2% EVM 920 MHz 13 dBm Constant Envelope π/2 Shift BPSK Modulation Transmitter for IoT

A sub-GHz transmitter which has a constant envelope π/2 shift BPSK modulator is described. To realize constant envelope and low EVM, we have designed that the modulator is composed of a specially designed root raised cosine filter ( α = 0.65 and fc=0.54fs) whose output directly drives ADPLL. The filter characteristic is designed that it passes slightly wider spectrum than that of Rx ( α = 0.5 and fc=0.5fs). Together with the efficient class E power amplifier, we have built a 13 dBm output power sub-GHz transmitter with 50 mW power consumption. Using this transmitter, we have experimentally confirmed 2% of EVM, which is significantly better than that of GMSK.