A pulsed load modulation (PLM) power amplifier with 3-level envelope delta-sigma modulation (EDSM)

Abstract

An X-band power amplifier (PA) based on the pulsed load modulation (PLM) architecture is developed. The PLM technique leverages on the load modulation characteristics incurred for modulated pulses with different duty cycles as the consequence of the interactions between switching PAs with the high-Q output filter. Though a high drain efficiency is promised by the PLM amplifier with a binary envelop input, the low coding efficiency of the 2-level pulse modulations including the 2-level Envelope Delta- Sigma Modulation (EDSM) reduces the effective gain of the PA and thus decreases the overall power added efficiency. The great amount of quantization noise also needs to be rejected with high-Q filter which adds a great burden to the output filter design. In this paper, it is proposed to feed the PLM PA with a 3-level EDSM signal for input with higher effective gain and lower quantization noise. The concept is demonstrated with an X-band PLM PA fabricated with discrete 0.25μm GaN HEMT. The proposed transmitter delivered 35.6 dBm output power with 40.5 % drain efficiency for 5 MHz WCDMA signal with 5.3 peak-toaverage ratio at 9.2 GHz.