@Laxman Chinnannavar your circuit has 10ms period (100Hz frequency) square waves as stimuli. This means you have frequency components at much higher frequencies. I should not go higher than 0.1ms step size for this kind of switching circuit. ALso to speed up simulation use higher rise and fall times for the input pulse generators. Having 100ps rise/fall time on a 100Hz square wave makes no sense and slows down simulation incredibly.

Ok, so the step size has to be adjusted accordingly to the input period. But still not understanding how the step size works and how it affects the plots.

@Laxman Chinnannavar if step size is too high you may incur in aliasing problems. If you sample a 1MHz sinusoid at 1us intervals you see a constant waveform, which is clearly wrong.