JPS62230105A - Power amplifier circuit - Google Patents

Abstract

PURPOSE:To amplify an analog signal without distortion while reducing power consumption by providing a bias resistor between input and output terminals of a complimentary push-pull emitter follower. CONSTITUTION:A bypass resistor 11 is provided between an input terminal 6 and an output terminal 7 of a booster circuit. The resistor 11 is selected to cause a voltage VBE (nearly 0.6V) of transistors (TR) 4,5 when a current slightly smaller than the maximum output current of an operational amplifier 1 flows. Then, an output waveform of the operational amplifier l to an input signal A is expressed as a signal B. When an output of the amplifier l is within + or -0.6V, only an output current of the amplifier l is fed to a load via the resistor 11. On the other hand, when the output of the amplifier l is at the outside of the range of + or -0.6V, the TRs 4,5 are operated in the booster operating region and the complementary push-pull emitter follower circuit amplifies the output current of the operational amplifier 1. Thus, the analog signal is amplified without distortion while keeping the power consumption small.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a power amplification circuit, and in particular, a complementary push-pull emitter follower provided with a bypass resistor between input and output terminals as an IC operational amplifier (hereinafter referred to as an operational amplifier). The present invention relates to a power amplifier circuit included in an output section of a power amplifier circuit.

[Prior art] Conventionally, an NPN transistor and a P
There is a power amplifier circuit that uses a complementary push-pull emitter follower using an NP type transistor as a booster circuit to increase the output current of an operational amplifier.

FIG. 5 shows a circuit diagram of such a power amplifier circuit. In the figure, 1 is an operational amplifier, and 2 and 3 are resistors. 4 is an NPN type transistor, 5 is a PNP type transistor,
It constitutes a complementary push-pull emitter follower and acts as a booster circuit to increase the output current of the operational amplifier 1.

6 and 7 are the input and output ends of this booster circuit. 8 is a load resistance, and 9 and 10 are positive and negative power supplies, respectively.

In the above configuration, the input signal is amplified by the operational amplifier 1 and then further amplified by the booster circuit. On the other hand, a part of the output current of the booster circuit is fed back to the input of the operational amplifier 1 via the resistor 2, and the operational amplifier 1 and the booster circuit are integrated to perform negative feedback control of the inverting amplifier type operational amplifier.

However, in the conventional power amplifier circuit, the output of the operational amplifier 1 is immediately amplified by a complementary push-pull emitter follower, so the small amplitude region (
Since the operational speed of the operational amplifier 1 is slow at approximately ±o, sy), crossover distortion occurs while passing through this region of approximately ±0.6V.

This state will be explained using the J signal diagram shown in FIG. Figure (A) is a waveform diagram of the input signal. The waveform of the output signal of the operational amplifier 1 corresponding to the input signal (input) j waveform is as shown in Figure (B). The section indicated by a in the figure is the section where the output of the operational amplifier 1 is within ±0.6V, and this ±0.6V is within ±0.6V.
Set a time commensurate with the operating speed of the operational amplifier 1 for the swing of v.

Meanwhile, the transistor 4 that constitutes the booster circuit of the mock-up
．． Since no bias is applied between B and 5 of 5, the output of this booster circuit becomes as shown in FIG. 5C, and crossover distortion occurs in section a.

FIG. 7 does not show the input/output characteristics of this booster circuit. As shown in the figure, there is a discontinuous region 11i (dead zone) or section in which the output does not change even if the input changes.

Furthermore, when there is no signal, a weak signal is generated near the bias limit between transistors 1 and B-5 of transistors 4 and 5, which increases power consumption and generates noise.

[Problems to be Solved by the Invention] As described above, conventional power amplifier circuits have the problems of causing crossover distortion and weak oscillation when there is no signal.

SUMMARY OF THE INVENTION An object of the present invention is to provide a power amplifier circuit that can amplify an analog signal without distortion while having a small number of components (and reducing current consumption), in view of the problems of the conventional example described above.

[Means and effects for solving the problems 1 The present invention has the following features:
Focusing on the fact that the output current is naturally small in the small amplitude region, the input stage is When the output current of the operational amplifier is small, power is supplied to the load via the bypass resistor, and the NPN and PNP transistors are placed in a zero bias state to reduce the power consumption in the booster circuit to almost zero. When the output current of the NPNl transistor and PN
It is characterized in that the booster circuit increases the output current of the operational amplifier by putting the P-type transistor in a forward bias state.

Hereinafter, the present invention will be explained in more detail using the drawings. Note that parts that are the same as those in the conventional example are represented by the same reference numerals.

FIG. 1 shows a circuit diagram of a power amplifier circuit of the present invention. The circuit shown in the same figure is different from the conventional power amplifier circuit shown in FIG.
They are different in that they have

The value of the bypass resistor 11 is selected so that when a current slightly smaller than the maximum output current of the operational amplifier 1 flows, a V[llE voltage (approximately 0.6 V) of the transistors 4 and 5 is generated.

In the above configuration, the output waveform of the operational amplifier 1 in response to the input signal shown in FIG. 2(A) is as shown in FIG. 2(B). When the output of the operational amplifier 1 is within the range of ±0.6V, the output current of the operational amplifier 1 is supplied to the load via the bypass resistor 11, while outside the range of ±0.6V is the booster operating region. Transistors 4 and 5 operate, and the complementary push-pull emitter small lower circuit amplifies the output current of operational amplifier 1.

FIG. 3 shows an equivalent circuit of the power amplifier circuit of the present invention in a region where the booster does not operate. When the booster is inactive, the power consumption of the transistors 4 and 5 is approximately zero, and the circuit is substantially equivalent to a circuit including only the bypass resistor 11.

Further, FIG. 4 shows the input/output characteristics of the booster circuit of the present invention. The portion excluding the area where the booster operates shows the voltage division characteristics of the bypass resistor 11 and the load resistor 8. As shown in the figure, although this input/output characteristic is nonlinear, there is no dead zone.

Further, although the input/output characteristics are nonlinear in this way, there is no problem in practice because it can be compensated for by a feedback circuit.

As described above, the power amplifier circuit of the present invention does not generate crossover distortion even when the operating speed of the operational amplifier is approximately 5, which is a level that can respond to the input frequency.
Good distortion rate performance can be obtained, and the original characteristics of low current consumption during no signal and a simple circuit configuration can be realized at the same time.

[Effect of the Invention J As described above, according to the present invention, an analog signal can be amplified without distortion while using a small number of parts and reducing power consumption.

Further, the power amplifier circuit of the present invention can be suitably used for intercoms and loudspeaker circuits of telephones.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of an amplifier circuit to which the power amplifier circuit of the present invention is applied, Figure 2 is a signal diagram of the circuit of Figure 1, and Figure 3 is an equivalent circuit in the small amplitude region of the circuit of Figure 1. Figure 4 is an input/output characteristic diagram of the booster circuit in Figure 1, Figure 5 is a circuit diagram of a conventional power amplifier circuit, Figure 6 is a signal diagram of the circuit in Figure 5, Figure 7 5 is an input/output characteristic diagram of the booster circuit of FIG. 5. FIG. 1... operational amplifier, 2.3... resistor, 4... NP
N type transistor, 5... PNP type transistor, 11... bypass resistor.

Claims (1)

[Claims] An operational amplifier, a complementary push-pull emitter follower for amplifying the output of the operational amplifier, a bypass resistor inserted between the input and output terminals of the complementary push-pull emitter follower, and the operational amplifier. A power amplifier circuit comprising a feedback circuit that performs negative feedback control.