JPS6119545Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power amplifier circuit that operates with almost the same power efficiency as a class B amplifier operation and does not generate switching distortion.

Conventionally, single-ended push-pull (hereinafter abbreviated as SEPP) circuits have been frequently used in power amplifier circuits for audio, and in order to achieve particularly good power efficiency, a predetermined idle current flows. Class B biased to perform class amplification operation
SEPP power amplifier circuit is adopted.

However, in a class B SEPP power amplifier circuit, the transistors that supply current to the load are different depending on the input period of the positive half cycle of the input signal and the input period of the input signal of the negative half cycle; Switching of the transistor is performed in accordance with the switching of the period, and there is a drawback that switching distortion occurs due to the carrier accumulation effect of the transistor.

The present invention has been developed in consideration of the above, and eliminates the above drawbacks, operates with almost the same power efficiency as class B amplification, and responds to the switching of the input period of the positive and negative half cycles of the input signal. The object of the present invention is to provide a power amplification circuit that does not cause transistors to switch due to switching, and the present invention will be explained below using examples.

The drawing is a circuit diagram of a power amplifier circuit according to an embodiment of the present invention.

In the power amplifier circuit of this embodiment, transistors 1 and 2 constituting the output stage have their collectors connected to positive and negative power supply terminals +B and -B, respectively, and their emitters are connected to one end through resistors 5 and 6, respectively. is connected to a grounded load 7 to form a SEPP circuit, and an input signal is applied to the input side of transistor 1 through a transistor 3 whose base is grounded, and to the input side of transistor 2 through a transistor 4 whose base is grounded. A bias circuit 8 configured to receive an input signal and generate a constant bias voltage between the emitters of transistors 3 and 4 using the output current of a voltage amplification stage (not shown).
is connected. On the other hand, transistors 3 and 4
A plurality of resistors 9 and 10 are connected in series between the base of transistor 3 and the emitter of transistor 1, and resistors 9 and 10 are connected separately between the base and emitter of transistors 3 and 4 to generate a voltage that turns on transistors 3 and 4 by the flowing current. A diode 11 is connected in series between the emitter of transistor 2 and the base of transistor 4, and a plurality of diodes 12 are respectively connected between the base of transistor 3 and the emitter of transistor 2, and between the base of transistor 4 and the base of transistor 4. 1, and separate resistors 13 and 14 are connected between the two emitters.

In the power amplifier circuit configured as described above, the voltage of the bias circuit 8 is set so that the power amplifier circuit performs approximately class B amplification operation.

Therefore, when there is no input signal, the transistor 3 is set to be always on due to the voltage drop across the resistors 9 and 13 due to the current flowing by the voltage of the bias circuit 8. Transistors 1 and 2 are set to always be in the on state due to a voltage drop in
is set to be always on due to the collector currents of transistors 3 and 4. The current of transistors 1 and 2 when there is no input is the voltage between the base and emitter of transistors 3 and 4, V _BE ,
It is determined by the voltage drop across diodes 11 and 12 and the resistance values of resistors 5 and 6.

When a positive half-cycle input signal is applied to this power amplifier circuit, the emitter potentials of transistors 3 and 4 move in the positive direction, and the base current of transistor 1 is input to the base current when there is no input signal. A current with a superimposed signal flows in, and a current that amplifies the input signal flows through the emitter of transistor 1, flows into load 7 through resistor 5, and causes load 7 to generate power that is the amplified input signal. Transistor 4 tends to turn off. On the other hand, when the emitter current of transistor 1 increases, there is almost no change in the voltage V _BE between the base and emitter of transistor 3 and the potential difference between both ends of diode 11, but a voltage drop occurs across resistor 5. increases. This increase in voltage drop occurring across resistor 5 causes diode 12 to turn off. However, the voltage across the resistor 14 is constant and does not change.
Also, since the transistor 4 is biased so that it can be turned on only by the resistors 10 and 14, the transistor 4 is not turned off but is maintained in the on state, and therefore the transistor 2 is also not turned off. No, it remains on.

On the other hand, when the diode 12 is turned off, a switching current flows in the opposite direction of the diode 12 due to the carrier accumulation effect of the diode 12. Since there is a path from the resistor 14 to the diode 12, the switching current flows through this path and misses the carrier, so the switching of the diode 12 is performed rapidly by reducing the impedance of this path, and the switching due to the switching of the diode 12 Almost no distortion occurs.

Furthermore, since the operation when a negative half-cycle input signal is applied is the same as above, a detailed explanation thereof will be omitted, but in this case as well, transistors 3 and 1, which do not directly contribute to the amplification effect, are also in the off state. It never turns on and remains on. The switching of diode 11 also occurs rapidly.

Therefore, regardless of the polarity of the input signal, or even when the polarity of the input signal is switched, transistors 1, 2, 3, and 4 are always maintained in the on state without turning off, and there is no switching. No switching distortion occurs. There is also almost no switching distortion due to diode switching. Further, the transistor that contributes to the amplification action and supplies current to the load changes depending on the polarity of the input signal, and its power efficiency is approximately the same as in the case of class B amplification operation.

Further, the connection point of the cathode of the diode 11 may be changed from the emitter of the transistor 1 to its base, and the connection point of the anode of the diode 12 may be changed from the emitter of the transistor 2 to its base. In this case, a reverse voltage is directly applied between the bases and collectors of transistors 3 and 4 by diodes 11 and 12, and the same effect as described above is performed and the same effect can be obtained.

The reason why a plurality of diodes connected in series to diodes 11 and 12 is used is to increase the base-collector voltage of transistor 3 or 4 during amplification.

As explained above, according to the present invention, all transistors always operate in the on state regardless of the polarity of the input signal, and switching does not occur, so that switching distortion does not occur.

Furthermore, the transistors that cause current to flow through the load are switched depending on the polarity of the input signal, and the power efficiency is almost the same as in the case of class B amplification operation.

[Brief explanation of the drawing]

The drawing is a circuit diagram of an embodiment of the present invention. 1, 2, 3 and 4...transistor, 7...
Load, 8...bias circuit.

Claims (1)

[Scope of utility model registration request] A single-entity push-pull amplifier circuit consisting of a first and second transistor connected to the emitter and a load through first and second resistors, respectively, is connected to the input side of the first and second transistors. Separately, a third and fourth transistor with a common base connected to a bias circuit that applies a constant voltage bias between each emitter is connected, and a separate transistor is connected between the base and emitter of the third and fourth transistors. 3 and a fourth resistor are connected, respectively, between the base of the third transistor and the emitter or base of the first transistor, and between the emitter or base of the second transistor and the base of the fourth transistor. At least one diode is connected between the base of the third transistor and the emitter of the second transistor, and between the base of the fourth transistor and the emitter of the first transistor. A power amplification circuit characterized in that a fifth and a sixth resistor are connected to each other separately.