why do resistor sharply decrease the P1dB of LNA

It is said that the resistor shunt or series at the ouput of the LNA would decrease the 1dB compression point of LNA. So the parastic resistor of inductor would decrease the 1dB compression point of LNA. i have simulated the schematic below and found that the 1dB compression point of LNA decreases shapely from 12dBm(with ideal inductor) to 8.5dBm(with inductor which Q value is 8). this result perfectly fits the theory above. But who can give a detailed mathematic explanation?

Hi,

I am really do not remember not how to explain it matematicly but I know from experience that if you increase current or voltage on transistor you will increase the P1dB and OIP3 axiom. But be careful if will increase NF also!

David.

first, your P1dB is refered to input or output?
secondly, I believe, the change of resistor value will change the inductor Q , then resulting in gain change. At last, it reflects on the change of the output P1dB change. The input P1dB will not change too much

Hi

I think attenuator at the amplifier output will decrease output 1db compression point.
Than if you use finite Q inductor you will have less power and less 1db compression
But input 1db will not change
Regards