Standard Cell Structure with Flexible P/N Well Boundaries for Near-Threshold Voltage Operation

Shinichi NISHIZAWA  Tohru ISHIHARA  Hidetoshi ONODERA  

Publication
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E96-A   No.12   pp.2499-2507
Publication Date: 2013/12/01
Online ISSN: 1745-1337
DOI: 10.1587/transfun.E96.A.2499
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on VLSI Design and CAD Algorithms)
Category: Physical Level Design
Keyword: 
standard cell design,  low power circuit design,  near threshold operation,  PN ratio optimization,  

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Summary: 
This paper propose a structure of standard cells where the P/N boundary ratio of each cell can be independently customized for near-threshold operation. Lowering the supply voltage is one of the most promising approaches for reducing the power consumption of VLSI circuit, however, this causes an increase of imbalance between rise and fall delays for cells having transistor stacks. Conventional cell library with fixed P/N boundary is not efficient to compensate this delay imbalance. Proposed structure achieves individual P/N boundary ratio optimization for each standard cell, therefore it cancels the imbalance between rise and fall delays at the expense of cell area. Proposed structure is verified using measured result of Ring Oscillator circuits and simulation result of benchmark circuits in 65nm CMOS. The experiments with ISCAS'85 benchmark circuits demonstrate that the standard cell library consisting of the proposed cells reduces the power consumption of the benchmark circuits by 16% on average without increasing the circuit area, compared to that of the same circuit synthesized with a library which is not optimized for the near-threshold operation.