Clock Distribution Techniques for Low-EMI Design

In modern digital ICs, the increasing demand for performance and throughput requires higher operating frequencies of hundreds of megahertz, and in several cases exceeding the gigahertz range. Following the technology scaling trends, this request will continue to rise, thus increasing the electromagnetic interference (EMI) generated by electronic systems. The enforcement of strict governmental regulations and international standards, mainly (but not only) in the automotive domain, are driving new efforts towards design solutions for electromagnetic compatibility (EMC). Hence, EMC/EMI is rapidly becoming a major concern for high-speed circuit and package designers. The on-chip clock signals with fast rise/fall times are among the most detrimental sources of electromagnetic (EM) noise, since not only they generate radiated emissions, but they also have a large impact con the conducted emissions, as the power rail noise localized in close proximity of the toggling clock edges propagates to the board through the power and ground pins. In this work, we analyze the impact of different clock distribution solutions on the spectral content of typical onchip waveforms, in order to develop an effective methodology for EMC-aware clock-tree synthesis, which globally reduces the EM emissions. Our approach can be seamlessly integrated into a typical design flow, and its effectiveness is demonstrated with experimental results obtained from the clock distribution network of an industrial digital design.

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