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Design >> RF Design >> How do you plot gm vs Vgs?
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Message started by naren on May 20^th, 2004, 3:57am

Title: How do you plot gm vs Vgs?
Post by naren on May 20^th, 2004, 3:57am

How do you plot gm vs. Vgs in Cadence?

Someone please help!

Please!

As this seems to be only way to easily choose Vgs for a required gm.

Title: Re: How do you plot gm vs Vgs?
Post by Andrew Beckett on May 20^th, 2004, 9:10pm

See my response on another thread - this should answer
your question:

http://www.designers-guide.com/Forum/?board=circuit;action=display;num=1079491622;start=1#1

Regards,

Andrew.

Title: Re: How do you plot gm vs Vgs?
Post by naren on May 21^st, 2004, 8:25pm

thanks a lot for ur reply....can u please tell how to do the including a file thing? in cadence to plot the gm?

pleaseee help me...I am new to cadence

Title: Re: How do you plot gm vs Vgs?
Post by Andrew Beckett on May 25^th, 2004, 3:07pm

Having created the file, you can then specify it under the
Setup->Model Files in the "spectre" interface in the Analog
Design Environment (Model files can be any spectre syntax
include file).

Regards,

Andrew.

Title: Re: How do you plot gm vs Vgs?
Post by Uncle Ezra on Oct 13^th, 2004, 5:17am

I still don't get it. How do you write spectre syntax file? And what kind of extension file you save as?
Please provide an example.

Thanks

Title: Re: How do you plot gm vs Vgs?
Post by Andrew Beckett on Oct 13^th, 2004, 1:05pm

Create a file somewhere, called (say) "saveit.scs"

The contents of this file should be:

Code:

// additional things to save
save M1:gm
// or could miss out the :gm bit to save all op point
// info for M1

The above M1 should reflect the instance name of the transistor in the netlist.

Then in the Setup->Model Files form, add the path to the saveit.scs file in the list of files included.

Set up your transient analysis as usual, and then run the simulation. Then use the results browser (Tools->Results Browser), to navigate to your results, and you should be able to find the operating point data for the device you've saved.

A little more info is in the other thread I referred to a while ago.

Sorry for not giving absolute step by step details, but I'm in a hotel and doing this from memory, and also I'm assuming some basic level of competance with the Analog Design Environment.

Regards,

Andrew.

Title: Re: How do you plot gm vs Vgs?
Post by uncle_ezra on Oct 13^th, 2004, 6:31pm

Got it !;D

Thanks Andrew

Title: Re: How do you plot gm vs Vgs?
Post by uncle_ezra on Oct 27^th, 2004, 2:52am

Hi Andrew,

Can you tell me how to plot gm vs. length for example? I know how you can get gm from the above method, however how do you sweep the length. I tried calling it a variable and doing a dc sweep but spectre did not allow me to do.

Thanks

Title: Re: How do you plot gm vs Vgs?
Post by uncle_ezra on Oct 27^th, 2004, 4:08am

Nevermind, the sweep seems to work. Is there any other method?

Title: Re: How do you plot gm vs Vgs?
Post by uncle_ezra on Oct 27^th, 2004, 4:19am

One other question, how do you get lambda and Kappa (u_nC_ox) and plot it against some sweep variable? Sure you can compute lambda=1/rds*Id and kappa=gm^2/(2*Id*W/L), but is there other way?

Thanks
Thanks