JPS6042644B2 - power amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power amplifier, and in particular is intended to minimize transient noise (hereinafter referred to as shock noise) when the power is turned on.

The transient sound generated when the power is turned on is not only unpleasant, but can also lead to damage to speakers and the like.

FIG. 1 illustrates an example of a conventional power amplifier.

In Fig. 1, A is an input terminal, and a signal applied thereto is amplified by an input differential amplifier composed of transistors Q2 and Q3, and a level shift circuit of transistors Q5 and Q6, and a level shift circuit of transistors Q, 3, and Amplified by an amplifier circuit composed of Q and O, the transistor Q
, 6, Q17, Q, 8, Q, and 0. Power is amplified by a class B push-pull output circuit, and an output signal is taken out from terminal D. Also, transistors Q, 2, Q, O
and Q constitute a constant current circuit, which supplies a constant current to a bias circuit of diodes D4 and D5 and transistor Q15, which set the idling current of the output circuit.

Next, the operation when the power is turned on will be explained.

In the circuit of FIG. 1, when power is applied to terminal E, resistors R and R are turned on. A bias voltage is supplied to the transistors Q, 2 from the transistors Q, 2, and the transistors Q, O, Q, . At this time, a transient current flows through the speaker S, producing a loud shock sound. Furthermore, when the output terminal D rises, charging of the capacitor Co starts through the resistors R and 3.
The terminal voltage of C2 increases. When the terminal voltage of the capacitor C2 becomes almost the same potential as the input terminal A, the transistor Q3 is activated. , Q and Q,O, Q,O operate, driving transistors Q, , and Q,9 to connect terminal D.
The amplification action is started by returning the potential to the operating voltage.
When the potential of the terminal D is restored, a shock sound is generated, and depending on the connection, the speaker may be burnt out. The present invention aims to provide a power amplifier that eliminates the shock noise caused by the above-described operation, and by using the circuit of the present invention, it is possible to realize a power amplifier that does not generate the above-mentioned shock noise. FIG. 2 shows an example of a concrete implementation of the circuit of the present invention. Components in FIG. 2 that perform the same functions as in FIG. 1 are designated by the same symbols. In Fig. 2, even if power is applied to terminal E, transistors Ql2 and QlO, Q
The constant current circuit configured by ll does not start operating immediately.

That is transistor Q2. , Q23, and when the power is turned on, the capacitor C2
Since the potential of transistor Q23 is low, transistor Q22 operates and the base potential of transistor Ql2 is lowered, so that the base potential of transistor Q23 is lower than that of transistor Ql. Since the base potential of the transistor Ql is higher than that of the transistor Ql. This is because it is in the 0FF state. Transistor Q9 and transistor Q2l are current supply circuits that supply current to capacitors C1 and C2, respectively.
A base bias is supplied to the base of transistor Q2O from the connection point between resistors Rl8 and Rl7, and a bias is applied to the base of transistor Q2O from the connection point between diode D2 and diode D6. Therefore, capacitor C2 is set to be charged with a higher bias voltage than capacitor C1. When capacitor C2 is charged, transistor 9
operates, transistors Q5, Q6 and transistor Ql
3, Ql4 starts operating. On the other hand, when the capacitor C2 is charged, the emitter potential of the transistor Q22 rises, so that the transistor Q12 starts operating and current is supplied from the transistor Qll. But transistor Q. and 3 transistors Qll by Ql4
Since the current supplied by is shunted to the ground potential, transistors Ql6 and Ql7 do not operate, and the output terminal D does not rise. Therefore, no shock noise is generated. transistor Q
Even after the capacitor has been charged by 2O and Q2l, only 3 pulses are applied to the capacitor C1. Since charging current is supplied from C1, the potential of C1 rises and becomes almost the same potential as that of capacitor C2. A part of the current flowing through transistor Q3 begins to flow to transistor Q2, and the currents of transistors Q5 and q decrease. The current in Ql4 also decreases. Therefore, transistors Ql6 and Ql7 start operating, and the output terminal D rises to a set voltage (usually νCC), starting a power amplification action. The rising curve of the output terminal at this time is determined by the rising characteristic of the input terminal A, that is, the time constant of the resistor R3 and the capacitor C1. If this time constant is appropriately selected, the rising curve of the output terminal will be gradual and no shock noise will be generated. Although the charging of the capacitor C1 by the transistor Q2O is not related to the reduction of shock noise, it is provided to hasten the rise time from when the power is turned on to the power amplifier until the sound output occurs.

In Fig. 2, the delay of the delay circuit is realized by using the rise of the capacitor at the NF terminal, but the circuit of the present invention can also be realized by adding another capacitor to configure the delay circuit, and the delay of the rise of the transistor can also be realized. It is clear that the circuit of the present invention can also be implemented using the delay time of a transistor circuit that uses time. As described above, according to the present invention, a power amplifier with a fast rise time and extremely low shock noise can be realized.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional power amplifier, and FIG. 2 is a circuit diagram showing a power amplifier according to an embodiment of the present invention. Rl, R2...R2l...Resistance, Cl, C2
...C4...Capacitor, Dl, D2...D
6...Diode, Ql, Q2...Q23...
...Transistor, A...Input terminal, B...
... Negative feedback terminal, C ... Ground terminal, D ...
...output terminal, E...power terminal, S...
··speaker.

Claims (1)

[Claims] 1. A differential amplifier with one base as an input terminal and the other base as a feedback terminal, an output circuit having a class B push-pull configuration, and a constant current circuit that supplies a first bias current to the output circuit. A power amplifier including a drive amplifier that receives an output of the differential amplifier and drives the output circuit,
second and third current supply circuits that detect a difference between the input terminal voltage and the negative feedback terminal voltage and a reference voltage to the input terminal and the feedback terminal, and supply current only when a power supply voltage is applied; a delay circuit for delaying the rise of the first bias current supply circuit, and when the power is turned on, the charging voltage of the feedback terminal by the third current supply circuit is equal to that of the input terminal by the second current supply circuit. A power amplifier characterized in that the voltage is set higher than a charging voltage, and the delay time by the delay circuit is set longer than the rise time of the differential amplifier and the drive amplifier.