circuit origins of the non-monotonic pull-up curve

We got into a discussion the other day about the origin of the
non-monotonic IV curve depicted on p. 20 of the cookbook. In my mind, the
"output enabled" IV curve should be a sum of the clamp (ESD diode and/or
parasitic well diode) and the FET characteristics. Therefore, when you
subtract the clamp curve from it, you should get the FET curve, with the
possible exception of some round-off errors. However, the "hump" you
really see in the pull-up or pull-down curve is much bigger than round-off
error. Is this easy to explain, or is it fairly subtle? Where did my
reasoning go wrong?

Greg Edlund
Advisory Engineer, Critical Net Analysis
IBM
3650 Hwy. 52 N, Dept. HDC
Rochester, MN 55901
gedlund@us.ibm.com
Received on Thu Dec 10 05:40:35 1998