vc on each of the lines 12R and 12L and each speaker 13 are output.
Since a potential difference is generated between the voltages Vd of the ground side terminals of R and 13L, it can be said that current is flowing through the speakers 13R and 13L. Therefore, when the transient current is output from the voltage regulator 15-1, pop noise is output from each of the speakers 13R and 13L.

In FIG. 4A, the control signal Vb is maintained at a low level, the field effect transistor 17-1 is turned off, and the ground side terminals of the speakers 13R and 13L are kept separated from the ground point. In this state, the control signal Va is switched from the low level to the high level, and the voltage regulator 15
-Transient current is output from -1, each line 12 at this time
Voltage Vc on R, 12L and each speaker 13R, 13L
The voltage Vd of the ground side terminal of is measured and shown with reference to the ground potential. 4B, in the same state, the control signal Va is switched to output a transient current, and the voltage Vc on each line 12R, 12L at this time is output to the ground side terminal of each speaker 13R, 13L. The measurement is shown with reference to the voltage Vd.

As is apparent from FIGS. 4A and 4B, when the transient current is output from the voltage regulator 15-1, the voltage Vc on each of the lines 12R and 12L and each speaker 13 are output.
Since there is no potential difference between the voltages Vd of the ground side terminals of R and 13L, it can be said that no current is flowing through the speakers 13R and 13L. Therefore, the voltage regulator 15
-When outputting the transient current from -1, each speaker 13R, 13R
No pop noise is output from L.

Through such an experiment, the voltage regulator 15-1 can be obtained by simply turning off the field effect transistor 17-1.
The transient current from does not flow into each speaker 13R, 13L,
It can be seen that pop noise is not output from the speakers 13R and 13L.

As described above, in this embodiment, when the transient current is output from the amplifier circuit 11, the audio mute circuit 17 is used.
Is turned off, the transient current is
The noise does not flow to R and 13L, and pop noise is not output from the speakers 13R and 13L. In addition, each speaker 13
By inserting one audio mute circuit 17 between the ground side terminals of R and 13L and the ground point, the two speakers 13
It is possible to prevent the pop noise from being output from the R and 13L, so that the circuit configuration can be simplified and the cost can be reduced. In particular, in a small and lightweight device such as a portable information terminal and a portable music player, the application of the present invention can bring about a great effect of reducing the mounting area.

The present invention is not limited to the above embodiment, but can be variously modified. For example,
Even if the number of speakers is three or more, the ground side terminals of these speakers may be commonly connected and the common connection point may be grounded through the audio mute circuit. Further, as the switch of the audio mute circuit, not only the field effect transistor but also other kinds of semiconductor switches, mechanical switches including contacts, or the like can be applied.

[0023]

As described above, according to the present invention, even when the left and right speakers are provided for stereo, only one mute switch is inserted between each speaker and the ground point. Therefore, compared with the conventional circuit, the number of mute switches can be reduced, and the circuit configuration can be simplified and the cost can be reduced.

Further, according to the present invention, when the power supply to the amplifier circuit is turned on and off, the mute switch is turned off to cut off the path through which the transient current flows through the speaker to the ground point. It prevents a large pop noise from being output.

[Brief description of drawings]

FIG. 1 is a block diagram showing an audio reproducing device to which an embodiment of an audio mute circuit of the present invention is applied.

FIG. 2 is a circuit diagram showing a more specific configuration of the audio reproduction device of FIG.

3A and 3B are diagrams showing respective signal waveforms in the apparatus of FIG.

4A and 4B are diagrams showing other signal waveforms in the apparatus of FIG.

FIG. 5 is a block diagram showing an example of a conventional audio reproducing device.

FIG. 6 is a block diagram showing another example of a conventional audio reproducing device.

[Explanation of symbols]

11 amplifier circuit 12R, 12L line 13R, 13L speaker 14 Microcomputer 15 Power supply control circuit 16 common connection points 17 Audio mute circuit

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5J092 AA02 AA41 CA48 CA49 CA87                       CA92 FA14 FR05 HA09 HA32                       KA00 KA01 KA33 KA62 MA21                       SA06 TA01 TA06                 5J500 AA02 AA41 AC48 AC49 AC87                       AC92 AF14 AH09 AH32 AK00                       AK01 AK33 AK62 AM21 AS06                       AT01 AT06 RF05

Claims (3)

[Claims] 1. An audio mute circuit comprising a mute switch inserted between a speaker and a ground point. 2. The audio mute circuit according to claim 1, further comprising control means for turning off the mute switch when the power supply to the amplifier circuit for amplifying the audio signal and applying it to the speaker is turned on. . 3. The audio mute circuit according to claim 1, further comprising control means for turning off a mute switch when power supply to an amplifier circuit for amplifying an audio signal and applying it to a speaker is turned off. .