JPS6212687B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an integrated circuit, particularly a driver circuit provided at the output section of an operational amplifier for driving a load.

Conventionally, the circuits shown in FIGS. 1 and 4 have been used as driver circuits of the above type.
Since the circuit shown in the figure is mainly used for one power supply, it has the disadvantage that crossover distortion occurs when used with two power supplies.
Furthermore, since the circuit shown in FIG. 4 is mainly used for two power supplies, crossover distortion does not occur, but when used with one power supply, there is a drawback that the output does not swing to ground.

The present invention improves these points and proposes a driver circuit that swings the output to ground even when one power supply is used and does not cause crossover distortion even when two power supplies are used. In an integrated circuit in which a driver circuit is provided between a unit and an output terminal for connecting a load, the driver circuit is connected between a pair of power supply lines by connecting a first transistor and a second transistor in series, and the series connection. point as the output terminal, and also includes a constant current source, a bias circuit that compensates for the voltage between the base and emitter of the transistor, and a third
transistors are connected in series between the pair of power supply lines, a fourth transistor and a first resistor are connected in parallel to the bias circuit and the third transistor, and the input terminal of the third transistor is Second
The input terminal of the fourth transistor is connected to the output terminal of the main amplification section through the resistor, and the input terminal of the first transistor is connected to the constant current source and the bias circuit. Further, the input terminal of the second transistor is connected to the connection point between the bias circuit and the third transistor. This will be explained in detail below with reference to the drawings.

First, referring to FIG. 1, in this figure 10 is a main amplifier section, and a load 20 is connected to the driver circuit 3 at the output terminal of this section.
Connected via 0. Circuits with such a configuration are often found in operational amplifiers. This driver circuit 30 consists of a constant current source 12 and transistors 14, 16, and 18. The base of the transistor 14 serves as an input terminal, and the connection point between the emitters of the transistors 16 and 18 serves as an output terminal 26. l ₁ and l ₂ are a pair of power supply lines; in this example, +V _CC is applied to line l ₁ , and line l ₂ is connected to ground. In other words, it is powered by a single power supply. 20 is the load, output terminal 26 and ground GND
connected between. In this circuit, when the output of the main amplifier section 10 completely turns on the transistor 14, the potential at point P drops to approximately the ground level, and the transistor 16 turns off. That is, the output voltage V ₀ swings to ground, and no power is supplied to the load 20.
Note that the potential of the point P of the transistor 18 is the output terminal 26.
Since it turns on only when the potential becomes lower than the potential _{by VBE} , in the case of this single power supply, it does not contribute to any operation and is in a dormant state.

This transistor 18 becomes effective when this circuit is used with two power supplies. That is, in this case, the situation is as shown in FIG. 2, and the operation is as follows.
That is, when the output of the main amplifier section 10 is at L level and the transistor 14 is turned off, the transistor 16 is turned off.
is turned on, and the output voltage V ₀ increases to the potential of the power supply V _CC . From this state, the output voltage of the main amplifier 10 rises and begins to conduct the transistor 14 , and the base current of the transistor 16 flows through the transistor 14 . The output voltage V ₀
begins to decline. When transistor 16 is on, transistor 18 is off because its base potential is higher than its emitter potential. output voltage
V ₀ falls near the ground level, specifically point P
The base voltage at which the transistor 16 is turned off is at a potential of
When the emitter voltage drops below V _BE , transistor 1
6 is turned off, but transistor 18 is also still off. Only when the potential at point P falls below the ground level and below V _BE of transistor 18 does transistor 18 turn on, supplying current to load 20 and driving output voltage V ₀ to the negative side. When the transistor 14 is completely turned on, the potential at point P is approximately equal to the potential of the negative power supply -V _EE , and the output voltage V ₀
is also driven close to it. In this way, the output voltage V ₀ does not follow the input voltage V _i near the zero point, but there is a portion where it changes stepwise as shown in the figure. In other words, crossover distortion occurs.

The circuit shown in FIG. 4 was designed to eliminate this crossover distortion, and the circuit shown in FIG.
and the emitter-base of transistor 18 by inserting two series connected diodes 32, 34 which produce a voltage equal to the 2V _BE they produce.
Using such a bias circuit, transistor 1
6 is also turned off when the potential at point P becomes less than V _BE , but the potential at point Q, which is two diodes below it, is then less than -V _BE , so transistor 18 is about to turn on. There is. Point P is +
V _BE , when point Q is -V _BE, both transistors 1
6 and 18 are both conductive and current (idling current) is flowing. Therefore, the potential at point 26 is almost exactly at ground level, and above that the potential of transistors 16, 1 is on the positive side, and thereafter on the negative side.
8, the crossover distortion of the output voltage V ₀ as shown in FIG. 2 does not occur.

However, this circuit still has the drawback that the output voltage V ₀ is not driven to ground when used with a single power supply. That is, in this case, the third
As shown in the figure, even when the transistor 14 is completely turned on and the point P has the lowest potential, the potential is V
_CESAT +2V _BE , and even if the saturation voltage _VCESAT of the transistor 14 is zero, it is still 2V _BE , and therefore the output voltage remains at _VBE , which is one less than _VBE .

In this way, the conventional circuits shown in Figures 1 and 2 can drive _V0 to O when using a single power supply, but crossover distortion occurs when using two power supplies. There is a drawback in that a circuit without a power supply cannot drive V ₀ to O when using a single power supply.

The present invention aims to improve these points, and an embodiment thereof is shown in FIG. As is clear from a comparison with FIG. 4, a transistor 36 is added to this circuit. Like the transistor 14, the transistor 36 has its base and emitter, that is, its input terminal, connected to the output terminal of the main amplifying section 10. That is, in detail, the base of the transistor 36 is connected to the main amplifier 1.
0 output, the collector is connected to point P, and the emitter is connected via a resistor 40 to the negative power supply _-VEE . The base of the transistor 14 is also connected to the main amplifier 1.
0, and a resistor 38 is inserted into the connection circuit.

The resistors 38 and 40 are used to adjust the ratio of currents supplied from the main amplifier section 10 to the bases of the transistors 36 and 14 to an appropriate value, and are set so as to satisfy the following conditions. In other words, in the case of a two-power supply system, when the output terminal 26 is at ground level, an appropriate idling current can be passed through the transistors 16 and 18, and when saturation is on the negative (-V _EE ) side, a specified sink current can be passed through the transistor 18. A base current that can be drawn is made to flow to the transistor 14. 1 power supply (-V _EE is grounded)
In this case, all the current of the constant current source 12 is transferred to the transistor 3.
6, the base current necessary for the transistor 36 to be saturated can be supplied to the transistor 36. If these conditions are satisfied, in the case of a single power supply system, the transistors 36 and 14 will work in a balanced state against saturation to the ground side, and the voltage at the output terminal 26 will be V ₀₁ = V _CE14 +
2V _BE -V _BE16 (Here, V _CE14 is transistor 14
The collector-emitter voltage at saturation, 2V _BE is the forward voltage drop of diodes 32 and 34, V _BE16
is the base-emitter voltage of transistor 16)
When this happens, the transistor 36 also moves toward saturation, so the potential at the output terminal 26 drops below V ₀₁ . Therefore, the collector current of the transistor 14 stops flowing, and eventually the transistor 36 is connected to the constant current source 12.
Since all of the current is absorbed and saturation occurs, both transistors 16 and 18 are cut off, and the output terminal 26 becomes the ground level. In the case of a two-power supply system, under the above conditions for resistors 38 and 40, transistor 1
Since idling current flows through 6 and 18 and class AB operation is performed, crossover distortion can be prevented.
Also, for saturation on the -V _EE side, this is due to the resistance 3
It is possible to achieve sufficient saturation under conditions of 8.40.

FIG. 6 shows a modified example, in which the output stage positive power supply side transistor 16 is replaced with Darlington connection circuits 16 and 44. The present invention can be similarly applied to such a case, but in this case, the three base-emitter voltages V _BE of the transistors 44, 16, and 18 are applied between the points P and Q.
In line with this, the diodes are 32, 34, and 42.
Connect the pieces in series. In FIG. 6, 46 is a bias resistor, and 48 is a pnp transistor, which constitutes the constant current source 12 described above.

Note that the diodes 32, 34 in FIGS. 3, 4, and 5 or the diode 3 in FIG.
Reference numerals 2, 34, and 42 are bias circuits for passing an appropriate idling current to the transistors 16 and 18, and the bias circuits do not need to be serially connected diodes.

As explained in detail above, in the present invention, the transistor 36 is added to the circuit of FIG. 4 which is designed to eliminate crossover, and the potential at point P is
Although the output voltage V ₀ remains at 2V _BE and only drops to V _BE , the transistor is used to further lower the P point potential, so both transistors 16 and 18 are turned off, and the output voltage V ₀ is completely reduced to zero. Can be lowered.

[Brief explanation of the drawing]

1 to 4 are circuit diagrams showing conventional operational amplifiers, FIG. 5 is a circuit diagram showing an embodiment of the present invention, and FIG. 6 is a circuit diagram showing a conventional operational amplifier.
This figure is a circuit diagram showing a partial modification of FIG. 5. In the drawing, 10 is the main amplifier section, 26 is the output terminal, 20
is the load, 30 is the driver circuit, 16, 18, 1
4 and 36 are first, second, third and fourth transistors, 12 is a constant current source, 32 and 34 are bias circuits, 38 and 40 are resistors, and V _CC and V _EE are power supplies.

Claims (1)

[Claims] 1. In an integrated circuit in which a driver circuit is provided between a main amplifier section and an output terminal for connecting a load, the driver circuit is connected between a pair of power supply lines by connecting a first transistor and a second transistor in series, and The series connection point is used as an output terminal, and a constant current source, a bias circuit for compensating the base-emitter voltage of the transistor, and a third transistor are connected in series between the pair of power supply lines, and the bias circuit and a fourth transistor and a first resistor are connected in parallel to the third transistor, and the input terminal of the third transistor is connected to the output terminal of the main amplification section via the second resistor, and the input terminal of the third transistor is connected to the output terminal of the main amplification section through the second resistor. The input terminal of the first transistor is connected to the output terminal of the main amplifier section, the input terminal of the first transistor is connected to the connection point between the constant current source and the bias circuit, and the input terminal of the second transistor is connected to the bias circuit and the third transistor. An integrated circuit characterized in that it is configured by being connected to a connection point with a transistor.