Nonlinear envelope tracking for efficiency optimization of power amplifiers

In this paper a new characterization method is proposed to optimize envelope tracking (ET) Radio Frequency power amplifier (RFPA) average drain efficiency in the presence of variable envelope RF signals with high peak-to-average power ratio (PAPR). The proposed method consists of measuring the input and output signal complex envelopes as well as instantaneous envelope efficiency of the tested RFPA in the presence of an original configuration of envelope and RF driving signals. The improvement of the average efficiency is obtained by optimizing the input power level of the RF driving signal only. This, results in a Nonlinear Envelope Tracking (NET) system that compensates for the efficiency drop in classic ET architectures. A drain efficiency improvement of 21 percentage points has been achieved with a class-J PA operating at 2 GHz in the presence of a Long Term Evolution (LTE) modulated signal that exhibits a PAPR of 14.4 dB while complying with the 3GPP LTE standard linearity requirements.