Layout-Aware Variability Characterization of CMOS Current Sources

Bo LIU  Bo YANG  Shigetoshi NAKATAKE  

IEICE TRANSACTIONS on Electronics   Vol.E95-C   No.4   pp.696-705
Publication Date: 2012/04/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E95.C.696
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Solid-State Circuit Design – Architecture, Circuit, Device and Design Methodology)
process variation,  current mismatch,  layout-dependent variation,  analog DFM,  

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Current sources are essential components for analog circuit designs, the mismatch of which causes the significant degradation of the circuit performance. This paper addresses the mismatch model of CMOS current sources, unlike the conventional modeling, focusing on the layout- and λ-dependency of the process variation, where λ is the output conductance parameter. To make it clear what variation parameter influences the mismatch, we implemented a test chip on 90 nm process technology, where we can collect the characteristics variation data for MOSFETs of various layouts. The test chip also includes D/A converters to check the differential non-linearity (DNL) caused by the mismatch of current sources when behaving as a DAC. Identifying the variation and the circuit-level errors in the measured DNLs, we reveal that our model can more accurately account for the current variation compared to the conventional mismatch model.