1 dB compression point and IIP3 difference in LNA ????

[Circuits]

Hello everyone,

I have a quick question.

I designed a LNA ( common Source Cascode LNA) for ultra low power application and everything is at the boundary for 220uW power dissipation.
S11=-10dB,S22=-11dB, S21=9.9dB, S12<-40dB, NF<2.5dB, Kf> 20

But my 1 dB compression point and IIP3 point do not make any sense. I am getting IIP3( -18dBm)< P1dB( -16dBm)? As I understand the difference between the 2 of them is 10dB approximately.
How can I make it correct without increasing my current ? I increased the source degeneration which improved the 1 dB compression point but no change in IIP3????????

Please advice.

Thank you in advance.

 

[Circuits]

Can anyone help me with this question ? I really need to finish this design by this Friday ...

 

[johnjoe]

Is your result obtained by simulation or measurement? And when simulation, please describe or show your simulation setup!

- - - Updated - - -

Maybe also small schematic would help.

 

[pstuckey]

The rule of thumb is that OIP3 = P1dB + 10 dB.

You have S21 of 9.9 dB. So your OIP3= -8.1 dBm which is about 8 dB higher than your P1dB, which is not too far off.

 

[johnjoe]

The rule of thumb is only valid for single transistor amplifier WITHOUT feedback. The power of your P1dB is input or output power?

 

[Circuits]

The power of P1dB is output and the design is Cascode LNA not single transistor.