JPS59148409A - Amplifier - Google Patents

Abstract

PURPOSE:To attain surely silencing operation with electronic circuit constitution by grounding an output of an amplifier in terms of AC before a transistor(TR) in the amplifier is driven into a saturated region after the interruption of power supply. CONSTITUTION:When the power supply is interrupted, a power supply voltage +Vcc is decreased comparatively rapidly, but the potential at a common connecting point of bias resistors R1, R2 is decreased slowly because a capacitor C4 for power supply ripple elimination is connected to the connecting point. On the other hand, a potential at a terminal 2 (output terminal of amplifier) is made almost equal to that at a terminal 5 by negative feedback via resistors R4, R5. As a result, when the difference of potentials at terminals 2 and 3 reaches a prescribed value, a TRQ11 is turned on, a base current flows to a TRQ12 and the TRQ12 is turned on. Thus, the rapid current change in an output signal being a cause to the generation of pop tone flows to ground via a capacitor C3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier equipped with a silencing circuit (muting circuit) suitable for use in audio equipment and the like.

2. Description of the Related Art It is known that a so-called pop sound is generated in a stereo device or the like when the power is turned on or disconnected. Since this pop sound is extremely annoying, various muting circuits have been proposed.

Prior to the present invention, various muting circuits were studied by the present inventor.To give an example, a large capacity capacitor charged via a diode is provided at the output end of an electromagnetic circuit. Furthermore, first and second switching transistors are provided that operate using the discharge and current of the capacitor as a power source when the power is cut off. Then, when the power switch is turned off, the mechanical switch, which works in conjunction with the power switch to close the circuit, supplies the discharge current of the capacitor to the first transistor.

When the first transistor is turned off, base current is supplied to the second transistor. The second transistor is provided between the output end of the amplifier circuit and the ground line. Therefore, when the power switch is turned off and the DC power that has not been supplied to the amplifier circuit begins to drop, the second transistor' is turned on in synchronization with the switching of the power switch. Then, the output end of the amplifier circuit is grounded via the second transistor, so to speak, and the generation of pop noises from the speaker can be prevented.

However, according to studies conducted by the present inventors, the above-described circuit configuration requires a mechanical switch that operates in conjunction with the power switch, which is expensive and increases production costs. Furthermore, a large capacity capacitor is required, which also contributes to high costs.

Furthermore, it has been found that the mechanical switches and large capacitors mentioned above pose an obstacle when implementing the muting circuit into a semiconductor integrated circuit.

Therefore, it is an object of the present invention to provide a silencing circuit that can reliably perform a silencing operation with a simple circuit configuration and is suitable for semiconductor integrated circuit implementation.

Hereinafter, an example of the present invention will be described with reference to the drawings. Note that FIG. 1 is a circuit diagram of an amplifier to which the dissipation circuit of the present invention is applied, and the internal elements indicated by the broken line 0 are made into a semiconductor integrated circuit (hereinafter referred to as an IC).

Transistors Q, +, Q++, which constitute the differential Nk
Transistor Q, which makes up the entire current mirror circuit, O4
, Darlington-connected transistors Q, s, and O6 constitute an amplifier. The transistor Q (diode D+,) transistor Q is for detecting the full saturation of the amplifier when lightning or power source is turned off, and the transistor Q, +p is used to connect the outside of the IO to perform muting operation based on the above detection result. It is set up in.

First, the circuit operation when the power supply voltage +vco (for example, 20V) is supplied via the power switch SWi will be described.

Since the bias resistors R, , R, are set to approximately the same resistance value, the base of the transistor Q1 is 1/2
oc voltage level.

Since the common connection point of the bias resistor b+RI+R* is connected to the ground potential via the No. 5 terminal and the power supply ripple removal capacitor "?'04," the common connection point is connected to the AC ripple superimposed on the power supply voltage +voo. It becomes practically insensitive to the ingredients.

An audio input signal is supplied from terminal T through capacitor O+. In addition, 08. , as, , O8, is a constant current circuit.

The change in the amplitude of the audio signal is caused by the transistor Q+,
It is converted into a current change by Q and t. transistor Q
* '(bW, h) The current change in transistor Q4 becomes Ft [change in that time.The current change in transistor Q4 is reflected in
EVB□ changes, and all Mth transistors 1. Transistor Q, s'ff:
The current 511 is controlled. (7) The change in the current flowing through the transistor 6 is transmitted as a feedback signal from the emitter of O6 through the negative feedback circuit consisting of the base of transistor Q? In addition, the output signal from the emitter of the 5 transistor Q6 is passed through the DC blocking capacitor C2 and the resistor Rook to the terminal T! as the output signal of the amplifier. and is supplied to load means RTJ such as other amplifiers and speakers.

While the above operation is being carried out, the transistors Q, z,
Q, the eyes are inactive and no muting action is performed.

That is, when the R91 constant voltage level of -1-V is supplied and the amplifier is performing normal amplification operation,
The base and emitter of transistor Q1 are reverse biased. As a result, no base current is supplied to transistor Q, and transistor Q1. is turned off.

Then, the output signal of the amplifier does not flow to the ground line via the transistor Q+*, and no muting operation is performed.

Next, we will discuss the muting operation when the power is cut off.

If the power supply is cut off at time 10 shown in FIG. 2, the power supply voltage +CO will drop relatively rapidly.

However, the potential at the common connection point of the bias resistors Rl + Rl is connected to the power source at this connection point, and the potential at the common connection point of the bias resistors Rl + Rl is connected to the pull removal capacitor C.
4 is connected, so it gradually decreases. In other words, the voltage difference between these two is 1o when the power is cut off.
The difference gradually becomes smaller.

By the way, the potential of the No. 2 terminal (i.e., the output terminal of the amplifier) is made almost equal to the potential of the common connection point of the bias resistors R, , R, (i.e., the No. 5 terminal) by DC negative feedback via the amplifier's resistors R41R11k. Ru.

／・・＜１． Potential difference between terminal 2 and terminal 3■
23 is also time t. It gradually decreases from

If the transistor Qu + Q+z is not arranged properly, the above 'r4r potential difference V23 is vOH(5at) Q
, 4+VB+! ! When Q 5 +vB]1IQ6 or less, transistor Q4 is driven to saturation. A large current flows through the emitter-collector path of ffh.

Therefore, the output transistors Qs and Qsti are strongly turned on! ! , the potential of the second terminal rapidly rises to the decreasing power supply voltage +v0°, causing pop noise.

In addition to this, according to the present invention, a muting circuit composed of transistors Q+++Q+z and the like is arranged to reduce pop noise when the power supply is cut off.

If the potential of the second terminal is 'k V z, then the transistor Q,
The emitter potential v8 of ++ is v2+v, , 6-46-4
-VB, and if the potential of terminal 3 is kVs, the base potential VB of transistor Q++ is vB-vBF3
Therefore, the four semiconductor elements D+, Qs +Qs
Since the forward voltages of the pn junctions of IQ6 are almost equal to each other, the difference between the base potential VB and the emitter potential of the Qth transistor can be approximated as follows.

■]! 1-vB5v2+VB]! lQG+vBEq5-
(Vs-V -V') BPQ3 FDIL: tV, -Vs-4V BF, - - (1) In this way, the above potential difference V. −■As shown in the equation below, the forward voltage V□ between the base and emitter of the transistor Qt+,
11, the potential V2 and the potential v3 are
When a potential difference occurs between the transistor Q++ and the transistor Q++, the transistor Q++ is turned on.

V2-V5+-4VB, >vBE, °, V, -Vs > 5 vB v
(2) Therefore, in the present invention, after tracing the source, the potential difference is
23 is -) -V vOlu(Fiat) (j4 BFtQ5 B
Before the FIQ becomes lower than 6 and the transistor Q4 is driven to the saturation region, the above equation (2) is satisfied and the Qth transistor is turned on.

As a result, paste tK is passed to transistor Q+'2 iL
, the transistor 2 operates in the on state. That is,
One end of the capacitor C3 is grounded, and the output terminal T atmosphere is grammatically grounded. Therefore, if there is a sudden change in the output signal that causes pop noise, the signal Ri is sent to the ground line via the capacitor 03. Therefore, in the muting circuit configured as described above, there is no need to provide a switch circuit like Neko's, and the pop sound that tends to occur when the power supply is disconnected can be completely eliminated due to unexpected circuit operation. It can be defended by 1.

Note that the diode D in the above circuit configuration.

is not limited to this, and may be replaced with a fixed resistor. Even if it is a bias circuit that is statically fixed to a voltage of about -2V, it is no problem.

Muding circuit ij: There is no need to provide a switch circuit with a mechanical structure, and it is suitable for C conversion.

An amplifier equipped with a silencing circuit according to the present invention can be applied to various electronic devices such as stereo equipment, audio circuits of television receivers, radio receiver towers, and the like.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the amplifier of the present invention, and Fig. 2 is a diagram showing changes in power supply voltage and bias voltage to explain the entire circuit operation. ...Transistor that constitutes the amplifier, DI...Diode for performing Sz-ting operation, Q-th, Q10...Transistor for performing all muting operations, +vo,...
·Power-supply voltage.

Claims (1)

[Claims] 1. A detection transistor (Q port) that detects all drops in the power supply voltage before the transistor (Q<) in the amplifier is driven to the saturation region after the power supply is cut off;
z) and a control transistor (ctrp) for AC grounding the output of the nuclear amplifier.