DE3332871

For a satisfactory cross-over behavior of the transistors T1 and T2 of push-pull amplifier comprising an input 2 and an output 3, it is necessary that the sum of the base-emitter voltages of the transistors T1 and T2 remains substantially constant. For this purpose a first voltage-current converter 5 is coupled between the base and the emitter of transistor T1, the inverting input of this converter being coupled to the base of transistor T1 via a first reference-voltage source 8 and the non-inverting input to the emitter of transistor T1. Similarly, a second voltage-current converter 9 and a second reference-voltage source 12 are arranged between the base and the emitter of transistor T2. The output currents of the first and the second voltage-current converters 5 and 9 are compared with each other in the combining circuit 14 which drives the control amplifier 15, which in its turn controls the base-emitter voltage of transistor T2 in such a way that the sum of the base-emitter voltages of transistor T1 and T2 remains constant. The push-pull amplifier exhibits a minimal amount of second-harmonic distortion, because only the difference of the errors introduced by the first and the second voltage-current converters 5 and 9 is of importance in this respect and these errors are substantially equal to each other due to the method of fabrication of the voltage-current converters.