Design of H-Bridge Class-D Power Amplifiers for Digital Pulse Modulation Transmitters

This paper presents an H-bridge class-D power amplifier (PA) for digital pulse modulation transmitters. The class-D amplifier can be driven by two-or three-level digital signals generated by a delta-sigma modulator (DSM) and provides a linear microwave output after filtering. Within the amplifier, the pull-up and pull-down devices are driven separately to improve the amplifier efficiency by minimizing the loss associated with shoot-through current. The H-bridge class-D PA system was tested with code-division multiple-access IS-95 signals at 800 MHz. Using binary DSM signals, a drain efficiency of 31% was achieved with an output power of 15 dBm and an adjacent channel power ratio of -43 dBc. With three-level DSM signals, a drain efficiency of 33% was achieved at same output power. An analysis of the factors governing amplifier efficiency is provided.