Novel design & implementation of a broadband and highly efficient doherty power amplifier

Abstract

The conventional Doherty power amplifier suffers from some disadvantages such as narrow bandwidth and large size due to its critical use of passive transmission lines as impedance inverters. In this work, a novel configuration is proposed, which promises to eliminate the above mentioned problems by replacing the quarter-wave transmission line with an adaptive, compact and broadband alternative. A highly linear, varactor-based impedance transformer is placed at the output of the carrier amplifier, which performs wideband load-modulation by adaptively biasing the varactors according to the input signal envelope. Power added efficiency of more than 49.5% is achieved at maximum power level (33dBm) over a wide bandwidth (1.8GHz-2.2GHz). The high power added efficiency has been maintained within the 6-dB back-off power range. At 6-dB backoff point, power added efficiency is more than 45.3% within the bandwidth of 1.8GHz to 2.2GHz. Third order harmonic distortion has been better than -42dBc within the entire power range over the above mentioned bandwidth. This verifies broadband performance of the proposed circuit. Moreover, 50% size reduction compared to conventional Doherty amplifier is achieved.