RE: [SI-LIST] : Adding inductors to ground?

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From: Martin thompson (Martin.J.THOMPSON@lucasvarity.com)
Date: Fri Mar 03 2000 - 09:08:19 PST


Hi Lee,
        Can I ask for some science to back this sort of comment up, otherwise I
have to choose between one comment saying its good and another saying
its bad. I suppose I could use some metric like 'number of typos in
message' to decide :-)

Thanks,
        Martin

                Martin Thompson.

 TRW Automotive Advanced Product Development,
 Stratford Road, Tel: +44 (0)121-627-3569
 Solihull, Fax: +44 (0)121-627-3584
 B90 4GW. UK mailto:martin.j.thompson@trw.com

-----Original Message-----
From: Ritchey Lee [SMTP:leeritchey@earthlink.net]
Sent: Friday, March 03, 2000 1:48 AM
To: si-list@silab.eng.sun.com%INTERNET
Subject: Re: [SI-LIST] : Adding inductors to ground?

It's a common practice that is a bad idea. Can't say how it got
started, but it's a sure way to degrade the performance of parts.

Lee

Chris Bobek wrote:

> Hi,
>
> I came across a schematic that shows the PLL ground of an IC connected
> to ground through an inductor. The Vcc pin of the device is connected
> to a bunch of caps and an inductor to Vcc.
>
> I understand and have used an inductor (or a resistor) with a bunch of
> decoupling caps on Vcc for applications like this. But, I've always
> tied the Gnd pin(s) directly to ground. It doesn't make any sense to me
> why you would want to add inductance in the path of any ground. It
> seems you would just add switching noise to your device.
>
> Can somebody explain whether this is common practice, or whether it was
> a poor design (sorry I don't have more information on the particular
> device).
>
> Thanks,
>
> Chris
>
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