FreeLists / si-list / [SI-LIST] Re: EMC Issue at 266 MHz

["Comcast Mail" <wojo10@xxxxxxxxxxx>]

Take a look at your clock, and then do a Fast Fourier Transform on it - then
you will see why.

        Wojciech
----- Original Message ----- 
From: <Jean_Pierre.Bouthemy@xxxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Cc: <Guy.Barange@xxxxxxxxxx>; <Herve.Wattier@xxxxxxxxxx>
Sent: Monday, March 01, 2004 1:24 PM
Subject: [SI-LIST] EMC Issue at 266 MHz


> Hi SI experts,
>
> I have a question regarding an EMC issue.
> Our system has failed the EMC radiated emissions with a 266.6 MHz emission
> +3dB above Class A gabarit !
> We have many 66.66 MHz clocks in our system, made with 50MHz oscillator
> feeding a PLL, whose 400 MHz VCO frequency divided by 6 gives 66.66 MHz.
> My question is the following:
> I could understand an emission at the odd harmonics:
>  - 66.66MHz x 3 =   200 MHz or,
> - 66.66MHz x 5 = 333.33 MHz or,
> - 66.66 MHz x 7 = 466.66 MHz or,
> - so on ...
>
> But I don't understand why we have problem with the fourth harmonic :
66.66
> MHz x 4 = 266.6 MHz !!
> => Does anyone have an idea ?
> => Is it possible the 266MHs emission doesn't come from our 66.66MHz
> clocks?
> => In this case wher could it be from?
>
> Thank you for your help.
> Regards.
>
> Jean-Pierre Bouthemy
>
>
> --------------------------------------------------------------------
> Jean-Pierre BOUTHEMY
> Hardware Design Engineer
> ALCATEL - Mobile Networking Division (MCG)
> Mobile Core R&D
> +33 (0)2 99 26 08 18
> mailto:jean_pierre.bouthemy@xxxxxxxxxx
> --------------------------------------------------------------------
>
>
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