# How to simulate this pulse in LTSpice?

A quick question,

I have this pulse as an input to some device:

I just need to simulate it in LTSpice. I have the values of voltage obviously, and I know how to simulate that fall time. I just need to know how to simulate that spike at the beginning of the pulse.

Edit: Here is a close up of the spike, measured:

Thank you!

• PIecewise-linear source function. You're just going to have to make a guess about how long that spike lasts --- is it 2 us or 200 ns? – The Photon Nov 25 '18 at 6:12
• I'm sorry but do you mean a voltage source in series? how can I do what you mean? About the spike, I assume I'll guess, I don't know if it matters that much. – Eran Nov 25 '18 at 6:20
• Okay so I've thought about what you said about the spike so I added an image of it as well... – Eran Nov 25 '18 at 6:25

Where you can use the measured values (overshoot and ripple) to determine the frequency and damping. $$\M\$$ is the peak overshoot, $$\\zeta\$$ is the damping.
$$M\approx 1-\frac{\zeta}{0.6}$$ $$\omega_d=\omega_n\sqrt{1-\zeta^2}$$ $$T=\frac{2\pi}{\omega_d}$$
You could also use a PWL source, as suggested in the comments, but that will onyl give you what you see on the oscilloscope, as oposed to what actually is. If you're fine with that, godspeed.