JPH0547007B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention can remove unnecessary noise when the power is turned on in an audio circuit configured to output the output stage emitter follower output via a differentiation circuit for cutting DC components. Concerning the Miyuto device.

2. Description of the Related Art In general, the audio monitor output stage 1 of a radio receiver or television receiver is output in an emitter follower type as shown in Fig. 3, and a differentiating circuit consisting of a capacitor 2 and a resistor 3 to cut direct current. 4
A monitor output 5 is provided through the monitor output 5, which is connected to an external device 6.

In such a DC cut method of the audio circuit output stage, when the power supply voltage is turned on, the
Assuming a rising waveform of the power supply voltage as shown in FIG. Therefore, the waveform of the monitor output 5 when the power supply voltage rises is as shown in FIG. 4c, and the rise is a waveform in accordance with E·e ^-t/CR .
However, E is the emitter steady DC voltage of the transistor 7, C is the capacitance of the capacitor 2, R is the resistance value of the resistor 3, and t is time.

Therefore, when the power supply voltage rises like this, Fig. 4c
When a signal like this is input to the connected external device 6,
The level of the signal shown in FIG. 4c exceeds the input level of the external device 6.

For example, if you connect output 5 to the external auxiliary input of a stereo amplifier, the power of the stereo amplifier is already turned on and the volume of the stereo amplifier has not been turned down completely. When the power supply voltage is turned on and off, the signal shown in Figure 4c is input to the stereo amplifier when the power is turned on, which may cause unnecessary loud sounds to be generated from the speakers connected to the stereo amplifier, or the speaker's voice coil may be damaged. There is a problem with burning out.

Problems to be Solved by the Invention These conventional audio circuits are not equipped with any means to remove noise when the power is turned on, which may cause discomfort to the user or cause damage to external equipment. It is becoming.

SUMMARY OF THE INVENTION An object of the present invention is to provide a mute device that can eliminate noise when the power is turned on.

Means for Solving the Problems The mute device of the present invention is configured to output the main stage emitter follower output via a differentiating circuit, and the power supply voltage of the output stage is controlled by a resistor and a forward direction relative to the power supply voltage. A voltage is applied to a series circuit with a diode, a connection point between one end of the resistor and one end of the diode is connected to the base of the first transistor, an emitter of the first transistor is connected to the other end of the diode, and a second The bases and collectors of the transistors and the base of the third transistor are connected to each other and to the collector of the first transistor, both emitters of the second and third transistors are connected to the other end of the resistor, The collector of the third transistor is connected to the input of the differentiating circuit, the collector potential Vs of the third transistor is compared with the reference setting potential Vr by a comparator, and when Vs≧Vr is detected, the flip-flop is set, and the set output of the flip-flop is set. is connected to the base of the fourth transistor to conduct between the collector and emitter in a state of Vs≧Vr, the collector of the fourth transistor is connected to the base of the first transistor, and the fourth transistor is connected to the base of the first transistor.
The emitter of the first transistor is connected to the emitter of the first transistor, and a signal is applied to the input of the output stage via a switch controlled by the set output of the flip-flop, and this switch is set to Vs≧
It is characterized by making Vr conductive.

Effect With this configuration, the power supply voltage of the output stage (emitter floor) and the voltage of the bias circuit are not made the same as the rise of the power supply voltage, and first, when the power supply voltage is turned on, the capacitor of the differentiating circuit is connected via the third transistor. Charge. Therefore, the terminal voltage of the capacitor gradually increases and the capacitor is not charged rapidly, so that no unnecessary differential output is generated. next,
When the capacitor reaches the voltage of the output stage (the emitter DC voltage of the emitter follower) as the reference setting voltage, the capacitor is stopped charging and connected to the signal line output stage, thereby eliminating the need to output unnecessary signals. It is possible to output the original signal.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows how a mute device is incorporated into an integrated circuit 8 for an audio monitor circuit of a television receiver. Components having the same functions as those in FIG. 3 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

The circuit configuration of the miute device is such that the power supply voltage of the output stage 1 is applied to a force train circuit including a resistor 9 and a diode 10 in the forward direction with respect to the power supply voltage.
Connection point P ₁ between one end J ₁ of the diode 10 and one end J ₂ of the diode 10
is connected to the base of the first transistor Tr ₁ , the emitter of the first transistor Tr ₁ is connected to the other end J ₃ of the diode 10, and the second transistor Tr 1 is connected to the base of the first transistor Tr 1.
The base and collector of Tr ₂ and the base of the third transistor Tr ₃ are connected to each other and to the collector of the first transistor Tr ₁ , and both emitters of the second and third transistors Tr ₂ and Tr ₃ are connected to the resistor. 9, the collector of the third transistor Tr ₃ is connected to the input of the differentiating circuit 4, and the collector potential Vs of the third transistor Tr ₃ is connected to the comparator ₁₁ .
is compared with the reference setting voltage Vr to detect Vs≧Vr, set the flip-flop 12, and transfer the set output of the flip-flop 12 to the fourth transistor Tr ₄
The fourth transistor Tr ₄
The collector of the transistor Tr ₁ is connected to the base of the first transistor Tr 1, the emitter of the fourth transistor Tr ₄ is connected to the emitter of the first transistor Tr ₁ , and the set output Q of the flip-flop 12 is connected to the input of the output stage 1. A signal 14 is applied through a switch 13 controlled by a switch 13, and the switch 13 is made conductive when Vs≧Vr.

With this configuration, when the television receiver is turned on, a current determined by the resistor 9 and the diode 10 flows as shown in FIG. 2a. Second,
The third transistors Tr ₂ and Tr ₃ constitute a current mirror circuit 15, and the current mirror circuit 15 is operated with a constant current. At this time, the flip-flop 12 receives the reset signal 16 when the power is turned on.
Since the flip-flop 12 has been reset, the output Q of the flip-flop 12 is at the "L" level, and the fourth transistor _Tr4 is cut off.
Further, since the switch 13 of the transistor 7 of the output stage 1 is open when the flip-flop 12 is at the "L" level, the base of the transistor 7 of the output stage 1 is open, and the transistor 7 is cut off. In this state, the current from the current mirror circuit 15 flows through the differentiating circuit 4 composed of the capacitor 2 and the resistor 3. Therefore, output terminal 1
The voltage at 7 gradually increases as shown in FIG. 2b. As the voltage at output terminal 17 increases, it is input to voltage comparator 11. The reference voltage value Vr of this voltage comparator 11 is determined by the transistor 7
Since it is set to the steady voltage of the emitter,
When the voltage Vs reaches the reference voltage value Vr, the output Q of the flip-flop 12 is inverted to the "H" level as shown in FIG. 2e. This turns on the transistor Tr ₄ , so no current flows from the current mirror circuit 15. At the same time, switch 13 is turned on, voltage 14 (signal + DC) is applied to the base of transistor 7, and a signal is output to output terminal 17.

In this way, the present invention provides that when the power supply voltage is turned on,
Since the capacitor 2 of the differentiating circuit 4 is charged with a constant current and the terminal voltage gradually rises, the voltage at the intersection _P2 between the capacitor 2 and the resistor 3 has a small waveform as shown in FIG. 2f. Then, when the voltage Vs reaches the reference setting voltage value Vr, the constant current is turned off and (signal +DC) is applied to the base of the transistor 7, causing the transistor 7 to operate. At this time, the voltage Vr
Since the emitter voltage of the transistor 7 and the voltage of the transistor 7 are equal, the signal voltage 14 is outputted without being differentiated by the differentiating circuit 4 and no unnecessary signals are output, and the DC component is cut by the capacitor 2 and applied to the external device 6. Ru.

In FIG. 1, a resistor 18 is interposed between the emitter of the transistor 7 of the output stage 1 and the ground, but this also applies to the current source.

As described above, the power-on mute device can prevent unnecessary signals from being generated when the power supply voltage is on.
In addition, the circuit shown in Figure 1 can be integrated into an integrated circuit, so there is no cost increase, and the DC cut capacitor 2 is used as a capacitor to create the voltage Vs waveform in Figure 1, so there is no cost increase. I won't let you.

Effects of the Invention As explained above, the mute device of the present invention is configured to output the output stage emitter follower output via a differentiating circuit, and when the power is turned on, a constant current is started to flow to the capacitor of the differentiating circuit, and this terminal Since a signal is applied especially to the output stage when the voltage reaches the reference setting value, by setting the reference setting value to the emitter steady DC voltage of the emitter follower transistor in the output stage, it is unnecessary to turn on the power. It is possible to prevent the generation of noise.

Especially when the monitor output of a television receiver or radio receiver is connected to the auxiliary input of a stereo amplifier, etc., and speakers are connected to the stereo amplifier, the volume of the stereo lamp may be sufficiently reduced when the stereo amplifier is turned on. Check the power supply voltage of the TV receiver or radio receiver when the
Even when turned on and off, the signal level generated at the monitor output is as small as an elbow, so no unnecessary sound is generated from the speakers, and the input level does not exceed the input level of the stereo amplifier, so excessive input does not occur to the speakers. There is no need to turn on and off the stereo amplifier, speakers, TV receiver, or radio receiver.
This is extremely advantageous in practice, as it can protect against abnormal signals when

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an embodiment of the present invention, Fig. 2 is a waveform diagram of the main part of Fig. 1, Fig. 3 is a conventional monitor output circuit diagram, and Fig. 4 is a waveform diagram of the main part of Fig. 3. It is. 1... Output stage, 2... Capacitor, 3... Resistor, 4... Differential circuit, 9... Resistor, 10... Diode, 11... Voltage comparator, 12... Flip-flop, 13... Switch, 15... ...Current mirror circuit, _Tr1 ...first transistor, _Tr2 ...second transistor, _Tr3 ...third transistor, _Tr4 ...fourth transistor.

Claims (1)

[Claims] 1. The output stage emitter follower output is configured to be outputted via a differentiating circuit, and the power supply voltage of the output stage is applied to a series circuit of a resistor and a diode in the forward direction with respect to the power supply voltage. , a connection point between one end of the resistor and one end of the diode is connected to the base of a first transistor, an emitter of the first transistor is connected to the other end of the diode, and a second
The bases and collectors of the transistors and the base of the third transistor are connected to each other and to the collector of the first transistor, both emitters of the second and third transistors are connected to the other end of the resistor, The collector of the third transistor is connected to the input of the differentiating circuit, the collector potential Vs of the third transistor is compared with the reference setting potential Vr by a comparator, and when Vs≧Vr is detected, the flip-flop is set, and the set output of the flip-flop is set. is connected to the base of the fourth transistor to conduct between the collector and emitter in a state of Vs≧Vr, the collector of the fourth transistor is connected to the base of the first transistor, and the emitter of the fourth transistor is connected to the base of the fourth transistor. applying a signal to the input of the output stage via a switch controlled by the set output of the flip-flop;
A miute device that makes this switch conductive when Vs≧Vr. 2. The mute device according to claim 1, wherein the reference setting voltage Vr is set to a steady emitter DC voltage of an emitter follower transistor in the output stage.