IIP3 vs OIP3 quiick questions plz

[ghb]

Please just for clarification.

Third order intercept describes the power level at which the third order harmonic gain would intercept that of the desired gain?

IIP3 describes how much power seen or received by the LNA at which this point intercepts? And OIP3 is what exactly? dBm out of the LNA with the given IIP3 power?

Say for example we have a 30 dB LNA. And the IIP3 is -10dBm would we expect the OIP3 to be +20dBm or would it be something different because of this high input power?

thanks so much for the help

 

[Y.C Park]

Please just for clarification.

Third order intercept describes the power level at which the third order harmonic gain would intercept that of the desired gain?

IIP3 describes how much power seen or received by the LNA at which this point intercepts? And OIP3 is what exactly? dBm out of the LNA with the given IIP3 power?

Say for example we have a 30 dB LNA. And the IIP3 is -10dBm would we expect the OIP3 to be +20dBm or would it be something different because of this high input power?

thanks so much for the help

HI

OIP3 = IIP3 + Gain that's right.
As I know, First, IP3 point is not the real thing. just extrapolated point in the simulation or test to get the your circuits linearity performance.
So, If you want to simulate this one, you can carefully check that 3rd order gain should be 3 times higher than 1st order gain. ( carefully extrapolate...^^)

It means your circuit's IIP3 is -10dBm and your gain is 30dB. In the simulation or test you can not get the 20dBm OIP3. Because that is imainary point.

Hope it help to you

 

[enrico]

Yes you are correct to affirm OIP3 [dBm] = IIP3 [dBm] + Gain [dB].

OIP3 is a hypothetical point where the 3rd order intermodulation products achieves the same amplitude of the fundamental tones. This must be understood as an extrapolation point not possible in practice because the transistor or non-linear device in between would achieve the avalanche point.

IP3 in general is a qualitative/quantitative parameter that indicates how linear is your device under test is.

An empirical rule says that IP3 [dBm] = P1dB [dBm] + 10 [dB], but in practice there are devices with IP3 up to 15 [dB] higher than the 1 [dB] compression point.

Cheers.

 

[ghb]

thanks much