High efficiency and linear power amplification for OFDM signal by combining dynamic bias and digital baseband predistortion

Abstract

This paper presents a technique that enables both efficiency and linearity enhancements for power amplifiers (PA) used in communication systems. It is here applied to a 100 W wide-band LDMOS push-pull amplifier (50-500 MHz) driven by OFDM signals. When the amplifier is driven by a CW signal and operates at a constant 28 V drain bias voltage, it exhibits 100 W output power with 60% power added efficiency (PAE). When it is driven by an OFDM signal, a 10 dB output power back-off is necessary to have a -25 dBc ACPR and PAE decreases down to 10%. By properly implementing an envelope tracking bias system 40 W output power along with 38% PAE and -27 dBc ACPR have been reached. Applying baseband digital predistortion provides additive improvements at high PAE (for only 1 point PAE lost the ACPR increases Pof 5 dB).