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Original question:

AFE7920EVM: How can I configure AFE7920 work as a repeater without FPGA and JESD？

AFE7920EVM: Repeater configuration for the EVM

Zeljko Jelic
Intellectual 318 points
Part Number: AFE7920EVM
Other Parts Discussed in Thread: AFE7920,

Hi,

I was wondering if it is possible to set up the AFE7920 eval board module in a repeater configuration, without FPGA board?

Kind regards,

Željko

  • +1
    TI__Guru* 78614 points

    Hi Zelijko,

    Yes, the AFE7920 supports JESD204 internal loopback. Basically, the RX ADC JESD204 output can be routed internally through internal connections to the JESD204 input of the TXDAC path. You can refer to config 5 of the Latte configuration.

    -Kang

  • 0 in reply to Kang Hsia
    Intellectual 318 points

    Hi Kang,

    Many thanks for your reply.

    Given that it is possible to use the AFE7920EVM board in the repeater mode together with the Latte config 5 script, I wanted to ask some additional questions, if it is not a problem.

    Currently the setup I am building consists of the AFE7920EVM board, an RF signal generator (a CW source), a spectrum analyzer, and a clock generator used to generate the external clock reference. 

    At the moment there is no FPGA of any sort in the setup to provide any kind of data signals, and all the control is supposed to happen through TI Latte software.

    I would like to use the signal from the RF source at 2245 MHz (in the S band) and send it to the ADC of the AFE EVM which should then forward that same signal to its DAC and from there a spectrum analyzer would record the spectrum. 

    Given the numbers I mentioned for the generated signal in the S band and the absent FPGA, do I need to modify anything in the config 5 script in the Latte software? Currently the default configuration 5 states:

    setupParams.fpgaRefClk = 245.76

    AFE.systemStatus.loadTrims = 1

    sysParams.FRef = 491.52

    sysParams.FadcRx = 2949.12

    sysParams.FadcFb = 2949.12

    sysParams.Fdac = 2949.12*3

    I am especially concerned about the fpgaRefClk and Fref, as I am not sure what values should they use. In addition, I have two physical (SMA) connections to the AFE EVM, namely from the RF source and to the spectrum analyzer. Is external clock reference also necessary here, as a third physical connection, and if so, is that a 10 MHz reference?

    Sorry for my detailed question, I am a bit of a novice in RF, so I want to make sure I am not doing something wrong.

    Best regards,

    Željko

  • 0 in reply to Zeljko Jelic
    TI__Genius 17831 points

    Hi Željko,

    There is no need to update the parameters that you show above as this clocking setup is still valid for your use case. The one thing that you will need to change in order to receive and output 2245 MHz is the Rx and Tx NCOs. The sysParams.txNco0 and sysParams.RxNco0 values should be updated to a value that is closer to 2245 MHz, for example they can be set to 2200. After this change you should now be able to send the 2245MHz to the Rx and output the 2245MHz on the Tx side. 

    Regards,

    David Chaparro