Envelope Switched Doherty Power Amplifier For RF Applications (Preprint)

摘要

This report was developed under a SBIR contract. A new concept of envelope switched Doherty amplifier is introduced. The proposed amplifier maintains maximum efficiency over a wide range of output power fluctuation. The essential idea is to drive two amplifier devices connected in Doherty configuration with a pulsed envelope signal. A high-Q, low loss filter is placed at the output to recover for linearity and to generate a time-varying equivalent load impedance for optimal efficiency performance. Ideally, for a pair of equally sized and identically biased Class B amplifiers, a maximum efficiency, 78.5%, should be maintained all the way down to the 6dB output back- off level. This concept is demonstrated in the experiment with a pair of GaAs FETs at a frequency of 1.87GHz in the PCS band. A maximum output power of 32.7dBm with a PAE of 46% is measured and a PAE of 34.4% is measured at 6dB back-off level including the filter loss at the power amplifier (PA) output. The proposed architecture can be applied in designing high efficiency PAs with non-constant envelope modulations.