trashbox
|
Hi guys, When I was deriving a formula from a simple circuit, I run into the diode-connected NMOS's equivalent resistance issue. The details are: In the attached figure, the formula Vref1=(1+R1/R2)Vgs1-Vgs2 is obvious for the left circuit when two NMOSs M1/M2 are both in saturation and sink the most of current because of large R1 and R2. However, if using diode-connected NMOS M5/M6 instead of the passive resistance, I can not derive the Vref2 from the right circuit. The simulation shows the formula for Vref2 is right. Would you please give me any advice? P.S., If I use 1/gm5=R1 and 1/gm6=R2 to derive Vref2 from Vref1, the result is not correct. I think 1/gm is a small-signal resistance and here the equivalent resistance should be a DC resistor.
|