Optimum Bias Calculation for Parallel Hybrid Switching-Linear Regulators

This paper presents an analysis of the bias constraints for switching and linear voltage regulators operated in a parallel-hybrid configuration. Particular emphasis is given to polar and envelope-tracking RF power amplifier (PA) applications requiring wideband dynamic voltage regulation. Ideal expressions are derived for the optimum current contribution of the switching regulator under quasi-static operating conditions. In contrast to previous work, it is shown that the optimum mean current contribution of the switching regulator is not necessarily the DC current to the load, but is a function of the DC and dynamic characteristics of the regulated output voltage. Theoretical maximum efficiency is derived for envelope waveforms that result from two-tone and sinusoidal amplitude modulation of the RF carrier.