Hi,
I have a few questions about ON resistance.
1) "MOSFET can serve as a switch; it can be on when it carries zero current." This statement somehow doesn't make sense to me. Ron is the equivalent resistance across D and S so if I_DS is zero, doesn't it mean infinite resistance, or an open ckt?
Is that statement measurable? I mean, how can I set up a test bench for the above statement and measure the ON resistance?
2) I need to figure out the ON resistance of an NFET with gate voltage and a passing voltage (Vref) given. So my coworker tells me, put a DC source (=Vref) at S and an AC source (AC magnitude =1, AC phase =0, DC voltage Vref) at D. Run the AC simulation and the ON resistance is the reciprocal of the drain current at DC.
Before running simulation, I don't expect to see any current at DC because I think as DC, VD=VS. However, after the AC sim, the AC voltage drop across D and S at 0Hz is 1V and there IS current flowing.
So my question is, intuitively, what should I expect to see the VDS at 0Hz?