A 43%-efficiency 20dBm sub-GHz transmitter employing rise-edge-synchronized harmonic calibration with 33.3% duty cycle

A high efficiency class-E power amplifier (PA) is proposed with only 3 external components. The PA is driven by a 33.3% duty cycle with a rise-edge-synchronized harmonic calibration. The 33.3% duty cycle operation lowers the drain voltage swing as well as the 3^rd harmonics, and the calibration optimizes the duty imbalance and the phase difference between the differential signals, improving the PA efficiency and eliminating the external harmonic filters. The PA fabricated in 40nm CMOS has achieved the output power of 20dBm and the TX efficiency of 43% with “only 3 external components” in the impedance matching network.