Loop Analysis and Stability Considerations of Hybrid PA Supply Modulators

This brief provides a detailed loop gain and stability analysis of hybrid power amplifier supply modulators. Design considerations, including the relations between the voltage and current loops, the rationale of current loop compensation to ensure stability and improve bandwidth, and the impacts of current loop on the overall system stability and efficiency, are studied with combined system loop gain modeled mathematically. The theoretical analysis is proven by simulation results. Based on the study, a hybrid supply modulator has been designed and fabricated in 65-nm CMOS. In measurements, stable voltage and current closed-loop operations have been verified, with a peak efficiency of 85% when tracking a 20-MHz LTE envelope.

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This paper provides a detailed analysis of the loop gain and stability of hybrid power amplifier supply modulators. The study examines the design considerations, including the relationship between voltage and current loops, the importance of current loop compensation for stability and bandwidth improvement, and the impact of the current loop on system stability and efficiency. The analysis is supported by simulation results, and a hybrid supply modulator has been successfully designed and fabricated.