Semi-custom design method based on standard cell extension

LI Bi-chen， SHEN Hai-bin， ZHENG Dan-dan， YAN Xiao-lang
（Institute of VLSI Design， Zhejiang University， Hangzhou 310027， China）

Abstract： Aiming at problem of insufficient optimization for critical path in VLSI design，a semi-custom design method based on standard cell extension was proposed. Critical path was analyzed on the basis of logical effort model. Extended cells with perfect driving capability were constructed by development language of Cadance according to analysis results，and timing information of extended cell might be simulated by hspice. Standard cells in optimal critical path with long timing-delay could be replaced by extended cells with ideal drive ability in order to achieve shortest timing-delay both of the cell itself and critical path，meanwhile design automation and flexibility could be realized and the very method had advantageous portability for mainstream technology. Physical design and timing simulation by four kinds of TSMC technology for a certain process chip were accomplished respectively with standard cell and extended cell method. The experimental results indicate that the semi-custom design methodology based on standard cell extension could shorten the critical path delay and improve circuit frequency effectively in mainstream technology design.
Key words：VLSI design； extended standard cell； optimization for critical path； logical effort model； semi-custom design