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ADS1278: Noise Free bits

Mahesh Hegde
Intellectual 400 points
Part Number: ADS1278

Hello All,

We are using this IC extensively but we are facing some issue w.r.t ENOB. As per the ADC1278, how many noise free bits can get from the design out of 24 bits? 

Thanks in advance. 

Regard, 

Mahesh Hegde

  • 0
    TI__Guru 66466 points
    Hi Mahesh,

    Thanks for your post!

    Noise-free bits can be calculated as log2(2*VREF / Vn_pp). In High-Resolution Mode, 5.5uVrms (36.3uVpp) equates to 17.1 noise-free bits with a 2.5V reference.

    Best Regards,
  • 0 in reply to Ryan Andrews
    TI__Guru 66466 points

    By the way, check out our Excel Calculator Tool for the ADS1x7x family of delta-sigma ADCs!

    ADS1x7x Excel Calculator Tool:


    Best Regards,

     

  • 0 in reply to Ryan Andrews
    Intellectual 400 points

    Hello Ryan,

    i understood that in ADS1278 17.5 bits can be obtained as ENOB and rest will be reflected as noise.

    However we do the modification in analog electronics also 17.5 bits is the maximum.

    Is my understanding correct? 

    Regards,

    Mahesh Hegde

  • 0 in reply to Mahesh Hegde
    TI__Guru 66466 points
    Hi Mahesh,

    Just to be clear - 17.1 is the Noise-Free Resolution, not ENOB. Officially, ENOB is calculated from dynamic range as DR-1.76/6.02. However, many people also use the term "ENOB" when talking about the Effective Resolution. The calculation for Effective Resolution in the ADS1278 is the same as Noise-Free Resolution, but replaces "Vn_pp" with "Vn_rms":

    Effective Resolution = log2(2*VREF / Vn_rms) = 19.79 bits.

    I did not fully understand your last comment - could you please explain it further?

    Best Regards,