Re: [SI-LIST] : SDRAM termination

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From: Andrew Phillips (andrew@scs.ch)
Date: Fri Nov 19 1999 - 05:12:08 PST


"Greim, Michael" wrote:
>
  Have you checked the interface lines with
> a scope yet? What do they look like? Your description is at
> to high a level to solve right now.
>

Before you rush off and do this don't forget to make sure you are using
decent oscilloscope probes (e.g. passive resistive type) in a proper
manner - otherwise you'll probably load down the signal too much and
what you see is not what is really there - the circuit may even suddenly
work!

Also make sure your oscilloscope has a decent bandwidth otherwise your
signal risetime that you see on the screen will be baloney. I tried to
use a crappy 500MHz Tektronix scope recently to look at some signals
with 200psec risetimes - forget it! The scope itself had an effective
risetime of about 1.5ns.

BTW - a question to others since I've wandered into this area - since
signal risetimes are forever shortening how are we ever going to be able
to measure them properly without having to pay out grillions for the
latest high-bandwidth scope? Are there better options?

Check out one of Howard Johnson's columns for good info on scope probes:

http://www.sigcon.com/articles/straight/probes.htm

Andrew Phillips
Supercomputing Systems AG
Zurich, Switzerland

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