Structured Analog Circuit and Layout Design with Transistor Array

Bo YANG
Qing DONG
Jing LI
Shigetoshi NAKATAKE

Publication
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E96-A    No.12    pp.2475-2486
Publication Date: 2013/12/01
Online ISSN: 1745-1337
DOI: 10.1587/transfun.E96.A.2475
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on VLSI Design and CAD Algorithms)
Category: Physical Level Design
Keyword: 
transistor array,  channel decomposition,  structured analog design,  manufacturability,  

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Summary: 
This paper proposes a novel design method involving the stages from analog circuit design to layout synthesis in hope of suppressing the process-induced variations with a design style called transistor array. We manage to decompose the transistors into unified sub-transistors, and arrange the sub-transistors on a uniform placement grid so that a better post-CMP profile is expected to be achieved, and that the STI-stress is evened up to alleviate the process variations. However, since lack of direct theoretical support to the transistor decomposition, we analyze and evaluate the errors arising from the decomposition in both large and small signal analysis. A test chip with decomposed transistors on it confirmed our analysis and suggested that the errors are negligibly small and the design with transistor array is applicable. Based on this conclusion, a design flow with transistor array covering from circuit design to layout synthesis is proposed, and several design cases, including three common-source amplifiers, three two-stage OPAMPS and a nano-watt current reference, are implemented on a test chip with the proposed method, to demonstrate the feasibility of our idea. The measurement results from the chip confirmed that the designs with transistor array are successful, and the proposed method is applicable.