What circuit can generate the waveform shown below upon receiving a falling edge trigger?
The closest I've gotten is that it looks like an RLC that got charged then the loop got closed. I'm guessing maybe I can use a transistor to close such a circuit, but honestly analog is really not my strong suit. I'd like to be able to alter the amplitude, decay time, and oscillation frequency, so please provide formulae.
For what it's worth though, the divisions on the oscilloscope are 5V and 0.1ms. An interesting twist on this is that it is powered by a 9V battery, but somehow the peak voltage is ~20V (it's not necessarily "double", it could be an arbitrary voltage). So, somehow the impulse must be able to have a higher amplitude than the power that drives it.
I should also add that the triggers come more than once, sometimes milliseconds apart. A delay to causing the pulse is fine as long as each trigger causes a pulse.
If you can recommend specific components (or types of components, e.g. ceramic vs electrolytic capacitors) I'd appreciate it.
Thanks!
Best Answer
Since you say up to 500 µs delay from the trigger edge to your exponentially decaying ringing signal is acceptable, here is a solution:
When the input trigger comes along, you have something close the switch for 500 µs. This could be a microcontroller or a dedicated timing circuit like a one-shot. During that time, current builds up in the inductor.
When the switch opens, the inductor current will get dumped onto C1, causing its voltage to rise. L1 and C1 are a resonant circuit that continually slosh the energy originally in the inductor back and forth between each other, generating a sine voltage on C1. R1 dampens these oscillations. Instead of a endless sine, which would be the result of theoretical ideal L1 and C1, you get a sine with a decaying amplitude envelope as shown in by your scope trace. The product of L1 and C1 set the frequency. Once you have that you can select R1 to get the desired damping.
In practise, the switch is probably best implemented by a N channel FET, but could also be a NPN transistor.