[SI-LIST] Re: SSN Measurement

From: "Ingraham, Andrew" <Andrew.Ingraham@xxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Date: Fri, 2 Aug 2002 18:00:58 -0400

>       I am trying to accurately measure SSO noise. However
> I am not sure my equipments are right for the job. Can anyone
> comment on these setup?
>       Agilent 2Gsa/s (or 4Gsa/s) scope
>       10:1 1MOhm Passive probe(comes with the scope)
 
You might want to consider investing in active probes.  Or making your
own passive probes out of smaller valued resistors.

The usual 10:1, 1Mohm passive probe is OK for signals below a few tens
of MHz, or risetimes in the 5-10ns and up range.  The ground clip is too
long, resulting in a sizeable loop.  Although the DC input resistance
may be big, so is the capacitive loading.  On many of these probes, the
input resistance (real part of the impedance) itself falls way off as
you go up in frequency, becoming a significant loss component.

>       (The rise time of my signal is 1ns.)
 
Then you're only getting a couple scope samples in a risetime.  You
won't see the shape of the risetime, and might miss capacitive coupling
that lasts only as long as the risetime.

Andy



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[SI-LIST] Re: SSN Measurement

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