In order to generate a short pulse off a permanent constant current signal, I made this circuit. It works well except that it created a very high frequency ripple which wreaked havoc all over the prototype board, not just the output, and brought the voltage of the entire board from 5V to 3V, sometimes less.
The frequency was so high that my 200Mhz oscilloscope couldn't see the wave but I could see that the line was very thick.
I solved the problem by adding a 15pF cap (C2) between the output and ground. Now the signal is perfect. Before, when my circuit had problems, it was the same, just without this cap. There was already a 330K resistor to ground and I thought that would be enough to avoid this type of interference.
I think that the voltage drop was due to other ICs being pulsed extremely fast albeit at undefined levels. Before finding out where the problem came from, the symptoms were not clear: The board worked as expected. Then the next day I changed something apparently not related and it started working unpredictably.
Is this phenomenon common? Should I be concerned about other flaws in my circuits which could be the cause of this? Or was it what is called "capacitor self-resonance"?
The triangle on the left is a Schmidtt trigger. I can't confirm if the same effect would appear if the signal source came from another ic or a power supply directly.
The board is a composition of three 595 shift registers, schmidtt triggers, a 557 clock, 2 or 3 mosfets and a bunch of schottky diodes. It's powered by a linear regulator, itself powered by a 15V power supply. Changing the power supply to a completely different one didn't change anything. All the ICs have decoupling caps, which I think have also no effect as far as this board is concerned. Adding them didn't produce anything visible.