Design Method of High Performance and Low Power Functional Units Considering Delay Variations

Kouichi WATANABE  Masashi IMAI  Masaaki KONDO  Hiroshi NAKAMURA  Takashi NANYA  

Publication
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E89-A   No.12   pp.3519-3528
Publication Date: 2006/12/01
Online ISSN: 1745-1337
DOI: 10.1093/ietfec/e89-a.12.3519
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on VLSI Design and CAD Algorithms)
Category: Circuit Synthesis
Keyword: 
delay variation,  dual-rail asynchronous circuit,  functional unit,  unflip-bit control,  

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Summary: 
As VLSI technology advances, delay variations will become more serious. Delay-insensitive asynchronous dual-rail circuits tolerate any delay variation, but their energy consumption is more than double that of the single-rail circuits because signal transitions occur every cycle in all bits regardless of the input bit pattern. However, in functional units, a significant number of input bits may not change from the previous input in many cases. In such a situation, calculation of these bits is not required. Thus, we propose a method, called unflip-bits control, makes use of the above situation, to reduce energy consumption. We evaluate the energy consumption and performance penalty for the method using HSPICE and the verilog-XL simulator, and compare the method with the conventional dual-rail circuit and a synchronous circuit. Our evaluation results reveal that the proposed asynchronous dual-rail circuit has a 12-60% lower energy consumption compared with a conventional asynchronous dual-rail circuit.