[SI-LIST] Re: clock 2nd harmonic
- From: "Rose, Michael" <mrose@xxxxxxxxxxxxxxxxx>
- To: "pakbazf@xxxxxxxxxx" <pakbazf@xxxxxxxxxx>
- Date: Thu, 17 May 2012 20:03:22 +0000
Right - the ones that appear in almost every appnote. Often they can cause more
problems than they fix - especially if there isn't enough dissipation damping
to knock down the Q. I've seen a clock driver Vcc ringing like crazy on both
edges when the filter is not properly designed.
Mike
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From: si-list-bounce@xxxxxxxxxxxxx [si-list-bounce@xxxxxxxxxxxxx] on behalf of
Faraydon Pakbaz [pakbazf@xxxxxxxxxx]
Sent: Thursday, May 17, 2012 3:56 PM
To: Rose, Michael
Cc: si-list@xxxxxxxxxxxxx; si-list-bounce@xxxxxxxxxxxxx; vinu@xxxxxxxxx
Subject: [SI-LIST] Re: clock 2nd harmonic
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Hi Mike;
By local LC filter, do you mean like Ferrite Bead and capacitor filter =
on
the AVdd of PLL that Reference Clock going into?
Thanks.
Regards;
Don Pakbaz
Silicon Solutions Engineering
IBM Systems & Technology Group
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I usually suspect duty cycle. A quick test is to run from a lab source
where you can vary DC. Also, you may want to characterize DCD jitter.
Another thing you could look for is excessive mounting inductance to Vc=
c
AND return. And if the clock source has local LC filter you could try
temporarily shorting around the inductor in case you're seeing some
resonance in the filter.
cheer, mike
________________________________________
From: si-list-bounce@xxxxxxxxxxxxx [si-list-bounce@xxxxxxxxxxxxx] on be=
half
of Vinu Arumugham [vinu@xxxxxxxxx]
Sent: Thursday, May 17, 2012 3:01 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: clock 2nd harmonic
Can't it be duty cycle distortion or for a differential clock, skew
between true and complement?
Thanks,
Vinu
On 05/17/2012 11:53 AM, Kevin Rhoads wrote:
> On 5/17/2012 2:43 PM, Joel Brown wrote:
>> I am having an EMI problem with the second harmonic of a 65 MHz cloc=
k.
>> There is a strong emission at 130 MHz.
> You do not get any harmonics without non-linearity. Where is there
> something that is non-linear that the clock touches?
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