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DAC38RF82EVM: Weird DAC output signal with Data Rate at 880MSPS

Alain Garot
Prodigy 60 points
Part Number: DAC38RF82EVM
Other Parts Discussed in Thread: DAC38RF82,

Hello,

I am evaluating DAC38RF82 with the evaluation board (DAC38RF82EVM) and the TSW14J57 pattern generator with high data rate.

A 1100 MHz / +6dBm signal is fed to the input of the LMK (J4 connector).

With the following configuration (Data Rate is 550 MSPS), all is right, it is possible to get a correct signal (about 400 MHz bandwidth) at the DAC output.

In order to get higher bandwidth signal, the following configuration is used (interpolation changed from x16 to x10, data rate is now 880 MSPS):

A file is sent to the TSW14J57 board (bandwidth about 140 MHz to begin), in frequency domain, the following spectrum is shown:

But, this time, after loading the file, the signal at the DAC output is not correct:

Here are the clock configurations (LMK and DAC):
PLL1:

PLL2:

Clock Outputs:

DAC Clocking:

Is there any limitation ?

Thanks for your help.

  • 0
    TI__Mastermind 23710 points

    Alain, after sending the pattern to the DAC from the TSW board did you press the reset dac jesd core button on the dac gui?

  • 0 in reply to Chase W
    Prodigy 60 points

    Hello Chase,

    10 days ago, I did several tests with reset of DAC JESD core (inclunding power off/on of both boards) and the result was always the same : weird signal at the DAC ouptut.

    I just tried again and, this time, the result is not the same, the signal at the DAC output is correct : 

    I do not explain why it was not the case several days ago... (the boards were off during 10 days Wink)

    With a test file with signal bandwidth of about 350 MHz, it is OK also : 

    In order to go higher, I made a test with a file in order to generate a signal with bandwidth of about 800 MHz (the DAC configuration remained the same) : 

    Unfortunately, after sending this file to the board and resetting the DAC JESD core, there is no signal at the DAC output.

    How can I find the issue ?

  • 0 in reply to Alain Garot
    Prodigy 60 points

    Hi Chase,

    Strangely, I just made new tests with the same file and it's OK this time, the following spectrum is visible at the DAC output : 

    I really do not explain this difference of behavior between the tests of 8 hours ago and those of now... There is something I need to understand to have deterministic results...

    What I noticed however is that, after resetting the JESD Core, the signal appears during less than one second then disappears and finally appears again and is stable. Sometimes, the last step (signal present and stable) does not occur...

    Any explanation about that ?

  • 0 in reply to Alain Garot
    TI__Mastermind 23710 points

    Alain,

    Sorry for a long delay here. I think this is just something to do with how the internal firmware of HSDC Pro is. I noticed that in the past when I was working with these devices frequently. If the output flashed on then off then simply resend the pattern from HSDC Pro and then reinit the link from the DAC side and that should solve it.

    Thanks, Chase