I'm not sure if it is your simulation or the circuit that is giving you trouble.. But if you look at the schematic it appears your op amp is using 5 volts. If so when the signal goes above 5 volts (like the top op amp) it won't work. Also not just every op amp will give a 1 Usec. pulse from ground to 5 volts, so maybe you will use a high speed comparator? Maybe you could add another set of op amps to your schematic so we can see the different steps? What do you do with the outputs?