Where does nonlinearity comes from LNA?

[fxxjssc]

Dear all,
Do any one know how nonlinearity come from LNA(inductive degenerated
common source). I am design lna with more than 3dBm P1db compression and
>10dbm IIP3 in 0.18um rf process.
Some paper and book said increase over-drive voltage will improve P1db
because gm becomes constant. But my simulation shows that when I set vgs more
than 1V (vth=0.5), P1db gets saturates too at 0dBm. what's possible reason?

Best wishes
fxxjssc

 

[alan6449]

u need to read some book on LNA..Here got good books ..u can download www.gigapedia.org

 

[milkdragon]

I think you have to identify if the linearity limitation comes from:1. output limited, 2. current limited 3. the Gm of the active device you use of the LNA. If it is output limited, it may mean your gain (impedance) is too high. If it is current limited, you can bump more current. Without increasing the size of your active device, bumping more current typically help non-linearity of the active device also

 

[khouly]

check the linearity part of this tutorial

**broken link removed**

wish this help u

khouly

 

[Yakeen]

Hi,

Which kind of LNAs are you designing ?

Narowband or Broadband

yakeen