High efficiency envelope tracking supply voltage modulator for high power base station amplifier applications

Abstract
Wideband supply voltage modulator with efficiency of 85.1% at 120 W average output power with 7.5 dB PAPR (Peak to average power ratio) (WCDMA, LTE, MC-GSM signals), and 91.7% at 130W output power with 0 dB PAPR (GSM applications), was built. Supply voltage modulator consists of a linear amplifier and a switching stage in parallel. The linear amplifier is controlled by an envelope signal, and a novel method for controlling the switching stage is presented, resulting in high efficiency and low sensitivity to component variations. Over 20%-unit efficiency improvement in back-off was achieved with the new control method. The measured efficiency was above 80% over 14 dB average power range with 7.5 dB PAPR test signal. Demonstrator circuit was built from discrete commercial components. An ET PA implemented with demonstrator modulator exhibited -60 dBc ACP linearity with dual carrier 7.5 dB PAPR WCDMA signal. For more wideband and compact ET PA implementation integrated circuit (IC) was fabricated and ET PA implemented with the IC modulator achieved -58 dBc ACP linearity with quad carrier 7.5 dB PAPR WCDMA signal. Wideband operation required special design for PA supply feed line design.