An Open Loop Digitally Controlled Hybrid Supply Modulator Achieving High Efficiency for Envelope Tracking with Baseband up to 200-MHz

Envelope tracking (ET) is an effective way to improve the efficiency of power amplifier (PA) for 5G communication systems. To understand the restriction of the hybrid supply modulator (HSM) for ultra-wide band ET applications, an extended power loss model and a Short Time Fourier Transform (STFT) methodology are put forward to be the fundamental guide of the control methodology. An average voltage alignment (AVA) algorithm is proposed, which aligns the current waveforms by using pre-cached envelope signals to reduce the power loss due to the mismatch. Furthermore, a digital low pass filter (LPF) is integrated in the AVA controller, aiming at eliminating the necessity of very high-speed switches in HSM, which reduces the difficulty of hardware facility. The prototype chip is fabricated with a standard 0.18μm CMOS technology and fulfilled with the discrete components on the PCB to verify the methodology and the system. Measurement results show that the proposed method extends the tracking bandwidth up to 200-MHz, and achieves 20% efficiency increment with the maximum 20 MHz switching frequency decrement comparing to the normal hysteresis comparison logic. A GaAs PA is introduced to measure the system linearity, and the ACPR of ET PA reaches-32 dBc. The proposed strategy successfully push the HSM ET application to hundreds of MHz compared with the previous level of 10-MHz.