IIP3 measurement of LNA: does amplitude show two signals?

[dot13]

iip3 measurement

When I measure IIP3 of an LNA, Agilent E4437B signal generator was used to generate two adjacent input signals. The question is, does the AMPLITUDE windows tell the sum of two-tone signals power or each one of them?
Thanks.

 

[vfone]

Re: IIP3 measurement

Is the power of each of them..

 

[jallem]

IIP3 measurement

That is right, is the same level for both(not the sum)

 

[dot13]

IIP3 measurement

Thanks.
But I found that the difference of foundamental power to input power setting is 3dBm less than the voltage gain measured. So should the input power minus 3dBm when I plot the IP3 extrapolation figure?

 

[vfone]

Re: IIP3 measurement

In your case if you measure the average power at the amplifier output using a power meter, it will indicate 3 dB more power (see the picture for different number of carriers).
The best would be to use a spectrum analyzer at the output, and record the level of each carrier.

 

[dot13]

IIP3 measurement

Maybe I didn't explain clearly.
Actually, I used a spectrum analyzer. And gained the fundamental and 3rd harmonic power from the output spectrum. While the fundamental power minus input power (setting in the signal generator) is 3dBm less than the voltage gain.

 

[vfone]

Re: IIP3 measurement

This is very unusual. Are you sure that you measured well the voltage gain? Confusing 0-to-Peak, Peak-to-Peak, or RMS, could give erroneous voltage gain.

 

[dot13]

IIP3 measurement

Yes, I'm sure the voltage gain is measured correctly. Because I got the same results both from VNA and NFA.