A High-Resolution and Robust 12-bit DPWM for Digital DC-DC Converters

Huey Chian FOONG  Meng Tong TAN  Yuanjin ZHENG  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E94-C   No.9   pp.1455-1463
Publication Date: 2011/09/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E94.C.1455
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Electronic Circuits
Keyword: 
DPWM,  DC-DC converter,  supply-insensitive,  process-insensitive,  high-resolution,  

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Summary: 
This paper presents the design and implementation of a supply and process-insensitive 12-bit Digital Pulse Width Modulator (DPWM) for digital DC-DC converters. The DPWM is realized by a ring oscillator-based segmented tapped delay line and a counter-comparator. The number of delay cells required is reduced by employing a proposed delay cell reuse technique. The ring oscillator of the tapped delay line is made insensitive to supply and process variation by biasing the differential delay cells with a supply-insensitive replica bias circuit. Simulation results show that the variation of the switching frequency of the DPWM at 1.02 MHz is 0.4% for supply voltage variation between 1.5 V and 2.5 V and 0.95% over the temperature range from -40 to 90. Monte-Carlo simulation was also performed to account for the effect of mismatch between the transistors of the ring oscillator. The worst case delay of the delay cells is 0.87% for 5% (3-σ) mismatch. The design was fabricated in CMOS 0.18 µm process and the fabricated DPWM achieved a supply sensitivity of 0.82% and a current consumption of 14 µA.