JPS6040017Y2 - power amplifier circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an improvement of a push-pull amplifier circuit, and more particularly to a power amplifier circuit that eliminates the occurrence of switching distortion.

Traditionally, power amplifier circuits for audio use single-empty push-pull (hereinafter referred to as 5EPP) as shown in Figure 1a.
(abbreviated as ) circuits are frequently used.

The conventional 5EPP power amplifier circuit shown in FIG.
The transistor 3 for the output stage is connected in an inverted Darlington to the emitter follower, and the resistor 5 is connected between the collector of the transistor 3 for the output stage and the common output terminal C point, and the transistor 2 for the drive stage 2 is connected to the emitter follower. A transistor 4 for the output stage is connected in an inverted Darlington to the transistor 4, and an emitter follower with a resistor 6 connected between the collector of the transistor 4 for the output stage and the common output terminal point C is connected in series. A bias circuit 8 for applying a constant bias voltage is connected between the bases of transistors 1 and 2.

Note that 7 is a load connected between the common output terminal point C and the ground, 9 and 10 are bias resistors of the output stage transistors 3 and 4, and 11 is an input signal source.

In the above conventional power amplifier circuit, when an unmanned signal is used,
The voltage of the bias circuit 8 drives the transistor 1 for the drive stage.
and 2, the output stage transistors 3 and 4 are set so as not to be cut off, and a predetermined idling current is passed through the output stage transistors 3 and 4.

However, when the input signal source 11 is excited to the negative side and the current flowing through the load 7 increases, the voltage drop across the resistor 6 caused by the current flowing through the resistor 6, which increases due to the input signal, causes the drive stage transistor 1 to become reverse biased. , since no current flows through the resistor 9, the output stage transistor 3
is in the cutoff state.

Similarly, when the input signal source 11 is excited to the positive side and the current flowing through the load 7 increases, the voltage drop across the resistor 5 caused by the current flowing through the resistor 5, which has increased due to the input signal, causes the drive stage transistor 2 to move in the opposite direction. Since this becomes a bias and current no longer flows through the resistor 10, the output stage transistor 4 is in a cut-off state.

As mentioned above, during the positive half cycle period and the negative half cycle period of the input signal, the output stage transistors are alternately switched, and the collector voltages of the output stage transistors 3 and 4 are 'NJQ3 and IQ4.゛ is cut off alternately as shown in the upper and lower sides of Figure 1, and switching distortion occurs in the load 7 due to the carrier accumulation effect of the transistor, which worsens the distortion rate of the power amplifier circuit. was there.

The present invention has been made in view of the above, and aims to eliminate the above-mentioned drawbacks, eliminate switching of the output stage transistor over the entire cycle of the input signal, and provide a power amplifier circuit that does not generate switching distortion. The present invention will be explained below using examples.

FIG. 2a is a circuit diagram of an embodiment of the power amplifier circuit of the present invention.

The power amplifier circuit of this embodiment has a transistor 1 for the drive stage.
and 2, transistors 3 and 4 for output stage, collectors of transistors 3 and 4 for output stage and common output terminal C
resistors 5 and 6, bias circuits 8, connected separately between the collectors of transistors 1 and 2 for the drive stage, and the positive and negative power supplies 1B and -B for bias. The conventional 5 resistors 9 and 10
Configure an EPP power amplifier circuit.

This conventional 5EPP power amplifier circuit is further provided with a driving stage transistor 12 whose base is connected to the base of the driving stage transistor 1 and whose collector is connected to the collector of the driving stage transistor 1. A bias circuit 8 is provided with a drive stage transistor 13 whose base is connected to the base of the drive stage transistor 2 and whose collector is connected to the collector of the drive stage transistor 2, and a resistor 14 is connected between the emitters of the drive stage transistors 12 and 13. Accordingly, the resistor 14 is set so that the drive stage transistors 12 and 13 perform class A push-pull operation.

In the power amplifier circuit of this embodiment configured as described above,
Transistors 1, 2, 12 for the drive stage during unmanned power signal
and 13 are properly biased, the sum of the collector currents of transistors 1 and 12 for the drive stage flows to resistor 9,
The output stage transistor 3 is biased by the voltage drop generated across the resistor 9, and a predetermined idling current flows therethrough.

Similarly, the sum of the collector currents of transistors 2 and 13 for the drive stage flows through the resistor 10, and the voltage drop generated across the resistor 10 biases the transistor 4 for the output stage, so that a predetermined idling current flows.

Next, the input signal source 11 is excited to the negative side, and a current that amplifies the input signal flows through the load 7 and the resistor 6 to the collector of the output stage transistor 4. When the current flowing to the load 7 increases, the resistor Due to the voltage drop across the resistor 6 due to the collector current of the output stage transistor 4 flowing through the output stage transistor 6, the emitter potential of the drive stage transistor 1 becomes higher than its base potential, and the drive stage transistor 1 enters a cut-off state.

However, the transistor 12 for the drive stage is properly biased and performs class A amplification operation, and is never cut off.

Therefore, the collector current of the transistor 12 for the drive stage flows through the resistor 9, a bypass voltage is applied to the transistor 3 for the output stage, and the transistor 3 for the output stage does not enter the cut-off state.

In addition, the input signal source 11 is excited to the positive side, and a current that is an amplified input signal flows through the collector of the transistor 3 for the output stage through the load 7 and the resistor 5. When the current flowing through the load 7 increases, it flows through the resistor 5. Due to the voltage drop across the resistor 5 due to the collector current of the output stage transistor 3, the drive stage transistor 2 enters a cut-off state.

However, the transistor 13 for the drive stage is appropriately biased and performs class A amplification operation, and is never cut off.

Therefore, the collector current of the driving transistor 13 flows through the resistor 10, a bias voltage is applied to the output stage transistor 4, and the output stage transistor 4 is not cut off.

From the above, the collector currents IQ3 and IQ4 of transistors 3 and 4 for the output stage become as shown in the upper and lower sides of Figure 2, and the transistors for the output stage do not switch over the entire period of the input signal. Without,
No switching distortion occurs.

In addition, transistors 1 and 2 for the drive stage constitute an inverted Darlington circuit separately with transistors 3 and 4 for the output stage, and the idling current of the transistors 3 and 4 for the output stage is It also has a negative feedback effect.

That is, as the temperature of the output stage transistors 3 and 4 increases and the idling current of the output stage transistors increases, the voltage drop across the resistors 5 and 6 increases.

However, since the potential between the bases of transistors 1 and 2 for the drive stage is fixed, the voltage between the base and emitter of transistors 1 and 2 for the drive stage decreases, and the voltage between the bases and emitters of transistors 3 and 2 for the output stage decreases. The bias voltage of transistor 4 is reduced, which also serves to reduce the collector current of transistors 3 and 4 for the output stage.

As explained above, according to the present invention, the output transistor does not enter the cut-off state even during the period when the output transistor does not contribute to the amplification effect, and switches even during the positive and negative half cycles of the input signal. Never.

Therefore, switching distortion does not occur, and the distortion factor of the power amplifier circuit does not deteriorate.

In addition, the circuit for this is extremely simple, just by using a common bias circuit and adding a transistor for the drive stage that performs class A push-pull amplification, and the transistors that make up the drive stage are connected in parallel. The current capacity of the transistor for the stage is 172 times the conventional current capacity.

Therefore, high-performance transistors can be used.

Furthermore, temperature compensation can be performed sufficiently as in the conventional case, and a very stable amplification effect can be achieved.

[Brief explanation of drawings]

FIGS. 1a and 1b are a circuit diagram of a conventional power amplifier circuit and a collector current waveform diagram of a transistor for the output stage. FIGS. 2a and 2b are a circuit diagram of a power amplifier circuit according to an embodiment of the present invention and a collector current waveform diagram of a transistor for the output stage. 1.2, 12 and 13...transistor for drive stage, 3 and 4...transistor for output stage, 7...load, bias... circuit,
11...Input signal source.

Claims (1)

[Scope of utility model registration request] A transistor for the first output stage is connected to the transistor for the first drive stage in an inverted Darlington connection, and a first resistor is connected between the collector of the transistor for the first output stage and a common output terminal. , a transistor for the second output stage is connected to the transistor for the second drive stage in an inverted Darlington connection, and a second resistor is connected between the collector of the transistor for the second output stage and the common output terminal. In a single-empty push-pull power amplifier circuit in which a bias circuit for applying a constant bias voltage is connected between the bases of transistors for the first and second drive stages, the transistor for the first drive stage a third drive stage transistor whose collector is connected to the base of the first drive stage transistor; a second drive stage transistor whose base is connected to the base of the second drive stage transistor; a fourth drive stage transistor whose collector is connected to the collector of the third drive stage transistor; and a third resistor connected between the emitters of the third and fourth drive stage transistors; A power amplification circuit characterized in that transistors for third and fourth drive stages are biased to perform class A push-pull amplification operation.