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# KCC's Quizzes: AQQ229 about IP3 lab measurement

IP3 (intercept point of order 3) is a spec one find in many RF component datasheet. It is directly linked with the linearity of a function behavior.

More precisely, It indicates the amount of the intermodulation products of order 3 that interfere with the baseband.

The above pictures show the lab setup and a Spectrum Analyzer screenshot to measure the IP3 of a device (DUT) in the lab.

Questions:

1. What are the frequencies provided by sources 1 and 2?
2. What is the IP3 measured in that test?

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[edited by: emassa at 5:46 PM (GMT -5) on 2 Mar 2023]
• Hi Kuo-Chang,

RF is not my strong suit but I'll give it a go.

1. The frequencies are 1.25GHz and 5 MHz

2. OIP3 = Pout +deltaP/2

deltaP = -10.9 - (-45.2) or -11 - (-44.9) = 34dB ish

OIP3 = -11 + 34/2 = +6dBm

• 1. The frequencies are f1=1245MHz, f2=1255MHz. f3=1235MHz and f4=1265MHz are IM products (2*f1-f2 and 2*f2-f1)

2.  Supposing the input level is well below P1dB, you can calculate IIP3 by adding to the input power level the difference (divided by 2) between the fundamental signal at the output and the IM levels (everything in dB). So: IIP3=34/2 - 11=6dBm

• 1) Fundamental Freqs    f1= 1245 MHz, f2= 1255MHz

2f1-f2= 1235 MHz,  2f2-f1= 1265 MHz

2) Delta -11dBm - (-45dBm) = 34dB = 2*(OIP3 - Pout) = 2 ( OIP3 - (-11dB) ) -- > OIP3 = 6dBm

I believe this was a 7dB Gain device (forgotten to be mentioned in the text :-) )  Then IIP3= 6-7 = -1dBm

you find OIP3, not IIP3. Without OP-Gain info, we cant calculate IIP3 ;-)

Edit: Added IM3 Frequencies 2f2-f1 and 2f1-f2 Frequencies.

• Ah, shoot - I thought the orange thing was a mixer but it looks like it's actually a combiner, so the two frequencies will be 1.245GHz and 1.255GHz.  The third order products are at 1.235GHz and 1.265GHz.  Told you RF wasn't my strong suit...

• If you know Pin, actually you can calculate IIP3. But in this case you're right, because the power used in the calculation is Pout (the only power known) so the calculated IP3 is OIP3. I will need to correct my answer.