Attenuating above 100MHz on squarewave (SPDIF digital audio)

James · 2004-12-28T20:57:26+00:00

Hi,We're producing a consumer item that outputs a SPDIF (digital audio) signal.The squarewave produced is 0.5V pk-pk with a data rate of 6.144Mbits/sec.Our previous design failed EMC (Europe) radiated emissions testing on theSPDIF output line, at frequencies around 100MHz and higher. To pass, thetesting house had to clip a ferrite around the lead.For the new design I want to put a basic filter in the circuitry before theSPDIF output socket in order to attenuate those 100MHz and higher signalsenough so that it passes the radiated emissions tests. However, we don'twant to reduce the slew-rate too much on the square-wave. I think as long asthe filter does not attenuate frequencies of 50MHz or lower that would befine for us.Could someone please suggest what filtering I could use. I'm thinking of aninline ferrite or an RC or LR low pass filter maybe? I guess this kind ofthing is done all the time for SPDIF, so is there a standard recommendedfilter circuit?We'll take it along to the EMC testing house and be able to swap valuesthere if needed, but I'd rather get it right, or nearly right, before we getthere TBH.Many thanks,James

Dec 28, 2004 20 Replies

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John Woodgate 21 years ago

I read in sci.electronics.design that Mac wrote (in ) about 'Attenuating above 100MHz on squarewave (SPDIF digital audio)', on Tue, 28 Dec 2004:

Your attempt is perfectly OK in my book. No apology necessary.

Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

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Attenuating above 100MHz on squarewave (SPDIF digital audio)

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