JPS6049369B2 - push-pull amplifier circuit - Google Patents

Description

[Detailed description of the invention] The present invention relates to improvements in push-pull amplifier circuits.

An object of the present invention is to provide a push-pull amplifier circuit with reduced switching distortion.

A conventional class B push-pull amplifier circuit is constructed as shown in FIG. In other words, its output stage is the power supply +B and -B
The drive stage consists of complementary output transistors 1 and 2 and resistors 5 and 6, whose collectors are commonly connected between the output terminal C and the output terminal C. It consists of connected driving transistors 3 and 4 and resistors 7, 8, 9, and 10, and is configured as a symmetrical circuit. The signal voltage source 13 is a voltage amplifying circuit as a front drive stage, and the circuit in which the DC potential at the output terminal C is biased to approximately zero is shown in a simplified manner. In the class B push-pull amplifier circuit as described above, in order to stabilize the bias, a diode is installed between the base point A of the driving transistor 3 and the base point B of the driving transistor 4 for temperature compensation and stabilization. 14 and 15 and variable resistor 16
A bias circuit configured by connecting the two in series is used.

The characteristics of this bias circuit are close to constant voltage characteristics. Now, upon application of the input signal voltage that causes the potential at point B to drop, the driving transistor 4 becomes conductive, and then the output transistor 2 becomes conductive, and output power is supplied to the load 11.

At this time, the potential at point A also decreases, and the driving transistor 3 enters the cutoff state, and the output transistor 1 also enters the cutoff state, and due to the application of the input signal voltage that increases the potential at point A, the driving transistor 3 becomes conductive. Then, the output transistor J1 becomes conductive and output power is supplied to the load 11. At this time, the potential at point B also rises, driving transistor 4
And the output transistor 2 is in a cut-off state.
In this manner, the output transistors 1 and 2 and the driving transistors 3 and 4 alternately perform amplification according to the polarity of the input signal voltage to generate an output to the load 11. Even if the variable resistor 16 is adjusted to cause the unmanned signal bias current to flow from the output transistor 1 to the output transistor 2 by a predetermined value at the time of an unmanned signal, the input signal voltage will not be applied. When the driving transistor 4 becomes conductive, the voltage drop across the resistor 10 increases, so the potential difference between points B and C increases, and the potential difference between points A and C decreases, causing the driving transistor 3 to become conductive. is in a cutoff state, and the output transistor 1 is also in a cutoff state.

Also, when the input signal voltage changes and the potential at point A increases due to the input signal voltage, drive transistor 3 becomes conductive, output transistor 1 also becomes conductive, and the potential difference between points A and C increases. , the driving transistor 4 and the output transistor 2 enter a cut-off state due to a decrease in the potential difference between points B and C. Even if the bias current is passed through the output transistors 1 and 2 during the unattended signal as described above,
When the input signal voltage is applied and the load 11 is excited to a large amplitude, no bias current flows through the output transistors 1 and 2, and when a sine wave input signal voltage is applied, the output transistor 1 has a voltage as shown by the solid line in Figure 2. emitter current h1
However, an emitter current 11El2 shown by the broken line in FIG. 2 flows through the output transistor 2, and the phase difference alternately becomes 180.
This has the disadvantage that a reverse polarity emitter current flows at a certain temperature, resulting in switching distortion.

The present invention eliminates the above-mentioned drawbacks and reduces switching distortion, and will be explained below using examples.

FIG. 3 is a circuit diagram of a push-pull amplifier circuit according to an embodiment of the present invention.

This embodiment further includes a driving transistor 3 in the class B push-pull amplifier circuit shown in FIG.

A resistor 17 is connected between the emitter and the base of the driving transistor 4, and a resistor 18 is connected between the emitter of the driving transistor 4 and the base of the driving transistor 3. In the push-pull amplifier circuit j of this embodiment, adjustment is made by the variable resistor 16 so that a DC bias current of an appropriate value flows through the output transistors 1 and 2 at the time of an unmanned signal. The base current of the output transistor 1 and the current flowing through the resistor 7 become the collector current of the driving transistor 3, and the emitter current of the driving transistor 3 is divided into the resistor 9 and the resistor 17. Similarly, the base current of the output transistor 2 and the current flowing through the resistor 8 become the collector current of the driving transistor 4, and the emitter current of the driving transistor 4 is the current flowing through the resistor 10 and the resistor 18.
The current is the sum of the currents flowing in and. Now, when the potential at point A increases due to the application of an input signal voltage that increases the potential at point A, that is, a positive input signal voltage, the driving transistor 3 becomes conductive, the output transistor 1 also becomes conductive, and the potential at point C increases. The load 11 is supplied with power obtained by amplifying the positive input signal. By applying this positive input signal voltage, the base current and emitter current of the output transistor 1 increase, and as mentioned above, the sum of the base current of the output transistor 1 and the current flowing through the resistor 7 flows into the collector of the driving transistor 3. flows. However, since the characteristic between point A and point B is close to constant voltage characteristic, the characteristic between point D of one emitter of driving transistor 3 and point E of emitter of driving transistor 4 is also similar to point A. Similar to the characteristics between point B and
A substantially constant current flows through the resistor 17 regardless of the input signal voltage.

Therefore, most of the increased base current of the output transistor 1 flows through the resistor 9. For this reason, the potential difference between points D and C increases, and the potential difference between points E and C decreases, so the current flowing from point C to drive transistor 4 through point E decreases. However, since the bias current of the driving transistor 4 is a substantially constant current flowing through the resistor 18 as well as the current flowing through the resistor 17, the driving transistor 4 operates without being cut off, and the output transistor 2 will no longer be in the cutoff state.

Furthermore, even when an input signal voltage in which the potential at point B decreases, that is, a negative input signal voltage is applied, the circuit shown in Figure 3 acts in the same way as above because it is a symmetrical circuit, and in this case it directly contributes to the amplification effect. The drive transistor 3 and output transistor 1 that are not in the cut-off state will no longer be in the cut-off state.

Therefore, when the input signal voltage is a sine wave, the emitter currents IEl and H2 of the output transistors 1 and 2 become as shown in FIG. 4, and operate like an oil-class push-pull amplifier circuit, causing switching distortion. This reduces the distortion rate.

Furthermore, when the positive input signal voltage is applied, the emitter current of the driving transistor 3 becomes even larger than in the previous case, and the potential difference between point D and point C becomes larger than in the above case. When the polarity of the potential difference with point E is reversed and the potential at point E becomes higher than the potential at point C, the resistor 18
The current flowing from point E to point C passes through the resistor 10 and the driving transistor 4 becomes cut-off, but in this case, the driving transistor 4 transitions smoothly to the cut-off state rather than abruptly. Since the output transistor 2 enters the cutoff state, the transition to the cutoff state of the output transistor 2 is also smooth, and the distortion rate is improved. Further, in the case where the emitter current of the driving transistor 4 increases when a negative input signal voltage is applied, the operation is similar to that described above.

Next, other embodiments of the present invention will be described.

FIG. 5 is a circuit diagram of a push-pull amplifier circuit according to another embodiment of the present invention. In this embodiment, a diode 19 is added between the resistor 9 and point C in addition to the circuit of the embodiment shown in FIG.
is also constructed by connecting a diode 20 between point C and the resistor 10.

By connecting diodes 19 and 20,
Diodes 21 and 22 are further connected to the bias circuit. Further, the variable resistor 16 is adjusted so that an appropriate bias current flows through the output transistors 1 and 2 when an unmanned power signal is applied.

Therefore, the operation of the push-pull amplifier circuit of this embodiment is similar to that of the above-mentioned embodiment, but in the above-mentioned embodiment, the amplitude of the input signal voltage is large and the emitter currents of the driving transistors 3 and 4 are large. In other words, when a positive input signal voltage is applied, the potential at point E becomes higher than the potential at point C, and when a negative input signal voltage is applied, the potential at point D becomes lower than the potential at point C. In this case, due to the action of the diode 20, the current flowing through the resistor 18 flows to the driving transistor 4 and does not cut off the driving transistor 4, and due to the action of the diode 19, the current flowing through the resistor 18 flows from the driving transistor 3 to the resistor 17.
The current will no longer flow into the drive transistor 3 and cause the drive transistor 3 to be cut off.

Therefore, the output transistors 1 and 2 are not cut off, and the emitter current shown in FIG. 4 flows, preventing switching distortion from occurring and reducing the distortion factor.

Also, resistors 17 and 18 in one embodiment and other embodiments.
The same effect can be obtained by using a constant current circuit in place of the resistors 17 and 18 instead of the current path.

As explained above, according to the present invention, in order to smoothly transition the output transistor to the cutoff state or to prevent the output transistor from being in the cutoff state, it is possible to reduce the switching distortion of the push-pull amplifier circuit. Liru.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional class B push-pull amplifier circuit. FIG. 2 is an emitter current waveform diagram of the output transistor of the class B push-pull amplifier circuit shown in FIG. FIG. 3 is a circuit diagram of a push-pull amplifier circuit according to an embodiment of the present invention. FIG. 4 is an emitter current waveform diagram of the output transistor of the push-pull amplifier circuit of FIG. 3. FIG. 5 is a circuit diagram of a push-pull amplifier circuit according to another embodiment of the present invention. )1 and 2...
- Output transistors, 3 and 4...drive transistors, 19 and 20...diodes.

Claims (1)

[Claims] 1. A push-pull amplifier configured with a symmetrical circuit in which the collectors of a pair of complementary output transistors are connected to an output end, and a driving transistor is connected to each of the output transistors in an inverted Darlington manner. A push-pull amplifier circuit, characterized in that a current path is provided between the base of the one driving transistor and the emitter of the other driving transistor. 2. The push-pull amplifier circuit according to claim 1, wherein the current path is a resistor. 3. The push-pull amplifier circuit according to claim 1, wherein the current path is a constant current circuit.