Low noise amplifier how does it work?

[aashishsharma]

Hey
I have used a LNA in one of my circuit. All I know about LNA is from design point of view, there uses parameters like noise figure iip3 point etc.
But I was rather curious on how actually LNA amplifies the signal and not the noise? I mean how it actually works?
Thanks in advance
Aashish

 

[ahmad1954]

we have several noise that affect our circuits such as flicker,thermal and 1/f. depend on which noise is dominant
LNA has circuits that filter noise and then amplify the original signal.

 

[aashishsharma]

depend on which noise is dominant
LNA has circuits that filter noise and then amplify the original signal.

Does that means that LNA IC to be used in circuit depends upon the kind of noise you expect? As far as i know LNA ICs are generic. I used MAX2644 LNA
but it doesnt specify any type of noise just frequecny of operation IIP3 OIP3 etc

 

[emresel]

As I know, LNA is not smthng like "amplifies the signal and not the noise", it is rather smthng "doesn't add extra noise during amplification".
It adds little noise as possible as while amplifying desired signal.

 

[aashishsharma]

thanks emresel that clears a lot.
can you tell me what is so special about LNA that it adds less noise as compared to other amplifier? I mean in architecture or something like that

 

[jiripolivka]

Low-noise amplifiers are designed with special first-stages that add a minimum noise to the amplified signal. This is measured by the noise figure. Most LNAs are matched to 50 Ohm lines and their design is best over a specific frequency band.
Special semiconductor materials are also used like GaAs HEMT or SiGe, to get the lowest noise.

 

[aashishsharma]

thanks jiripoivka