SU1480094A1 - Output stage of operational amplifier - Google Patents

Abstract

The invention relates to radio engineering. The purpose of the invention is to reduce nonlinear distortion. The output stage contains a voltage amplifier at transistor 1 and resistor 2, a circuit of 3 pre-biased diodes, r-4 current, a two-stroke emitter follower on transistors 5 and 6, a pre-biased diodes 7 and 8, resistors 9 and 10 and g-raes 11 and 12 currents as well as power supply buses 13 and 14. The collector currents of transistors 5 and 6 are determined by the ratio of the volt-ampere x-to base-emitter transitions of the transistors themselves and the diodes in circuit 3. In addition, the collector current of transistor 5 depends on the value of resistor 9 and the value of the current generated by Mr. 11, and the collector current of transistor 6 depends on the nominal value of resistor 10 and the magnitude of the current generated by g-rm 12. The goal is achieved by introducing resistors 9 and 10, by which the x-ki of output transistors 5 and 6, as well as the magnitude of the load, do not affect the operation of transistors 5 and 6. 1 ill.

Description

The invention relates to radio engineering and can be used in automation devices, measuring equipment, radio devices for various purposes.

The purpose of the invention is the reduction of nonlinear distortion.

The drawing shows a circuit diagram of the output stage of the operational amplifier.

The output stage of the operational amplifier contains a voltage amplifier on the first transistor 1 and resistor 2, a circuit 3 of forward biased diodes, a first current generator (GT) 4, a push-pull emitter follower on the second and third transistors 5 and 6, the first and second forward biased diodes 7 and 8, and the second and the third resistors 9 and 10, the second and third current generators (GT) 11 and 12, as well as the first and second bus 13 and 14 of the power source.

The output stage of the operational amplifier operates as follows.

In the absence of a signal, a potential is applied to the base of transistor 1, which supports this transistor in its initial conducting state. A current formed by GT 4 flows through transistor 1, which maintains circuit 3 in a forward-biased state, which in turn supports transistors 5, 6 and diodes 7, 8 in open state. Collector currents of transistors 5 and 6 are determined by the ratio of current-voltage characteristics ( CVC) of the base-emitter transitions of the transistors and diodes themselves in circuit 3, and in addition, the collector current of transistor 5 depends on the value of resistor 9 and the current generated by GT 11, and the collector current of transistor 6 depends on the value of resistor 10 and then and formed HT 12.

With the passage of the negative half-wave of the signal, the conductivity of transistor 1 decreases, which leads to an increase in the potential at its collector, which, in turn, leads to an increase in potential at the bases of transistors 5 and 6. In this case, the base current of transistor 5 increases, leading to an increase in the voltage drop by its base-emitter junction, the increasing current of the emitter of transistor 5 leads to an increase in the voltage drop across diode 7. Since circuit 3 is connected in parallel with the circuit formed from the base-emitter junction of transistor 5, the diode s 7, 8 and the emitter-base junction of transistor 6, the increase in the voltage drop across the base-emitter junction of transistor 5 and the diode 7 leads to a decrease in the same magnitude of the voltage drop between the base of the transistor 6 and the output of the circuit. GT 12 sets a certain value to the emitter of transistor 6, so that transistor 6 remains in a conducting state, keeping the voltage drop at the base-emitter junction approximately at the same level. Therefore, the decreasing voltage between the base of the transistor 6 and the output of the circuit turns out to be applied to the diode 8. When locking the diode 8, the presence of the resistor 10 will maintain the connection between the output of the lower arm and the load of the circuit. In this case, when the diode 8 is locked, there is no jump-like decrease in current and distortion is in the form of a low-frequency signal . The upper arm of the circuit works similarly when passing the positive half-wave of the signal, i.e. transistor 5 remains in a conductive state, and resistor 9 maintains the connection between the output of the upper arm and the load of the circuit.

When the load changes in the case of the passage of the negative half-wave of the signal, a change occurs. The voltage drop at the base-emitter junction of the transistor 5 and diode 7, which leads to a corresponding voltage drop across the diode 8, and therefore, the operation mode of the transistor 6 does not change, it does not depend on the characteristics transistor, since the GT 12 supports the operation mode of the output transistor 6.

The upper arm of the circuit works similarly when passing a positive half-wave of the signal. Those. the characteristics of the output transistors 5 and 6, as well as the magnitude of the load, do not affect the operation mode of the output transistors of the circuit, which ensures high reliability and reduced distortion.

Claims (1)

Claim The output stage of the operational amplifier, containing a voltage amplifier made on the first transistor, the base of which is the input of the output stage of the operational amplifier, the emitter of the first transistor is connected through the first resistor to the first bus of the power source, and the collector through a series-connected circuit of forward biased diodes and the first generator current - to the second bus of the power source, a push-pull emitter follower, made on the second and third transistors, connected according to the scheme with a common collector, base which are connected to the output of the first current generator and the collector of the first transistor, respectively, the emitters are connected through the second and third current generators to the first and second busbars of the power supply, respectively, and to each other through the first and second directly biased diodes, the connection point of which is the output of the operating stage amplifier, while the first and second transistors have one structure, and the third transistor has a different structure, distinguished by the fact that, in order to reduce non-linear distortions, the second second and third resistors connected in parallel to the first and second forward biased diode, respectively.