From: Doug Hopperstad (email@example.com)
Date: Fri Apr 27 2001 - 11:59:38 PDT
I have a question regarding edge rates. Is there a standard for the edge
rate points, i.e. 90%/10% or a specific voltage point like 2v, 0.8 v? I have
some data sheets that indicate the edge rates are determined by the percent
method and other data sheets (SSTL) that call out for ViH/ViL point for the
markers. My Scope is defaulted at the 90/10 percent setting and if I use it,
I get fairly good timing numbers of ~ 600pS. However, the vendor of the
component is calling out to use Vref +/- 0.35 volts with Vref normally at
1.25 volts. If I measure the edges in the lab with that method, my timing is
an insane 180pS per the 0.7 volt delta. My overshoot is not reflective of
the faster edge rates.
Can anyone provide some insight into the different procedures called out in
the design specification books?
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