Hi Guys,

The parameter cdd is defined as dQd_dVd (Intrinsic part of Cdd) (alias=lx33). Now I want to measure the parasitic capacitance at the drain of one MOS transistor. The simulation bench is shown in this post. A voltage source is applied to the drain of one NMOS transistor. A DC analysis is run. The parameter cdd is about 29 fF in the printed DC operating points of that NMOS. An AC analysis is run, too. Then I calculate the total parasitic capacitance at the drain based on the small signal impedance. The result is about 58 fF. The detailed formula is I(V0)/V(V0)=omega * Cd. What's wrong with my analysis?


Thank you in advance
Yawei