Help me get the wT value for this LNA

[jason_class]

LNA

Hello All

Please see that on the bottom right hand slide which mentioned working at the frequency 1.59GHz (10Grps) , fT =5.56GHz. 5.56GHz which is equaivalent to 35Grps. Given NFmin around 2.2dB
Any one can tell me how to get the fT value ?
I try to use the formula FmimP = 1+2.4 gamma/alpha [w/ wT]. But still do not get it.
Please help me to understand how to get this. The rest I can find but only this wT is a hinder as a start. Please show me the right way.
Thank you

rgds and thanks
Jason

 

[vistapoint]

Re: LNA

It's from Lee's book. wT=35Grps (5.57GHz) is an approximation for thansistor of this size. To get the exact wT, use wT = gm/(Cgs+Cgd). You can get all the values from calculation or simulation.

 

[jason_class]

Re: LNA

That's true. Thanks for your help.
But I am wondering since we have expression for Fmin , we have NFmin value, why we cannot evaluate the value of wT from the Fmin equation?
Anyone please enlighthen
Thank you all


rgds and thanks
Jason

 

[vistapoint]

Re: LNA

Because both wT and alpha are decided by the transistor size and bias condiction, which are designed.

I think you choose bias current, then wT-->transistor size -->gm -->get alpha -->check Fm-->good?-->change wt if not...

That's true. Thanks for your help.
But I am wondering since we have expression for Fmin , we have NFmin value, why we cannot evaluate the value of wT from the Fmin equation?
Anyone please enlighthen
Thank you all


rgds and thanks
Jason

 

[jason_class]

Re: LNA

Dear Vistapoint,

Thanks a lot. I will give it a try. A good classmate who is also a member here explained to me about finding the wT from the Id value. I will compare these results. Will post back after calculation.
Kindly help out later
Thanks a lot


rgds and thnaks
Jason

 

[jason_class]

Re: LNA

Dear Vistapoint and Everyone there,

Just a silly question. May I know if all the transistor involved work in saturation regions?

Then say if I have a design example that gives me only w0, Rs, Leff, Cox, NFmin, gamma and alpha. Then I have the Wopt,power equation to find the width first. Then I have no other way to find wT but to use the formula F= 1+2.4.(gamma/alpha).(w/wT)
Will this be one of the many ways of design as well?

However, NF min has any relation with Fmin,power(equals to1+2.4[gamma/alpha].[w/wT]) which can be decribed in any equation? By they way, NFmin is not 10log(Fmin,power) right?

Kindly enlighthen.


Thank you

rgds and thanks
Jason

 

[vistapoint]

Re: LNA

First, I am a newbie too and maybe I am not clear about some questions myself.

If you have width, you have gm. Why can't you calculate wT?