Envelope tracking power amplifiers with reduced peak-to-average power ratio RF input signals

This paper presents a new technique to reduce the peak-to-average power ratio (PAPR) of the RF input signals used in envelope tracking (ET) power amplifiers without degrading the linearity and efficiency performance of the RF stages. Due to heavy gain compression, ET amplifiers can suffer from inefficient driver stages. The reduced PAPR RF input signal improves the efficiency of the driver amplifier thereby potentially improving the overall efficiency of the ET amplifier. This technique is demonstrated for a single carrier WCDMA signal using a dynamic supply modulator and a RF stage based on a GaAs HVHBT. The measurement shows that a power added efficiency (PAE) of 74% can be maintained for the RF stage while the PAPR of the RF input signal is reduced from 7.6 dB to 5.2 dB. The overall PAE accounting for the supply modulator is greater than 50% with an average output power of greater than 26 W and an adjacent channel leakage ratio of less than -45 and -53 dBc at 5- and 10-MHz frequency offsets, respectively.