The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Simulators >> Circuit Simulators >> Varactor Simulation and Plotting the graphs?
https://designers-guide.org/forum/YaBB.pl?num=1518059309

Message started by umberabbas on Feb 7^th, 2018, 7:08pm

Title: Varactor Simulation and Plotting the graphs?
Post by umberabbas on Feb 7^th, 2018, 7:08pm

I want to use MOSFET as a MOS-cap varactor (both inversion and accumulation mode). I have first tried it with the inversion mode by connectiong the body to the Vcc. I did the DC analysis for the MOSFET and I am getting the following curve but I want to have it like C vs Vg, C vs Vtune and Vtune vs Freq. Kindly tell me how can i get it.

Title: Re: Varactor Simulation and Plotting the graphs?
Post by umberabbas on Feb 7^th, 2018, 7:43pm

simulator lang=spectre
global 0
parameters vcntrl=100m Vg=100m

View name: schematic

C1 (net4 net03 0) nvar_12rf w=(2u) l=(2u) ny=3 nx=3 m=1

Vg (net4 0) vsource dc=Vg mag=1m type=sine freq=60G

Vcntrl (net03 0) vsource dc=vcntrl type=dc

simulatorOptions options reltol=1e-3 vabstol=1e-6 iabstol=1e-12 temp=27 \

tnom=27 scalem=1.0 scale=1.0 gmin=1e-12 rforce=1 maxnotes=5 maxwarns=5 \

digits=5 cols=80 pivrel=1e-3 sensfile="../psf/sens.output" \

checklimitdest=psf

ac ac freq=60e9 param=Vg start=10m stop=300m step=10 annotate=status

dcOp dc write="spectre.dc" maxiters=150 maxsteps=10000 annotate=status

dcOpInfo info what=oppoint where=rawfile

dc dc param=vcntrl start=10m stop=300m step=0.1 oppoint=rawfile \

maxiters=150 maxsteps=10000 annotate=status

modelParameter info what=models where=rawfile

element info what=inst where=rawfile

outputParameter info what=output where=rawfile

designParamVals info what=parameters where=rawfile

primitives info what=primitives where=rawfile

subckts info what=subckts where=rawfile

save C1:1 C1:2

saveOptions options save=allpub

Title: Re: Varactor Simulation and Plotting the graphs?
Post by umberabbas on Feb 7^th, 2018, 7:45pm

These are the generated graphs

Title: Re: Varactor Simulation and Plotting the graphs?
Post by Geoffrey_Coram on Feb 8^th, 2018, 5:06am

Most MOSFET models don't include non-quasi-static effects, or what they have available is NQS for the channel current. I think to get the C vs freq plot, you need a model that accounts for "dynamic inversion charge" as described in the manual for the MOSVAR manual (developed originally at Arizona State, but now maintained by the Compact Model Coalition).

Title: Re: Varactor Simulation and Plotting the graphs?
Post by Ken Kundert on Feb 8^th, 2018, 9:08am

To see C as a function of Vtune, simply perform an AC analysis at a fixed frequency while sweeping Vtune. Plot the current through the capacitor. As long as there is no series resistance or non-quasistatic effect, you are free to choose the frequency for your convenience. I recommend choosing a frequency that allows you to scale the current so directly see the capacitance in Farads.

-Ken