Compact models and delay computation of sub-threshold interconnect circuits

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Ultra-low power designs extensively exploit the sub-threshold region of operation of Complementary metal-oxide semiconductor (CMOS) circuits. Though sub-threshold circuit operation shows huge potential towards satisfying the ultra-low power requirement, increased crosstalk and delay have become serious design challenges particularly for sub-threshold interconnects. In this paper, novel analytical time-domain models governing the output voltage and crosstalk-induced delay of CMOS gates driving coupled resistive---capacitive interconnect in sub-threshold domain are presented. Subsequently, the transient analysis of simultaneously switching two and three coupled interconnects is carried out. It is demonstrated that the modeling of driver by linear resistance can lead to about 38 % average error in the estimation of propagation delay. The numerical results illustrate that the proposed model quite accurately estimates the performance of coupled on-chip interconnects. An average error of less than 7 % is observed in estimation of waveform shape and delay.