ad9631 rx I/Q signal peak clipping

Hi ad9361 experts:

    When I used vivado to observe the rx signal, and found that I/Q signal was too large with peak clipping. As the picture below shows:

   The value of the I/Q signal sometime is 0xffff, which reaches the peak. I am using FAGC. I tried to lower the overload threshold, but the problem still existed. And I changed gain control  mode to MGC, and lower the gain, still not solved. Could you give me some advice? 

Thanks a lot.

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  • 0
    •  Analog Employees 
    on Jan 9, 2019 9:14 AM over 1 year ago in reply to xiji

    What is the input signal power that is fed at Rx port ?

    If you are looping back Tx to Rx put 20 dB attenuation on Tx path and try.

  • Besides, what does the normal I/Q signal look like? Thanks

  • +1
    •  Analog Employees 
    on Jan 10, 2019 11:34 AM over 1 year ago in reply to xiji

    Are you looping back tx to rx? Instead of looping back can you give a fixed amplitude tone at rx input, set the gain mode to fast attack and then see the Rx output.

  • Thanks for your reply. Forgive me for not answer your question. I am not looping back tx to rx. I inputed a fixed amplitude signal at rx input, and set the gain mode to fast attack. Still the Rx output peak clipping, any suggestion please? Thanks a lot.

  • Hi srimoyi:

      When I set parameter ctrl_outs_index to 0x0A, I found that the control output 1 is always high, which means that Rx FIR filter always overflows, even when there is no signal input into the ad9361. My RXFIRConfig/TXFIRConfig is as below:

    AD9361_RXFIRConfig rx_fir_config = {
    1, // rx
    -6, // rx_gain
    2, // rx_dec
    {10,22,22,-8,-41,-40,0,26,
    -4,-49,-32,34,49,-25,-78,-13,
    86,55,-81,-108,45,150,15,-174,
    -100,160,191,-102,-272,-4,318,148,
    -306,-310,218,458,-50,-556,-188,563,
    467,-448,-741,196,951,191,-1030,-679,
    915,1211,-552,-1703,-96,2043,1052,-2095,
    -2337,1666,4030,-377,-6498,-3087,12409,27546,
    27546,12409,-3087,-6498,-377,4030,1666,-2337,
    -2095,1052,2043,-96,-1703,-552,1211,915,
    -679,-1030,191,951,196,-741,-448,467,
    563,-188,-556,-50,458,218,-310,-306,
    148,318,-4,-272,-102,191,160,-100,
    -174,15,150,45,-108,-81,55,86,
    -13,-78,-25,49,34,-32,-49,-4,
    26,0,-40,-41,-8,22,22,10}, // rx_coef[128]
    128, // rx_coef_size
    {1280000000,320000000,160000000,80000000,40000000,20000000}, // rx_path_clks[6]
    20172411 // rx_bandwidth
    };

    AD9361_TXFIRConfig tx_fir_config = {
    1, // tx
    0, // tx_gain
    2, // tx_int
    {-2,-9,-17,-16,-1,14,11,-11,
    -21,1,29,17,-27,-38,12,56,
    18,-61,-58,44,97,-1,-120,-65,
    112,141,-60,-202,-37,224,163,-182,
    -290,64,378,122,-384,-344,275,547,
    -41,-666,-295,633,674,-401,-1004,-42,
    1173,657,-1070,-1352,598,1983,305,-2354,
    -1674,2211,3563,-1132,-6271,-2114,12592,26382,
    26382,12592,-2114,-6271,-1132,3563,2211,-1674,
    -2354,305,1983,598,-1352,-1070,657,1173,
    -42,-1004,-401,674,633,-295,-666,-41,
    547,275,-344,-384,122,378,64,-290,
    -182,163,224,-37,-202,-60,141,112,
    -65,-120,-1,97,44,-58,-61,18,
    56,12,-38,-27,17,29,1,-21,
    -11,11,14,-1,-16,-17,-9,-2}, // tx_coef[128]
    128, // tx_coef_size
    {1280000000,160000000,80000000,40000000,40000000,20000000}, // tx_path_clks[6]
    19611989 // tx_bandwidth
    };

    Dose my setting affect the performance of ad9361 RX FIR? Or the peak clipping has no connection with these RXFIRConfig/TXFIRConfig?

    Thanks

  • Thanks for your help. This problem is due to my error ILA setting. The signal is OK. AD9361 works well. Thanks.

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