IC EMI using FFT

Discussion in 'The Projects Forum' started by skydrome1, Dec 11, 2011.

  1. skydrome1

    Thread Starter New Member

    Dec 11, 2011
    Hi all,

    I'm quite new here, please pardon me for any poor questions!

    I'm working on a project to compare the differences in EMI between an Asynchronous and Synchronous FIFO. I've created test circuits using Synopsys NanoSim, and have been told to compare the Fundamental Harmonics by performing a FFT on the supply current.

    My results are in dBA (y axis) by frequency (x axis). How should I interpret my results? I've been told that the lower is better; why is that so?

    Lastly, my supply current is negative. Does this mean that the "lower is better" only is applicable for the amplitude of my FFT or does that mean actual lower value? It seems that all my harmonics are negative.

    Any help is greatly appreciated. Thanks.
  2. skydrome1

    Thread Starter New Member

    Dec 11, 2011
    Umm... Maybe I should supplement my query with more information.

    I find it quite odd that my fundamental harmonic is higher for my asynchronous design while under load than my synchronous design, especially since my asynchronous design has a much lower absolute peak current draw (about -40 mA) than my synchronous one (almost -0.1 A).

    As such, I need to know how to compare the harmonics of the two designs after performing the FFT on each design's supply currents. Should I only compare the fundamental harmonics, or not? And what do the harmonics represent in the first place?

  3. t06afre

    AAC Fanatic!

    May 11, 2009
    This question is well inside the scope of the forum. But I think your question ended up in the wrong section. It would also help to to see some pics of your FFT diagram. Hard to help then you not have the full picture :)
    Ps I Think the mods will move your question to the proper section soon
  4. skydrome1

    Thread Starter New Member

    Dec 11, 2011
    Oh ok. Thanks!

    I thought it would fall under this section since it's got to do with integrated circuits :D

    I've uploaded two screenshots of my 8X8 FIFO circuits. One is asynchronous, the other is synchronous. The input rate is 1GHz, if I am not wrong.

    Would you like me to post my circuit diagrams too? :)

    Thanks again!