Help me get the wT value for this LNA

Status
Not open for further replies.
J

jason_class

Member level 5
Joined
Sep 24, 2004
Messages
80
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
914
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
 

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.
 

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
 

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...


jason_class said:
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
Click to expand...
 

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
 

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
 

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?
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…