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DAC38J84: DAC38J84 in 4 channel mode with NCO enabled

min hu
Intellectual 990 points
Part Number: DAC38J84

Hi ,

I have some questions about NCO function.

My Design Requirements: output BW = 300MHz, Center frequency = 800MHz.

My Design Plan:

1.since BW = 300MHz, the minimum data rate = 600MHz, considering FIR filter limit useful BW to about 40% of data rate,so  minimum data rate = 750MHz.

2.Center frequency = 800MHz, upper frequency = 950MHz, so minimum DAC sample rate = 1900Msps.

so, i choose data rate = 1000MHz, with 2x interpolation ,DAC sample rate = 2000Msps.

I tend to use as more channel as possible,my question is :

1.can i use DAC38J84 in 4 independent mode and with NCO enabled for my design?

2.if YES,what NCO frequency should be?

I need your professional suggestion,looking forward to your reply! 

  • 0
    TI__Guru* 91947 points

    Min,

    The device only has two NCO's. One is used by CHA and CHB, the other by CHC and CHD. You can only get two different frequencies out at one time. Since these are complex mixers though, the phase of CHA will be shifted 90 degrees with respect to CHB. The same goes for CHC with respect to CHD. The attached TI Designs document provides more information regarding using this device as an arbitrary waveform generator.

    Regards,

    Jim

    Arb Waveform TI design.pdf

     

  • 0 in reply to jim s
    Intellectual 990 points

    Hi,Jim
    Thanks for your reply, here is my idea：
    It is true that DAC38J84 only has two NCO's,but if NCO = Fs/2, I/Q data will be independent:
    Iout = {+I1, -I2, +I3, -I4…}
    Qout = {+Q1, -Q2, +Q3, -Q4…}

    since i need 300MHz banwidth center frequency 800MHz signal,

    1> i set data rate to 1066.6Msps,

    2> 2x interpolation enabled, NCO = 1066.6MHz,(sample rate = 1066.6x2=2133.2Msps)

    3> baseband signal is centered on the first Nyquist domain which is 266.65MHz +/_ 150MHz ,

    the output should centered on 3/8*Fs,that is : I will get I/Q output signal centered on 799.95MHz +/_ 150MHz , and I/Q output are independent.

    can DAC38J84 do this???

    Regards,
    Hoo

  • 0 in reply to min hu
    Intellectual 990 points

    AD9164 remote test tool is convenient,I use it to test my idear,due to lower sample rate limit,the sample rate is 2 times the condition of my application.

    I get the expected output at 1600MHz(2 times the condition of my application)