Envelope delta-sigma modulation with adaptive dither for direct-conversion transmitter and switch-mode power amplifier

A new encoder for radio frequency switch-mode power amplifiers is described. The encoder is designed for a transmitter architecture that uses envelope delta-sigma modulation (ESDM) and a direct conversion transmitter architecture. The ESDM is modified to include a dither signal that shapes the out-of-band spectrum while simultaneously maintaining good SNDR. The out-of-band dither can also be used to improve the power efficiency of the switch-mode power amplifier by rectifying the dither signal to recycle power. The encoder is designed to be implemented in a FPGA. Simulation and experimental results with an LTE modulated carrier are shown to demonstrate the concept.