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AD9361 ADC data dropout

Question asked by strack on Aug 14, 2014
Latest reply on Aug 15, 2014 by strack



I'm seeing an odd problem with the data received from the ADC (AD9361 Rx data interface). I'm examining the ADC data with ChipScope within a modified version of the FPGA reference design and I see good data (expected waveform and magnitudes) for a while then it suddenly drops to near 0 values for both I and Q.  I'm using a two-board setup with the ZedBoard and FMCOMMS2, where one board is transmitting to the other. Here are the details:

  • The data dropout only occurs when transmitting over the air, a cabled connection works flawlessly
  • The AD9361 ENSM is set to FDD mode
  • When our custom packet is not being transmitted, null (0) data is being sent to the DAC
  • The Rx dropout always occurs at the same sample point in the packet
  • The dropout is temporary and good data returns for the next frame
  • AGC is disabled, the MGC setting is 0x14 (Register 0x109). I've tried various MGC settings and enabling AGC but this doesn't change the behavior
  • No software is running on either system
  • The ADC data captured with ChipScope emanates from an untouched portion of the FMCOMMS2 FPGA reference design (adc_data_i1, adc_data_q1 output from axi_ad9361_rx.v)
  • ADC sample magnitudes are in the expected range when the data is good


Since we are at both ends of the link, I realize the problem could be on the Tx or Rx side. I'm not suspecting the modifications made to the FPGA since everything works as expected when using a cabled connection.


Any suggestions on what to look at next would be appreciated.