Practical Considerations of a Nested Spread Spectrum Modulation to Reduce Electromagnetic Emissions

This paper explores the use of spread spectrum clocking (SSC) to reduce electromagnetic emissions in clocked electronic systems by dispersing energy across the frequency spectrum around the clock signal’s central frequency. Unlike the widely adopted conventional frequency modulation (FM) technique, this study focuses on an advanced nested frequency modulation approach, where a second modulation stage is introduced. This secondary modulation helps further distribute the energy into the unoccupied gaps between adjacent sidebands within the Carson bandwidth, thereby reducing peak emissions. A detailed analysis of the relationship between the two modulation frequencies and their impact on overall emission reduction is presented through simulation examples and measured results.