So I built (copied) an active quench circuit with capacitive coupling. It follows Mario's first circuit. here
A few changes in the circuit. I couldn't find any use for the I_3 reset part. And I put a one shot in front of I_2.
The Schottky diode is normally biased on, when the spad fires the current stops flowing, voltage drops and that's what the comparator senses. The diode (I think) is mostly to isolate the spad from the comparator input capacitance. (Hmm I'll have to try it without the schottky.)
So this is all working fine up to about 5V of over voltage. 'scope shot with 1 sec persistence.
Above 5V I run out of quenching voltage. And I start to see events like this,
Where it takes a few micro seconds to reset itself. I'm not really sure what's going on here.
Anyway, long story short I'm ready for a fast mosfet driver.
John L. you mentioned these before, got a recommendation?
George H. ps piglet, I wound a little pulse transformer,
If I drive that through 100 ohms I get L/R ~1 us, but knowing nothing of transformers... well I've got to think about it. (or solder something up.) Geo