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Nick

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Plotting Cgs vs time
Jun 07^th, 2006, 3:09am

Hello,

I am using SpectreRF transient analysis and would like to see how the Cgs of a transistor varies with time when the latter is driven by a large sin signal. I have used the infotimes field at the advanced options of transient analysis to save more than one operating points, but have not managed to find a way to plot the values of the model parameters. I would like to do so for the whole transient simulation.

Thank you,
Nick

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Nick

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ACWWong Community Fellow Offline Posts: 539 Oxford, UK	Re: Plotting Cgs vs time Reply #1 - Jun 7^th, 2006, 4:16am if you save infotimes then you can plot cgs at those times using: OPT("/I0","cgs") from the calculator... for every point in a transient seems overkill... i guess this is not required as if you chose say 10 infotimes a cycle you should get a very good idea of cgs variation...
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Nick

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Re: Plotting Cgs vs time
Reply #2 - Jun 7^th, 2006, 4:29am

Thank you for the answer.
This leads to another problem...

I am using RF transistors that seam to be described by a macro model developed around the model of the standard ones. The result is that I cannot use any transistor parameter / operating point annotation on the schematic or functions of the calculator such as vt, opt...etc

What I usually do is print results (i.e. op.points) in the print result window, or check values from the calculator browser.

Given that, do you know of another way to plot the saved results?

Thanks,
Nick

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ACWWong

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Re: Plotting Cgs vs time
Reply #3 - Jun 7^th, 2006, 5:11am

if its a macromodel RF fet instantiating a standard fet but with several RF addons (like Rg, Rs, Rd, Rb, etc.) then can you not just decend in the schematic before the annotation and calculator select functions to work on the standrad fet ? ie use something like OPT("/I0/I1","cgs")

If you use the results browser, you can right/centre click to bring up options for expression or plot. Have tried this ? e.g. if my migrate to in the results brower to
psf->Run1->tran_info-tran_info->sweepvariable->"An_infotimeX"->tran-X_tran_Info-
info-I0(my fet)->cgs
then right/centre click to get the expression you get:

pv( "I0" "cgs" ?result "tran_info-tran_info" ?resultsDir "/simulationDirectory/testbench/spectre/schematic" )

this will should do the same thing as OPT("I0","cgs")

hope this helps

rgds,

aw

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Nick

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Re: Plotting Cgs vs time
Reply #4 - Jun 7^th, 2006, 6:50am

Thanks! That was useful.
Plotting the expression from the results browser worked. For some reason the opt will not work. Also I cannot instantiate the standard FET model, because the RF transistors are coming directly from a tech library.

Another question: can you do the same thing with dc sweep? i.e. is it possible to sweep a gate dc voltage and monitor how the transistor parameters vary for different voltages? I am trying to find the equivalent of infotimes for the dc analysis in order to save all the operating points.

Thanks,
Nick

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ACWWong Community Fellow Offline Posts: 539 Oxford, UK	Re: Plotting Cgs vs time Reply #5 - Jun 7^th, 2006, 7:00am This topic was discussed in the circuit simulators forum look at the topic: How to plot a MOS's Vth vs TEMP curve?
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Nick Junior Member Offline Posts: 21	Re: Plotting Cgs vs time Reply #6 - Jun 7^th, 2006, 7:14am Thanks for your help, parametric analysis makes sense ::) Best regards, Nick
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