A practical repeater insertion method in high speed VLSI circuits

Abstract

In today's design of VLSI high speed circuits, frequency has a major impact on the number of repeaters that needs to be inserted. A microprocessor operating at less than 200 Mhz might require several hundred repeaters, while one operating at greater than 500 Mhz may require a number in the thousands. The following paper describes an efficient and simple way to automatically determine buffer placement based on maintaining equal transition time for all gate input signals across the net. A maximum allowable transition time is determined (limited by the frequency of the circuit), and correlated with the interconnect Elmore Delay. A Spice RC model having nodes with physical locations (X, Y coordinates) can be obtained by extraction tools providing standard parasitic format (SPF). This can then be used with the results of the algorithm for repeater placement to determine the exact physical location desired for each repeater.