JPH0522049A - Complementary multistep amplifier circuit - Google Patents

Abstract

PURPOSE:To always obtain the characteristic of high stability by stabilizing the bias current of a transistor in a final output step by a variable bias voltage source and stabilizing the bias current of the drive step of the other step by a DC constant current source. CONSTITUTION:A thermally coupled variable voltage source 5 is provided at transistors 1 and 2 in the output step so as to compensate the increase of the bias current with the temperature increase of the output step transistors 1 and 2. A DC constant current source 6 is connected between the emitters of drive step transistors 3 and 4, and an output current from this DC constant current source 6 is set at the suitable bias current value of the drive step transistors 3 and 4. A capacitor C is parallelly connected to this DC constant current source 6, AC impedance is lowered and an influence from the drive step to the drive ability of the output step transistors 1 and 2 is reduced. Therefore, even when the voltage of the bias voltage source is considerably changed, the bias current value of the drive step transistors 3 and 4 is fixed.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a complementary multi-stage amplifier circuit, and more particularly to a complementary multi-stage amplifier circuit in which the bias current of its drive stage is stabilized. 2. Description of the Related Art A conventional complementary multistage emitter follower amplifier circuit is constructed as shown in FIG. In the output stage which is the final stage in FIG. 3, the emitters of the NPN transistor 1 and the PNP transistor 2 are connected via output resistors R1 and R2, and the load RL is connected to the connection point. The collectors of the transistors 1 and 2 are supplied with power from voltage sources V1 and V2. The signal from the input signal source S is supplied to the NPN transistor 3 and the PNP.
It is supplied to the bases of the transistors 1 and 2 in the output stage via the drive stage including the transistor 4 and the like, and is supplied to the load RL via the emitter. Drive stage transistor 3
A resistor R3 is connected between the emitters of and. Normally, it is extremely difficult to maintain a constant bias current supplied to each transistor, and in particular, an increase in element temperature due to heat generation due to transistor loss changes the bias current. That is, when the temperature of the transistor itself rises due to the loss current flowing in the transistor, the threshold value of the forward base-emitter voltage of the transistor decreases, and as a result, the collector current of the transistor increases and the loss increases. Due to this increase in loss, the temperature of the transistor itself further rises, and the positive feedback phenomenon that occurs between the element (transistor) temperature and the collector current is generally called thermal runaway, and there is a risk of destruction of the element. Further, the bias current is also greatly related to the AC characteristic in the amplification stage, and the fluctuation of the bias current deteriorates the high frequency characteristic of the amplifier circuit. As described above, it is extremely important to stabilize the direct current bias current value of the transistor. Conventionally, as shown in FIG. 3, in the final stage (output stage) where the most current flows and the heat generation is large. In order to stabilize the bias current, the correction element thermally coupled to the transistors 1 and 2 changes the output voltage from the bias voltage source 5 connected to the voltage source V3. As the compensating element, an element such as a thermistor whose resistance value has a negative temperature coefficient, or an element such as a diode whose temperature coefficient of its forward voltage drop is equal to that of the transistor's forward base-emitter voltage. Is used. As described above, in the conventional multi-stage complementary amplifier circuit, in order to stabilize the current in the final stage, the correction element thermally coupled to the transistor in the final stage. The bias voltage source is controlled by the feedback. However, since the final stage transistor has a large current and a large amount of heat generation, its temperature change is
Compared to the temperature change of the transistor in the drive stage, the change is large, and the degree of decrease in the base-emitter threshold voltage is also large. As a result, the increase amount of the final stage transistor bias current becomes larger than the increase amount of the drive stage transistor bias current. The output voltage from the bias voltage source 5 is for compensating for the increase in the bias current due to the temperature rise of the final stage transistor, so it is effective for stabilizing the bias current of the final stage transistor, but It cannot be said to be effective for the bias current of. That is, since the heat generation of the final-stage transistor is larger than that of the drive-stage transistor, the change in the output voltage of the bias voltage source 5 caused by the temperature rise of the final-stage transistor causes the bias current of the drive-stage transistor to be reduced more than necessary. Will be lost. As described above, in the conventional complementary multi-stage amplifier circuit, since the stabilizing transistor is limited to the final stage transistor, it is not possible to stabilize the bias currents of the other drive stages in the multi-stage configuration, and the amplifier There was a problem that deterioration of performance and characteristics was unavoidable. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a complementary multi-stage amplifier circuit capable of stabilizing the bias current of each stage even in a multi-stage complementary amplifier circuit. In order to solve the above-mentioned problems, the complementary multistage amplifier circuit according to the present invention comprises at least one drive stage composed of a pair of positive and negative transistors and a final output stage. In the complementary multi-stage amplifier circuit, a first circuit that keeps the bias current of the transistor of the final output stage constant, and a second circuit that supplies a bias current of a predetermined constant value to the transistor of the drive stage. , And are configured. According to the present invention, the bias current of the transistor in the final output stage is stabilized by, for example, the variable bias voltage source in the front stage using the correction element thermally coupled to the transistor, while By stabilizing the bias currents of the other drive stages with an independent DC constant current source, the influence of the variable voltage source to compensate for the increase in bias current due to heat generation of the final output stage transistor is driven. The transistor is not affected and the stability is improved. The present invention will now be described with reference to the drawings. FIG. 1 is a circuit showing an embodiment of a complementary multistage amplifier circuit according to the present invention, showing an emitter follower amplifier circuit. In the figure, circuit elements denoted by the same reference numerals as those in FIG. 3 are similar circuit elements. Although the basic configuration of this embodiment is similar to that of the conventional circuit shown in FIG. 3, in this embodiment, the variable voltage source 5 thermally coupled to the transistors 1 and 2 in the output stage is used.
Is provided to compensate for an increase in bias current due to a rise in temperature of the output stage transistor. A DC constant current source 6 is connected between the emitters of the drive stage transistors 3 and 4. The output current from the DC constant current source 6 is set to an appropriate bias current value for the drive stage transistors 3 and 4. A capacitor C is connected in parallel to the DC constant current source 6 to lower the AC impedance and reduce the influence of the drive stage on the drive capability of the output stage transistor. According to the embodiment shown in FIG. 1, even if the voltage change of the bias voltage source 5 due to the temperature rise of the transistor of the final output stage is largely changed, the bias current value of the drive stage transistor is a constant value. . Further, since this system is independent of the bias voltage source 5, it is possible to stabilize the characteristics of the entire amplifier circuit without directly receiving the temperature change of the output stage transistor as in the conventional case. FIG. 2 shows another embodiment of the complementary multistage amplifier circuit according to the present invention. In this embodiment, the DC constant current source 6 in the embodiment shown in FIG. 1 is widely marketed, that is, a so-called "three-terminal type voltage regulator I".
It is configured by using C ″ 7. 3-terminal regulator I
The input terminal IN of C7 is connected to the emitter of the transistor 3, the output terminal OUT is connected to the emitter of the transistor 4 via the resistor R4, and the common terminal COM is connected to the emitter of the transistor 4. According to the embodiment shown in FIG. 2, since the DC constant current source can be easily constructed and the circuit scale can be reduced, the stray capacitance formed between the DC constant current source section and the surroundings is reduced even during high frequency operation. Also, there is no fear that the stray capacitance bypasses the AC drive current and deteriorates the high frequency operation characteristics of the circuit. Also,
Since the reference signal source built in the three-terminal type voltage regulator IC is stable, the DC bias current value can be controlled stably, and adjustment and correction of each circuit are not necessary. In the above embodiments, the number of drive stages is one, but the present invention can be applied to a circuit having an arbitrary drive stage, and transistors of other types such as FETs can be used as transistors. Further, it goes without saying that any other kind of constant current source can be used as the DC constant current source. As described above, in the complementary multi-stage amplifier circuit according to the present invention, the stabilization of the bias current of the transistor in the final output stage is performed by, for example, the correction that is thermally coupled to the transistor in the front stage. In addition to the variable bias voltage source that uses a device for power supply, the bias current of the other drive stage is stabilized by an independent DC constant current source. The drive stage transistor will not be affected by the variable voltage source to compensate for the increase in bias current,
Highly stable characteristics can always be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an embodiment of a complementary multistage amplifier circuit according to the present invention. FIG. 2 is a circuit diagram showing another embodiment of the complementary multistage amplifier circuit according to the present invention. FIG. 3 is a diagram of a conventional complementary multistage amplifier circuit. [Description of Reference Signs] 1, 2, 3, 4 Transistor 5 Bias voltage source 6 Constant current source 7 3 terminal type voltage regulator IC

Claims (1)

What is claimed is: 1. A complementary multi-stage amplifier circuit comprising at least one drive stage composed of a pair of positive and negative transistors and a final output stage, wherein a first bias current of a transistor of the final output stage is made constant. A complementary multi-stage amplifier circuit comprising: a circuit; and a second circuit that supplies a bias current of a predetermined constant value to the drive-stage transistor.