AD9959 Output Viewing

I am looking to use an AD9959 Eval board to generate three single-tone signals. However, I am having trouble with several items in achieving this.

1. When I try to communicate new parameters to the board (currently attempting using single tone on single channel), they appear to load successfully, but when I attempt to read back the loaded parameters, all items default back to what I presume are the board's default settings. What, if any, error screens could I expect to show up to help me determine if this is an error in the load process or in the read process? SYNC CLK appears to respond to the load-read process but it is somewhat fickle (could be chalked up to a bad cable).

2. I would like to view the output via oscilloscope and have as such connected the output of DAC0 (J3) through a 10k resistor in order to observe the voltage. Is there any reason that this would be an insufficient setup that I am unaware of?

3. In a worst-case scenario, which outputs would provide the most reliable way to troubleshoot whether or not the board is defective or has failed? Both LEDs indicate that the board is both on and communicating properly via USB, and the board is successfully identified in the software.

At present, I have the board in PC mode, using the internal crystal. Input voltages are supplied via TB and SMA cable to J17. The 1.8V supply draws 68mA while the 3.3V supply draws ~127mA.

Any guidance would be most appreciated.

  • 0
    •  Analog Employees 
    on Oct 14, 2020 4:03 AM 1 month ago

    Hi,

    To answer your questions:

    1. As far as I know, there is no error screens when there is a problem with the load or read process. The only indicator in the evaluation software is the USB status and DUT type on the bottom left corner of the window. Just to check, is the View Channel set to the programmed channel on the Debug window when reading the registers?

    2. The output of DAC0 for AD9959 is at J2. You can directly connect this output to the oscilloscope and just make sure that the output frequency is within the bandwidth of the scope.

    3. There is no particular output channel that would be the most reliable in troubleshooting but I would recommend channel 0 since this is the default channel in the software.

    May we know the details on the three single-tone signals that you would like to obtain? You can also share your current evaluation software setup for us to assess.

    Best regards,

    Mark

  • Hi Mark,

    Thanks for the response and the clarification!
    I am presently trying to load the sample code that is included with the software, specifically "All Channels on @10_20_30_40MHz", although my end goal is to generate three signals somewhere in the range of 5-10MHz.

    I believe that an incorrect understanding of the REF CLK hookup may have been to blame for the issues with sending data to the board, but I am still in the process of finding an appropriate clock source for it given my current resources.

    Am I correct in understanding that this board does not have an onboard oscillator, only the clock circuit?

  • 0
    •  Analog Employees 
    on Oct 16, 2020 2:14 AM 1 month ago in reply to j.car

    Hi,

    The AD9959 evaluation board does not have an onboard oscillator. You have to supply the reference clock to J9 using a signal generator or to X2 using a crystal that would require some modifications on the board.

    Best regards,

    Mark

  • Understood. I think I have arrived at the solution I need with regards to programming and viewing the outputs. The only note I would make is that it seems like the connector J2 on my board does not provide an output, but its filtered counterpart J6 does; this seems to be true for all of the SMA outputs on my board. 

    As a parting thought, I should mention that it is my intention to sum the three signals generated by this board together into a singular waveform; is there any immediate reason that this couldn't be achieved with a summing amplifier?

  • Update: I have everything working as desired at this point! As a note to anyone else who finds this in the future, I find that a summing amplifier configuration works best with resistors on the order of 1k-10k ohms.