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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 5^th, 2007, 2:55am

Title: plotting fT of a MOS transistor with Spectre
Post by vivkr on Mar 5^th, 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 5^th, 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 6^th, 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 6^th, 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 31^st, 2011, 9:55am

sheldon wrote on Mar 6^th, 2007, 2:59am:

Vivek,

Seems to be an issue with the attachment.

Sheldon

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 17^th, 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 28^th, 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