Wideband Envelope Tracking Power Amplifiers With Reduced Bandwidth Power Supply Waveforms and Adaptive Digital Predistortion Techniques

TLDR

When envelope tracking is applied to broadband signals such as WCDMA and 3GPP LTE, the wide bandwidth of the envelope signal makes it difficult to implement the dynamic supply modulator efficiently and accurately. This paper presents a new technique to reduce the bandwidth of the dynamic power supply waveform used in wideband envelope‑tracking power amplifiers. The authors propose reducing the supply waveform bandwidth to improve modulator efficiency and introduce a linearization method to correct the resulting nonlinearity, demonstrating feasibility on a single‑carrier WCDMA signal with 7.6‑dB PAPR using a GaAs HBT PA. Reducing the supply waveform bandwidth from 20 MHz to 4 MHz and applying linearization yields a 28 W, 12 dB gain envelope‑tracking PA with 49 % power‑added efficiency and a 0.67 % rms error, achieving –53.9/–54.2 dBc adjacent‑channel leakage at 5/10 MHz offsets.

Abstract

This paper presents a new technique to reduce the bandwidth of the dynamic power supply waveform used in wideband envelope tracking power amplifiers (PAs). When the envelope tracking technique is applied to broadband signals such as WCDMA and 3GPP LTE, the wide bandwidth of the envelope signal makes it difficult to implement the dynamic supply modulator efficiently and accurately. We show here a technique to reduce the bandwidth of the power supply waveform, thereby allowing better efficiency for the supply modulator; 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 a 7.6-dB peak-to-average power ratio using a GaAs high-voltage HBT PA. The bandwidth of the power supply waveform is reduced from 20 to 4 MHz. After linearization, the reduced bandwidth envelope tracking PA exhibits an average output power of 28 W, an average gain of 12 dB and an overall power-added efficiency of 49%. The measured normalized rms error is as low as 0.67% with an adjacent channel leakage ratio of -53.9 and -54.2 dBc at offset frequencies of 5 and 10 MHz, respectively.