A Spurious-Free Switching Buck Converter Achieving Enhanced Light-Load Ef ficiency by Using a -Modulator Controller With a Scalable Sampling Frequency Mohammad K. Alghamdi , Student Member , IEEE, and Anas A. Hamoui

Abstract

This paper presents a spurious-free switching buck converter with enhanced light-load ef ficiency for use in noise-sen- sitive portable electronics. The proposed sw itching buck converter achieves low output noise by using a delta-sigma-modulator controller. Its light-load ef ficiency is enhanced by: 1) scaling the switching frequency of the buck converter ( i.e., the sampling frequency of its -modulator controller) with the load current; 2) switching its operation from continuous conduction mode (CCM) to discontinuous conduction m ode (DCM) at light loads; and 3) using a new low-power current-sensing circuit. The modulator is designed with an input-feedforward architecture, which enables the switching frequ ency of the controller to be scaled without disturbing the stability of the feedback loop of the buck converter, and also reduces the controller quiescent current. The proposed switch ing buck converter was fabricated in 0.13- m digital CMOS. Measurements results demonstrate that this buck converter achieves a sp urious-free output with a noise floor below dBm and voltag e ripples below 70 mV over its full loading range (2 mA to 800 mA ). Furthermore, it achieves a power ef ficiency higher than 70% over this entire range, with a peak ef ficiency of 95.1%.