An Open-loop Digitally Controlled Supply Modulator for Wideband Envelope Tracking

Envelope tracking (ET) is one of the important ways to increase the efficiency of power amplifier (PA). The supply modulator (SM) is critical to fulfil the ET strategy. This paper provides a ripple tracking method based on an open-loop digital controller for SM with one switching amplifier (SA) to efficiently track the envelope of PA. The digital controller combines the strong abilities of caching the envelope signals in advance and the powerful envelope shaping as well as the filtering capability to conquer the intrinsic obstacle of close-loop delay, accelerating the tracking speed and decreasing the operation frequency of SM. The performance of SM is highly enhanced based on the proposed circuit model with error correction technique. The proposed ripple tracking method realizes excellent average power tracking (APT) performance compared with that of multi-level SM structure and decreases the hardware requirements, significantly. A test SA chip is fabricated with a standard 0.18 μm CMOS technology and the test platform of whole SM system is established. The measurement results show that the proposed platform achieves very high efficiency of 88% in tracking the envelope of 10-MHz ~ 100-MHz OFDM baseband signals.