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Unexpected results in FDD and TDD mode of AD9361

Question asked by aslam on Jun 7, 2018
Latest reply on Jun 12, 2018 by aslam

Hi, I am using AD-FMCOMMS2-EBZ with Zedboard. I have captured the ADC outputs with FDD and TDD mode and measured the energy in both case (rfdc, bbdc, and quad trackings are enabled in both case). The observed energy difference bw them is 4dB, which is obvious because in FDD approach we are receiving noise plus DC of its own transmitter. However, when we took FFT of ADC outputs we observed that there is an offset bw FDD and TDD mode in all frequency, which is not expected. The offset should be only at DC. One can see the results in the following diagram.

 

 

Can anyone explain why I am having the results?

Next Question: I have my own design 802.15.4 compliant transceiver. I measured the sensitivity and SNR of the transceiver in TDD and FDD mode. The sensitivity is decreased by 1dB in FDD approach, but SNR is decreased by 4 dB, which is again strange for me. Since SNR and sensitivity has linear relation, sensitivity should also be decreased by 4 dB.  

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