Evaluation of Isolation Structures against High-Frequency Substrate Coupling in Analog/Mixed-Signal Integrated Circuits

Daisuke KOSAKA  Makoto NAGATA  Yoshitaka MURASAKA  Atsushi IWATA  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E90-A    No.2    pp.380-387
Publication Date: 2007/02/01
Online ISSN: 1745-1337
DOI: 10.1093/ietfec/e90-a.2.380
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Analog Circuit Techniques and Related Topics)
substrate coupling,  equivalent circuit modeling,  guard ring,  guard band,  deep n-well,  substrate noise analysis,  S21 measurement,  F-matrix computation,  

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Substrate-coupling equivalent circuits can be derived for arbitrary isolation structures by F-matrix computation. The derived netlist represents a unified impedance network among multiple sites on a chip surface as well as internal nodes of isolation structures and can be applied with SPICE simulation to evaluate isolation strengths. Geometry dependency of isolation attributes to layout parameters such as area, width, and location distance. On the other hand, structural dependency arises from vertical impurity concentration specific to p+/n+ diffusion and deep n-well. Simulation-based prototyping of isolation structures can include all these dependences and strongly helps establish an isolation strategy against high-frequency substrate coupling in a given technology. The analysis of isolation strength provided by p+/n+ guard ring, deep n-well guard ring as well as deep n-well pocket well explains S21 measurements performed on high-frequency test structures targeting 5 GHz bandwidth, that was formed in a 0.25-µm CMOS high frequency.