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First connect DC source "Vgs" to an NMOS transistor. Another DC source for Vds and ground to source and connect bulk to source. Now sweep DC Vgs using DC sweep. In order to plot "gmoverid" you need this file.
Please find herewith the stimulus file (It can have any name,. In this case it is "stimulus"). The procedure to use this file with spectre is as follows.
1) Open this "stimulus" file. Here TN1, YN2, TP1, TP2 are the transistor's "instance name". You should replace it with your own instance names. The command "save TN1:all" saves all the DC parameters. The command "save TN2:gm" saves only the gm of the TN2 transistor.
2) On the "Analog Environment" goto "Setup" then "Simulation files" and then on "Stimulus file" add the path of this "stimulus.txt" file.
3) Now do the DC or transient sweep as required (Say you sweep "Vgs" and want a plot of "gmoverid").
4) Now on the "Analog Environment Window" goto "Tools" and then "Results Browser".
5) Click "dc-dc". Here you can see all the saved parameters. Right click "gmoverid" it and plot it.
The file is attached in the button of the post. Just save this text in stimulus file from line "simulator...........".
Please click helped me button if this post is useful to you.
by using the method you suggested for getting ft for an nmos with 400n/180n vgs=1.4 vds=1.8, im getting cgg of 724.522af and gm of 233.635u an ft of 49.125Mhz , instead of getting some thing in GHz's, is there anything im missing, help me with this. Thanks in advance.
Added after 1 hours 47 minutes:
hi, can you tell me one more thing, how to do noise analysis in cadence spectre, i would like to see flicker noise and thermal noise of mosfet, how would be the test bench. Thanks in advance.
I use AC and S parameter simulate the ft of NMOS and PMOS in cadence spectre, two kinds of simulation results, then use ft = gm/(2 * pi * Cgg) verify , found simulation of NMOS and calculation results is same, calculation results of PMOS are much smaller than the simulation results, I can get gm, and Cgg using DC analysis. "ft=gm/2pi*Cgg" is suitable for PMOS?