Handling a pulse that is only 0.7 ns wide is certainly a challenge.? For SPICE simulations, if you were to use 1 ns rise and fall times, and if you say that the desired pulsewidth is 0.7 ns at the pulse's 50% point (which is likely how it is specified), then you need to subtract 1 ns from the intended pulsewidth, to come up with the "on" time ("Ton") of your SPICE current pulse source.? Obviously that doesn't work for a 0.7 ns pulsewidth!? So you must decrease the Trise and Tfall times of your PULSE source in SPICE.? For example:
I1 N001 N002 PULSE(0 5mA 1us .0.5n .0.5n 0.2n 15u 20)
would give you 20 pulses that are 0.7 ns wide at 50% = 2.5 mA.
Just be aware that Ton is the time AT 100% of the pulse amplitude, so mentally add half the rise and fall times to get the effective pulsewidth at 50%.? Conversely, subtract half of (Trise+Tfall) from the desired pulsewidth, to get Ton for SPICE.
Remember to never set Trise or Tfall to 0.? That signals SPICE (and LTspice) to substitute non-zero default values, and they won't be anywhere near 0.? It's a SPICE thing.
Andy
