(Caveat: "young player" at large here.)
The circuit below (not my creation) debounces a push button and generates a 1us negative pulse when it's pressed. I breadboarded it and it works as expected, but I am trying to understand the purpose of the reverse biased diode.
My understanding is that as the first inverter goes high, the 100pF capacitor charges through the 10k resistor, which normally pulls the node to logic level 0, giving a short pulse of logic level 1 to the last inverter, creating the desired negative pulse.
But what is the purpose of the diode shown in the schematic? I don't see any way it would ever be anything but reverse biased, nor that it could ever be subjected to its reverse breakdown voltage.
I tried to remove it (it's unspecified in the schematic, I used an 1N4148) and compare single shot references on the scope (measured at the 10k node), but could see absolutely no difference between the signals with or without the diode.
(Actually not really sure about the 1k resistor's role either as I'd expect the HC input to draw so little current that there'd be no voltage drop over it.)