A single input transformer-less push-pull microwave power amplifier

A transformer-less push-pull RF power amplifier (PA) is described based on the totem-pole configuration. This involves stacking two transistors one on top of another and driving them in anti-phase. A variable attenuator and delay line are included so that the gain and phase relationship of the signals driving the two transistors can be accurately manipulated. It is shown, that as the gain and phase are swept, an optimum exists where efficiency is maximum and the second harmonic distortion (HD
₂
) suppressed. These are the metrics used to define correct push-pull operation. At the optimum setting, a practical amplifier operating at 680 MHz achieved an efficiency of 52% at 23.6 dBm output power (P
_OUT
), with 48 dB HD
₂
suppression.