Subject: [IBIS-Users] Clamp curve subtraction
From: Derwin Mattos (dhm@cypress.com)
Date: Thu Jun 26 2003 - 11:08:21 PDT
IBIS developers/users,
I'm attempting to work through the non-monotonic
issues raised in the standard.
Can someone tell me if I'm missing something?
The IBIS standard recommends the subtraction of clamp curves from
pull-up and pull-down curves. This can cause "non-monotonic"
warning messages to pop up during a syntax check.
When I want to replace my clamp curves with curves
measured from silicon (to improve clamp accuracy), the
combined curve has the potential of being non-monotonic
because the pull-down/pull-up curve has the original clamp
subtracted from it.
I'm thinking that double-counting clamps at the outputs
is not a significant issue (most signal overshoot occurs
at receiving-ends, not driving-ends), so would like to NOT do the
clamp subtraction. A simple note explaining why would
be included in the model.
My preference is for input clamp curve accuracy, not output driver
clamp curve accuracy.
Are there any write-ups on this particular issue?
As an IBIS user, what is your preference? Do you require that
the clamp curves be subtracted? Why? Is it a technical reason?
Thanks so much for any feedback/guidance. It would be much
appreciated.
Regards,
Derwin
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