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DAC3482: Side Band Correction

Terry Liu70
Intellectual 490 points
Part Number: DAC3482
Other Parts Discussed in Thread: DAC38J84

Tool/software:

Hi TI Experts,

I have a question about IQ modulator Sideband Correction. QMC gain and phase values are used in my application to correct sideband. A 31.25MHz sine wave at DAC3482 output is used to calibrate QMC gain, phase values, sideband could be corrected to -80dB. Offset values are used to correct LO.

The problem is, when I change DAC output frequency, sideband get worse. I then did QMC calibration at multi-frequencies, it seems different DAC output frequency requires different QMC phase values. The test data are listed below.

IQ Modulator LO = 3.5GHz.

DAC Output        Gain I    Gain Q  Phase

78.13M                  1920    1943       156

75.00M                  1920    1943       152

68.75M                  1920    1943       180

62.50M                  1920    1943       180

50.00M                  1920    1943       181

40.00M                  1920    1943       190

31.25M                  1920    1943       193

The real waveform in my application is wideband, thus keep sideband to be low on various frequency is important to ensure good system EVM. So, I like to know, how can I correct sideband for a wide frequency range? Use delay settings? 

Thanks,

T.L.

  • 0
    TI__Guru* 78174 points

    Hello

    QMC adjustment typically can hold only for certain frequency ranges. For every frequency change, you will have to make some fine adjustments as you have found above.

    If you want a wider bandwidth coverage, you will have to implement I/Q based delay setting such as the one in DAC38J84

  • 0 in reply to Kang Hsia
    Intellectual 490 points

    Hi Kang,

    Thanks for the reply. I was aware of delay settings, yet DAC3482 datasheet didn't say enough information on delay settings. 

    Further questions about delay,

    1, Is 3482 uses the same delay FIR as 38J84?  3482 adopts 8 bit delay while 38J84 uses 16 bit. How do I calculate 8bit delay value for 3482?

    2, Is there any guideline on how to identify delay values during calibration process?

    Thanks,

    T.L.

  • +1 in reply to Terry Liu70
    TI__Guru* 78174 points

    T.L.

    The DAC3482 utilizes analog based delay settings whereas the DAC38J84 utilizes digital based delay settings. 

    We currently cannot recommend our customers to use DAC3482 analog delay settings due to limited delay range. Therefore, if you need to implement the delay, you will have to do this in the FPGA or with the DAC38J84.

    Kang.