JPS6217889B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a quasi-complementary push-pull output circuit.

In the push-pull output circuit, for example, the first
As shown in the figure, there is a resistance between the base and emitter.
Output transistors _{Q 2 and} Q ₄ provided with R ₁ and R 2 are driven by drive transistors Q ₁ and Q ₂ .

The reason why the resistors R ₁ and R ₂ are provided is because of the leakage current in the drive transistors Q ₁ and Q ₃ .
The purpose is to prevent the bias currents of the output transistors Q ₂ and Q ₄ from changing.

Therefore, in the conventional push-pull output circuit, the values of the resistors R ₁ and R ₂ were set to R ₁ =R ₂ .

The inventor of this application believes that in a quasi-complementary type push-pull output circuit, the above-mentioned resistor
It has been found that setting the values of R ₁ and R ₂ equally increases crossover distortion.

The present invention was made in order to provide a quasi-complementary push-pull output circuit that improves crossover distortion under small idling current.

In this invention, the value of the resistance provided between the base and emitter of an output transistor connected in an inverted Darlington is set to be larger than the value of the resistance provided between the base and emitter of the other output transistor. It is something.

Outline of typical inventions disclosed in this application is as follows.

That is, a Darlington-connected first output transistor circuit for obtaining one half-wave output;
and a second output transistor circuit connected in an inverted Darlington to obtain the other half-wave output, and the first output transistor circuit includes a first transistor _Q1 and a transistor identical to the first transistor. a second transistor Q ₂ of conductivity type and having its base connected to the emitter of the first transistor; said second output transistor circuit has a second transistor Q2 of conductivity type opposite to said first transistor; A fourth transistor _Q3 having the same conductivity type as the first transistor and whose base is connected to the collector of the third transistor.
a transistor _Q4 , and at least one of the bases of the first transistor and the third transistor or the emitter of the second transistor and the third transistor. Bias circuit connected between
Q ₅ ′, Q ₆ ′, Q ₇ ′: Equipped with Q ₅ , Q ₆ , Q ₇ , and the second
A load is connected to a common connection point between the emitter of the transistor and the collector of the fourth transistor;
and a second resistor _R2 connected between the base and _emitter of the fourth transistor of the second output transistor circuit. The quasi-complementary push-pull output circuit is characterized in that the value of the second resistor is set larger than that of the first resistor.

Hereinafter, the present invention will be specifically explained with reference to Examples.

Constant current transistor Q ₁₃ as a load and Darlington-connected transistors Q ₁₁ and Q ₁₂ constitute a large-amplitude class A amplifier circuit, and the large-amplitude signal formed here is transmitted to Darlington-connected transistors Q ₁ and Q ₂ and inverted Darlington-connected transistors Q ₃ and Q ₄ form a class B amplified output that forms a positive half-wave output and a negative half-wave output, respectively.

A transistor _Q5 provided in a closed loop including the above transistors _Q1 , _Q2 , _Q4 , a resistor _R3 provided between its base and emitter, and a diode-connected series transistor provided between its base and collector. Transistors Q ₆ and Q ₇ constitute a bias circuit, and the bias voltage formed between the emitter and collector of the transistor Q ₅ is applied to the above drive via the base and emitter of the transistor Q ₈ based on the midpoint voltage. Applied to the emitter of transistor _Q3 . Between the base of this transistor _Q3 and the base of the other drive transistor _Q1 ,
A diode-connected transistor _Q9 is provided to offset the voltage between the base and emitter of the transistor _Q8 .

Note that the bias circuit is driven with a constant current by a constant current transistor _Q10 in order to stabilize the bias voltage.

As mentioned above, there is a drive transistor between the base and emitter of the output transistors Q ₂ and Q ₄ .
Resistors R ₁ and R ₂ are provided to prevent bias fluctuations due to leakage current in Q ₁ and Q _3. However, in order to improve crossover distortion under small idling current, the above resistor R ₁ ,R ₂
The value of is set to R ₁ <R ₂ .

Under the conventional technology in which the resistance values of the resistors R ₁ and R ₂ are set equal, a minute signal current flows from the state in which only idling current flows to the output transistors Q ₂ and Q ₄ to the output transistor Q ₂ . In the minute current region where the current begins to flow, in other words, at the rise of the positive half-wave signal, the bias of the other drive transistors _Q3 and _Q8 decreases by the increase in the voltage between the base and emitter due to the signal current of the transistor Q2 _. I will do it. This is because the output transistor _Q2 is provided in a closed loop to which a constant bias voltage is applied. In other words, the transistor Q ₅ that constitutes the bias circuit
Since the voltage between the base and emitter of Q ₇ and transistors Q ₈ and Q ₉ is constant, the above output transistor
The increase in the voltage between the base and emitter of _Q2 acts to reduce the bias voltage of the drive transistors _Q3 and _Q8 .

Therefore, as shown in FIG. 3, the output signal V _OUT
On the positive side, no distortion occurs.

On the other hand, at the start-up time when only the above-mentioned idling current is flowing and a minute current begins to flow toward the output transistor Q ₄ , this signal current increases the voltage between the base and emitter of the output transistor Q ₄ . However, this transistor Q ₄ is not configured in a closed loop including the above bias circuit, so transistors Q ₃ and Q ₈
Since the increase in the voltage between the base and emitter of Q2 is small, the other output transistor _Q2 does not turn off immediately. That is, the increase in the voltage between the base and emitter of the transistors Q ₃ and Q ₈ is due to the output current signal converted to the base current of the output transistor Q ₄ and hardly changes in the small output current region. In other words, when transistor Q ₄ is conductive, transistors Q ₁ and Q ₂ remain conductive due to the idling current, so the current amplification factor when transistor Q ₄ is conductive is substantially reduced. .

Therefore, if the resistance R ₁ = R ₂ , the unbalance of the amplification factor due to the above-mentioned reason will cause crossover distortion in the negative part b of the output waveform, as shown in Figure 3. .

In this embodiment, the resistor R ₂ is increased to compensate for the unbalance of the amplification factor.

For example, if resistance R ₁ is 1KΩ, resistance R ₂ is
The resistance is increased to 5KΩ.

Thereby, it is possible to increase the amplification factor of the drive transistor _Q3 and improve crossover distortion at the time of falling.

Note that this resistor R ₂ is used not only to prevent bias fluctuations due to leakage current of the drive transistor Q ₃ as described above, but also to prevent bias fluctuations between the base and the collector during positive half-wave output when the output transistor Q ₄ is off. Since the resistor is used to prevent notching distortion by configuring a discharge path for the charge charged to the junction capacitance, the value of the resistor should be selected with this consideration in mind.

In addition, in this embodiment circuit, in order to obtain a large positive output amplitude, the bootstrap capacitor _C2 is used as the power supply voltage for the drive transistor _Q1 and the constant current transistors _Q10 and _Q13 .

The present invention is not limited to the above-mentioned embodiment. For example, as shown in FIG. 2, the bias circuit is connected to a diode (diode-connected transistors...Q ₅ ' to Q ₇ ') between the bases of the drive transistors Q ₁ and Q ₃ . , the closed loop that includes this bias circuit does not include the output transistor Q ₄ that forms a negative half-wave output, so the same crossover distortion as described above occurs. resistance like
R ₁ <R ₂ . In this way, the method of applying the bias voltage can be modified in various ways, but
It always involves similar problems.

Therefore, the present invention can be widely used in semi-complementary push-pull output circuits.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams of quasi-complementary push-pull output circuits, respectively, and FIG. 3 is a waveform diagram of a conventional quasi-complementary push-pull output circuit.

Claims (1)

[Claims] 1 A first output transistor circuit connected in Darlington to obtain one half-wave output, and a second output transistor circuit connected in inverted Darlington to obtain the other half-wave output, The first output transistor circuit has a first transistor and a second transistor having the same conductivity type as the first transistor and whose base is connected to the emitter of the first transistor. The output transistor circuit includes a third transistor of a conductivity type opposite to that of the first transistor, and a fourth transistor of the same conductivity type as the first transistor, the base of which is connected to the collector of the third transistor. a base of the first transistor and a base of the third transistor.
a bias circuit connected between at least one of the base of the transistor of the second transistor and the emitter of the second transistor and the emitter of the third transistor; a load is connected to a common connection point with the collector of the fourth transistor; a first resistor connected between the base and emitter of the second transistor of the first output transistor circuit; In a quasi-complementary type push-pull output circuit including a second resistor connected between the base and emitter of the fourth transistor of the transistor circuit, the value of the second resistor is set larger than that of the first resistor. A quasi-complementary push-pull output circuit characterized by: