A circuit having the primary function of changing the phase of a signal by 180°. The phase inverter is most commonly employed as the input stage for a push-pull amplifier. Therefore, the phase inverter must supply two voltages of equal magnitude and 180° phase difference. A variety of circuits are available for the phase inversion. The circuit used in any given case depends upon such factors as the overall gain of the phase inverter and push-pull amplifier, the possibility that the input to the push-pull amplifier may require power, space requirements, and cost.