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DAC data rate

John w74532
Prodigy 20 points

Other Parts Discussed in Thread: DAC3283, DAC5674

I have  been working on DAC's . Now recently i started working on DAC3283 I have some questions.

 

1. If  FDAC in 200MSPS and interpolation is 2x then can i generate o/p signal of 200MHZ? If not why?

I appreciate your reply

John

 

 

 

  • 0
    TI__Expert 5820 points

    John


    first, Nyquist theorem limits the maximum data rate to fs/2, so you cannot generate a 200 MHz signal with 200 MSPS fDAC.

    Furthermore,

    The interpolation filters inside the DAC limit the input bandwidth to 0.4 * fDAC/interpolation for real signal and 0.8 * fDAC/interpolation for complex signal.

    In your case, with 200 MHz fDAC and 2x interpolation, maximum input bandwidth out of the DAC is [0, 40] MHz for real signal and [-40, 40] MHz for complex signal.

    For generating 200 MHz output signal, set fDAC to 400 MSPS with 2x interpolation, then generate a baseband signal (around DC) and use the DAC coarse mixing option of fs/2 to move it to 200 MHz.

    Regards,



  • 0 in reply to Hamza Fraz
    Prodigy 20 points

    Thanks for the quick reply Hamsa

    Some more questions :)

    >>Well so if I am using 200Mhz DAC clock with interpolation 2x why should the DATA clock be 200/(interpolation) ~200/2=100MHz?  likewise if 4x interpolation DATA clock should be 200/4=50MHz?

    >>Does Nyquist rate has anything to do with this DATA clock as well?  What is the relation between Nyquist rate and interpolation and DATA clock and DAC clock?

    >>So if i have a present setup which can generate ~1kHz with 200MHz DAC clock and 2x interpolation so just by changing the register setting to Fs/2 i can generate 100MHz frequency . Here bandwidth of FIR does not play any role?

     

     

    Regards- John

     

     

     

  • 0 in reply to John w74532
    TI__Expert 5820 points

    John,

    please refer to DAC5674 datasheet for a good explanation of why and how to use interpolation DACs.

    If your DAC CLK is 200 MHz, and you are using 2x interpolation, make sure your 1 KHz baseband signal is sampled at 100 MHz. And yes, you can move the 1 KHz signal to ~ 100 MHz by mixing it with fs/2.

    Regards,