A pair of transistors of opposite type used together. A pair of n-p-n and p-n-p bipolar transistors can be used to achieve push-pull operation.
Complementary MOSFETs – PMOS and NMOS – can be combined in complementary MOS (CMOS) technology. CMOS transistors are used for low-dissipation logic circuits. Such devices are used in conjunction with other similar stages all having essentially capacitive input impedance and therefore zero d.c. current flow. In the basic inverter (see diagram) the p-channel device conducts when the input is low and the n-channel device conducts when the input is high, thus giving an output that is inverted.