Applying bipolar transistors in dynamic power supply transmitters

Dynamic power supply transmitters (DPST), including the techniques of envelope tracking (ET) and direct polar (DP) modulation, have a century of success in some applications. The original motivation was to improve the energy efficiency of the final power amplifier (PA), and that remains true today. These are methods to improve overall energy efficiency across wide signal and tuning bandwidths. Not all transistor types perform equally well in the various DPST architectures. This paper provides a quick review of DPST techniques and then examines how the presently available bipolar transistors apply to the various DPST options. It is concluded that bipolar transistors are presently much more suitable for ET than for DP implementations. Measurements demonstrate and explain this difference.