ad9371 ORX noise raised at frequency edges

Hi breadjyy ,

We have also observed same thing in our design. Tx and ORx at 245.76MSPS. Would like to know if your Tx output is clean or are you observing any spurious at offset of 122.88MHz or 245.76MHz from LO. If possible share the spectrum snapshot with 1GHz span. How does the ORX plot look if sine wave is given as input?

Thanks

Dear Sumala，

my DAC looks fine. You can see some spurious, but no spectrum regrowth at 100MHz~300MHz region. 

At Orx side due to the IQ rate of 307.2MHz the span of received orx signal is around 300MHz.

Can you try with default lower sampling rates(lower sampling rates of 122.88Msps for TX and ORX) same configuration as above snippet and then check  for any improvement in the ORX noise shaping?

It works fine with 122.88MHz. Actually the entire project was originally running at 122.88MHz. The Orx signal has flat noise shape. If the signal is shifted, the DC and IQ imbalance is also good compensated. 

So, this is due to the typical sigma delta ADC behavior of the chip. If  you increase the oversampling ratio, that is, the decimation rates for the Half band and the FIR filters, then this will push the noise further and you will see flatter noise floor. 

You need to filter out the edges externally if you want to use higher sampling rates or use a lower sampling rate and BW to mitigate this issue.

So, this is due to the typical sigma delta ADC behavior of the chip. If  you increase the oversampling ratio, that is, the decimation rates for the Half band and the FIR filters, then this will push the noise further and you will see flatter noise floor. 

You need to filter out the edges externally if you want to use higher sampling rates or use a lower sampling rate and BW to mitigate this issue.

Thanks Srimoyi.