JPH061870B2 - Amplifier circuit - Google Patents

Description

The present invention relates to an amplifier circuit having a mute function suitable for an integrated circuit.

[Conventional technology]

Conventionally, various amplifier circuits have been proposed, but among them, the circuit shown in FIG. 2 is known as an amplifier circuit having a mute function.

This circuit constitutes a differential amplifier circuit with transistors Q ₅ and Q ₆ and a constant current source I _2, and the collectors of the transistors Q ₅ and Q ₆ are connected to the primary side of a transformer T ₂ with a center tap. The secondary side of the transistor T ₂ is connected to the speaker SP ₂ , the base of the transistor Q ₅ is led to the first input terminal 2, the base of the transistor Q ₆ is connected to the collector resistance R of the transistor Q ₇ , The other terminal of the resistor R is led to the second input terminal 2, and the base of the transistor Q ₇ is led to the mute control terminal 5.

Now, when a "high" signal is input to the mute control terminal 5,
The transistor Q ₇ is turned on, and the base terminal of the transistor Q ₆ is grounded via the saturation resistance of Q ₇ .

Further, the signal (or external noise) applied to the second input terminal 2 is greatly attenuated by the saturation resistance of the resistor R ₁ and the transistor Q ₇ , and almost no signal is transmitted to the base of the transistor Q _6. Absent. Therefore, it can be seen that it has a mute function.

The first input terminal 1 is grounded.

[Problems to be solved by the invention]

In the conventional amplification circuit with a mute function described above, in order to greatly reduce the amplification factor at the time of mute, there is a method of making the resistance value extremely large or making the overdrive current of the transistor for mute control large. However, the former increases the offset voltage of the output, and the latter increases the current consumption, which is not preferable.

Further, in both cases, when the bias current of the transistor of the differential pair, that is, the current value of the constant current source is large, the amplification factor becomes large,
There was a drawback that the signal leaked to the output.

The present invention applies a strong negative feedback to the differential pair of the differential amplifier circuit to significantly reduce the gain during mute, cancels the negative feedback during amplification to obtain desired characteristics, and also loads at the time of switching between the two states. It does not change the DC state of the circuit.

[Means for solving problems]

The amplifier circuit of the present invention includes a multi-emitter type first transistor whose base is led to a first input terminal and a multi-emitter of the same polarity as the first transistor whose base is led to a second input terminal. A second transistor of a second type, the first emitter of the first transistor and the first emitter of the second transistor being connected, and being connected to the first output terminal of the mute control circuit. ,
The second emitter of the first transistor and the second emitter of the second transistor are independently connected to the second and third output terminals of the mute control circuit, respectively. The collectors of the second transistors are each connected to a load circuit.

〔Example〕

Next, the present invention will be described in detail with reference to the drawings according to its embodiments.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. The _first emitters of the multi-emitter transistors Q ₁ and Q ₂ are connected to the collector of the transistor Q ₄ ,
The second emitters of the transistors Q ₁ and Q ₂ are respectively the first collector and the second collector of the multi-collector type transistor Q ₃ .
Independently connected to the collector of. The transistors Q ₃ and Q ₄ have a differential configuration, the bases of the transistors Q ₃ and Q ₄ are respectively derived as the first and second mute control terminals 3 and 4, and the bases of the transistors Q ₁ and Q ₂ are respectively. Derived as first and second input terminals 1 and 2,
The collector is a transformer T with a speaker SP ₁ on the secondary side.
₁ and the center tap of the transformer T ₁ is connected to the higher power supply 6.

In such a configuration, assuming that a signal of "high" is input to the first mute control terminal 3 and a signal of "low" is input to the second mute control terminal 2, the current from the constant current source I ₁ is given by the transistor Q ₃ . Half of each flows through the transistors Q ₁ and Q ₂ . Also the transistor Q ₄ are turned off, naturally emitter of the transistors Q ₁ and Q ₂ are AC isolated.

Considering the amplification factor in this state, the transistors Q ₁ , Q
₂ is biased with a constant current from the emitter side, so that strong negative feedback is applied, and the amplification factor is almost zero. Therefore, an ideal mute operation state is set.

Also, "low" in the first mute control terminal 3, when the signal of "high" to the second mute control terminal 4 has entered, since the transistor Q ₃ is turned off, the transistor Q ₄ is turned on, a constant current The current of the source I ₁ flows through the transistor Q _{4 to} the emitter connection point of the transistors Q ₁ and Q ₂ ,
It becomes a normal differential amplifier circuit. Further, even when switching between both operating states, the current flowing through the primary side of the transformer T ₁ is always a constant value, so that noise does not occur.

FIG. 3 shows a second embodiment of the present invention. The operating current voltage is lower than that of the embodiment shown in FIG. The operation of the circuit is similar to that of FIG.

〔The invention's effect〕

As described above, according to the present invention, a multi-emitter transistor is used as a transistor of a differential pair, and the emitter is connected to the output of the mute control circuit so that a simple circuit has a substantially ideal mute operation state. An amplifier circuit that does not generate switching noise can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional amplifier circuit with a mute function, and FIG. 3 is a circuit diagram showing a second embodiment of the present invention. . Q _{1 to} Q ₁₅ ... Transistor, R ... Resistor, I _{1 to} I ₃
…… Constant current source, T _{1 to} T ₃ …… Transformer, SP _{1 to} SP
₃ ... Speaker, 1 ... First input terminal, 2 ... Second input terminal, 3 ... First mute control terminal, 4 ... Second
Mute control terminal, 5 ... Mute control terminal, 6 ...
High-side power supply, 7 ... Low-side power supply.

Claims (1)

[Claims] 1. A multi-emitter type first transistor whose base is led to a first input terminal and a multi-emitter type transistor whose base is led to the second input terminal and which has the same polarity as that of the first transistor. A second transistor,
The first emitter of the first transistor and the first emitter of the second transistor are connected to each other and to the first output terminal of the mute control circuit, and the second emitter of the first transistor is connected. And a second emitter of the second transistor are independently connected to the second and third output terminals of the mute control circuit, respectively, and collectors of the first transistor and the second transistor are respectively loaded. An amplifier circuit characterized by being connected to a circuit.