A Theoretical Method to Optimize Load-Modulation Behavior for a 62.5–72.5 GHz Asymmetrical Load Modulated Balanced Amplifier in 100-nm GaAs

This article proposes a theoretical method to optimize load-modulation behavior in the design of a 62.5–72.5 GHz high-efficiency asymmetrical load-modulated balanced amplifier (ALMBA). To optimize the load-modulation behavior of an ALMBA, the impact of the current ratios on the load-modulation behavior and the efficiency performance is theoretically developed. Based on that, an efficiency distribution diagram is visualized to identify an optimum design space, thereby guiding the optimization of load-modulation behavior in an ALMBA design. To verify the proposed method, the 62.5–72.5 GHz ALMBA microwave monolithic integrated circuit (MMIC) is designed and implemented in a 100-nm gallium arsenide (GaAs) pHEMT technology. Measured results demonstrate that the ALMBA achieves a saturated output power exceeding 21.1 dBm, along with power-added efficiency (PAE) > 21.1%/15.1%/11.5% at peak/6/8 dB output back-off (OBO) across the band, respectively. Specifically, at the center frequency of 67.5 GHz, the ALMBA attains a small-signal gain of 18.8 dB, a saturated output power of 22.4 dBm with peak PAE of 22.8%, 6 dB OBO PAE of 19%, and 8 dB OBO PAE of 15.4%. Compared to state-of-the-art at V-band, the proposed ALMBA MMIC achieves the highest 6 and 8 dB OBO PAE in a 100-nm GaAs process.