Bandwidth-Enhanced Mixed-Mode Outphasing Power Amplifiers Based on the Analytic Role-Exchange Doherty-Chireix Continuum Theory

A novel theory and design methodology for continuous-mode dual-input outphasing amplifiers (CM-OPA) is proposed to enhance the bandwidth of mixed-mode Chirex PAs. The design procedure relies on a modified analytical role-exchange Doherty-Chireix continuum theory which doubles the design space for the realization of high-efficiency PAs with a mode of operation continuously changing between the Chireix mode and two role-exchange hybrid Doherty-Chireix outphasing modes as the frequency varies up and down, respectively. Using this theory, a mixed-mode CM-OPA with constant output power back-off level and constant saturated power is developed. The CM-OPA theory is first verified at the current-source reference planes for a frequency range from 1.3 GHz to 2.0 GHz for a GaN HEMT. The proposed CM-OPA is then implemented at the package reference planes using the embedding model to synthesize the combiner circuit across the entire frequency bandwidth. The 1.3 to 2.0 GHz bandwidth-enhanced CM-OPA was fabricated and characterized using both continuous-wave and modulated signals. When driven by a 20-MHz LTE signal with 7.1 dB peak-to-average-power ratio (PAPR), the proposed CM-OPA achieves better than -45 dBc adjacent channel leakage ratio (ACLR) and higher than 44% power-added efficiency (PAE) after digital predistortion linearization at 1.3/1.6/1.8 GHz.