JPH0345566B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a muting circuit that can perform effective muting at the final stage of an amplifier and can sufficiently reduce shock noise when muting is ON or OFF.

Conventionally, when mutating an amplifier, a transistor is inserted between the signal circuit and ground and this transistor is made conductive, or a diode bridge is inserted in series in the signal circuit and this diode bridge is used. Switching methods have been adopted, but none of these methods have the ability to drive a load, so the problem is that they can only be used in limited cases as muting in the final stage of an amplifier.

Furthermore, with conventional muting circuits, it has been impossible to sufficiently reduce the shock noise when switching between muting ON and OFF.

The purpose of the present invention is to solve this problem by providing a current amplification function to the muting circuit itself, so that effective muting can be performed even when connected to the final stage of the amplifier. The object of the present invention is to provide a muting circuit that has the following characteristics. Furthermore, it is an object of the present invention to
The purpose of the present invention is to provide a muting circuit that sufficiently reduces the shock noise during ON/OFF switching, making it virtually inaudible.

Next, the muting circuit of the present invention will be explained based on an embodiment thereof. FIG. 1 is a circuit diagram showing a first embodiment of the muting circuit of the present invention. In the figure, 1 is a signal input terminal,
2 is a voltage amplification section. The output terminal of this voltage amplifying section 2 is connected to a series circuit of a transistor 3, a first diode 4, and a resistor 5, which constitute a first constant current circuit.
It is connected to the connection point of both series circuits of the resistor 6, the second diode 7, and the transistor 8 constituting the second constant current circuit, and these two series circuits form a bias circuit. ing. This bias circuit includes an NPN transistor 9 as a first transistor, a resistor 10,
As a resistor 11 and a second transistor
A current amplification stage consisting of a PNP transistor 12 is connected. transistor 3 and a transistor 13 whose base is commonly connected to the base of transistor 3;
and transistor 14 constitute a first current mirror circuit, each forming a first output, that is, the first constant current circuit, a second output, and an input. A second current mirror circuit is configured by the transistor 8 and the transistor 15 connected to their bases, and the second output of the first current mirror circuit is connected to the input of the second current mirror circuit. The transistor 8 forms the output of the second current mirror circuit, that is, the second constant current circuit.

A third current mirror circuit is constituted by the transistor 16 and the third transistor 17, and the collector of the transistor 16 which forms the output of this third current mirror circuit is connected to the transistor 14 which is the input of the first current mirror circuit. The collector of the transistor 17 constituting the input is connected to one end of diodes 18 to 22 as constant voltage elements. The emitters of a transistor 23 and a fourth transistor 24 serving as a third constant current circuit are connected to the other ends of the diodes 18 to 22. This fourth
The collector of the transistor 24 is connected to the negative power supply 25,
Further, the base is connected to a positive power supply 27 via a resistor 26. Moreover, this fourth transistor 24
The base of is grounded via a capacitor 28. A series circuit of a resistor 29 and a switch 30 is connected to this capacitor 28.

On the other hand, the base of the transistor 23 constituting the third constant current circuit is connected to the transistor 31,
32, 33, 34, diode 35, 36, 3
7, 38 and resistors 39, 40, 41, 42, and each constant current circuit of the voltage amplification section 2, and determines the operating bias of the voltage amplification section 2. There is.

Next, the operation of the mutating circuit configured as described above will be explained.

Now, considering the state in which the switch 30 is open, a voltage approximately equal to the voltage of the positive power supply 27 is applied to the mutating control input terminal 43, so the transistor 24 is in the OFF state.
The current of the transistor 23, which is the third constant current source, flows to the diodes 18 to 22 and the transistor 17, and the same current flows to the transistor 16 due to the current mirror effect, and to the transistor 3 due to the current mirror effect of the transistor 14. 13 flows into transistor 8 due to the current mirror effect of transistor 15, and the current flows through diode 4.
A current flows through a bias circuit consisting of resistors 5 and 6 and a diode 7, and the output signal of the voltage amplifying section 2 is current-amplified by the transistors 9 and 12 and appears at the output terminal 44.

On the other hand, when the switch 30 is closed, the base-emitter voltage of the transistor 24 is changed from the voltage obtained by adding the base-emitter voltage of the transistor 17 to the forward voltage of the diodes 18 to 22 as the voltage of the muting control terminal 43. Since the values of the resistors 26 and 29 are selected to be sufficiently small with respect to the applied voltage (hereinafter referred to as threshold voltage), the transistor 24
It is in the ON state, and the emitter voltage of the transistor 24, that is, the anode voltage of the diode 22, becomes smaller than the threshold voltage, and the collector current of the transistor 23, which is the third constant current source, does not flow toward the diodes 18 to 22. flows into transistor 24. Therefore, from the transistor 17 to the transistor 16, the transistors 13 and 14 forming the first current mirror circuit, and the second
Current does not flow through each transistor of transistor 15 that constitutes the current mirror circuit, and no current flows through the bias circuit consisting of diode 4, resistors 5, 6, and diode 7. , 12 are turned off, and the output of the voltage amplifying section 2 is completely cut off.

Here, considering the state when the switch 30 changes from the ON state to the OFF state, the voltage of the muting control terminal 43 is determined by the resistor 26 and the capacitor 28 from a voltage sufficiently lower than the threshold voltage. gradually increases with a time constant,
When the threshold voltage is approached, the diodes 18 to 22
As the voltage at the mutating control terminal 43 increases, the current in the diodes 18 to 22 increases, and the voltage at the mutating control terminal 43 becomes higher than the threshold voltage. After the transient, all of the collector current of transistor 23 flows into the diode, causing switch 30 to
It becomes OFF state. Here diodes 18-22
Since the change in current is directly supplied to the bias circuit consisting of the diode 4, resistors 5 and 6, and diode 7 due to the current mirror effect, it directly corresponds to the change in the amount of muting. Further, when the switch 30 changes from the OFF state to the ON state, the amount of muting gradually changes in accordance with the time constant determined by the resistor 29 and the capacitor 28 in a similar operation.

In this embodiment, a capacitor 2 is used for ON/OFF switching of muting by the switch 30.
Since it has a time constant determined by 8 and resistor 29, (1) it is possible to lower the level by moving the modulation noise caused by the signal being suddenly turned ON and OFF to the low frequency range where it is less unpleasant to the ear; (2) The offset voltage that is inevitably generated in the DC amplifier connected to the front stage of the muting circuit shifts the modulation noise caused by fluctuations due to ON/OFF of muting to the low frequency range where it is less harsh on the ears. , the level can also be lowered, making it possible to reduce the clicking noise caused by muting.

Also, by inserting a resistor in series with the emitter of the transistor that makes up the current mirror circuit,
It is clear that similar effects can be obtained by changing the mirror coefficient by changing this resistance.

Next, a second embodiment of the present invention will be described based on FIG. 2. This embodiment is the second transistor in the first embodiment shown in FIG.
PNP transistor 12, PNP transistor 4
5 and an NPN transistor 46 in a Darlington connection, and FIG. 2 is a diagram showing the vicinity of this second transistor. Typically
Since the PNP transistor inside the IC has a low DC current amplification factor, the embodiment shown in Fig. 1 had the disadvantage that it became difficult to drive when the load became heavy. Since it is constructed by darlington-connecting the and NPN transistor 46, it is possible to sufficiently drive even a heavy load, that is, a small load resistance. Here, the transistor 47 constitutes a current mirror circuit with the transistor 15,
Operates as a constant current source. Now transistor 4
Assuming that the base current of transistor 6 can be ignored, the collector current of transistor 45 is the sum of the current sucked by the constant current source of transistor 47 and the current flowing through resistor 48. By making the collector current of this transistor 45 almost equal to the current of the diode 7, the potential difference between both ends of the diode 7 and the potential difference between the base and emitter of the transistor 45 are also made almost equal, and the output of the voltage amplification section is at almost zero potential. Since the potential appears as it is at the output terminal 44, no offset occurs. That is, this embodiment has the effect of minimizing the occurrence of offset and allowing sufficient drive even when the load resistance is small.

Next, a third embodiment of the present invention will be described based on FIG. 3. This example is illustrated in FIGS. 1 and 2.
Two diodes 49 and 5 are used as the first diode 4 in the first and second embodiments shown in the figure.
0 are connected in series, and a diode 51 is connected to the emitter of the NPN transistor 9 to increase the reverse breakdown voltage between the base and emitter. In the embodiment described above, when an excessive input is applied to the input terminal 1 while the muting is ON, and a very large signal also appears at the output of the voltage amplification section 2, the reverse breakdown voltage of the diode 4 or the reverse voltage of the transistor 9 is A signal component exceeding the withstand voltage appears in the output, and as a result, the muting effect becomes smaller. In this third embodiment, a diode 51 is connected in series with the series connection of diodes 49 and 50 and the emitter of the transistor 9, so that a sufficient muting effect can be obtained even for such an excessive signal. This results in approximately twice the reverse resistance.

As described above, according to the present invention, the first constant current circuit, the first diode, and the first transistor mainly handle the positive half wave of the signal, and the first constant current circuit mainly handles the negative half wave of the signal. A current amplification circuit is configured in which the second constant current circuit, the second diode, and the second transistor are arranged symmetrically about the input terminal and the output terminal, and the current amplification circuit is connected to three current Since it is configured to be controlled by a muting control circuit equipped with a time constant circuit via a mirror circuit, when the current values of the first and second constant current circuits reach a predetermined value, the signal becomes conductive. In addition, it is possible to obtain an extremely excellent muting effect in which the signal is cut off when the current value becomes approximately zero, and a time constant circuit allows the current to gradually change when muting is switched on and off. The first and second constant current circuits always draw the same current, including the transient state of switching, and the positive and negative sides of the input and output terminals always operate under the same conditions, so in principle, no fluctuation occurs. Therefore, the effect is that the shock sound when switching between muting ON and OFF is sufficiently reduced and becomes almost audibly undetectable.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the muting circuit of the present invention, FIG. 2 is a main part circuit diagram showing a second embodiment, and FIG. 3 is a circuit diagram showing a third embodiment of the muting circuit of the invention.
FIG. 2 is a circuit diagram of main parts for showing an embodiment of the present invention. 1...Signal input terminal, 2...Voltage amplification section, 3...
...first constant current circuit, 4...first diode,
7... Second diode, 8... Second constant current circuit, 9... First transistor, 12... Second transistor, 18-22... Constant voltage element, 23
...Third constant current circuit, 24...Fourth transistor, 25...Negative power supply, 27...Positive power supply, 30...
...mutating switch, 43...mutating control input terminal, 45...PNP transistor, 46...NPN transistor, 47...
...Transistor, 49-51...Diode.

Claims (1)

[Claims] 1. A first constant current circuit 3, a first diode 4,
A second diode 7 and a second constant current circuit 8 are sequentially connected in series to form a bias circuit whose signal input terminal is the connection point between the first diode and the second diode, and the second constant current circuit 8 is connected in series. The base of the first transistor 9 is connected to the connection point between the current circuit and the first diode, and the base of the second transistor 12 is connected to the connection point between the second diode and the second constant current circuit, The collector of the first transistor is connected to a positive power supply 27, the collector of the second transistor is connected to a negative power supply 25, and the emitters of the first transistor and the second transistor are connected to each other to generate a signal. A current amplification circuit is configured as an output terminal 44, the first constant current circuit 3 is composed of a first output part of a first current mirror circuit 14, 3, 13,
The second constant current circuit 8 is composed of the output portions of second current mirror circuits 15 and 8, which receive the second output of the first current mirror circuit as an input. The outputs of the third current mirror circuits 17 and 16 are used, and are applied to the collector of the third transistor 17, which constitutes the input section of the third current mirror circuit, through constant voltage elements 18 to 22 having a predetermined voltage. Third
A bypass circuit including a fourth transistor 24 to which the constant current circuit 23 is connected, and whose emitter is connected to the connection point between the third constant current circuit and the constant voltage element, and whose collector is connected to the ground or the negative power supply. and time constant circuits 28 and 29 are provided at the base of the fourth transistor serving as the muting control input terminal 43, and the voltage of the mutating control input terminal is gradually changed via the time constant circuit. As a result, the currents flowing through the third current mirror circuit, the first current mirror circuit, and the second current mirror circuit gradually change accordingly,
A muting circuit characterized in that muting ON-OFF operates with a predetermined time constant.