Short-term Optimized Spread Spectrum Clock Generator for EMI Reduction in Switching DC/DC Converters

摘要

We present here a prototype of a Spread Spectrum Clock Generator designed for switching DC/DC converters, which has been optimized in accordance to EMC international regulations to improve EMI reduction with respect to standard approaches. Such an optimization has been obtained trough the theoretical computation of the power spectrum as measured by a spectrum analyzer when a chaotic or random-like PAM modulating signal is employed. To experimentally validate the achieved theoretical results, the circuit has been fabricated in CMOS 0.18 $mu{rm m}$ technology, and embeds two simple and effective modulators, the first one relying on a full analog hardware, the second one on a simple digital core. Measurements on a DC/DC converter in accordance with EMC regulations confirm that the prototype can achieve a 7 dB EMI reduction improvement with respect to classical solutions based on out of audible triangular waveforms.