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Regarding AD9361 integration with custom DSP of QPSK + RRC

Category: Software
Product Number: AD9361
Software Version: vivado 2019.1

Hello support team, 

We have implemented AD9361 custom HDL for Tx chain having indentical functionality logic as per AD9361 reference manual figure 80.Further I have added QPSK HDL and it is working as per expected, I am getting raw QPSK output as required. my QPSK symbol rate is 7.68 MSPS and I am keeping the Tx IQ rate as 30.72 MSPS. I am getting below response. 


Now, I have added RRC at the QPSK output with interpolation factor of 4. my RRC output is perfect and the 12 bit IQ data going to AD9361 custom logic is also correct. but I am not getting the correct output. my RRC is generating exact 30.72 MSPS output IQ rate. so I should get +/-5.84 MHz filtered QPSK lobe. but I am getting incorrect 30.72 MHz lobe. 


Here, I am seeking you support that raw QPSK is working accurate with AD9361 but adding RRC is not working peroperly. I have validated my QPSK +RRC which is working 100% correct and the data (IQ) I am sending to AD9361 is also correct. below is the FFT generated from 12 bit IQ data which is further going to AD9361 HDL. that means, my AD9361 is getting correct input. 



If you need any further information related to AD9361 custom logic for review , please let me know. 

  • Hi  

    it looks some rate mismatch issue in the datapath configuration. 
    Let's try both independently to understand the issue clearly.

    1) in FPGA QPSK and In AD9361 FIR - RRC and interpolation and decimation
    2) use external RRC and try bypassing AD9361 FIR. The FPGA rate and AD9361 input rate should match.

    3) are you using filter wizard while generating the coefficients.?

    Regards,

    SJ

  • Hello, 

    1. I am using FPGA QPSK and RRC (co-efficients from MATLAB). The results are perfect up to RRC output. 

    2. I am not using AD9361 FIR , As I am using defualt main.c file from SDK. 

    3. I observed that my AD9361 is generating spectrum BW 4 times higher than expected. i.e., for example if my external RRC is 7.68 MSPS, my QPSK is 1.92 MSPS , MY AD9361 Tx IQ rate is also 7.68 MSPS. It should generate main lobe of 2.592 MHz (considering roll off =0.35), but it is generating 10.368 MHz . 
    I have checked for different IQ rates , the behaviour is same. I am using custom AD9361 logic. we are following figure 80 of AD9361 reference manual

    If possible, we can schedule a call where our engineer can showcase the same to you.

  • Hello support team, 
    Is there any feedback?