A Spurious-Free Switching Buck Converter Achieving Enhanced Light-Load Efficiency by Using a $\Delta \Sigma$-Modulator Controller With a Scalable Sampling Frequency

Abstract

This paper presents a spurious-free switching buck converter with enhanced light-load efficiency for use in noise-sensitive portable electronics. The proposed switching buck converter achieves low output noise by using a delta-sigma-modulator (ΔΣ) controller. Its light-load efficiency is enhanced by: 1) scaling the switching frequency of the buck converter (i.e., the sampling frequency of its ΔΣ-modulator controller) with the load current; 2) switching its operation from continuous conduction mode (CCM) to discontinuous conduction mode (DCM) at light loads; and 3) using a new low-power current-sensing circuit. The ΔΣ modulator is designed with an input-feedforward architecture, which enables the switching frequency 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 switching buck converter was fabricated in 0.13-μm digital CMOS. Measurements results demonstrate that this buck converter achieves a spurious-free output with a noise floor below -60 dBm and voltage ripples below 70 mV over its full loading range (2 mA to 800 mA). Furthermore, it achieves a power efficiency higher than 70% over this entire range, with a peak efficiency of 95.1%.