JPH06204759A - Push-pull circuit - Google Patents

Abstract

PURPOSE:To obtain a push-pull circuit capable eliminating distortion in an output waveform while suppressing power consumption for the entire output. CONSTITUTION:When a signal voltage to be outputted to an external load is applied from an input terminal 12 to based of a couple of NPN transistor(TR) Q1 and a PNP TR Q2 connected in common, voltages shifted by + or -1VBE with respect to an input signal level are generated in emitters of the TRs Q1, Q2 and given respectively to bases of a push TR Q4 and a pull TR Q3. Thus, the TR Q4 is turned on when an input signal is positive, from which a current nearly equal to a collector current IC4 is outputted, and the TR Q3 is turned on when an input signal is negative, to which a current nearly equal to a collector current IC3 is received, and then a signal of the same waveform as that of the input signal is outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called push-pull circuit, and more particularly to a push-pull circuit provided at an output stage of an integrated circuit and driving a low impedance load connected to the outside.

[0002]

2. Description of the Related Art Generally, when a low-impedance load is connected to an output terminal of an IC (integrated circuit), a buffer circuit such as a so-called emitter follower circuit or a voltage follower circuit is provided at the output stage, and an output is provided through the buffer circuit. By taking out, it is possible to reduce the influence on the internal circuit. However, in these buffer circuits, a large amount of current flows in a low impedance load connected to the outside, so that a sufficient drive current does not flow in the constant current circuit that drives the buffer circuit, and the output waveform is distorted. In order to prevent this, it is usually necessary to flow a large amount of drive current through the constant current circuit.
As the power consumption of the entire C increases and becomes uneconomical,
The amount of self-heating also increases.

[0003]

Therefore, a push-pull circuit as shown in FIG. 3 is known as a circuit with few such problems. In this circuit, the emitters are connected to each other and the NPN is connected to the output terminal 28.
Type transistor 21 and PNP type transistor 22 are provided. The base of the transistor 21 is connected to the constant current source 25, and the collector is connected to the power supply Vcc. On the other hand, the base of the transistor 22 is the diode 2
It is connected to the constant current source 25 via 6, 27 and the emitter of the PNP transistor 23 whose collector is grounded, and the collector is grounded. A signal voltage having a waveform as shown in FIG. 4A is input to the base of the transistor 23 from the input terminal 29.

When the signal shown in FIG. 4 (a) is input to such a circuit, the collector current of the transistor 23 does not flow during the signal period indicated by the symbol A in FIG.
The transistor 21 turns on and the transistor 22 turns off. Therefore, a current substantially equal to the collector current of the transistor 21 is output from the output terminal 28 and flows to an external load (not connected), so that the output voltage has a D waveform as shown by symbol A ′ in FIG. 4B. Becomes

On the other hand, in the signal period shown by reference character B in FIG. 4A, the collector current of the transistor 23 flows, so that the transistor 22 is turned on and the transistor 21 is turned off. For this reason, a current substantially equal to the collector current of the transistor 22 flows from the output terminal 28, so that the output voltage has a waveform as shown by symbol B'in FIG. 4 (b).

However, in this circuit, since the push transistor 21 and the pull transistor 22 are driven by the common transistor 23, in particular, when the frequency of the input signal is several hundred KHz or more, FIG. b) C
There was a problem that a whisker-like waveform distortion appears in the part of.

The present invention has been made to solve the above problems, and an object thereof is to obtain a push-pull circuit capable of eliminating distortion of an output waveform while suppressing power consumption of the entire IC.

[0008]

A push-pull circuit according to the present invention comprises: (i) a push transistor for outputting a current from an output terminal corresponding to a positive period of a sine wave input signal; and (ii) a sine wave A pull transistor that takes in current from the output terminal corresponding to the negative period of the input signal, (iii) a push drive control transistor that controls the drive of the push transistor in response to a sine wave input signal, and (iv) a sine A pull drive control transistor for controlling the drive of the pull transistor in response to the wave input signal.

[0009]

In the push-pull circuit according to the present invention, drive control is performed by the drive control transistor provided separately for each of the push transistor and the pull transistor.

[0010]

EXAMPLES The present invention will be described in detail below with reference to examples.

FIG. 1 shows a push-pull circuit according to an embodiment of the present invention. This circuit has an NP in which the emitters are connected to each other and are connected to the output terminal 11.
N-type transistor Q4 and PNP-type transistor Q3
Is provided. The base of the transistor Q4 is connected to the constant current source 13 and also to the emitter of the PNP type drive control transistor Q2, and the collector is connected to the power supply VCC. On the other hand, the base of the transistor Q3 is connected to the constant current source 14 and also to the emitter of the NPN type driving transistor Q1, and the collector is grounded. A signal voltage having a waveform as shown in FIG. 4A is input to the base of the transistor 23 from the input terminal 29. The collector of the drive control transistor Q2 is grounded, and the collector of the transistor Q1 is connected to the power supply VCC. The bases of these transistors Q1 and Q2 are both connected to the input terminal 12.

The operation of the push-pull circuit having the above configuration will be described. When a signal having a waveform as shown in FIG. 2 is input from the input terminal 12, the collector current IC1 of the transistor Q1 flows and the collector current IC2 of the transistor Q2 changes during the period indicated by the symbol A in FIG. Not flowing. As a result, the base potential of the push transistor Q4 rises by 1VBE above the input signal voltage, and the transistor Q4 is turned on. Also, pulling transistor Q3
Since the base potential of the transistor Q3 does not drop, the transistor Q3 is turned off. Therefore, during this period A, the collector current IC3 of the transistor Q3 does not flow, only the collector current IC4 of the transistor Q4 flows, and a current substantially equal to this flows through a low impedance load (not shown) connected to the output terminal 11. Flowing. As a result, the output voltage of the output terminal 11 has a waveform as shown by the symbol A'in FIG.

On the other hand, during the period indicated by the symbol B in FIG. 2A, the collector current IC2 of the transistor Q2 flows, but the collector current IC1 of the transistor Q1 does not flow.
As a result, the base potential of the pulling transistor Q3 is 1
It drops by VBE and transistor Q3 turns on. Further, since the base potential of the pushing transistor Q4 does not rise, the transistor Q4 is turned off. Therefore, during this period B, the collector current IC4 does not flow through the transistor Q4, only the collector current IC3 of the transistor Q3 flows, and a current substantially equal to this flows from the external low impedance load through the output terminal 11. As a result, the output voltage of the output terminal 11 has a waveform as shown by the symbol B'in FIG. 2 (b).

As described above, in the present embodiment, the signal voltage to be output to the external load is applied to the bases of the pair of NPN transistor Q1 and PNP transistor Q2 whose bases are commonly connected, and the signal level is output with respect to this signal level. ± 1VBE each
The shifted voltage is output, and each output voltage is applied to the bases of the push transistor Q4 and the pull transistor Q3 to drive these transistors. Therefore, even when a low impedance load is connected to the output terminal, a low current circuit for driving the output end is not required, and only the current consumed by the connected load is supplied. . As a result, waveform distortion due to insufficient output current cannot occur essentially.

Further, since a required amount of current is supplied in association with the load, it is not necessary to constantly supply a large current consumption at the output stage as in the case of the emitter follower, and the current consumption inside the IC is greatly increased. Can be reduced. By the way,
When the current consumption under the same load was measured, the current required for the driving constant current circuit was 200 to 200 for the emitter follower type.
While it was 250 μA, it was 15 to 20 μA in the push-pull circuit of this embodiment, and a sufficiently stable output could be obtained with a small current consumption.

Further, unlike the case of the conventional push-pull circuit, the occurrence of whisker-like waveform distortion was not recognized even for an input signal having a frequency of several MHz band. Furthermore, the improvement of the output dynamic range was also recognized.

[0017]

As described above, according to the present invention,
A drive control transistor is separately provided for each of the push transistor and the pull transistor,
Since it was decided to perform drive control independently by these,
As in the case of the conventional push-pull circuit, there is an effect that waveform distortion does not occur even in the case of a high frequency input signal.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a push-pull circuit according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing waveforms of an input signal and an output signal of the push-pull circuit of FIG.

FIG. 3 is a circuit diagram showing a push-pull circuit in a conventional example.

FIG. 4 is an explanatory diagram showing waveforms of an input signal and an output signal of the push-pull circuit of FIG.

[Explanation of symbols]

11 output terminal 12 input terminal 13 and 14 constant current source Q1 NPN transistor (for pull drive control) Q2 PNP transistor (for push drive control) Q3 PNP transistor (pull transistor) Q4 NPN transistor (push transistor)

Claims (1)

[Claims] 1. A push transistor that outputs a current from the output terminal in correspondence with a positive period of a sine wave input signal, and a pull transistor that takes in a current from the output terminal in response to a negative period of the sine wave input signal. Drive transistor, a push drive control transistor for controlling drive of the push transistor in response to the sine wave input signal, and a pull drive control for controlling drive of the pull transistor in response to the sine wave input signal. A push-pull circuit comprising: a transistor.