RF input power of LNA - some questions

[adnan siddqui]

RF input power of LNA

The input power of my receiver is -100dBm (.1 pw).I want to design LNA using BJT but how can I calculate or recognized that my LNA is able to sense such a small signal at the input.What parameter of the BJT indicate us about the sensitivity of transistor.

 

[mrm]

Re: RF input power of LNA

You parameter is Noise Figure. Thermal noise is -173.8+10Log10(useful signal bandwith in Hertz). Your LNA can sense signal as waek as those calculated in this way plus the noise figure of the LNA itself.
Bye

 

[RF_beginner]

hello mrm, can you tell me how the formula you offered comes from or how to deduced it? what is the theory basis?

 

[FANT]

Re: RF input power of LNA

Look here, it is not directly related, but a good tutorial:

hXXp://www.ctjc.com/tutorial.htm

P.S. Remove the XX and add tt


Mandi

 

[mrm]

Re: RF input power of LNA

My formula comes from thermodynamic equilibrium: -173.8 is nothing but 10*Log10(Kb*T) where Kb is Boltsman's constant. This formula describes the noise due to the thermal turbulence of electrons inside a conduction band (electron sea model) and is the most accurate. This description fails when describing otherphenomenous like the ones inside a semiconductors. For this reason we introduce noise figure, that describes the degradation in noise performances due to all oter effects but thermodynamics and that is simply a macroscophical parameter. U can fin more in every book on RF design (Gonzaes, Vizmuer etc.)
I hope I've been clear...Bye MRM

 

[mrm]

Re: RF input power of LNA

My formula comes from thermodynamic equilibrium: -173.8 is nothing but 10*Log10(Kb*T) where Kb is Boltsman's constant. This formula describes the noise due to the thermal turbulence of electrons inside a conduction band (electron sea model) and is the most accurate. This description fails when describing otherphenomenous like the ones inside a semiconductors. For this reason we introduce noise figure, that describes the degradation in noise performances due to all oter effects but thermodynamics and that is simply a macroscophical parameter. U can fin more in every book on RF design (Gonzaes, Vizmuer etc.)
I hope I've been clear...Bye MRM

 

[ahmad_abdulghany]

Re: RF input power of LNA

Hello,

I want a tutorial about the design of BJT LNA, i want to build it with discrete components at freq. ~ 100MHz,

Thanks for help,
Ahmad,

 

[DDavid]

Re: RF input power of LNA

Hi,

I attach some papers about it but if you need schematic
I already have it! (I hope you have orcad)

David

 

[MW+RF=Netpig]

RF input power of LNA

thanks

 

[DDavid]

Re: RF input power of LNA

So you need orcad schematic or genesys simulation???

David