JPS6040206B2 - Amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifying device, and more particularly to an amplifying device having an integrated structure.

In an IC chip, diodes and transistors occupy a smaller area than resistors and capacitors, so diodes and transistors are used as much as possible.

An example of an integrated amplifier device is shown in FIG.

In this circuit, a resistor R and diodes D, , D2
are connected in series with each other, and the diodes D,,D2
A forward voltage drop occurs across both ends of , and this voltage remains constant regardless of fluctuations in the power supply voltage. Therefore, the resistor R and the diodes D, D2 constitute a constant voltage generating circuit. The constant voltage output of this constant voltage generation circuit is supplied to the bases of transistors Q4 and Q5, and the transistors Q and Q5 and resistors R6 and R7.
constitute a constant current generating circuit. Transistor Q,,
Q2 forms the basis of a rhombic amplifier.

Transistors Q6 and R7 constitute a so-called mirror circuit. Transistor Q3 constitutes an amplifier circuit and RNF,,R
NF2 and capacitor CNF constitute a negative feedback circuit.
Resistors R2 and R3 constitute a bias circuit, and the input signal is passed through a DC cut capacitor CIN to transistors Q and
supplied to the base of The output of the amplifier is connected to the capacitor Co
It is output via uT and muting switch SW. The muting switch SW activates the coil RL' which is excited by the transistor Q which becomes conductive when the voltage across the capacitor C charged via the resistor R8 exceeds the voltage determined by the base-emitter voltage of the Zener diode Dz and the transistor Q. Therefore, opening and closing operations are performed. In the above amplifier, when the power supply voltage is cut off, the voltage across the diodes D, D2 is, for example, 1.4
Since the potential is held until it drops to about V, an unbalance in potential occurs between various elements in a differential amplifier circuit, etc., while the switch SW generates a pop sound at the discharge end that is held during the discharging time of the capacitor C. Noise is generated as a cause.

Furthermore, if the discharge of the capacitor C is not completed when the power is turned on again, the muting time will be insufficient and noise may occur at the output terminal. Furthermore, when the power is cut off, capacitor C. The charge remaining in UT is transferred to transistors Q4 and Q.
5, the presence of the capacitor CoUT causes more noise. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an amplifier that eliminates the drawbacks of the conventional amplifier and eliminates the generation of noise that causes pop sounds when the power is turned off and turned on again.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 shows a circuit according to an embodiment of the present invention.

This circuit consists of a capacitor CoFF in parallel with a resistor R,
The circuit is identical to the circuit of FIG. 1, except that it includes a transistor Q9 having a base followed by a resistor R, 3 at the connection point A between the resistor R and the diode D. The emitter of the transistor Q9 is connected to the connection point between the capacitor C and the resistor R8, and the collector is grounded. In FIG. 3, the change in the power supply voltage of the above circuit when it is cut off is shown by a solid line A, and the change in potential at point A is shown by a solid line.

As is clear from the figure, when the power supply voltage is cut off, the power supply voltage drops toward zero, but the potential at point A immediately becomes a negative potential and rises toward zero as the capacitor CoFF discharges. Therefore, transistors Q4 and Q5 are immediately turned off, and capacitor C is turned off. There is no sudden discharge of UT, and when transistor Q is turned on, the charge in capacitor C is immediately discharged, switch SW is immediately opened, and pop noise is prevented. In FIG. 4, another embodiment circuit of the present invention is shown.

In this circuit, the constant voltage generating circuit includes diodes D4 and D5 and a resistor R. A transistor Q, which receives the difference between the divided voltage of the voltage dividing circuit consisting of 2 and the power supply voltage between the base and emitter, and becomes conductive.
. This circuit differs from the circuit shown in FIG. 2 in that it is comprised of diodes D, D2 connected so that the collector currents of transistors Q and O flow in the R direction. Further, a capacitor CoFF is connected to be charged by the above-mentioned divided voltage output. The output point B of the voltage divider circuit is further connected to transistors Q, . are connected to the emitters of transistors Q, . The base of is connected to the power supply line via resistors R and o. Transistor Q, . The collectors of resistors R, . is connected to the base of the transistor false through. Other parts are second
It is the same as the circuit shown in the figure. Now, when the power is cut off, the power supply voltage drops as shown by line A in Figure 5. At this time, as the capacitor COFF discharges, the voltage at point B gradually decreases as shown by line C, and transistors Q, . , Q9 are turned on and immediately discharge the capacitor C. On the other hand, transistors Q and o are turned off, transistors Q4 and Q5 are also turned off, and no noise is generated. During this time, switch SW is also quickly opened, and no noise is output. As described above, according to the present invention, it is possible to obtain an amplifier device with a simple configuration that does not generate noise that causes pop sounds or the like when power is cut off.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional amplifier device, FIG. 2 is a circuit diagram showing an embodiment of the present invention, FIG. 3 is a voltage waveform diagram of a part of the circuit in FIG. 2, and FIG. Another embodiment of the invention, FIG. 5 is a voltage waveform diagram of a part of the circuit of FIG. Explanation of main symbols, Q,, Q2...Transistor forming a differential amplifier circuit, Q, false...Transistor forming a constant current circuit, Q6, Q7... - Transistor forming a mirror circuit, SW... switch, RL... coil, Q... transistor forming a muting circuit. Tsutomu no Zuzo 2 Figure 3 Figure 4 Kuzuj Figure

Claims (1)

[Claims] 1. A differential amplifier circuit with negative feedback that operates when a power supply voltage is supplied, a constant current source that supplies a constant current to the differential amplifier circuit, and an input of the differential amplifier circuit. a DC bias circuit that biases a DC voltage to the amplifier circuit; a switch inserted in series with the output terminal of the amplifier circuit via a first capacitor C_O_U_T; and a second capacitor charged under the supply of the power supply voltage.
An amplifier device including a capacitor C1 and a switch drive circuit that closes the switch when a voltage across the second capacitor is equal to or higher than a predetermined value, and a shorting switch that short-circuits both ends of the second capacitor when in an on state. and a control circuit that temporarily turns on the shorting switch and deactivates the constant current source when the power supply voltage is cut off. 2 The short circuit switch has a collector emitter connected to the second
Transistor Q connected to each end of the capacitor
_9, the control circuit includes a third capacitor C_O_F_F that is charged under the supply of the power supply voltage, and when the power supply voltage is cut off, the charge stored in the third capacitor is discharged. 2. The amplifier device according to claim 1, wherein said transistor is configured to be turned on for a while. 3. The short-circuit switch is composed of a first transistor Q11 and a second transistor Q_9, which is turned on when the first transistor is turned on, and whose collector and emitter are connected to both ends of the second capacitor, respectively, and the control circuit is It includes a third capacitor C_O_F_F that is charged while the power supply voltage is supplied, and when the power supply voltage is cut off, the first and second transistors are temporarily turned on by discharging the accumulated charge in the third capacitor. 2. The amplifying device according to claim 1, wherein the amplifying device is configured to be in the state.