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Design Languages >> Verilog-AMS >> Transconductance gm in angelov model
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Message started by Kem on Jun 9^th, 2011, 5:13am

Title: Transconductance gm in angelov model
Post by Kem on Jun 9^th, 2011, 5:13am

Hi all,

I'm working with the Angelov model and i must expand it. I have to use transconductance gm and i have calculated it as follow:

gm = ddx (Ids, V (g)).

gm seems Somehow to be allways 0 even though it should not be.

Has anyone ever had this problem? how can i solve it ?
Thanks in advance

kem

Title: Re: Transconductance gm in angelov model
Post by marekm on Jun 9^th, 2011, 9:53am

The ddx() of a state variable will be 0. I suspect you want to use something that has a direct algebraic dependence on V(g).

BTW, we work with Prof. Angelov on keeping his model (and the GaN version) up-to-date, see the design kit http://www.tiburon-da.com/design_kits/Angelov_DK.zip

You can see how we get gm in that model. It's an ADS design kit, but you can unzip and then find the models in the veriloga directory.

Title: Re: Transconductance gm in angelov model
Post by Ken Kundert on Jun 10^th, 2011, 1:27am

Marek,
How can you say that the derivative of Ids with respect to V(g) is zero without knowing how Ids relates to V(g)?

Kem,
How can anyone help you when give so little information?

-Ken

Title: Re: Transconductance gm in angelov model
Post by Kem on Jun 10^th, 2011, 2:35am

@ Marekm,
Thanks a lot for replying. That's exactly what i need: the last section. I'm trying to understand it. I have to implement the pucel and pospiezalski equation in angelov. and i would like for verification to calculate each noise model using the parameter of the other one.

@ ken
i want to expand the angelov model with the noise equation of pospiezalski and pucel . The Pucel equation look at the gate like
: Cgs0_T * Cgs0_T * 4.0 * `P_K * T * NoiseR / gm.

i have realised gm=ddx(Ids,V(g)) allways return a zero.

kem

Title: Re: Transconductance gm in angelov model
Post by marekm on Jun 10^th, 2011, 11:14am

Hi Ken,

My answer was specific to the Angelov model (which I'm familiar with and in that specific model, Ids = V(xt2)). Sorry for the confusion,

Marek

Title: Re: Transconductance gm in angelov model
Post by Ken Kundert on Jun 10^th, 2011, 12:22pm

Marek,
Oh, I see. You do know how Ids relates to V(g).

Kem,
Can you see how nobody but Merek could answer your question, and he could only answer it because he had detailed knowledge about the model that you did not give. Asking for help like you did is a bit of an art, and to maximize the chance of getting a meaningful answer, you have to give enough information so that people who are not intimately familiar with what you are doing can help you. That means you have to give more information. At a minimum, you should have given enough of the model so that we could see the relationship between Ids and V(g).

-Ken