IP3 is low for a power amplifier

I've designed a class AB PA with simulated output P1dB=26dBm, but the simulated output IP3 is less than 20dBm. Generally, the IP3 is about 10dB over P1dB value. But the IP3 of my PA is less than P1dB!

Can anyone explain this?

BTW, the PA is a two stage cascode CMOS amplifier and simulation is done with spectreRF. A sweep PSS is done for P1dB simulation and PSS+PAC is done for IP3 simulation.

Could you pls upload your simulation files?

Sorry, the simulation files is on the company's workstation and I haven't permisstion to download it. If you need any detailed information about the simualtion setup or the PA circuit I can tell you.

hello everyone,
i designed an LNA but OIP3 values are nearly -6 and -9 dB.. i think they are very small, what should i do to increase them..
with "they" , i mean 2*f1-f2 and 2*f2-f1
shouldn't they be equal, by the way ?
king regards

Hi Emmetin,

To increase the IP3 basically you need to optimize your matching circuit at the output. Why output? because the equation for IP3 is

Output_IP3(OIP3) = Pout + delta/2 and

the equation for Input_IP3 is

(IIP3) = OIP3 - Gain,

so the output match directly impacting the IP3. Play with the output match and another thing you can do is to see the IP3 circles in smith chart and match to the highest value.

The IP3 never be equal for both sides, normally the left hand side is lower than the right hand side.

Mani

thank you kmmaran,
i will try your advices immediately.
regards

That is called "memory effect" of a amplifier.