JPS588766B2 - Push-pull output circuit - Google Patents

Description

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

As the output stage circuit of high output IC (integrated circuit), npn
A push-pull output circuit that does not use a mixture of transistors and pnp transistors is effective.

The basic circuit of this circuit is shown in FIG.

In the same figure, Q+ constitutes a drive transistor, and Q2
+Q3 constitutes an output transistor.

Since the collector output and emitter output of the transistor Q1 drive the output transistors Q2 and Q3, respectively, the transistors Q2 and Q3 operate in a complementary manner.

The switching diode Q4 provided between the collector and output terminal of the drive transistor Q1 is
This is to reduce the power source impedance when driving the ground side output transistor Q3, and when this diode Q4 is turned on, the accumulated charge of the output capacitor C is used as a power source to operate the driving transistors Q1 and Q3.

On the other hand, the resistor R1 provided on the emitter side of the drive transistor Q1 is for forming an alternating current path when driving the power supply side output transistor Q2 (transistor Q3 is OFF).

Also, bias diodes Q5 and Q6 are level matching diodes, and the switching diode Q
This is to make 4 conductive when there is no signal.

CS constitutes a constant current load circuit for the drive transistor Q1.

In this circuit, all the amplifying transistors in the output stage are np.
Since it can be configured with n transistors (or pnp transistors), it is suitable for semiconductor integrated circuits, but it has the disadvantage of inferior distortion characteristics, especially crossover distortion, compared to complementary circuits.

The reason for this will be explained below.

In this circuit, in order to quickly operate the ground side output transistor Q3, it is necessary to maintain the diode Q4 in a conductive state by flowing a bias current through the diode Q4 even when there is no input signal.

However, this poses a problem when operating the power supply side transistor Q2.

This is because the diode Q4 acts as an alternating current shunt between the base and emitter of the output transistor Q2, and until this diode Q4 is cut off, the collector signal of the drive transistor Q1 is almost always conductive. As a result, the input signal is not amplified by the output transistor Q2 during this period, resulting in crossover distortion.

In order to reduce the crossover distortion mentioned above, it is necessary to reduce the bias current of the diode Q4.
It would be good if it could be quickly shut down,
This is extremely difficult.

This is due to the following reason. The current flowing through the emitter resistor R1 of the drive transistor Q1 is approximately the current (2) flowing from the constant current load circuit CS.

and the bias current I flowing through the diode Q4.
The current is the sum of D and D.

Therefore, the bias current ID of the diode Q4 is obtained by the following equation (1).

VBEQ3 is the base-emitter voltage of the transistor Q3, and ■o is the constant current flowing through the constant current load circuit CS.

Here, since VBBQs/Rt fluctuates due to temperature and variations in device characteristics during manufacturing, ID<O may occur due to fluctuations in VBE/R1, so the bias current I
D must be set taking into consideration the temperature changes and variations described above, and as a result, the bias current ID must be set large.

The present invention was made to solve the above problem, and its purpose is to provide a push-pull output circuit with reduced crossover distortion.

Another object of the present invention is to provide a push-pull output circuit that improves the increase/decrease voltage characteristics of the idling current ID of a switching diode.

Still another object of the present invention is to
The object of the present invention is to provide a push-pull circuit with improved temperature dependence.

The basic configuration of the present invention for achieving the above object includes at least a drive transistor, a first output transistor, a second output transistor, and a second output transistor.
It comprises an output transistor, a constant current load circuit, a first resistance means, a switching means, and a bias means, the collector of the drive transistor is coupled to the constant current load circuit via the bias means, and the constant current load circuit is connected to the first resistor. The emitter of the drive transistor is connected to a second power supply voltage supply point via the first resistance means, and the base of the first output transistor is connected to the bias means and the constant current load circuit. The collector of the first output transistor is connected to the first power supply voltage supply point, and the emitter of the first output transistor is connected to the collector of the second output transistor. The base of the second output transistor is connected to the emitter of the drive transistor, and the second output transistor is connected to the output point of the push-pull output circuit.
In the push-pull output circuit, the emitter of the output transistor is read directly to the second power supply voltage supply point, and a switching means is connected between the output point of the push-pull output circuit and the collector of the drive transistor. A constant current circuit for flowing a constant current having a current value approximately equal to the constant current flowing through the constant current load circuit is connected between the emitter of the transistor and the second power supply voltage supply point, and a constant current circuit is connected between the base of the drive transistor and the emitter of the drive transistor. A second resistance means having a resistance value approximately equal to the resistance value of the first resistance means is connected between the first resistance means and the first resistance means. , the present invention will be explained in detail.

FIG. 1 is a circuit diagram showing a basic example of a push-pull output circuit according to the present invention.

The output transistors Q2 and Q3 are driven by signals from the collector and emitter of the drive transistor Q1, respectively, and a constant current load circuit CS is connected to the collector side of the drive transistor Q1.
In a push-pull output circuit, a switching diode Q4 is provided between the output terminal and a resistor R1 is connected to the emitter side, and a constant current corresponding to the constant current load ■0 is applied to the emitter of the drive transistor Q1. A circuit CS' is provided, and the current values of the current 0 flowing through the constant current load circuit CS and the current I0' flowing through the constant current circuit CS' are set to be substantially equal.

In addition, a resistor R2 is provided between the base and emitter of the drive transistor Q1, and its resistance value is set to the output transistor Q3.
The resistance value of the resistor R1 is set substantially equal to the resistance value of the resistor R1 connected between the base and emitter of the resistor R1.

It should be noted that setting the constant current to ■0-■0' and setting the resistors to R1-R2 means that they are within a feasible range.

According to the embodiment circuit as described above, the object can be achieved for the following reasons.

According to the circuit of this embodiment, direct current flows as follows.

A constant current ■ is applied to the collector of the drive transistor Q1.

flows into the resistor R2, and a current with a current value of VB BQI / R2 flows through the resistor R2.

On the other hand, a constant current I is applied to the emitter of the drive transistor Q1.
o', a current having a current value of VBBQ3/Rl flows through the resistor R1.

Here, ■o=■o', and VBEQI/R2=Va
Since EQ3/R1 (base-emitter forward voltage VBE is almost equal for transistors Q1 and Q3 of the same size in the same IC), the output transistors Q2,
In order for the idling current Id to flow through Q3,
If the current amplification factor of transistor Q3 is hFF, then a current equal to 1/hFE of the idling current (emitter direct current of output transistor Q2) must flow to the base of output transistor Q3 through diode Q4 and drive transistor 4Q1.

When the idling current is approximately 30 mA, the bias current of the diode Q4 can be set to an extremely small value of 0.3 mA.

This reduces crossover distortion.

This bias current is then applied to the base of the transistor.
For changes in emitter voltage VBE, resistance R1=
By setting R, 2, there is no influence due to cancellation, and therefore the temperature characteristics can be improved.

In addition, for changes in power supply voltage, constant current ■0, ■0'
If it is made to change in the same way, the bias current will only change by 1/hFE of the increase/decrease in the idling current,
Therefore, the increase/decrease voltage characteristics can be improved.

Next, FIG. 2 shows a specific example circuit of the present invention.

In the figure, a portion surrounded by a broken line is configured within the semiconductor integrated circuit, and is connected to an external circuit or supplied with power via external pins ① to ②.

Portions 1 to 11 surrounded by dashed-dotted lines in the circuit of this embodiment
1 shows the main parts of the circuit of this embodiment, and will be explained below in correspondence with the basic implementation circuit.

The transistors Q25 and Q26 constitute the drive section 1 of the output stage, and the transistor Q26 corresponds to the drive transistor Q1 in the embodiment shown in FIG.

The transistor Q25 constitutes an emitter floor amplifier circuit and is provided to enhance the driving ability of the driving section 1.

In this example circuit, the collector of the transistor Q25 is particularly connected to the output terminal ■ in order to increase the output signal amplitude of the lower output stage. According to this, the amplitude is set to Vcc/2 (midpoint potential). −(VBEQta +VB
You can get up to BQ30).

With this connection, compared to a Darlington connection in which the collectors of the upper transistors Q and 25 are connected to the collector of the transistor Q26, the output level loss for the voltage corresponding to VBEQ25 and VBEQ27 can be reduced.

In addition, Darlington-connected transistor Q28,
Q29 constitutes one output amplification section 2,
This corresponds to the output stage transistor Q2 of the embodiment shown in FIG.

Transistor Q3o constitutes the other output amplifying section 3, and corresponds to the output stage transistor Q3 of the embodiment shown in FIG.

The transistor 20 acts as a constant current load 5, and corresponds to the constant current load circuit CS of the embodiment shown in FIG.

Also, the transistor Q21 is connected to the constant current load 5! It constitutes a constant current circuit 6 provided accordingly, and corresponds to the constant current circuit CS' of the embodiment shown in FIG.

The constant current load 5 is a transistor Q that constitutes the drive section 1.
The constant current circuit 6 is connected to the collector side of the transistor Q26, and the constant current circuit 6 is connected to the emitter side of the transistor Q26.

Further, the impedance means 10 constituted by a resistor R16 corresponds to the emitter resistor R1 of the embodiment shown in FIG.

The impedance means 11 formed by the resistor R15 corresponds to the resistor R2 in the embodiment shown in FIG. 1, and its resistance value is set to be substantially equal to the resistance value of the resistor R16.

Further, a diode (diode-connected transistor) Q27 constitutes the switching means 4, and corresponds to the switching diode Q4 in the embodiment of FIG.

Further, series-connected diodes Q22 to Q24 (diode-connected transistors) connected between the constant current load 5 and the collector of the drive transistor Q26 constitute a biasing means 9, which biases the diode Q27 in the forward direction when there is no signal. This corresponds to the diode circuits Q5 and Q6 of the embodiment shown in FIG.

Further, 7 constitutes a current circuit, which is composed of transistors Q17 to Q19 and a resistor R11.

This constant current circuit drives the constant current load 5 and the constant current circuit 6, as well as configuring a bias circuit of the first stage circuit described later.

In this way, the constant currents of the constant current load 5 and the constant current circuit 6 are determined based on one constant current, so not only do they flow the same current, but they also fluctuate in the same way. Therefore, a relative balance between the two can be maintained.

Therefore, as explained above, the increase/decrease voltage characteristics can be improved.

Note that in the figure, transistors Q10 and Q11 are amplification transistors that constitute a differential amplification circuit.

Further, the transistor Q13 t Q15 constitutes an output circuit of the differential amplifier circuit, and drives the transistor Q25 of the drive section 1.

Further, 8 is a power supply circuit, which includes a Zener diode Dz
, }, and is configured to make the power supply of the differential circuit constant.

Output (W) - Distortion rate (TH) in the above specific example circuit
D) The actual measurement results of M property are shown in FIG.

In the same figure, the characteristic curves l1 and l2 indicated by solid lines are respectively expressed by the frequency f of the input signal as f=I KHZ ,1
The circuit of this embodiment set to 0KHZ is shown.

The characteristic curves "1" and "12" indicated by broken lines indicate actual values of the conventional circuit under similar conditions.

As shown in the figure, it will be understood that the distortion factor (THD) can be significantly improved by applying the present invention.

Moreover, a comparison of frequency (Hz) and distortion rate (envy) characteristics is shown in FIG.

Curve l3 shows the circuit of this embodiment, and curve l3' shows that of the conventional circuit.

It will be understood from the figure that the distortion rate can be significantly improved.

Note that the parameters at this time indicate the case where the output is 1 W and the load is 8 Ω.

[Brief explanation of drawings]

Figures 1 and 2 are circuit diagrams showing one embodiment of the present invention, Figure 3 is a circuit diagram showing an example of a conventional circuit, and Figure 4 is an output-distortion characteristic diagram of the circuit in Figure 2. , FIG. 5 is a frequency-distortion characteristic diagram of the circuit of FIG. 2. Q1-Qa, Q10-Q30...Transistor (including diode-connected ones), R1, R2, R10-R1
9, R01~RO6...Resistance, C, C1, C01~CO
7... Capacitor, 1-7... External pin, l1-l3 (
l1' to l3')... Characteristic curve, 1... Drive section, 2, 3
... Output stage amplifier section, 4 ... Switching means, 5 ... Constant current load circuit, 6 ... Constant current circuit, 7 ... Constant current circuit,
8...Power supply circuit, 9...Bias circuit.

Claims (1)

[Claims] 1 At least one drive transistor, a first output transistor, a second output transistor, a constant current load circuit, a first resistance means, a switching means, and a bias means are provided, and the collector of the drive transistor is connected to the constant current through the bias means. coupled to a load circuit, the constant current load circuit being connected to a first power supply voltage supply point, the emitter of the drive transistor being connected to a second power supply voltage supply point via the first resistor means, and the first output The base of the transistor is connected to a circuit connection point where the bias means and the constant current load circuit are connected, the collector of the first output transistor is connected to the first power supply voltage supply point, and the collector of the first output transistor is connected to the first power supply voltage supply point. The emitter is connected to the collector of the second output transistor and also to the output point of the push-pull output circuit, the base of the second output transistor is connected to the emitter of the drive transistor, and the emitter of the second output transistor is connected to the output point of the push-pull output circuit. The push-pull output circuit is connected to the second power supply voltage supply point and includes a switching means connected between the output point of the push-pull output circuit and the collector of the drive transistor, the emitter of the drive transistor and the collector of the drive transistor. A constant current circuit for flowing a constant current having a current value approximately equal to the constant current flowing through the constant current load circuit is connected between the two power supply voltage supply points, and the constant current circuit is connected between the base and emitter of the drive transistor. A push-pull output circuit characterized in that a second resistance means is connected having a resistance value approximately equal to the resistance value of the first resistance means.