Linearity improvement of envelope tracking power amplifier using gain compensated predistortion

This paper describes a gain compensated predistortion (PD) for linearity improvement of an envelope tracking power amplifier (ET PA). Generally, gain of a power amplifier (PA) decreases as its supply voltage reduces, degrading linearity of an ET PA. For the linearity improvement, we adopt a PD for the RF input as well as an envelope shaping of the supply voltage. By the PD, AM-AM response of the ET PA is improved. The ET PA is implemented using a CMOS supply modulator and a class-AB HBT PA. The CMOS supply modulator has a hybrid structure for high efficiency and wide bandwidth. Measured results for an LTE signal show the PD for the ET PA is an effective technique for good linearity.