Unity Gain Frequency (Viewdraw and SMASH)

[Someone2]

Hi guys,

I need to measure the Unity Gain Frequency of a PMOS and an NMOS. I'm using Viewdraw to generate the schematic and SMASH for the circuit simulation.

Saw one post here in the forum, of a guy that was doing this using Cadence, and was trying to do the same sim. I tried using the exact same schematic I saw there, but SMASH won't generate the OP results, and thus I cannot measure anything.

I have found a lot of information on how to get the ft for Op-amps in internet but I don't find any info for single MOS devices.

Could anyone help me out here?

Thanks!

 

[Someone2]

Bumping the question up. Hope someone can help me with this, I basically just need a schematic or a spice testbench.

Added after 4 hours 5 minutes:

What I have tried doing is biasing the MOSFET into saturation region and running an AC sweep simulation. But there is one problem with this approach, I don't know if there should be an exact VGS to do this, because if I change the VGS the frequency at which Io/Iin = 1 changes as well.

This is the netlist, which is basically just a NMOS transistor.

* MENTOR GRAPHICS WIRELIST CREATED WITH VERSION 6.3.17
* OPTIONS   : -J -H -V -C50 -N -M -X -A -.CIR 

M1I581 VDD INN VSS VSS NCH L=0.5U W=4U M=1
+ AD=1.92e-012 PD=8.96e-006 AS=1.92e-012 PS=8.96e-006

* DICTIONARY 1
* GND = 0

And here is my SMASH test bench:

*************************** INCLUDE FILES ***********************
.INC '..\Viewdraw\Netlists\test.cir'

.LIB '..\..\Models\mos.lib' tt

******* Parameters **********************************************
.param vsup=5
.H 1fs 1fs 10ns 125m 2
.PowerUp 20n 100n
.Method TRAP
.Eps 1u 1m 1n
.ac dec 10 10 100G op=no

************* Power Supplies ************************************
V_VDD VDD 0 'vsup'
V_VSS VSS 0 'LO'

************ Input Signals  *************************************
V_INP INP VDD DC 2V AC 1V

************ Print & Probe Signals*******************************
.printall
.trace ac im(V_IN) im(V_VDD)

************ Measurements  **************************************
.measure ac MOS_ft when im(V_VDD)=im(V_IN) TD=1K
.measure ac CURRNT find im(V_IN) at=MOS_ft
.end