Wideband envelope tracking power amplifier with reduced bandwidth power supply waveform

This paper presents a new technique to reduce the bandwidth of the dynamic power supply waveform for use in wideband envelope tracking power amplifiers (PAs). When the envelope tracking technique is applied to the broadband signals such as WiMAX and LTE, the wide bandwidth of the envelope signal makes it difficult to implement the dynamic power supply efficiently and accurately. We show here for the first time a technique to reduce the bandwidth of the dynamic power supply voltage, thereby allowing better efficiency for the dynamic power supply; and a linearization method for correcting the nonlinearity caused by the bandwidth reduction. The feasibility of this technique is demonstrated for a single carrier WCDMA signal with 7.8-dB PAPR using a GaAs HVHBT PA. The bandwidth of the power supply signal is reduced from 20 MHz to 5 MHz. After linearization, the reduced bandwidth envelope tracking PA exhibits an average output power of 25 W, an average gain of 13 dB and an overall power-added efficiency of 50%. The measured normalized RMS error is as low as 3.98% with an adjacent channel leakage ratio of -41 dBc and -48 dBc at offset frequencies of 5 MHz and 10 MHz, respectively.