Take a look at this:

ADL5315
https://www.analog.com/media/en/technical-documentation/data-sheets/ADL5315.pdf

part.

 

The circuit is a comparator with a hysteresis as explained but since it switches after reaching a voltage and while headed in the opposite direction it reminded me of a differentiator but is is not.

It Detects a change in direction once it hits a certain voltage limit. It’s a strange use of a comparator, comparators are usually used as inverting and the thresholds are reached at a high and low point not after such a high or low point is reached.

 

hi W,
For the thresholds are reached at a high and low point , these are usually described as a Window comparator.

Attached a couple of PDF's for Comp Apps, you may find them of interest.
E

 

@ericgibbs thanks and looking at those pubs I agree, usually the input is on the inverting input which makes a high low window... if you look at the output triggers on our example note that this is not the case for our circuit in question.

It triggers at the onset of a rise but will never trigger until after the input signal falls (in fact if the input signal stayed at top without dropping or kept rising (i know not realistic) it would never trigger down. this is a 3V rising pulse.