High-Frequency Flying Capacitor Four-Level Drain Supply Modulator

This paper presents a high-frequency, four-level drain supply modulator (DSM) based on a flying capacitor multilevel (FCML) architecture, designed for envelope tracking in radio-frequency power amplifier applications. Operating from a single dc supply voltage, the proposed FCML-DSM employs a simple state-machine-based active balancing of the flying capacitors and control of the output voltage levels at switching rates up to 25 MHz. A hardware prototype of the FCML-DSM is presented, utilizing an FPGA controller and GaN transistors as switching devices in the power stage. The experimental prototype has an output voltage range from 0 V to 20 V, discretized into equally spaced levels, and achieves an average efficiency of 95.4% for output powers exceeding 10 W while tracking a 35 MHz 16-QAM signal envelope.