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Design >> Analog Design >> simulating transistor fT
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Message started by vivkr on Sep 17^th, 2007, 11:59pm

Title: simulating transistor fT
Post by vivkr on Sep 17^th, 2007, 11:59pm

Hi,

I am wondering how one could extract the "fT" parameter from DC analysis. Normally, one can use OP in the Calculator
in Spectre and get "gm", "gmoverid" etc., but not "fT". Any suggestions would be appreciated.

Regards
Vivek

Title: Re: simulating transistor fT
Post by didac on Sep 18^th, 2007, 2:23am

Hi,
I think that it must be done via formula extracted from the parameters:

ω_T=gm/C_gs

Hope it helps,

Title: Re: simulating transistor fT
Post by vivkr on Sep 18^th, 2007, 2:37am

Hi,

The problem is getting the correct value of CGS. I don't think that is easy to get it directly from the
calculator using the OP option when using Spectre with the BSIM3 model. How do you do it?

The CGS parameter in the list is not the actual CGS of the transistor when using BSIM3.

Thanks
Vivek

Title: Re: simulating transistor fT
Post by didac on Sep 18^th, 2007, 6:03am

Hi Vivek,
Usually I use only aproximations and then I do the fine tunning, if you want to do the correct calculation of ft I think you should go to the definition:frequency at which current gain it's zero, I did this simulation in the past using the parameter h21 but not in spectre(I used ATLAS for modelling a device) but if I remeber right sp analysis of spectreRF calculates hybrid parameters as well(I cannot check right now because our license server is down...), another possibility I suppose will be to calculate the Cgs using calculation taking into account gate channel and overlap capacitances but I then you should dig into geometrical parameters of transistor that I don't know if can be accesed directly using op of dc analysis.
Hope it helps,