[SI-LIST] Re: Decoupling of Oscillator
- From: David Lieby <dlieby@xxxxxxxxxx>
- To: martin@xxxxxxxxxxxxxx
- Date: Thu, 21 Nov 2002 08:14:53 -0800
Martin,
One of the worst EMI problems I ever worked on resulted from
circuit two. The BEAD in the ground really caused problems.
When it was replaced with a zero ohm jumper things were not
too much better.
A nice solid ground for the return currents helps so much.
dav0
David Lieby, SI Engineering
Acuson Corporation, a Siemens Company
1230 Shorebird Way
Mountain View, CA 94043
Building E
P.O. Box 7393
Mountain View, Ca 94039-7393
(650)694-5030
Martin Euredjian wrote:
>
> From: Philip Ross Wellington
>
> > Some provided Pi filters for the
> > ground but that didn't work well logically because of the return path
> > inductance and Signal Integrity (not even coined back then) induced
> > problems.
>
> On datasheets I've seen recommended isolation/filtering networks that look
> like this:
> (values chosen at random)
>
> RAW_VCC -----------BEAD-------------- VCC'
> | | | |
> | | | |
> 22uF 0.1uF 0.1uF 22uF
> | | | |
> | | | |
> RAW_GND -----------BEAD-------------- GND'
>
> versus:
>
> RAW_VCC -----------BEAD-------------- VCC'
> | | | |
> | | | |
> 22uF 0.1uF 0.1uF 22uF
> | | | |
> | | | |
> RAW_GND ----------------------------- GND'
>
> Is there any merit to the first approach, say, for a clock, or a device with
> a PLL, or a sensitive analog sub-section? Both in terms of circuit
> operation and EMI/RFI concerns.
>
> I've also seen a couple where the beads are replaced with low or 0 ohm
> resistors.
>
> Thanks,
>
> ===============================
> Martin Euredjian
> eCinema Systems, Inc.
> voice: 661-305-9320
> fax: 661-775-4876
> martin@xxxxxxxxxxxxxx
> www.ecinemasys.com
> ===============================
>
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