Clock tree optimization for Electromagnetic Compatibility (EMC)

Electromagnetic Interference (EMI) generated by electronic systems is increasing with operating frequency and shrinking process technologies. The clock distribution network is one of the major causes of on-chip EMI. In this paper, we discuss the EMI problem in clock tree design. Spectrum analysis shows that slew rate of clock signal is the main parameter determining the high-frequency spectral content distribution. This is the first work to consider maximum and minimum buffer slew rates in clock tree synthesis to reduce EMI. In this paper, we propose a dynamic programming algorithm to optimize the clock tree considering both traditional metrics and Electromagnetic Compatibility (EMC). Our experimental results show that slew can be controlled in a feasible range and high-frequency spectrum contents can be reduced without sacrificing the traditional metrics such as power and skew. With the efficient optimization and pruning method, the biggest benchmark is able to complete in four minutes.