Re: [SI-LIST] : Overshoot/Undershoot

Bill Dempsey (bdempsey@dnaent.com)
Mon, 23 Feb 1998 16:51:03 -0600

D. C. Sessions wrote:

> Bill Dempsey wrote:
>
> > I have a question. When the term "undershoot" is used
> > on this mail group is it to be interpreted as "negative overshoot"?
> > Or in fact are some engineers having undershoot problems?
>
> Alas, 'tis true. For too many years the digital crowd, having
> heard the term 'undershoot' but never really worked with it,
> assumed that it was what is known more precisely, negative-going
> overshoot. Books, articles, and instrumentation all made
> this usage the only one known to many young and impressionable
> engineers.

I was feeling like an idiot...until that was the Tektronix scope
allowedme to measure "negative overshoot". Yea! Once I could show that
to other engineers they started to see the light.

You're correct about the 0v vs. -2v etc... that was just a generic
reference. It seems that some engineers who have had control
theory, where these terms usually are introduced, have no problem
agreeing that "positive going" signals overshoot when flying past the
desired point. Flip the graph (scope) over and suddenly we lose
our heads? Unreal.

Thanks for the feedback.
Bill D.

>
>
> > My experience would indicate that most persons referring to
> > undershoot really mean overshoot below 0V.
>
> Well, sometimes they mean overshoot below -2v, and a very few
> deal with other signalling levels, but essentially correct.
>
> --
> D. C. Sessions
> dc.sessions@tempe.vlsi.com