JP4356237B2 - Muting circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a muting circuit for turning on / off an audio signal, suppressing distortion at the time of sound rise at the time of mute release, and rise time at the time of mute on and after release, thereby canceling mute release without feeling uncomfortable in listening. It relates to a circuit to be performed.
[0002]
A conventional muting circuit uses a circuit in which a collector of an npn transistor is connected to an audio signal line as a switching element for turning on / off an audio signal as disclosed in Japanese Patent Laid-Open No. 5-325405. FIG. 3 shows a common part of these circuits.
[0003]
In this circuit, when mute is on, the transistor 2 is turned on by passing a current through the base of the transistor 2, the positive potential side of the audio signal is conducted to the ground through the emitter of the transistor 2, and the negative potential side is the base of the transistor 2 The audio signal line 1 is muted when the output is clipped by the pn junction between the collectors.
[0004]
When the mute is released, the base current to the transistor 2 is cut off and the transistor 2 is turned off, so that the audio signal line 1 is opened and the audio signal returns to its original state, thereby operating as a muting circuit.
[0005]
In Japanese Patent Laid-Open No. 5-325405, an integration circuit is configured with a resistor 6 and a capacitor 3 to operate with a time constant for on / off of the mute operation. At the time, the mute operation without a sense of incongruity in the audition was performed by performing an operation of gradually releasing.
[0006]
However, in this case, since a delay occurs when the mute is turned on and a sufficient effect cannot be obtained, when the mute is turned on, the resistor 37 is bypassed and the transistor 37 is turned on to accelerate the rise of the mute operation. At the time of release, an operation of gradually releasing by the discharge of the capacitor 34 was performed.
[0007]
[Problems to be solved by the invention]
However, in the above method, the audio signal can be turned off without any problem when the mute is turned on, but when the mute is released, the base current of the transistor 2 is cut off and the transistor 2 is gradually turned off by the discharge of the capacitor 3. On the positive potential side of the audio signal, mute is gradually released, whereas on the negative potential side of the audio signal, the current to the base of the transistor 2 is cut off, so that the pn between the base and collector of the transistor 2 Since there is no voltage clip due to bonding, only the negative potential side of the audio signal rises, and the sound becomes asymmetrical as shown in FIG. 4 and rises while being distorted. there were.
[0008]
In addition, a circuit that accelerates mute-on and gradually releases the release causes the base impedance of the transistor 37 to have a certain value due to the effects of the resistors 32 and 38, the diode 36, and the resistor 30 when the mute is off. When the audio signal exceeds a certain amplitude level due to the pn junction between the base and the collector, the negative potential side is voltage clipped, and there is a problem that distortion occurs on the negative potential side of the audio signal in a normal audio output state.
[0009]
In the present invention, in the muting circuit, distortion caused by vertical asymmetry of the audio signal at the time of sound rise at the time of mute release is suppressed, the operation is instantaneous when mute is on, and mute is gradually released at the time of release. The present invention provides a circuit for a mute release circuit that does not cause a sense of incongruity in the trial listening.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, in the present invention, in the muting circuit, the switching element for turning on / off the audio signal is one in which the collector of the npn transistor is connected to the audio signal line, and the one in which the emitter of the npn transistor is connected. The circuit that generates the signal uses an integration circuit that operates with different time constants when the signal to the switching element is on and off, so that it operates instantaneously when mute is on and when the sound rises when mute is released This is characterized in that the distortion caused by the vertical asymmetry of the audio signal is eliminated and the mute is gradually released.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The invention according to claim 1 of the present invention is a muting circuit for turning on / off an audio signal, comprising a circuit using a switching element for turning on / off the audio signal. It has the effect of suppressing distortion at the time of rising.
[0012]
According to a second aspect of the present invention, in the muting circuit according to the first aspect, the switching element for turning on / off the audio signal is one in which the collector of the npn transistor is connected to the audio signal line, and the npn transistor It consists of an emitter connected, and has the effect of suppressing distortion at the time of voice rise.
[0013]
The invention according to claim 3 of the present invention comprises a circuit for controlling the operation of the switching element in the muting circuit according to claim 1, and operates instantaneously during the mute operation and gradually when released. Has the effect of releasing the mute.
[0014]
According to a fourth aspect of the present invention, in the muting circuit according to the third aspect, the circuit comprises a circuit for controlling the operation of the switching element, and the mute signal to the switching element is released when the mute is turned on. By operating with different time constants depending on the time, the operation is instantaneous during the mute operation and gradually cancels the mute when released. Hereinafter, an embodiment of the present invention will be described with reference to FIG.
[0015]
(Embodiment)
FIG. 1 is a diagram showing a circuit configuration. In FIG. 1, an audio block 30 transmits an audio waveform, and the generated audio waveform is transmitted to a subsequent block. The mute signal generation circuit 8 receives a mute command from the mute signal 7 to perform switching. An action of sending an on / off signal to the element 29 is performed. The switching element 29 receives the on / off signal from the mute signal generation circuit 8 and turns on / off the sound waveform of the sound block 30. The switching element 29 turns on / off the sound waveform based on the mute command. Consists of devices.
[0016]
Next, a specific example of the present invention will be described with reference to FIGS. FIG. 1 shows an example of a muting circuit according to the present invention, and FIG. 2 shows a waveform of a mute operation in the circuit example of FIG. The mute signal 7 instructs the mute signal generation circuit 8 to mute. When the signal is HI, the mute operation is performed. When the signal is LOW, the mute operation is performed. The mute signal generation circuit 8 includes switch transistors 14 and 19, bias setting resistors 13 and 15 of the transistor 14, bias setting resistors 17 and 18 of the transistor 19, a capacitor 12 for integrating the mute signal, and a switching element 29. It comprises an impedance conversion transistor 22 for connection, bias setting resistors 20 and 21 of the transistor 22, and current limiting resistors 23 and 24 to the switching element 29.
[0017]
The transistor 19 is turned on when the HI signal is received from the mute signal 7 and the transistor 14 is turned on. At this time, the operation of the transistor 14 is slightly delayed due to the integration circuit of the capacitor 12 and the resistor 15, but the delay time is reduced by setting the constant of the resistor 15 to about 22 kΩ and the constant of the capacitor 12 to about 2.2 uF. Since it can be suppressed to about 10 ms, there is no inconvenience due to delay in the mute operation.
[0018]
When the transistor 14 is turned on, a mute signal is generated and the mute signal is transmitted to the switching element 29 via the transistor 22. The transistor 22 is grounded at the base and is used to make the impedance on the output side very high.
[0019]
This is because if the impedance of the signal line to the switching element 29 is low in the mute release state, the audio signal is clipped by the pn junction between the base and collector of the transistor 26 and the pn junction between the base and emitter of the transistor 25. Since distortion occurs in the signal, this is to prevent this.
[0020]
When the mute is canceled, the transistor 19 is turned off by receiving the LOW signal from the mute signal 7 and the transistor 14 is turned off, thereby shutting off the signal to the switching element 29 and releasing the mute.
[0021]
At this time, the transistor 14 is gradually turned off by the integrating circuit of the capacitor 12 and the resistor 13. At this time, if the constant of the resistor 13 is set to about 220 kΩ, an effect that the sound rises smoothly in the trial listening can be obtained. The switching element 29 includes transistors 25 and 26.
[0022]
The emitter of the transistor 25 and the collector of the transistor 26 are each connected to the audio signal line 1, and the collector of the transistor 25 and the emitter of the transistor 26 are each connected to the ground. When a mute-on signal is received from the mute signal generation circuit, a current flows through the bases of the transistors 25 and 26, whereby the transistor 25 mutes the negative potential side of the audio signal and the transistor 26 mutes the positive potential side of the audio signal. .
[0023]
Thereby, the operation of muting both potential sides of the audio signal symmetrically in the vertical direction is performed. When the mute is released, the base current of the transistor 25 is gradually cut off, so that the negative potential side of the audio signal is gradually opened, and the base current of the transistor 26 is gradually cut off, so that the positive potential side of the audio signal is It is gradually released. As a result, the effect is obtained that both potential sides of the audio signal are vertically symmetrical and gradually return to the original as shown in FIG.
[0024]
【The invention's effect】
As described above, according to the present invention, the muting circuit operates instantaneously when mute is on, and is composed of an asymmetry of the audio signal when the sound rises when mute is released. Thus, an effect of suppressing the output of unpleasant sound in the trial listening can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of the present invention, a circuit configuration, and one circuit example. FIG. 2 is a waveform diagram for explaining the operation of one circuit example shown in FIG. FIG. 4 is a waveform diagram for explaining the operation of the circuit of the prior art shown in FIG. 3. FIG. 5 is a circuit diagram of the prior art.
1 audio signal line 2 transistor 3 capacitor 4 capacitor 5 capacitor 6 resistor 7 mute signal 8 mute signal generation circuit 9 audio output 10 audio input 11 DC power supply 12 capacitor 13 resistor 14 transistor 15 resistor 17 resistor 18 resistor 19 transistor 20 resistor 21 resistor 22 Transistor 23 Resistor 24 Resistor 25 Transistor 26 Transistor 27 Capacitor 28 Capacitor 29 Switching element 30 Audio block 31 Transistor 32 Resistor 33 Diode 34 Capacitor 35 Resistor 36 Capacitor 37 Transistor 38 Resistor

Claims (1)

A switching element for connecting the collector of an npn transistor to an audio signal line and an emitter of an npn transistor different from the npn transistor to turn on / off the audio signal; a mute signal generating circuit for controlling the operation of the switching element; In the muting circuit, the mute signal generation circuit includes an integration circuit that integrates the control signal to the switching element with different time constants when the mute is on and when the mute is on, and when the mute is on , the integration circuit The muting circuit according to claim 1, wherein the switching element is turned on instantaneously by the step S3 and the switching circuit is gradually released by the integration circuit at the time of release.

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