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Plotting curves for gm/Id technique

garvind25

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Hi,



I wanted to know if I can plot the various curves needed in gm by Id technique using LTSpice XVII. I basically need to plot the following curves for n channel and p channel devices:



fT vs gm/Id

gm/gds vs gm/Id

Id/W vs gm/Id



How can I do so using LTSPice? If it is not possible, pls advise me on how I can do so using any other windows based free tool.



Many thanks in advance,

Arvind Gupta
 

mwb

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If I recall correctly, LT spice does not give you direct access to gm. You'll need to calculate it.

Its easier to do get gm/id in ngspice or Qucs
 

garvind25

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If I recall correctly, LT spice does not give you direct access to gm. You'll need to calculate it.

Its easier to do get gm/id in ngspice or Qucs
Thanks for your reply. I have ngspice. But how to enter the schematic in it for plotting the various graphs? As I know, ngspice does not have any GUI for schematic entry. BTW are you aware if ngspice can be used with LTSpice interface?

Regards,
Arvind Gupta
 

mwb

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I doubt you can use ngspice as the simulator for ltspice. I recommended qucs or xschem in your other post.
 

garvind25

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I doubt you can use ngspice as the simulator for ltspice. I recommended qucs or xschem in your other post.
OK (and thanks for your quick reply). I will use xschem then. I have two queries aligned to it.

1. Should I use NGSpice with Xschem? Or does XSchem have a default simulator with it?
2. Are you aware of any tutorial which shows how to plot any of the above mentioned graphs? I am new to xschem also...

Regards,
Arvind Gupta.
 

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