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A High-Resolution and Robust 12-bit DPWM for Digital DC-DC Converters
Huey Chian FOONG Meng Tong TAN Yuanjin ZHENG
IEICE TRANSACTIONS on Electronics
Publication Date: 2011/09/01
Online ISSN: 1745-1353
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Electronic Circuits
DPWM, DC-DC converter, supply-insensitive, process-insensitive, high-resolution,
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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.