2-Phase 3-Level ETSM With Mismatch-Free Duty Cycles Achieving 88.6% Peak Efficiency for a 20-MHz LTE RF Power Amplifier

This letter presents a 2-phase 3-level (2P3L) envelope tracking supply modulator (ETSM) for a long-term evolution 20 MHz (LTE20) radio frequency power amplifier as a solution for the ET system. This 2P3L ETSM that is composed of only switching converters achieves high efficiency, fast transient response, and a small output current ripple. To properly operate the proposed 2P3L ETSM, 4 pulse width modulatiop (PWM) signals with a 90 degrees phase shift from each PWM signal are required without any mismatch between duty cycles. To remove the mismatch, a time-division multiplexing comparator and a duty-cycle calibrator are proposed. Thanks to the proposed techniques, the proposed ETSM fabricated in 0.18-mu m CMOS achieved the highest peak dynamic efficiency of 88.6% with an LTE20 signal, which is superior to the state-of-the-art systems.