Effect of the class of switching-mode power amplifiers on the efficiency of band-pass delta-sigma architectures

This paper studies the impact of using a non-50-% duty cycle square-wave as an input signal, on the efficiency performance of different types of switching-mode power amplifiers (SMPAs). This investigation is important when the power amplifier (PA) is fed with bi-level pulses with a duty cycle different from the typical value of 50 %. This is the case in bandpass delta-sigma (BPDS) modulation where the duty cycle of the output pulses may vary from 0 % to 100 % based on the type of modulation and signal statistics. Simulation results show that the class-E PA is less sensitive to the variation of the duty cycle than the class-F and the class-D modes of operation. Therefore class-E PA is the best choice to be employed in band-pass delta-sigma based transmitter designs. Besides the PAs performance comparison, a correction on the efficiency calculation of the SMPAs driven by a duty cycle varying signal, is proposed in this paper.