Envelope-tracking power amplifier with enhanced back-off efficiency using average switch current control of supply modulator

This paper presents an envelope-tracking power amplifier (ET PA) for handset applications with enhanced efficiency at a back-off power region. The supply modulator consists of a linear regulator and switching converter. The supply of the linear regulator is boosted to 5 V and that of the switching converter is directly connected to a battery, forming a power management IC. Since the supply voltages of the two amplifiers are asymmetric, the average switch current level is not properly adjusted by itself according to the envelope level. For the optimum operation over the entire power region, average switch current level is adjusted by detecting the input envelope level. For a 10-MHz long term evolution signal with a 6.5 dB peak-to-average power ratio, the proposed supply modulator delivers a peak voltage of 4.5 V to a 6.5 Ω load with a measured efficiency of 76.2 %. At an average output power of 27 dBm, the proposed ET PA delivers a power-added efficiency (PAE) of 40.7 %, which is 8.6 % higher than that of a standalone PA. In the back-off power region, the PAE is improved by up to 2.8 % and 10.7 % compared to the conventional ET PA and stand-alone PA, respectively.