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Linux/DAC37J82: DAC config

Part Number: DAC37J82

Tool/software: Linux

Hello folks!

We have DAC37J82 chip and try to configure it to work properly under following conditions: FIF=150 MHz, Fdac=1600 MSPS, 8x interpolation, 0 dBFS digital input, LMF=821, PLL is disabled.

We expected to get the same or close to single tone spectral plot as given in DAC37J82.pdf (revised may 2014). You can find it on figure 11 on page 15 of mentioned document. According to the document, SFDR in our case is typically 72 dBc, but the picture from the DAC output we have is a little bit different. Spectral plot we’ve got contains useful tone at FIF(150 MHz) with 0 dBc level as well as strong tone at FIF*2 (300 MHz) with its level approximately 20 dBc. We guess that something wrong with configs we send to the DAC, but we steel can’t find the correct one. So the question is how to configure the DAC to achieve the same result as one given in official document?

Thank you in advance!

 

  • Val,

    Since the DAC input data rate is at 200MHz (1600MHz / 8), you can only send data at the Nyquist rate or lower. So sending data at 150MHz is to high. You must stay below 100MHz. Give this a try.

    Regards,

    Jim

  • Thanks for your reply!

    We try to make output signal in a different way. We're forming single tone with frequency 20MHz on FPGA. Then we send it to the DAC input via JESD at 200MHz rate. Then we use an on-chip full complex mixer block as a digital quadrature modulator to move our tone to desired place (150MHz). We've configured corresponding NCO registers to get 130MHz sine and cosine for the complex mixing. As mentioned above spectral plot we’ve got contains two tones: at 150 MHz  (0 dBc) and at 300 MHz (approximately 20 dBc). Why do we have tone at multiple frequency after FULL COMPLEX mixer? How can we get SFDR close to one mantiond in the document using an on-chip modulator?

    Best regards!

  • e2e.cfgVal,

    After duplicating your latest setup, I have a tone at 150MHz at -7.5dBm and a tone at 300mHz that is at -77dBm. Is there a chance you may have a register setting programmed incorrectly? The configuration file I used for the DAC is attached.

    Regards,

    Jim

  • Thanks a lot, Jim!

    The DAC is working correctly now.

    Best regads!