An Efficiency-Enhanced Hybrid Supply Modulator With Single-Capacitor Current-Integration Control

• Published in: IEEE journal of solid-state circuits 2016-02, Vol.51 (2), p.533-542
• Main Authors: Tan, Min, Wing-Hung, Ki
• Format: Article
• Language: English
• Subjects: Bandwidth; Class-AB; efficiency; envelope tracking; hybrid supply modulator (HSM); Inductors; linear amplifier (LA); Linearity; Modulation; polar amplifier; RF power amplifier (PA); single-capacitor current-integration (SCCI) control; stability; Switches; Voltage control
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2015.2490224

This paper presents a high-efficiency wideband hybrid supply modulator (HSM). We show that proper control of the average current from the class-AB linear amplifier (LA) and proper selection of the inductor value are essential to efficiency optimization. In line with the above criteria, a single-capacitor current-integration (SCCI) control method is proposed. Current integration is achieved by using a single capacitor, circumventing the need of the high-speed full-range current sensor required for conventional HSMs and reducing the design complexity greatly. The ripple current of the LA is controlled indirectly, and enhanced efficiency is achieved by enforcing the average output current from the LA to be around zero. A wideband LA is proposed to suppress the output voltage ripple. A proof-of-concept design using an inductor with an optimized value of 100 nH is fabricated in 130 nm CMOS technology. It switches at a peak frequency of 50 MHz, achieves up to 8% efficiency improvement when compared to recent works, and is able to track a 0.8 V pp sinusoidal signal with high fidelity up to 10 MHz. The measured output voltage ripple is reduced to below 8 mV. The peak conversion efficiency is 88.3% at the maximum output power of 23 dBm.