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Standard cell libraries content optimization  

Authors
 Kalashnikov V.S.
 Semenov M.Y.
Date of publication
 2016

Abstract
 Standard cell libraries or Digital Design Kits (DDK) include thousands different cells. Different vendors provide the cells with various functions, driving strengths, transistor’s gate lengths, Vt options. At the same time there is no unique approach how many and what cells should be included in DDK and what content is sufficient. The main purpose of this article is to investigate and provide recommendations on DDK content based on real designs.
METHODS
A methodology of DDK content analysis has been proposed. It is based on data extracted from sign-off layout databases that are ready for tape-out. A special tool for post-processing of extracted data has been developed. Applying this methodology we have provided the data mining for standard cell libraries from different vendors for various technologies (90nm, 55nm and 28nm) based on actual cells usage in real designs.
RESULTS
Below are main outcomes of the analysis:
1) identified “top twelve” functions which should be optimized and included at the highest priority list for all standard cell libraries;
2) high Vt cells usually dominate in real designs across analyzed designs (usage 63-83%);
3) mixed gate-length cells approach should be considered as higher priority addition in library for low power applications;
4) cells with regular P/N ratio are the most used across analyzed designs but custom P/N ratio cells are widely used by synthesis tools (up to 16%);
5) low drive strength cells are the most used cells in designs (70-77%) whereas amount of high drive strength cells is quite small (1-2%);
These results facilitates well balanced and proper set of functions and cells in DDK both at early phases of development and final DDK.
Keywords
 digital library, standard cell library content, low power standard cell, high performance standard cell, multiple voltage threshold cells, mixed gate length cells, low leakage cell, P/N ratio, low drive strength cells, high drive strength cells.
Library reference
 Kalashnikov V.S., Semenov M.Y. Standard cell libraries content optimization // Problems of Perspective Micro- and Nanoelectronic Systems Development - 2016. Proceedings / edited by A. Stempkovsky, Moscow, IPPM RAS, 2016. Part 2. P. 217-224.
URL of paper
 http://www.mes-conference.ru/data/year2016/pdf/D011.pdf

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