Wideband Doherty Power Amplifier in Quasi-Balanced Configuration

A new architecture of wideband Doherty power amplifier is presented based on a quasi-balanced configuration. It is revealed that by grounding the isolation port of the branch-line quadrature coupler at the output of a balanced PA, a standard Doherty circuitry can be formed. Based on this discovery, this paper exhibits the design of wideband Doherty power amplifier using wideband standalone PAs and wideband quadrature couplers. It is further unveiled that by loading the isolation port with different reactance, an optimal Doherty behavior can be maintained across the entire frequency range. As a proof-of-concept demonstration, a first-pass prototype experimentally presents desired Doherty characteristics across a wide bandwidth from 1.9 to 2.5 GHz, achieving 50-78% of peak efficiency and 43-56% of efficiency at 6-dB power back-off.