JPH09294029A - Push-pull amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure the large amplitude of an output signal by setting the bias and signal levels of two output transistors TR independent of each other. SOLUTION: The DC component of the collector signal of a TR 16 is eliminated by a 1st capacitor 8, and only the AC component of the collector signal is applied to the base of a 1st TR 14. The DC level of the base of the TR 14 is decided by the ratio between the 1st and 2nd resistances 10 and 11 and the power voltage Vcc, and the AC level of the base of the TR 14 is decided by the capacity value of the capacitor 8 and the total value of both resistances 10 and 11. Thereby, the bias and the AC signal level of the base of the TR 14 can be freely set. The DC component of the collector signal of a TR 17 is eliminated by a 2nd capacitor 9, and only the AC component of the collector signal is applied to the base of a 2nd TR 15. Thus, the bias and the signal level of the base of the TR 15 can also be freely set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a push-pull amplifier circuit for amplifying the power of an output signal, and more particularly to a push-pull amplifier circuit capable of sufficiently securing the amplitude of an output signal.

[0002]

2. Description of the Related Art A push-pull amplifier circuit is widely used because it has an advantage that an output signal is large and even-numbered distortion and power supply ripple are canceled as compared with single amplification. As a form of the output transistor of the push-pull amplifier circuit, a combination of an NPN transistor and a PNP transistor,
Some use two NPN transistors.

A combination of an NPN transistor and a PNP transistor has an advantage that power consumption is small because one of them is turned on while the other is turned off. However, the use of the PNP transistor has a problem that the frequency characteristic of the output signal is deteriorated.
Therefore, although the power efficiency is not high, it is preferable to use two NPN transistors in consideration of the frequency characteristics of the output signal.

FIG. 2 is a circuit diagram showing a push-pull amplifier circuit using two such NPN transistors. A direct current bias is applied to the transistor (1) from a power source (2), and an AC signal is applied from a signal source (3). Is applied. Then
Output signals having opposite phases to each other are generated at the collector and the emitter of the transistor (1). Therefore, the NPN transistor (4) that forms the output transistor
In (5), signals having opposite phases are applied and driven.

As a result, a push-pull amplified output signal is obtained at the output terminal (6).

[0006]

However, in the circuit of FIG. 2, the dynamic range of the transistor (1) is narrow (about Vcc / 2) and the amplitude of the output signal cannot be made large. Further, there is a problem that the degree of freedom in designing the bias is narrow.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and a differential amplifier for amplifying an input signal to generate output signals having mutually opposite phases, and one output of the differential amplifier. A first capacitor to which a signal is applied, a second capacitor to which the other output signal of the differential amplifier is applied, first and second resistors for applying a DC voltage to the AC signal from the first capacitor, and A first and a third resistor for applying a DC voltage to the AC signal from the second capacitor, and a signal from a connection point of the first and second resistors is applied to the base.
A signal from a connection point of the transistor and the third and fourth resistors is applied to the base, a second transistor whose collector is connected to the emitter of the first transistor, and an output connected to the emitter of the first transistor. And a terminal.

[0008]

FIG. 1 shows an embodiment of a push-pull amplifier circuit according to the present invention. (7) is a differential amplifier for amplifying an input signal and generating output signals having mutually opposite phases,
(8) is a first capacitor to which one output signal of the differential amplifier (7) is applied, (9) is a second capacitor to which the other output signal of the differential amplifier (7) is applied, (10) ( 1
1) is a first and second resistor for applying a DC voltage to the AC signal from the first capacitor (8), and (12) and (13) is a first resistor for applying a DC voltage to the AC signal from the second capacitor (9). A third transistor and a fourth resistor, (14) is a first transistor to which a signal from the connection point of the first and second resistors (10) and (11) is applied to the base, and (15) is the third and fourth resistors.
It is a second transistor in which a signal from the connection point of the resistors (12) and (13) is applied to the base, and the collector is connected to the emitter of the first transistor (14).

In FIG. 1, the same circuit elements as those in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted. The alternating current signals from the signal source (3) in FIG. 1 have opposite phases to each other and form transistors (16) (1)
7) applied to the base of transistor (16) (1
Signals of opposite phases are generated at the collector of 7). An output signal having a dynamic range close to the power supply voltage is generated at the collectors of the transistors (16) and (17).

The collector signal of the transistor (16) is
The direct current component is removed by the first capacitor (8), and only the alternating current component is applied to the base of the first transistor (14). The DC level of the base of the first transistor (14) is determined by the resistance ratio of the first and second resistors (10) and (11) and the power supply voltage Vcc. In addition, the first transistor (1
The AC level of the base of 4) is determined by the capacitance value of the first capacitor (8) and the total resistance value of the first and second resistors (10) and (11). Therefore, the bias of the base of the first transistor (14) and the AC signal level can be freely set.

The collector signal of the transistor (17) is
The direct current component is removed by the second capacitor (9), and only the alternating current component is applied to the base of the second transistor (15). The bias and signal level of the base of the second transistor (15) can be set similarly to that of the first transistor (14). That is, since the bias and the signal level of the first transistor (14) and the second transistor (15) can be set independently, the degree of freedom in designing the bias circuit is increased. At the same time, since the signal can be changed in a wide dynamic range, the amplitude of the output signal can be increased.

The signals applied to the bases of the first transistor (14) and the second transistor (15) need to have the same frequency characteristics. Meanwhile, the first transistor (14)
And the base bias level of the second transistor (15) is different. Therefore, the ratio of resistors R1 and R2 in FIG.
The ratio of 4 is maintained at a predetermined value and the resistances R1, R2, R
The frequency characteristics are made equal by adjusting the absolute values of 3 and R4.

In the configuration shown in FIG. 1, the differential amplifier (7) includes a first transistor (14) and a second transistor (1).
5) can be driven. The two output signals of the differential amplifier have few amplitude and phase errors, and accurate signal transmission is possible.

[0014]

As described above, according to the present invention, since the bias and signal level of the two output transistors can be set independently, the degree of freedom in designing the bias circuit is increased. At the same time, since the signal can be changed in a wide dynamic range, the amplitude of the output signal can be increased.

Further, according to the present invention, since the two output transistors can be driven by the differential amplifier (7), the two output signals can be accurately transmitted with little error in amplitude and phase.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a push-pull amplifier circuit of the present invention.

FIG. 2 is a circuit diagram showing a conventional push-pull amplifier circuit.

[Explanation of symbols]

 (7) Differential amplifier (8) First capacitor (9) Second capacitor (14) First transistor (15) Second transistor

Claims (3)

[Claims] 1. A differential amplifier that amplifies an input signal and generates output signals having mutually opposite phases, a first capacitor to which one output signal of the differential amplifier is applied, and an output of the other of the differential amplifier. A second capacitor to which a signal is applied, first and second resistors that apply a DC voltage to the AC signal from the first capacitor, and third and fourth resistors that apply a DC voltage to the AC signal from the second capacitor A first transistor to which the signal from the connection point of the first and second resistors is applied to the base; and a signal from the connection point of the third and fourth resistor to the base, and the collector to the first A push-pull amplifier circuit comprising: a second transistor connected to the emitter of the transistor; and an output terminal connected to the emitter of the first transistor. 2. A differential amplifier that amplifies an input signal to generate output signals having mutually opposite phases, a first capacitor to which one output signal of the differential amplifier is applied, and an output of the other of the differential amplifier. A second capacitor to which a signal is applied, first and second resistors that apply a DC voltage to the AC signal from the first capacitor, and third and fourth resistors that apply a DC voltage to the AC signal from the second capacitor A first transistor to which the signal from the connection point of the first and second resistors is applied to the base; and a signal from the connection point of the third and fourth resistor to the base, and the collector to the first A second transistor connected to the emitter of the transistor; and an output terminal connected to the emitter of the first transistor, the direct current voltage level being determined by the resistance ratio of the first and second resistors. Push-pull amplifier circuit is characterized in that so as to determine the magnitude of the AC signal by the sum of the first and the resistance value of the second resistor. 3. A differential amplifier that amplifies an input signal and generates output signals having mutually opposite phases, a first capacitor to which one output signal of the differential amplifier is applied, and an output of the other of the differential amplifier. A second capacitor to which a signal is applied, first and second resistors that apply a DC voltage to the AC signal from the first capacitor, and third and fourth resistors that apply a DC voltage to the AC signal from the second capacitor A first transistor to which the signal from the connection point of the first and second resistors is applied to the base; and a signal from the connection point of the third and fourth resistor to the base, and the collector to the first A second transistor connected to the emitter of the transistor; and an output terminal connected to the emitter of the first transistor, wherein the direct current voltage level is determined by the resistance ratio of the third and fourth resistors. Push-pull amplifier circuit is characterized in that so as to determine the magnitude of the AC signal by the sum of the third and the resistance value of the fourth resistor.