• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 10 subscribers
  • Views 432 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DAC38RF89: The power of signal is loss 6dB

user6193156
Intellectual 290 points
Other Parts Discussed in Thread: DAC38RF89

art Number: DAC38RF89

The cofiguration of DAC38RF89 is follow. I use DUC1 as I data path, and DUC2 as Q data path. I enable the MIXERAB and the NCOAB of the two path, and add adjacent DAC path AB sample(Q data) to I data,then output the sum.

But at the output, the power of signal is loss 12dB. When I set MIXERAB_GAIN=1,the power is loss 6dB.

Why are the power losses 12dB and 6dB respectively in the two case?

  • 0
    TI__Genius 13310 points

    Hi,

    You should see some loss of power that results from the mixing, however it should not be at the level of 12dB. Is your Q data phase shifted by 90 degrees? This could cause you to have more loss when mixing the two channels.

    For the MIXERAB_GAIN = 1, it is correct to see a gain of 6dB. This register is used to add a gain of 6dB when enabled and when disabled there is no gain.

    Regards,

    David Chaparro

  • 0 in reply to David Chaparro
    Intellectual 290 points

    Hi，David

    After mixing, the power loss of the signal is 9dB.

    But in the chapter 8.3.17.4 of datasheet, the gain of the Digital Quadrature Modulator is  -3dB. Who produces the -6dB gain?

    Regards，

    Su

  • 0 in reply to user6193156
    TI__Genius 13310 points

    Hi Su,

    In that section of the datasheet they state that the DQM has a gain of 0.707 or -3dB when MIXERAB_GAIN = 0 and a gain of 1.414 or +3dB when MIXERAB_GAIN = 1. When MIXERAB_GAIN is changed from 0 to 1 we go from a gain of -3dB to +3dB, which gives a total gain of +6dB.

    Regards,

    David

  • 0 in reply to David Chaparro
    Intellectual 290 points

    Hi,David

    See the following figure,if input data is 0dBm,when MIXER_GAIN=0,at point A, the power is -9dBm,not -3dBm(who produces the extra -6dB gain?).

    When add adjacent DAC path AB sample(Q data) to I data，the power losses 3dBm(the power at B point is -12dBm,who produces the -3dB gain?).

    Q data phase is shifted by 90 degrees.

    Regards,

    Su

  • 0 in reply to user6193156
    TI__Genius 13310 points

    Hi Su,

    The power loss(-9dBm) between the 0dBm point and A point is caused by the complex mixer. The loss is not desirable and that is why you have the choice of using the MIXER_GAIN to add 6dB of gain in the mixer to help recover some of the lost power.

    The power loss(-3dBm) between point A and B is caused by the process of summing the two DAC outputs.

    Another thing to take note of is that you should have the mixer and NCO’s set to sync from “Sync_out from JESD”.

    Regards,

    David