A Multi-Loop-Controlled AC-Coupling Supply Modulator With a Mode-Switching CMOS PA in an EER System With Envelope Shaping

Abstract

This paper presents an ac-coupling supply modulator, consist of a 25-MHz three-level switching amplifier and a wide-bandwidth assisting linear amplifier, and a CMOS power amplifier (PA), in an envelope-elimination-and-restoration system with envelope shaping (EER-ES) for low-cost, low-precision, long-term evolution (LTE) applications. The EER-ES system removes the difficult phase-path signal generation block by driving PA with original radio frequency (RF) signal and alleviates the supply modulator requirements by shaping the envelope. For the supply modulator, the ac-coupling topology takes the advantage of the shaped envelope to reduce the linear amplifier power consumption and achieve instantaneous higher voltage than the supply. The three-level topology with the real-time flying capacitor calibration is implemented as the switching amplifier to achieve high efficiency, small output voltage ripple, and fast transient response. A multi-loop control is designed to enhance the switching amplifier speed, thus improving the overall efficiency. A high-pass filter (HPF) is designed to further extend the bandwidth of the supply modulator from 33.9 to 69.2 MHz without additional current consumption. The EER-ES system is fabricated in a UMC 65-nm process. The supply modulator achieves a 0.5–2.5-V output voltage from a 2.4-V input voltage with standard 1.2-V devices. It measures 88.7% efficiency tracking a LTE-20-MHz 16-quadratic-amplitude modulation (QAM) envelope. The EER-ES system measures a power-added efficiency (PAE) of 35.7% with a 2% improvement by ES.