Re: [SI-LIST] : Measuring noise with Differntial probe

Adrian Shiner (adrian.shiner@virgin.net)
Sun, 12 Sep 1999 18:20:46 +0100

Excellent Web Site...Expertise always has to be measured against the next person...teachers shold produce ex pupils who have the ability to better than themselves. If Doug has been teaching a long time then I know where my money
is on the fact.

Adrian

Howard Ji wrote:

> Doug is THE expert at Noise mesurements.
>
> At 09:08 AM 9/9/99 -0600, Grasso, Charles (Chaz) wrote:
> >I would like to suggest you look at
> >Doug Smiths web page http://emcesd.com.
> >
> >In this he descibes a low capacitance probe
> >with a 1GHz bandwidth and includes the
> >theory of operation.
> >
> >Doug is an expert at Noise measurements.
> >
> >Thank you
> >Charles Grasso
> >Advisory Engineer
> >StorageTek
> >1 StorageTek Drive
> >Louisville CO 80027 M/S 4247.
> >Tel:303-673-2908
> >Fax:303-661-7115
> >email:grassc@louisville.stortek.com
> >RMCEMC Web Site: http://www.ewh.ieee.org/r5/denver/rockymountainemc/
> >
> >
> >
> >
> >-----Original Message-----
> >From: Ingraham, Andrew [mailto:Andrew.Ingraham@compaq.com]
> >Sent: Thursday, September 09, 1999 7:34 AM
> >To: 'si-list@silab.eng.sun.com'
> >Subject: RE: [SI-LIST] : Measuring noise with Differntial probe
> >
> >
> >>When I measure PWR-GND noise of high-frequency(~100MHz) IC, I have two
> >>options.
> >>One is using the standard Active (FET) probes, the other is using a
> >>differential probe.
> >>
> >>The results of two measurement are slightly different.
> >>
> >>Which must I believe ?
> >
> >Believe neither. Any hi-freq. measurement should be suspect. Every probe
> >will affect the signal and its display in some way.
> >
> >Are you probing the same exact two points, and are both probe leads VERY
> >short? Probing a signal and ground pin that are only an inch apart from
> >each other, can introduce sizable errors.
> >
> >The differential measurement *ought* to be better, *if* the diff. probe is
> >sufficiently accurate and wide bandwidth, as it avoids the ground loop.
> >
> >Try doing a differential measurement with two FET probes, and see how it
> >differs from the other two. Try various combinations to get a feel for how
> >these changes affect what you measure.
> >
> >Regards,
> >Andy Ingraham
> >
> >
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