EPC with dynamic bias control for SSPA for SPACE applications

This paper describes the design, implementation, and characterization of an Electronics Power Conditioner (EPC) with dynamic drain bias control that maintains efficiency of PA over a range of output power levels. The Drain voltage of power devices is varied in a known fashion against the input RF drive variations dynamically, to obtain better efficiency values over a range of output power. As a consequence, efficiency performances can be greatly improved as compared to classical back-off solutions. The employed 15-Watt C-band SSPA operates with 30% efficiency at an output power of 42 dBm. A coupler and detector from the PA provide a sample of RF input and a temperature detector provide the temperature data to the drain-bias controller, which is based on a buck dc-dc converter. The converter is designed with forward topology using resonant reset technique. Another low power push-pull converter is also used for providing housekeeping supply as well as low power supplies to the PA. When compared with a PA with constant drain bias (8V), the average efficiency of the PA with dynamic biasing is improved by 8.3%. Over an output power between 42–37.5 dBm, the drain bias varies from 8V to 5V, and the efficiency improves from 13.7 % to 22% at the lower power level. The efficiency figures include the losses in the dc-dc converter.