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DAC39J84: Complex bandwidth (BW) of DAC39J84

Yilun Xu
Prodigy 80 points
Part Number: DAC39J84

Hi there,

There is a term "complex bandwidth (BW)" in Table 11 of DAC39J84 datasheet (SLASE48A).

In our case, we have DAC39J84 running at 1 GSPS (without interpolation). Therefore, the analog bandwidth is 500 MHz in our system according to Nyquist theorem.

However, the BW in Table 11 is 1250 MHz (I believe it will be 1000 MHz with 1 GHz Fs in our case).

It seems that there is a factor of 2 between the complex bandwidth (1000 MHz) and the analog bandwidth (500 MHz).

My question is what the definition of complex bandwidth is. What is the relationship between the complex bandwidth and the analog bandwidth?

Thanks and best,

Yilun

  • 0
    TI__Mastermind 20755 points

    Hi Yilun,

    The analog bandwidth for most DAC is just Fs/2. In any interpolation modes, the useful bandwidth is typically 80% of the effective nyquist rate (DAC output data rate divided by 2) due to interpolation filter roll-off. It seems in this datasheet, the term complex bandwidth is referring to the useful bandwidth. Hope this helps.

    Regards, Chase

  • 0 in reply to Chase W
    Prodigy 80 points

    Hi Chase,

    I saw the BW equation in the Table 11: "BW = Complex bandwidth (= f_DATA × 0.8 with interpolation, = f_DATA without interpolation)".

    Let's not consider any interpolation here. In my case, f_DATA = 1 GSPS, f_DAC = 1 GSPS. Therefore, analog bandwidth = 0.5 GHz, BW = f_DATA = 1 GHz.

    Do you mean that the analog bandwidth and the complex bandwidth (BW) are different things?

    Thanks and best,

    Yilun

  • +1 in reply to Yilun Xu
    TI__Mastermind 20755 points

    Yilun,

    Correct, the complex bandwidth accounts for two sides of the NCO where without mixing there is only real data being transmitted.

    Regards, Chase

  • 0 in reply to Chase W
    Prodigy 80 points

    Hi Chase,

    That makes sense. Thanks!

    Best,

    Yilun