Hi, all,
Now I am doing the IP3 measurement of certain device. Please refer to the attached Setup.bmp file for the measurement setup![Image]()
. First, I wanted to confirm that the test system will not generate IP3. So I bypass the DUT and did the measurement. Unfortunately, 3rd order IMD signal was quite strong. With main signal (@f1, @f2) being 10 dBm, the IMD signals (@2f1 – f2, @2f2 – f1) are around -68 dBm. Since this power level is greater than the noise level, it is necessary to modify the test system. I found one reference by Agilent, as the attached Agilentsetup.bmp![Image]()
, low pass filter and/or isolator are added in the setup.
My questions are
1) For the low pass filters connected to the SG1 and SG2, the cut-off frequency should be lower than the harmonics (say, < 780MHz), or it should be only a little bit greater than the f1 (=410 MHz). For the low pass filter connected to the SA, its cutoff should be < 780MHz? Would these newly added filters increase the intermodulations?
2) In Agilent’s setup, it is mentioned that attenuator and/or isolator is preferable. In my case, since I don’t have isolators at hand, would there be any alternatives? Or purchasing the isolator is a must?
Your help would be really appreciated!
With my best wishes,
Yours,
Yiliu
Now I am doing the IP3 measurement of certain device. Please refer to the attached Setup.bmp file for the measurement setup
My questions are
1) For the low pass filters connected to the SG1 and SG2, the cut-off frequency should be lower than the harmonics (say, < 780MHz), or it should be only a little bit greater than the f1 (=410 MHz). For the low pass filter connected to the SA, its cutoff should be < 780MHz? Would these newly added filters increase the intermodulations?
2) In Agilent’s setup, it is mentioned that attenuator and/or isolator is preferable. In my case, since I don’t have isolators at hand, would there be any alternatives? Or purchasing the isolator is a must?
Your help would be really appreciated!
With my best wishes,
Yours,
Yiliu
You did not specify which spectrum analyzer you are using or how you have optimized the analyzer's dynamic range. An easy test would be to insert an attenuator in place of your DUT [or change the analyzer's attenuation] to observe the nature of the change in the amplitude of the distortion products.
The analyzer's attenuator setting, along with its reference level, must be set so that the optimum signal level is present at the analyzer's mixer in order to achieve the maximum dynamic range. Different analyzers have different attenuator capabilities. For example 8590 and 8560 series analyzers have attenuators with 10 dB steps, ESA instruments have 5 dB steps, PSA instruments have 2 dB steps, and the E4406A has 1 dB steps. Smaller steps give you more flexibility to set the optimum mixer level. An external attenuator could be utilized with an analyzer that does not have sufficiently fine attenuator steps.
Agilent has a Product Note: 5980-3079EN, Optimizing Dynamic Range for Distortion Measurements, that could be helpful. Although this document contains information specific to the PSA series instruments, much of the information is applicable regardless of the analyzer used.