Digital Multiphase PWM Integrated Module Generated from a Single Synchronization Source

Abstract

This paper introduces a new architecture for a high-resolution digital pulse-width modulator (HR-DPWM) which generates multiple output phases, all synchronized and derived out of a single reference source. Constructed through digital standard-cell delay chain and simple combinatorial logic, the module produces PWM signals with configurable on-time, period and time-delay (between phases) with resolution of a single delay-element. To minimize the statistical error spread (e.g. jitter error) between phases, a single delay-line is utilized to generate a master time-base while combinatorial logic assigns per-phase independent duty ratio settings. The resultant module minimizes the time-diversity error between phases, as any uncertainty in the on-time generation is identical between phases. The solution is compact, flexible and scales with the number of phases. Since the entire architecture is realized through standard cells, the solution also scales with fabrication technology and is described by HDL, which translates onto hardware using automated process. The HR-DPWM module has been designed and fabricated on a 0.18µm 5V CMOS process, totaling 0.08mm2 of effective silicon area. Experimental results of a four phase 13-bit HR-DPWM are provided, demonstrating high accuracy and linearity characteristics with time resolution of 200ps and excellent matching and tracking between all phases.