Cut-off frequency is defined by fT=gm/2piCg

Where gm=dID/dVG is transconductance and pi=3.14 and Cg is total gate capacitance. 

You can obtain capacitance of gate using ac solution.

By an ac solution you can have drain current versus gate voltage too. then you can define proper function satisfying above equation for fT  in tonyplot and enjoy!!

(dydx (drain current,gate voltage))/(6.28 *abs(c gate>gate))

Cut-off frequency is defined by fT=gm/2piCg

Where gm=dID/dVG is transconductance and pi=3.14 and Cg is total gate capacitance. 

You can obtain capacitance of gate using ac solution.

By an ac solution you can have drain current versus gate voltage too. then you can define proper function satisfying above equation for fT  in tonyplot and enjoy!!

(dydx (drain current,gate voltage))/(6.28 *abs(c gate>gate))

Thank you very much...for your valuable reply.

You can also refer this paper.

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