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https://designers-guide.org/forum/YaBB.pl Design >> Analog Design >> plotting fT of a MOS transistor with Spectre https://designers-guide.org/forum/YaBB.pl?num=1173092144 Message started by vivkr on Mar 5th, 2007, 2:55am |
Title: plotting fT of a MOS transistor with Spectre Post by vivkr on Mar 5th, 2007, 2:55am Hi, I recall having seen this somewhere on the forum but cannot find it. I would like to plot the fT of a MOS transistor using the operating point information as I sweep the operating point using parametric analysis (say by varying Vgs). However, the list of parameters available does not include fT. It does include Gm, but then, the various other parameters are not available in a convenient form and there are only the partial derivatives (Cgs, Csg, etc.). How can one get a plot of fT? Regards Vivek |
Title: Re: plotting fT of a MOS transistor with Spectre Post by Andrew Beckett on Mar 5th, 2007, 1:09pm I suspect you found this: http://www.designers-guide.org/Forum/YaBB.pl?num=1133481722/0#0. I've not measured ft for many years - I recall doing it in HSPICE in the dim and distant past for a colleague (in a previous job) who was doing device characterization - but I think I did it then by looking at a frequency response and extrapolating some part of a curve to find an intercept point. I've forgotten the details though... (it was 16 years or so ago, so I suppose I'm allowed to forget some things!). Andrew. |
Title: Re: plotting fT of a MOS transistor with Spectre Post by sheldon on Mar 6th, 2007, 2:58am Vivek, Attached is an example testbench illustrating how to measure ft. A pseudo-Wilson mirror is used to servo the base[gate] voltage so that the collector [drain] current matches the reference current. Please look it over and let me know if you have any questions. BTW, the basic methodology can be extended to other measurements, for example, Noise Figure. Also this testbench directly mesures the ft so it can be used with in-line subcircuit-based device models, etc. Best Regards, Sheldon |
Title: Re: plotting fT of a MOS transistor with Spectre Post by sheldon on Mar 6th, 2007, 2:59am Vivek, Seems to be an issue with the attachment. Sheldon |
Title: Re: plotting fT of a MOS transistor with Spectre Post by jmw2011 on May 31st, 2011, 9:55am sheldon wrote on Mar 6th, 2007, 2:59am:
MOS transistor Drain current is not determined by Gate current. How is your test method supposed to work? |
Title: Re: plotting fT of a MOS transistor with Spectre Post by ywguo on Jun 17th, 2011, 8:04am Hi jmw2011, While Sheldon's testbench need to be changed a little to bias MOSFET, it is correct to calculate the current gain (id/ig) for measuring ft. Please note that ig is small signal current here. Please refer to Gray's book for details. Analysis and Design of Integrated Circuits by Gray, Hurst, Lewis, and Meyer, 4th ed., pp. 55 - 58. Best Regards, Yawei |
Title: Re: plotting fT of a MOS transistor with Spectre Post by rajanarender_suram on Jul 28th, 2011, 2:01am Hi attached the finding method for Ft of nmos, the ugb of the i_probe current ft of the transistor Rgds Raja |
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