Digital Multi-Level Closed Loop Design for Wideband Envelope Tracking Systems

In this paper, we present a closed loop multilevel envelope tracker (ET) based on multiple high bandwidth (BW) digital low dropout (DLDO) voltage regulators, tested on WiFi 802.11ac 80 MHz signal in high level simulation platform. The multilevel concept is based on high speed switching between different voltage levels. The suggested architecture can cope with very high BW without an efficiency penalty and does not require any external inductor. Despite the existing highly non-linear power amplifier (PA) in our system, this architecture provides a solution in terms of band edge (BE) mask limitation, with efficiency of 85% for the ET driver, when using PA output power of 19dBm, and reaching 40% efficiency boost based on 28nm simulations. Most of the components are fully digital and synthesizable, which has a big advantage compared to analog alternatives in efficiency, noise and size, improve time-to-market and of course assures robustness and flexibility. The paper presents the main challenges of this topology, which are the plant non-linearity and DLDO branch transition, and are solved using a shared digital controller, and adaptive control.