The use of two matched devices in such a way that they operate with a 180° phase difference. The output circuits combine the separate outputs in phase (Fig. a). One common means of achieving the desired 180° phase shift in the inputs is a transformer-coupled input circuit (Fig. b). Complementary transistors may also be used (Fig. c), in which case no phase shift is required in the inputs.

Push-pull circuits are frequently used for class A and class B amplification and are then termed push-pull amplifiers. A push-pull amplifier that is suitably biased to give negligible output current when no input signal is present is termed a quiescent push-pull amplifier.

(a) Output of transformer-coupled push-pull operation

(b) Transformer-coupled class A push-pull operation

(c) Complementary transistor push-pull operation