Hi,

I have a problem with parasitic noise sources of rs & rd of NMOS switch in simulating the simple sample and hold circuit noise with pnoise. When I look at the noise sources from noise summary, I see that in addition to id noise of NMOS switch, there are two other noise sources rs & rd.

I saw that rs & rd noise changes with the pulse width of the clock but I could not find the reason for that noise? In some simulations, these are the dominant noise sources.

What is the reason for that noise or has anyone encountered this problem before?