A Symbol-Based Power-Tracking Supply Modulator Integrated With a 28-GHz CMOS PA for 5G FR2

This article presents a supply-modulated power amplifier (PA) system architecture for a high-efficiency transmitter (TX) that utilizes a symbol-power-tracking (SPT) technique to support 5G new radio (NR) frequency range 2 (FR2) bands. Conventional analog envelope tracking (ET) supply modulators (SMs) suffer from limited supportable bandwidth due to a decoupling capacitor required at the PA supply node, which makes loop compensation difficult. As a result, analog ET techniques often require complex loop compensation circuits and struggle to meet the stringent specifications of next-generation communication systems. To support wider channel bandwidths, the proposed architecture adopts an SPT supply modulation technique, realized through a single-inductor multiple-output (SIMO) dc–dc converter, enhancing overall SM-PA system efficiency. The full integration of the SM and PA using a single process helps to mitigate voltage overshoot on the PA supply node during fast SPT transitions, contributing to enhanced device reliability and longer lifetime. In addition, an SPT-adaptive biasing scheme is implemented to adjust the PA bias according to the supply voltage, maintaining linearity across multiple supply levels for the PA. The SPT-PA system is fabricated using a 28-nm CMOS process. The SPT modulator achieves a 20-ns/V transition time with nonuniform supply voltage distribution. It supports a 400-MHz 5G FR2 64-quadrature amplitude modulation (QAM) signal at a 28-GHz PA operating frequency, achieving a 21-mW power saving at a 10-dB power back-off (PBO) level. The die size is 1.5 mm².