Push-Pull Totem-Pole RF Power Amplifier with Reactive Matching Networks

Abstract

Push-pull RF power amplifiers (PA) are generally composed of two single ended amplifiers operating in anti-phase. Transformers or baluns are used to split the input signal for the amplifiers, and combine their outputs. An alternative approach described here, is the asymmetric totem-pole amplifier which consists of two N-channel FETs stacked one on top of each other, with the output taken from their common node. The upper device operates as a sourcefollower to supply current to a load, and the lower as a common-source amplifier to sink current. A reactive inductorcapacitor matching network matches the high input impedance of the source-follower to 50 Ω. Under simulation, a 680 MHz prototype achieved 69.5% drain efficiency at a 25.1 dBm 1 dB compression point (P1dB). Simulated waveforms verified that the two paths of the PA operated in anti-phase. A practical PA achieved a 23.5 dBm P1dB at 48.1% drain efficiency. The measured second harmonic distortion (HD2) was suppressed by -47 dBc relative to the fundamental as is typical of a push-pull PA.