I am designing a high IIP3 LNA.and meet some difficults to imprive IIP3,what should I do? How many methods can be use to improve the LNA's IP3?
Thanks!
Although it could increase your NF but might still ok if your NF is already over 1dB. to prove that you could run system simulation and changing NF said 1.5 or 2.0, unlikely it will drop your senstivity much unless you have no margin, besides increasing bias will also increasing gain which will help senstivity as well.
btw, make sure your test gears are setup up properly, sometimes poor ip3 was not generated by DUT but by test gears.
well, i also encount the same problem now.
there are several methods to improve IP3 or linearity:
1. increase bias
2. increase Vgs
3. decrease gain
4. decrease input signal amplitude
5. new schematic topology
.....
Hi,
go thru the answers before. Additionally make sure that your Emitter has a very good ground. About 1mm distance creates an inductivity of about 1nH. That can make the difference of 10dB. Just have a very short distance from ground, that is important.
1. make sure LNA is unconditionally stable by:
a. running circuit simulation with pcb layout data addon
b. doing VSWR testing on LNA, suggest 3:1 at least
2. check your bias circuit and Vcc de-coupling circuit working fine, I readed some papers claimed de-coupling circuit caused poor ip3
3. are you design a wide band LNA? did that worest IIP3 happen at lower frequency which normally has higher gain?