Design and Stability Analysis of the Variable-Sawtooth-Based PWM Controller for the AC-Coupled Envelope Tracking Supply Modulator

This letter analyzes the proposed variable-sawtooth-based PWM controller for the AC-coupled envelope tracking (ET) supply modulator (SM). The ET SM includes a linear amplifier and a switching power modulator (SPM). The SPM maintains the voltage across the AC-coupling capacitor and provides an output current in a power-efficient manner. A 10-MHz constant frequency is employed in the proposed SPM to reduce the interference to the communication system. It utilizes a pulse-width-modulation controller but contains a voltage main loop and a current auxiliary loop, improving the transient response performance at the expense of complicated control loops. This letter analyzes the stability condition and design methodology to determine key parameters. The simulation and measurement have verified these theoretical analyses.