Clock tree synthesis for prescribed skew specifications

Abstract

In ultra-deep submicron VLSI designs, clock network layout plays an increasingly important role in determining circuit performance including timing, power consumption, cost, power supply noise and tolerance to process variations. It is required that a clock layout algorithm can achieve any prescribed skews with the minimum wire length and acceptable slew rate. Traditional zero-skew clock routing methods are not adequate to address this demand, since they tend to yield excessive wire length for prescribed skew targets. The interactions among skew targets, sink location proximities and capacitive load balance are analyzed. Based on this analysis, a maximum delay-target ordering merging scheme is suggested to minimize wire and buffer area, which results in lesser cost, power consumption and vulnerability to process variations. During the clock routing, buffers are inserted simultaneously to facilitate a proper slew rate level and reduce wire snaking. The proposed algorithm is simple and fast for practical applications. Experimental results on benchmark circuits show that the algorithm can reduce the total wire and buffer capacitance by 60% over an extension of the existing zero-skew routing method.