JPS62120707A - Noise mute circuit - Google Patents

Abstract

PURPOSE:To simplify the circuit constitution and to reduce remarkably number of components by comparing a voltage of a signal line with a reference voltage set slightly larger than a peak of noise when no signal exists on the signal line. CONSTITUTION:At first the reference voltage V1 is set to a value slightly larger than the peak of noise on a system applied to an input terminal 1. When the input is only the noise to the system, an output of a comparator 3 is a positive voltage, a diode D1 is turned off and a base current ib is fed to a transistor (TR) Q1 from a position power supply 5 through a resistor R3 and the TR Q1 is turned on, then the muting is applied. When a signal is inputted, the output of the comparator 3 is a negative voltage while the signal voltage exceeds the reference voltage V1. The diode D1 is turned on in this case to draw an electric charge charged in a capacitor C1. Since a time constant C1.R2 is set smaller, the capacitor C1 is discharged at a high speed to release the muting.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a noise muting circuit that prevents the output of unnecessary noise components by performing muting when there is no signal in an audio equipment or the like.

[Prior Art of the Invention #11 Conventionally, there was a circuit of this type as shown in FIG. In the figure, 11 is an input terminal, which is led to an output terminal 12 through a resistor R11 and is connected to a rectifier circuit 13. The output of the rectifier circuit 13 (resistors R12, R13,
A time constant circuit consisting of capacitor C11 (usually C11
It is led to the inverting input terminal of the inverter 14 via R12<C11R13). A reference voltage 15 (voltage value ■11) is input to the non-inverting input terminal of the comparator 14.

The output of comparator 14 is connected to the base of transistor Q11 through resistor R14. Transistor Q11
The signal is connected to the output terminal 12, and the emitter is grounded.

In addition, specifically, the rectified current 13 is a half-wave rectifier circuit (sixth
(Fig. 7) or a double-wave rectifier circuit (Fig. 7) are used. Figure 6 shows the operational amplifier 21, diodes D2, D3 and resistor R1.
9 and R20, and FIG. 7 shows a double-wave rectifier circuit consisting of continuously connected operational amplifiers 22 and 23, diodes D4 and D5, and resistors R21 to R25. Since this is a conventionally known circuit, its operation will be omitted.

In this configuration, the operation will be explained.

When the signal applied to the input terminal 11 is only system noise, the output of the rectifier circuit 13 is small, and therefore the voltage applied to the inverting input terminal of the comparator 14 is smaller than Vll applied to the non-inverting input terminal. Become. Therefore, the output of the comparator 14 becomes a positive voltage, turning on the transistor Q11 and applying muting.

Furthermore, when a signal is applied to the input terminal 11, the rectifier circuit 13
The output of the comparator 14 becomes larger, the voltage applied to the inverting input terminal of the comparator 14 becomes larger than Vll, and the output of the cobalator 14 becomes a negative voltage.

This turns off the transistor Qll, and the input signal appears at the output terminal 12 through the resistor R11.

In addition, in order to turn off the transistor Q11 immediately when a signal is input and not turn on the transistor Q11 even if the signal is temporarily interrupted, it is recommended to set the time constant as C11R12<<C11R13. Common.

[Problems to be solved by the invention] Since the conventional noise mute circuit is configured as described above, it has a large number of circuit parts and is disadvantageous in terms of cost, so a simpler circuit is expected. It had been.

Means for Solving Problem E] This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and by immediately comparing the input signal with the reference voltage, it can be realized with a simple circuit configuration and at low cost. Noise
It is intended to provide a mute circuit.

[Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described based on the drawings. 1st
In the embodiment shown in the figure, 1 is the input terminal, and the resistor R
1 to the output terminal 2, and is also connected to the inverting input terminal of the comparator 3. A reference voltage 4 (voltage V1) is connected to a non-inverting input terminal of the comparator 3. The output of comparator 3 is connected to the cathode of diode D1, and the 7th node of diode D1 is connected to resistor R2.
connected to. The other end of the resistor R2 is connected to the base of a transistor Q1 whose emitter is grounded.

A resistor R3 is connected between the base of the transistor Q1 and the positive power supply terminal 5, and a resistor R3 is connected between the base of the transistor Q1 and the positive power supply terminal 5.
A capacitor c1 is connected between the source terminals 6. The resistor of transistor Q1 is connected to output terminal 2. Note that the resistance value is set to R2<<R3.

In this configuration, the operation will be explained.

The voltage waveforms at point A-C in FIG. 1 are shown in FIGS. 2(a) to 2(C). First, the base t\lightning voltage 1 is set to a value slightly larger than the peak value of the system noise applied to the input terminal 1. When the input is only noise on the system, the output of the comparator 3 becomes a positive voltage, and the diode D1 is turned off.] - The base ffi source 1b is supplied from the positive power supply 5 through the resistor R3 to the transistor Q1, and it turns on. , muting is applied.

When a signal is included in the input, the output of the comparator 3 becomes a negative voltage when the signal @ voltage exceeds the reference voltage v1. At this time, the diode D1 turns on and extracts the charge stored in the capacitor C1. Since the time constant CIR2 is set small, the capacitor C1 is discharged at high speed. Then, the base of the transistor Q1 becomes a negative voltage and turns off, canceling muting.

The output of comparator 3 is frequently reversed to positive or negative depending on the signal, but the time constant CI that charges capacitor C1
Since R3 is made large, the next discharge is performed while the signal is present, before the capacitor C1 is fully charged (that is, the base of the transistor Q1 remains negative). When the signal is completely gone, capacitor C1 is gradually charged.

As a result, the base of transistor Q1 has a positive electric ratio,
When a sufficient base current ib can be supplied, the transistor Q1 is turned on and muting is applied.

In this way, the number of circuit components can be significantly reduced while the operation is the same as that of the conventional technology.

Note that in the above embodiment, the same signal as the signal applied to the input terminal is output, and muting is applied to the output when this is only noise. Of course, it may also be a part of .

Further, the comparator 3 may be replaced by an operational amplifier. Furthermore, the reference voltage ■1 for comparison is shown in Figure 3 (a).
It is also conceivable to apply a divided voltage using series resistors R4 and R5, as shown in FIG.

That is, in FIG. 3(b), a reference voltage v1 is connected in series with a resistor R7 between the non-inverting input of the comparator 3 and the ground, and a resistor R6 is connected between the output of the comparator 3 and the non-inverting input.
The diagram (C) is configured to connect the
In addition to the configuration shown in FIG. 3(a), a resistor R6 is further connected between the output of the comparator 3 and the non-inverting input. As shown in FIG. 4, it is also possible to use a transistor Q2 instead of the diode D1 on the output side of the comparator 3, which is effective when the current drawing ability of the sparator 3 is small.

In FIG. 4, the base of a transistor Q2 is connected to the output of the comparator 3, the emitter is connected to a resistor R2, and the collector is connected to the terminal of a capacitor (C1) on the negative power supply 6 side.

[Effects of the Invention] As described above, according to the present invention, since the input signal is immediately compared with the reference voltage, the circuit configuration can be simplified and the number of parts can be significantly reduced. As a result, it is possible to provide an inexpensive noise muting circuit that has the same performance as conventional circuits.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the noise mute circuit according to the present invention, FIGS. 2(a) to (C) are waveform diagrams of various parts of the circuit in FIG. 1, and FIGS. 3(a) to (C) ) and FIG. 4 are circuit diagrams showing other embodiments of the present invention, FIG. 5 is a circuit diagram showing a conventional noise mute circuit, and FIGS. 6 and 7 are circuit diagrams showing the circuit shown in FIG. 5, respectively. FIG. 2 is a circuit diagram showing an example of a rectifier circuit. 1...Input terminal 2...Output terminal 3...' Comparator 4...Reference voltage Dl...Da, Diode Ql... ...Transistor patent applicant Pioneer Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 9M Ru = 2 Name: Noise Mute Circuit 3, Relationship with the person making the amendment Patent applicant address: 1-4-1 Meguro, Meguro-ku, Tokyo 153 @ Nam (501) No<Ionia Co., Ltd. 1, page 3 of the specification Correct "9. Continuous connection 0." written in line 5 to "0. Cascade connection 0." 2. Bright Il ["0. Base power supply 0." written on page 116, line 7] [9. Base current 6. ” will be corrected. that's all

Claims (2)

[Claims] (1) A comparator that compares the voltage value of the signal line with a reference voltage value set slightly larger than the peak value of noise when no signal is present on the signal line, and a comparator that is connected to the output side of the comparator. A constant circuit, a control means provided between the comparator output and the time constant circuit to control discharge of the time constant circuit, and a muting transistor controlled by the output of the time constant circuit. noise mute circuit. (2) The noise mute circuit according to claim 1, wherein the control means is a diode connected in series between the comparator output and the time constant circuit.