JPH0115217Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a muting signal generation circuit used in a muting circuit to prevent noise generation when switching a switch, and in particular, to a muting signal generation circuit used in a muting circuit to prevent noise generation when switching a switch. It is an object of the present invention to provide a muting signal generating circuit capable of generating an appropriate muting signal during both switching from ON to OFF.

In a tape recorder, when a playback switch is switched from off to on or from on to off, noise is generated due to the switch switching.
For this reason, a normal tape recorder is provided with a muting circuit to prevent the noise from occurring. Therefore, when switching the playback switch from OFF to ON, muting must be canceled after the switching noise has disappeared, and when switching from ON to OFF, muting must be performed before the noise occurs. Therefore, in the past, mutating was performed using a muting signal generation circuit having two different time constants.

The present invention has been developed in view of the above points, and is a simple circuit capable of generating appropriate muting signals in response to switching from OFF to ON and from ON to OFF with a single circuit. It is an object of the present invention to provide a muting signal generating circuit having the following configuration.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a switch that is switched in conjunction with the playback switch of a tape recorder, for example, the collector is connected to the power supply (+V _CC ) via a resistor 3, the emitter is connected to ground, and the base is connected to the resistor 4 and the switch 1. The power supply (+
a first transistor 5 connected to V _CC ), a second transistor 5 whose collector is connected to the base of the first transistor 2 and whose emitter is connected to ground;
7 is a capacitor constituting a time constant circuit for adjusting the voltage applied to the base of the second transistor 5, and 7 is a muting signal output terminal.

Next, the operation will be explained. In the state shown in FIG. 1 in which the switch 1 is off, the first and second transistors 2 and 5 are not biased and are off, so the output terminal 7 receives an "H" muting signal. It has occurred. When the switch 1 is turned on at time t ₀ , the second transistor 5 becomes biased and immediately turns on, and the base of the first transistor 2 is grounded by the collector-emitter path of the second transistor 5. Transistor 2 remains off. There is a possibility that the first transistor 2 is turned on instantaneously immediately after the switch 1 is turned on and before the second transistor 5 is turned on, but the operating speeds of the first and second transistors 2 and 5 are equal. , and even if the first transistor 2 is turned on, it is only for a short time.
No effect on operation.

However, when the predetermined time (T _D ) has elapsed after turning on switch 1 and reaches time t ₁ , capacitor 6
is charged to a predetermined voltage, the base voltage of the second transistor 5 decreases, and the second transistor 5 is turned off. Then, when the second transistor 5 is turned off, the first transistor 2 is turned on, the voltage at the output terminal 7 becomes "L", and the generation of the muting signal is stopped. This is the operation of the muting signal generation circuit when switch 1 is turned on from off, and it can continue to generate the muting signal during the noise generation period (T _D ) caused by switch switching, so the noise can be suppressed. It can definitely be prevented.

Next, when the switch 1 is turned from on to off at time _t2 , the base bias of the first transistor 2 is immediately removed, so the first transistor 2 is immediately turned off. Therefore, the voltage at the output terminal 7 also becomes "H" immediately, and a muting signal is generated. Therefore, noise generated after the switch is turned from on to off can be reliably prevented.

When switch 1 is turned off, capacitor 6 immediately starts discharging. The diode 8 is arranged to prevent the first transistor 2 from being biased due to the discharge of the capacitor 6, and the resistor 9 is also used as a discharge resistance of the capacitor 6, so its value is set small. ing.

FIG. 2 shows voltages at various parts in the circuit of FIG. 1. Figure 2A shows the voltage at point A in the circuit of Figure 1.When switch 1 is turned on at time _t0 , the voltage becomes a predetermined voltage, and when switch 1 is turned off at time _t2 , the voltage becomes zero. It shows. Figure 2 (b) shows the voltage at point B, and the time
Capacitor 6 rises at t ₀ and works as a time constant circuit
is differentiated by the action of , resulting in a waveform as shown in the figure.
Until time _t1 , the voltage is sufficient to turn on the second transistor 5, and after time _t1 , the voltage drops to such a level that the second transistor 5 cannot be turned on. Further, when switch 1 is turned off at time _t2 , the voltage at point B becomes a negative value, and then draws a differential waveform and becomes zero. FIG. 2C shows the base voltage of the first transistor 2, and the _second
When the transistor 5 is turned off, the value becomes a predetermined value, and when the first transistor 2 is turned on and the second transistor 5 is turned on at time _t2 , the value becomes zero and becomes a value that turns off the first transistor 2. FIG. 2D shows the voltage at the output terminal 7, which becomes a predetermined value "H" during the period up to time _t1 when the first transistor 2 is off and the period after time _t2 , and a mutating signal is generated. . Also, the time
The period from t ₁ to time t ₂ is zero "L", and no muting signal is generated. Therefore,
If the signal generated at the output terminal 7 is used to drive a muting circuit (not shown), the switch 1
It is possible to perform muting according to the switching of the switch, and it is possible to reliably prevent the generation of noise caused by the switching of the switch.

As is clear from the operation of the circuit shown in FIG. 1 and the voltages at various parts shown in _FIG .
It is a practical circuit that can be expected to have a wide range of applications because it is possible to realize a circuit that no longer generates a muting signal after the period of time has elapsed and generates a muting signal immediately when the switch is turned from on to off with a single and simple circuit configuration. be.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing voltages at various parts thereof. Explanation of main drawing numbers, 1...Switch, 2...1st
Transistor, 5... Second transistor, 6...
capacitor.

Claims (1)

[Scope of utility model registration request] A circuit for generating a muting signal in response to switching of a switch, the circuit comprising: a first transistor having a collector connected to an operating power source and a base connected to the operating power source via the switch; and a collector connected to the first transistor. and a second transistor, the base of which is connected to the operating power supply via a time constant circuit and the switch, respectively, and when the switch switches, the first transistor
A muting signal generation circuit configured to generate a muting signal to the collector of a transistor.