Well, I think u did not catch the point quite well.
1dB compression point is the power level where the amplifier's gain is compressed by 1dB.
For example, a LNA's gain is 15dB at small signal input
while the input signal increase, the gain will reduce due to non-linearity of the LNA.
When the gain is reduced to 14dB, then the input power now is the input-referred 1dB compression point Pin-1dB, the out put power now is the out-put referred 1dB compression point Pout-1dB. The unit of those two figure of merit is dBm, that is the power input with respect to 1mW.
1dB and 1dBm are totally different thing.
1dB is a ratio actually and 1dBm is power value.
Dear Chun,
Using PSPICE put a bitonal signal (2 senoidals signals with a small frequency difference between them), simulate, change to FFT
IP3=(Poutput(dBm)-Pimd3rd(dBm))/2 + Poutput(dBm)
Poutput are the sum of the bitonal output (example 1MHz 1.1MHz)
Pimd3ard are the sum of the two IMD3 componentes (example 0.9MHz 1.2MHz)
I hope you understand me
Daniel