EMI Reduction in Switching Power Converters and Digital Circuits via Spread Spectrum Technique

In both digital computing platforms and switching power converters Electromagnetic Interference (EMI) is mainly due to timing signals, such as clock signals, widely employed in the first ones, or the control pulse-trains used in the latter case. Spread Spectrum (SS) techniques introduce a controlled jitter in the timing signals (usually by means of Frequency Modulation) spreading the power of their spectral components over a bandwidth which depends on the jitter characteristics. The most common solutions to achieve spreading is by using either a triangular (adopted in many standard, such as the Serial-ATA, PCI-express, etc.) and cubic modulation profile. Notably, this last solution reduces the peak value of the spectrum by more than 7dB with respect to the unperturbed signal and has been employed in several commercial products from Intel, IBM, and Cypress.  We proved that non-periodic (e.g. chaotic) modulating signals ensure an optimally flat EMI spectrum and a further 9dB reduction with respect to the previously mentioned solutions. We also implemented a 3GHz low-EMI SS clock generator for Serial Advanced Technology Attachment II (SATA-II) applications guaranteeing the largest know EMI reduction. Notably, if one takes into account the model of the EMI receiver used in the measurements (in compliance with EMC standards), the resulting effect of all modulating waveforms is however different. In this setting we showed that none of the industrial products (by Cypress, TI, ON Semiconductors, Fujitsu, …) is capable to minimize EMI if measured according to EMC standards. We offered a way to perform such an optimization and implemented the corresponding solution in a CMOS asic.


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ERC Sector:

  • PE7_2 Electrical engineering: power components and/or systems
  • PE7_4 (Micro and nano) systems engineering
  • PE7_7 Signal processing

Keywords:

  • Electromagnetic interference
  • Power conversion
  • Serial ATA

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