fast discrete PHEMT one-shot

https://www.dropbox.com/scl/fi/agatzclr8pvr5470g6mc4/Phemt_One_Shot_1.jpg?rlkey=cwnx0qd7ajgnh8otf627x5lku&raw=1

Regular monostables are terribly slow. This one has low prop delay and
high rep-rate, if the sim is to be believed.

SAV541 is mostly specified as an RF part, but it's a dynamite switch.

I can post a link to the files if anybody wants to play with this. All
my values are first guesses, no math involved, and it works!

My SAV541 Spice model is a revision of Phil Hobbs' original.
Mini-Circuits is adamant that they will never provide Spice models, a
typical RF-bigot attitude.