[SI-LIST] Re: overshoot and undershoot different swing
- From: "Jim Whitehead" <jim.whitehead@xxxxxxxxxxxx>
- To: <rajeev.kommera@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 3 Apr 2007 19:14:59 -0400
Rajeev, I've seen a few responses to your question and would just like
to add a couple of things to their comments:
1. Overshoot is when the waveform goes beyond the intended magnitude in
either the positive (rising edge) or negative (falling edge) direction.
Say it peaks to 2.6V prior to settling at 2.5V (rising edge)... or peaks
to -.5V prior to settling at 0V (falling edge).
2. Undershoot is when the waveform dips below the intended magnitude in
either the positive (rising edge) or negative (falling edge) direction
prior to settling at the desired level.
In addition to the prior explanations for a potential reason this
happening:
I'm not sure what your topology is or what technology you are using,
however, consider that you may have a stronger drive/sink capability of
your source... or other components on the net are acting as a stiffer
pullup or pulldown.
You probably already know that overshoot and undershoot are not
automatically a bad thing. Ultimately, you just have to ask yourself if
you can live with its magnitude (do you violate Vih/Vil etc... or turn
on protection diodes and degrade the interface over time), where it is
in the waveform (does it settle prior to the signal being needed) and
what is it feeding (is it a clock, transparent latch, etc..)
Hope that helps.
Cheers,
Jim
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of rajeev.kommera@xxxxxxxxx
Sent: Monday, April 02, 2007 10:36 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] overshoot and undershoot different swing
Hi all,
We are having 76 MHZ clock output from FPGA in our design.
I am seeing on oscilloscope that the overshoot and undershoot is not
same.
I want to know whether it is necessary that overshoot and undershoot
values needed to be same? If yes then what factors effects the values to
be different?
Regards,
Rajeev.
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