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DAC908 as BaseBand generator for TRF370315

fabrizio de rosa
Prodigy 40 points
Other Parts Discussed in Thread: TRF370315, DAC908, TRF3705

Hello everybody, I would like to use the DAC908 (one for I and one for Q) as BaseBand inputs for the TRF370315.

At the very beginning I was thinking to ac couple the two devices in order to interface them (different common mode), but I studied a bit more and I found that TI has released a full resistive configuration in order to interface TRF370315 with DAC56x2.

TI also released a simple xls file (slwc083) usefull to find the correct values to interface the modulator with the DAC56x2.

I would like to know:

1) If I can use this configuration also for the DAC908

2) If the values I inserted in the xls file (and reported below) are correct

3) If there is a better solution to interface the two devices

4) If there are drawbacks I did not think about

Thank you

  • 0
    TI__Mastermind 18065 points
    I agree that you can use the DAC56x2 as a guide. Reference the app note: www.ti.com/.../slaa399.pdf. This discusses interfacing current source DAC to RF modulators. There is an example in the document that has resistor values that should work for you. The excel spreadsheet you copied looks to have given weird values. R2, R3 should not be in the kohm range.

    You may also consider switching to the TRF3705 modulator. The TRF3705 modulator operates with a 0.25 to 0.5V common mode voltage so you can connect directly without the need for a translation network.

    --RJH
  • 0 in reply to RJ Hopper
    Prodigy 40 points
    Thank you, I ended up with the same conclusion! Waiting for the board to be ready to check the results! Thanks again