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# how to plot Vth vs Vgs in cadence

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#### xiantongma

##### Newbie level 5

When the short-channel (0.35u), Vth is not constant, it is the function of Vgs. now I want to do Vgs dc scanning, plot Vth vs Vgs graphics, how can I plot this in cadence? I spent a few hours last night,but i did not find Vth. Hspice there is .Probe par ( "vth")

spectre op vth

sweep the vgs and plot the OP("device" "vth")

Operation Point Analysis in Cadence can gives u only one value for Vth parameter. U don't able to plot Vth vs Vgs during DC sweep.
Simple way to do it is using Parametric Analysis. U need to set DC OP analysis, output variable e.g. "Vth" == OP("/M1","vth"). Than u can do Parametric Analysis with sweep over Vgs.
U hope u know Cadence enough to do this.

Points: 2

### werank

Points: 2
ids vgs plot

HSPICE is easy.
YOU can use lv9(m*).

thankx，finally i want to plot （gm/id） vs （vgs-vth），how should i do

It's impossible by using Cadence graphic tools.
U should use OCEAN/SKILL script in such manner:

simulator( 'spectre )
design( "...")
resultsDir( "..." )
modelFile(...)
analysis('dc ?saveOppoint t)
temp( 27 )

for( i 0 10
Vgs = Vgs + 0.2 * i
desVar( "VGS" Vgs)
run()
Gm = OP( "\M1" "gm")
Id = OP( "\M1" "id")
Vth = OP( "\M1" "vth")
GmId = Gm / Id
Vov = Vgs - Vth
; Here u should store/printing data
)

Dont' forget push "helped me" button. So participiants of forum thank for help.

How to make vector and drawing one i don't know. U can use external tool for drawing graphs.

hitblda

Points: 2

### hitblda

Points: 2
hspice .probe vth

thankx

vth vs temp

DenisMark said:
It's impossible by using Cadence graphic tools.
U should use OCEAN/SKILL script in such manner:

simulator( 'spectre )
design( "...")
resultsDir( "..." )
modelFile(...)
analysis('dc ?saveOppoint t)
temp( 27 )

for( i 0 10
Vgs = Vgs + 0.2 * i
desVar( "VGS" Vgs)
run()
Gm = OP( "\M1" "gm")
Id = OP( "\M1" "id")
Vth = OP( "\M1" "vth")
GmId = Gm / Id
Vov = Vgs - Vth
; Here u should store/printing data
)

Dont' forget push "helped me" button. So participiants of forum thank for help.

How to make vector and drawing one i don't know. U can use external tool for drawing graphs.

hi
ur method really usefull i think,
thank u very much.

DenisMark said:
Operation Point Analysis in Cadence can gives u only one value for Vth parameter. U don't able to plot Vth vs Vgs during DC sweep.
Simple way to do it is using Parametric Analysis. U need to set DC OP analysis, output variable e.g. "Vth" == OP("/M1","vth"). Than u can do Parametric Analysis with sweep over Vgs.
U hope u know Cadence enough to do this.

Hi
would u please explain how to set ' output variable "Vth" == OP("/M1","vth") '
thank u very much ...

how to find vth from id vs vgs graph

It's only example how to solve given task. But u can extend this example and make a demo and share this experience for EDA Board participiants.

' output variable "Vth" == OP("/M1","vth") '
Use ADE/Outputs/Setup in appeared form fill name: "Vth" and expression e.g. "OP("/M1","vth")"; press ADD button. I think u know this way.

Thanks for every one

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