SU1713083A1 - Power amplifier output stage - Google Patents

Abstract

The invention relates to electronics and can be used in various electronic devices, such as consumer electronics. The purpose of the invention is to reduce distortion when the quiescent current stabilizes. When the quiescent current stabilizes, the power amplifier reduces distortion by eliminating switching distortions caused by locking the pre-stage, as well as simplifying the quiescent current control circuit. 1 Cpf-ly, 1 il. '

Description

The invention relates to radio electronics and can be used in various radio electronic devices, for example, in home appliances.

The purpose of the invention is to increase the stabilization of the quiescent current while simplifying the bias control circuit.

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

The output stage of the power amplifier contains the first and second transistors 1 and 2, the first and second current sensors 3 and 4, the first and second diodes 5 and 6, connected in the forward direction, the bias circuit on the third and fourth transistors 7 and 8, the bias control unit in the first and second controlled current generators 9 and 10, the first and second resistors 11 and 12, the first and second controlled current generators 9 and 10 being implemented on transistors 13, 14 and parametric voltage dividers on zener diodes 15,16 and resistors 17.18. The drawing also shows an amplifier.

driving the output stage of the power amplifier, comprising an input differential stage 19 and an output push-pull stage at the transistors 20, 21 connected according to a common emitter circuit, and a common negative feedback circuit 22.

The output stage of the power amplifier works as follows.

Consider two interconnected and simultaneously occurring processes, the amplification of an alternating current signal and the automatic stabilization of the quiescent current.

AC signal strength. The alternating current signal is fed to the input of the differential stage 19. From one output of the differential stage 19, the signal goes to the base of transistor 20, and from the other output to the base of transistor 21, forming a voltage amplifier. In this amplifier, the transistor 20 plays the role of the active element of the voltage amplifier, and the transistor 21 plays the role of the dynamic load. The transistors 7 and 8 form a bias circuit of the output stage of the amplifier. The resistance of the transistor 7 and 8 of the variable component of the current flowing in the collector circuit of the transistor is small, therefore the variable component of the collector of transistor 20 is almost equal to the variable component of the collector of transistor 21 and is an ac voltage amplified signal received at the input of the output stage of the power amplifier. The signal from the collector of transistor 20 is supplied to the base of transistor 1, and from the collector of transistor 21 to the base of transistor 2. Transistors 1 and 2 amplify the positive and negative half-waves of the input signal with respect to current.

At the output of the power amplifier, a full AC signal is extracted, amplified both in voltage and current. A portion of this signal is fed through the negative feedback circuit 22 to the other input of the differential stage 19, whereby the entire power amplifier is covered by a common negative feedback P0, the variable signal. The consequence of this is an improvement in the accuracy of waveform reproduction. Due to the effect of a common negative feedback, the amplitude of the variable signal at the output of the output is almost independent of the change in the parameters of the elements forming the power amplifier, and is determined by the expression

one

Ur

Usbix-

TO

where K is the transfer coefficient of the circuit 22 for the variable signal;

Wow the amplitude of the signal at the input of the power amplifier.

The automatic stabilization of the quiescent current of the power amplifier proceeds as follows.

The quiescent current of the output stage in transistors 1 and 2 is adjusted and set automatically. The quiescent current, for example, on the current sensor 3, converts the RF voltage that controls the controlled current generator 9.

As the quiescent current increases, transistor 1 increases the voltage drop across current sensor 3. This voltage drop reduces the current drawn by the controlled current generator 9 from the supply circuit of transistor 7. The bias voltage of transistor 1 decreases and the quiescent current is maintained at a predetermined level. When the quiescent current of transistor 1 decreases, the voltage drop across current sensor 3 decreases, the current drawn by the controlled current generator 9 from the base circuit of transistor 7 increases, transistor 7 fights up, increasing the bias voltage of transistor 1, and restores the set current of rest. Similarly, with the help of the transistor 8 of the controlled current generator 10 and the current sensor 4, the quiescent current of the transistor 2 is regulated. Because the collector-emitter junction resistance of the transistors 7 and 8 varies over a wide range, the range and accuracy of the quiescent adjustment are increased,

5 which increases the thermal stability of the power amplifier. Since transistors 7 and 8 are controlled along the base circuit, the quiescent current control circuit does not have a shunt effect on the operation of transistors 20 and 21 and

0 no need to increase their current. This means that the efficiency of the power amplifier and its gain when the feedback loop is open increases, which reduces the nonlinear distortion of the output signal.

Since each of transistors 1 and 2 has an individual, deep and precise adjustment of the quiescent current, the need to select the parameters of transistors 1 and 2 (this

0 was done previously to ensure small non-linear distortion of the output signal) is completely eliminated, the need for individual adjustment of the quiescent current of each particular power amplifier is also eliminated.

When a positive half-wave is amplified by a voltage drop on current sensor 3 and diode 5, which limits this drop to 0.7–1 V, the controlled

0 current generator 9, and transistor 7 is open and saturated due to the current flowing through its base circuit through resistor 11. The presence of diodes 5 and 6 allows the resistance of current sensors 3 and 4 to vary freely without fear of reducing the efficiency of the power amplifier.

A controlled current generator 10 controlled by a voltage drop on current sensor 4, which is less for a given time.

0 0.7-1 V, supports using the transistor 8, the quiescent current of the transistor 2 at a given level. Due to this, the specific switching distortions of the Step type, characteristic of two-stroke class B output stages, are significantly reduced.

When the negative half-wave is amplified, the picture changes; The controlled current generator 10 is now locked, the transistor 8 is open and saturated. At a given level

supported by a transistor 7, controlled by a current generator 9 and a current sensor 3 of the quiescent current of transistor 1.

Thus, regardless of the change in ambient temperature, the downturn current of the two-stage output amplifier stage of the power amplifier is maintained at a predetermined level thanks to the closed automatic quiescent current control system of each of the transistors 1 and .2, thereby stabilizing the quiescent current while simplifying the bias control circuit .

Claims (2)

1. An output stage of a power amplifier comprising first and second transistors having a different structure and connected according to a common collector circuit, 20 first and second current sensors, an bias circuit connected between the bases of the first and second transistors, and an offset control unit, the first and second the inputs of which are connected to the first terminals of the first and second current sensors, respectively, and the first and second outputs are connected respectively to the first and second control inputs of the bias circuit, the bias circuit being made on the third and fourth - 30 is a transistor having a different structure, the collectors are connected. the emitters are the corresponding pins of the bias circuit, and the bases are the first and second control inputs of the bias circuit, the displacement control unit is made on the first and second controlled current generators, the outputs of which are respectively the first and second outputs of the displacement control unit, different In order to improve the stabilization of the quiescent current while simplifying the bias control circuit, the first and second diodes in the straight direction are inserted, connected in parallel to the first and second current sensors, the first outputs s are connected to the collectors of the first and second transistors, and the second terminals c of the first and second supply rails, wherein the outputs of the first and second current generators actuated and respectively the second and first power rails including introducing respective first and second resistors. 2. The amplifier cascade according to claim 1, which also includes the fact that each of the controlled current generators is made on a transistor and a parametric voltage divider connected between the power buses of the output stage of the power amplifier, and the tap of which is connected with the base of this transistor, the collector of which is the output, and the emitter - the control input of the corresponding controlled current generators.