Multi-Harmonic EMI Reduction Optimization of Spread Spectrum in Multiple-RBW Environment

We investigate here both from a theoretical and practical point of view the problem of optimizing EMI reduction by means of spread spectrum clocking when lower harmonics need to be analyzed with a smaller RBW, and higher harmonics with a larger one. This situation is indeed a trade-off, where a designer can trade performance in terms of EMI reduction for lower harmonics with that achieved for higher harmonics. Two approaches are considered and analyzed. The first trade-off, denoted as Single Triangular Modulation, consists in the standard and commonly adopted triangular based spreading, where the role of the parameters is investigated with the aim of optimizing EMI reduction both in the lower part and the upper part of the spectrum. The second one, denoted as Double Triangular Modulation, is inspired by a recent Application Note and it is much more complex from an implementation point of view, being based on two simultaneous triangular modulations with different parameters. The comparison shows very similar performance, so that the adoption of the more complex approach results questionable.