MOS CV Characteristics

How do you simulate the CV characteristics of a MOSFET in PSPICE?
I am trying to use the .AC and the .DC(.STEP) analysis. When I try to sweep with gate current vs the gate voltage, the gate current remains at zero.Any suggestions....?

Connect both drain and source to ground.
Connect a current source to gate.
Simulate in DC. Observe the transience.

Note the transience of current source I = CgVgs.dVgs/dt
, therefore CgVgs = I/(dVgs/dt)

Plot Cgs as a function of Vgs.

Bias the MOSFET use DC voltage source as you want, remember to insert a large inductor between the DC voltage source and your drain, gate, source etc. After this, connect a 1V AC source to the gate, perform a AC simulation on the frequency range you care, then plot out the current flow through this AC voltage source, since the AC voltage is 1V, the current is the conductance of the MOSFET seen from gate. The capacitance is this AC current divided by 2*PI*freq, since then you get the MOS capacitance versus frequency for a fixed DC bias, sweep the DC voltage source (Vgd), you can get the 2 dimensions plot for MOS Cap versus Vgd and frequency. To simplify the simulation, you can specify a single point AC simulation (e.g AC simulation on 1GHz) then you can get the CV curve for MOS Cap on 1GHz.

Please look at hspice demo. There is a hspice demo .sp file contains a lot of simulation decks for mos cap curve plot.