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DAC38RF82: modes set-up, help needed

Vincenzo Pizzolante
Mastermind 25616 points
Part Number: DAC38RF82
Other Parts Discussed in Thread: DAC38RF89

hi,

We have four DACs that we want to operate them at 2500MSPS input data rate and interpolation 2 (using DAC38RF89), or 3333MSPS input data rate and interpolation 2 (using DAC38RF82).

We need to use each of the four DACs we have in our board, to output one analog I-channel and one Q-channel (no modulation inside DAC so NCOs unused). From what I understand, this means that we are confined to the “real input” rows of “Table 9” of “SLASEA6B –FEBRUARY 2017–REVISED AUGUST 2017” datasheet. Thus if we want to utilize 4 JESD lanes for each DAC IC, we have no “official” available modes to work with, i.e. the device does not support such a setup. Am I correct?

The alternative we are thinking, is to keep 8MSbits per TX (MSByte), use mode 82121 with 2TX, leave out lanes RX1, RX3, RX5, RX7 and disable the unconnected lanes from register JESD_LN_EN. Should we expect any problems with the interface using this approach? 

Is there any other way you can suggest for using 4 JESD lanes per DAC?

thanks a lot in advance

KR

Vincenzo

  • 0
    TI__Guru* 91947 points

    Vincenzo,

    Based on your requirements, you only have two options.

    1. LMFS = 82380, dual 12 bit input data, int 2x, DAC sample rate = 6666MHz, input data rate = 3333MHz, and a serdes rate = 12.498Gbps. 

    2. LMFS = 8212, dual 16 bit input data, int 2x, DAC sample rate = 5000MHz, input data rate = 2500MHz, and a serdes rate = 12.5Gbps.

    If you want to use 4 lanes per DAC, you need to change your interpolation factor to 8x, and then you can operate in LMFS = 4421 mode, DAC sample rate = 5000MHz, data rate = 625MHz, and a serdes rate = 12.5Gbps.

    Regards,

    Jim 

  • 0 in reply to jim s
    TI__Mastermind 25616 points
    hi Jim,

    thanks for the prompt reply...

    If I use 44210 mode, in order to have 2TX, I have to provide an I/Q pair per DAC.

    Doesn’t this mean that I am operating the path for internal modulation?

    How can I get baseband output in this way?

    thanks a lot in advance
    KR
    Vincenzo
  • 0 in reply to Vincenzo Pizzolante
    TI__Mastermind 25616 points
    hi Jim,

    do you have fb?

    thanks a lot in advance
    KR
    Vincenzo
  • 0 in reply to Vincenzo Pizzolante
    TI__Guru* 91947 points

    Vincenzo,

    In this mode, you would use one I/Q pair per DAC, but the I/Q data you send would be real data. The mixer and NCO would be bypassed and this will allow you to get baseband data out. The issue is your bandwidth will be low (~0.4 * data rate) due to the interpolation filter.

    Regards,

    Jim

  • 0 in reply to jim s
    TI__Mastermind 25616 points
    hi Jim,

    To avoid reducing the rate, for the moment we use 82121 with 2TX 8-bit.
    We have tested this and looks promising for the moment (just few dB SNR loss).
    we can close this

    thanks again
    KR
    Vincenzo