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DAC5682ZEVM clock and transformer output questions

Liang Geng
Prodigy 80 points
Other Parts Discussed in Thread: DAC5682Z, CDCE72010, THS4211

Hi,

I am working on a DE4 board interfacing with DAC5682Z EVM.

The requirement of the clkin of the EVM is 1Vrms, what is the most common way of generating this clock? I suppose for the purpose of synchronizing FPGA and DAC, the clock should be generated from the clock network if FPGA? But what do I do about the 1Vrms requirment?

 

Also I've configured the DAC EVM to transformer output to evaluate the pure DAC signal. I've read that the transformer output blocks DC component. Does that mean the this DAC would not be able to converter a square wave signal etc.?

Best wishes,

Liang

  • 0
    TI__Genius 17360 points

    Hi Liang,

    We generally use a clock generator and jitter cleaner. The most common ones we use are the CDCE72010 or the LMK04800. These chips are capable of supplying high quality clock signals (low jitter) to our DACs and ADCs. Without a low jitter clock, the noise floor of both DACs and ADCs rise and significantly impacts SNR performance. This same chip can be used to provide a synchronized clock to the FPGA, DAC, and any other devices in the system. As far as a 1Vpp signal, we usually use a fully differential LVPECL output from the clocking chips which will be greater than 1Vpp.

    Transformers cannot pass DC levels nor can they pass an infinite number of harmonics. The passband of the transformer will be specified in the part's datasheet. If you generate a square wave with the DAC and use the transformer output, you will get a ground centered and slightly distorted square wave at the output. If you need a DC coupled output then you would need to use a differential to single-ended amplifier on the output. For a square wave, the amp should have a bandwidth much higher than the frequency of your square wave to account for harmonic content.

    Regards,
    Matt Guibord

  • 0 in reply to Matt Guibord
    Prodigy 80 points

    Thanks Matt. This is really helpful!

    How would I configure the board to get a pure DAC output without any modulation nor transformers?

    I also found J4 SMA does not have any signal when I configure the board to transformer output. Is that correct? what is J4 for though.

     

    Best wishes,

    Liang

  • 0 in reply to Liang Geng
    TI__Genius 17360 points

    Liang,

    J4 can be used in conjuction with J3 to provide a fully differential, DC coupled output. In order to do so, the transformer should be removed and resistors R20, R23, and R27 should be installed. J1 and J2 can be used similarly for channel B.

    If you need a DC-coupled singled-ended signal out then an amplifier can be used to convert from differential to single-ended. For instance, take a look at the THS4211.

    Regards,
    Matt Guibord