Current pulsing circuit, troubleshooting
I am hoping someone with more experience may be able to offer an explanation as to what is happening.


For the left-hand circuit: -

V2 (the pulse signal) has a peak of 10 volts and feeds a source follower M1. The output from the source might peak at 6 volts (or thereabouts) and this would naturally produce a gate drive to M2 that would reasonably turn it on. Given that M2 doesn't have a source resistor it would be able to deliver a decent drive to the coil of several-to-plenty of amps (device dependent).

The introduction of the 1 ohm resistor: -

This upsets the drive capabilities quite a lot. M2 will produce an output at its source of a few volts when being driven by the 6 volts at the gate and this will limit the current in the drain. I estimate that the source may rise to 2 volts and this of course is across a 1 ohm resistor. The impact is that the peak current delivered to the coil is limited to about 2 amps (2 volts / 1 ohm).