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# help: how to plot gm-vs-vgs in cadence wavescan

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#### xiaofeixia

##### Junior Member level 3

i want to plot the gm-vs-vgs wave in cadence warescan
who can tell me how to plot model parameters in cadence
thanks a lot

wavescan plot vs

which simulator r u using? spectre???

gm vs vgs

Gm is Operation Point parameter. U can get one value of Gm for given Vgs value when u do DC Operation Point Analysis. Such way u can't sweep Vgs, so using CADENCE/SPECTRE u can't plot gm-vs-vgs drawing. If only u've got familiar with OCEAN/SKILL.
Another way to plot gm-vs-vgs is to do AC sweep. U need to place 2 vdc sources with dc voltage VGS, one between gate and source, next one between drain and source. Set ac voltage of the first source equals 1V. Set AC sweep analysis relatively Vgs at certain frequency. Gm value will be Gm=Iac(drain)/1V => Gm=Iac(drain) [A/V]. So u can plot gm-vs-vgs.

The necessity of gm-vs-vgs drawing looks stranger, i hope u know what u need.

If it's helpfull to u don't forget press "helped me" button.

### xiaofeixia

Points: 2

DenisMark said:
Gm is Operation Point parameter. U can get one value of Gm for given Vgs value when u do DC Operation Point Analysis. Such way u can't sweep Vgs, so using CADENCE/SPECTRE u can't plot gm-vs-vgs drawing. If only u've got familiar with OCEAN/SKILL.
Another way to plot gm-vs-vgs is to do AC sweep. U need to place 2 vdc sources with dc voltage VGS, one between gate and source, next one between drain and source. Set ac voltage of the first source equals 1V. Set AC sweep analysis relatively Vgs at certain frequency. Gm value will be Gm=Iac(drain)/1V => Gm=Iac(drain) [A/V]. So u can plot gm-vs-vgs.

The necessity of gm-vs-vgs drawing looks stranger, i hope u know what u need.

If it's helpfull to u don't forget press "helped me" button.

i think by using below spectre commands u can generate plot

sweep1 dc dev=VGS start=0 stop=1.8 step=0.2 //analysis sweep of vgs
save X1.M2:ids X1.M2:gm
/// where M2 is transistor whose ids and gm are plotting

after run invok wavescan
click on M2:gm appear on the screen
you will see Y-axis gm
X-axis Vgs(w.r.t sweep parameter)

### xiaofeixia

Points: 2

wavescan plot vs axis

DenisMark said:
Gm is Operation Point parameter. U can get one value of Gm for given Vgs value when u do DC Operation Point Analysis. Such way u can't sweep Vgs, so using CADENCE/SPECTRE u can't plot gm-vs-vgs drawing. If only u've got familiar with OCEAN/SKILL.
Another way to plot gm-vs-vgs is to do AC sweep. U need to place 2 vdc sources with dc voltage VGS, one between gate and source, next one between drain and source. Set ac voltage of the first source equals 1V. Set AC sweep analysis relatively Vgs at certain frequency. Gm value will be Gm=Iac(drain)/1V => Gm=Iac(drain) [A/V]. So u can plot gm-vs-vgs.

The necessity of gm-vs-vgs drawing looks stranger, i hope u know what u need.

If it's helpfull to u don't forget press "helped me" button.

in cadence, i can plot VF("Vout") but can not plot IF("/M0/D") , do you know why??

It seems u didn't save this current.
Choose this terminal current though ADE "Outputs/To Be Saved". Or save all currents though ADE "Outputs/Save All" set "Select device currents" to "all" and set "Set cubcircuit probe level" value.

ocean wavescan plot

there will be calculator. So, u can calculate the gm and vgs seperately.

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