JPS5921531Y2 - Muting circuit for direct coupled amplifier - Google Patents

Description

[Detailed description of the invention] The present invention relates to a muting circuit for a direct coupling amplifier.
By connecting a switching element to the final stage amplifier element and activating the switching element to ground the output terminal when the power is turned on, accurate muting can be achieved from the time the power is turned on until the amplifier returns to its normal operating state. The purpose of the present invention is to provide a muting circuit that can be applied.

FIG. 1 shows a circuit diagram of an example of a conventional direct coupling amplifier.

In the figure, when the power is turned on at time t1, transistor X2. X3 is turned on, thereby charging the capacitor C1 and increasing the potential at point a.

On the other hand, when the potential at the base (point b) of the transistor X1 reaches about 0.6 V at time t3 if the transistor X1 is of silicon type, the transistor X1 turns on.
The potential at point a decreases.

When the potential at point a reaches approximately 0.6 .mu., the amplifier enters its normal operating state.

During this time, the potentials at point a, point b, and point C are respectively curved I in Fig. 2.
~III.

However, in this conventional amplifier, the potential at point a is from time t2 to
Because of the rapid fluctuation during the period t3, there were drawbacks such as noise being extracted at the output terminal 2.

Conventionally, there are amplifiers that are equipped with a time constant circuit to prevent (muting) this noise when the power is turned on, but in order to completely mute the noise, it takes a while even after the amplifier has returned to its normal operating state. Since the time constant/number circuit is set so that muting is applied for a while, even if an input signal is received after the normal operating state is reached, it takes time until the input signal is extracted. There was a drawback.

Furthermore, in this type of amplifier, once the power is turned on, the capacitor of the time constant circuit is charged, so that muting cannot be applied if the power is turned on again immediately after being turned off.

The present invention eliminates the above-mentioned drawbacks, and one embodiment thereof will be described below with reference to the drawings.

FIG. 3 shows a circuit diagram of one embodiment of a muting circuit for a direct coupled amplifier according to the present invention.

In the figure, X4 is a transistor whose base is connected to the emitter of transistor X3 via a resistor R.
Its collector is connected to the output terminal 2, and its emitter is grounded.

Muting circuit 4 with resistor R and transistor X4
is constructed, and forms the main part of the circuit of the present invention.

The other configurations are similar to the conventional circuit shown in FIG.

In the figure, first, when the power is turned on at time t1, the current from the power supply terminal 3 flows through the rolling resistor R1.
The voltage is supplied to the coupling capacitor C3 via the capacitor C3, and charges the capacitor C3.

Here, the base of the transistor X1 is held at approximately zero by the coupling capacitor C2 and the input equivalent resistance R2, so the transistor X1 is in an off state.

Therefore, power supply current is supplied to the bases of transistors X2 and X3, and transistors X2 and X3 are turned on.
As a result, the capacitor C1 is charged and the potential at point a increases.

On the other hand, since the emitter current of the transistor X3 is supplied to the base of the transistor X1 via the resistor R3, the potential of the transistor increases.

At this time, since the resistor R3 uses a large value resistor,
The rise in potential at point a is slower than the rise in potential at point a.

Here, if each transistor is made of silicon, as shown in FIG. 2, the potential at point a (curve I
) becomes about 0.6 V or more, transistor X4 turns on, and this causes output terminal 2 to
Grounded via.

Also, at time t3, the potential of the point (curve II) is approximately 0.6
At V, transistor X1 turns on, which causes transistors X2 . Since the base current of X3 decreases, the potential at point a decreases.

When the potential at point a becomes about 0.6 V, which is the same as the potential at point a,
Transistor X4 is turned off and the amplifier is in normal operation.

As described above, according to the present invention, since the output terminal 2 is grounded during the period from time t2 to t3, the noise generated by the voltage fluctuation at point a as shown in FIG. 2 is extracted to the terminal 2. Noise is definitely muted.

In this case, the circuit of the present invention does not set the muting time using a time constant circuit such as a differentiating circuit or an integrating circuit as in the conventional example, but directly sets the muting time by changing the emitter potential of the transistor X3. 4, the voltage at point a fluctuates, that is, from the time the power is turned on until the amplifier reaches its normal operating state (time t2).
~t3) can be muted accurately.

Note that the period from time t1 to t2 is actually extremely short, and the voltage at point a does not fluctuate that much, so virtually no noise is extracted to the output terminal 2, and it does not affect hearing at all. There isn't.

Although this embodiment has been described for a three-stage amplifier, the present invention can be similarly applied to other direct coupled amplifiers as long as the terminals of the transistors in the final amplifier stage change as shown by curve I in Fig. 2. obtain.

Further, even if the potential at point a is 0°6 V or more in a normal operating state, the transistor X4 can be operated reliably when the power is turned on by appropriately dividing the voltage.

Further, the present invention is not limited to the structure in which muting is performed directly by the transistor X4 as in this embodiment, but, for example, the structure may be such that the transistor X4 is used simply as a switching element and a muting transistor is connected to this element.

As mentioned above, the muting circuit of the direct coupled amplifier according to the present invention has a predetermined value that appears in the amplifying element for a certain period of time when the power is turned on between the connection point between the final stage amplifying element and the output terminal of the direct coupled amplifier and the ground. Since the configuration has connected switching elements that are turned on by the above voltage, noise will not be generated during the period when the voltage of the final stage amplifying element is fluctuating (i.e., from the time the power is turned on until the amplifier returns to its normal operating state). This allows the amplifier to be accurately muted only during the period in which the signal is being generated, unlike conventional circuits that use a time constant circuit to set the muting time and apply muting. Therefore, the input signal can be retrieved immediately after muting is canceled, and muting is ensured each time the power is turned on even if the power is turned on and off repeatedly. Furthermore, it can be easily configured, and since the operation timing of the muting circuit is not influenced by the time constant circuit, the operation is reliable. Since the voltage is directly used, there is no need to provide a special detection circuit.

[Brief Description of the Drawings] Fig. 1 is a circuit diagram of an example of a conventional direct coupling amplifier, and Fig. 2 is a circuit diagram of the circuit shown in Fig. 1 and the circuit shown in Fig. 3 at points a and b.
, a voltage characteristic diagram at point C, and FIG. 3 is a circuit diagram of one embodiment of a muting circuit for a direct coupling amplifier according to the present invention. 1...Input terminal, 2...Output terminal, 3
...Power terminal, 4...Muting circuit, X1 to X4...Transistor, R, R3
...Resistance, C1, C2...Conductor.

Claims (1)

[Scope of utility model registration request] In a muting circuit for a direct-coupled amplifier that prevents noise generated when the power is turned on from being output to the output terminal, the output side is connected to the connection point between the final-stage amplification element of the direct-coupling amplifier and the output terminal, and the output side of the direct-coupled amplifier is A muting circuit for a direct coupled amplifier, the input side of which is connected to a terminal at which a voltage of a predetermined value or higher appears for a certain period when the power of the element is turned on, and a switching element that is short-circuited by a voltage of the predetermined value or higher.