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Original question:

ADS1291 ENOB and Noise-Free-Bits Calculation

ADCS7476: ADCS7476

Deyan Zhelev
Prodigy 20 points
Part Number: ADCS7476

Could you please help me to calculate the correct ENOB for ADCS7476? I am expecting a result below 12, but not sure which parameter to include in the notorious formula:

ENOB=(SINAD-1.76)/6.02

Shall I consider the minimum value of SINAD=70, given in table 6.5 in the datasheet? Or to use the minimum value of SNR (70.8 below 85°C or 70.6 for 125°C). Or maybe I need to consider the SINAD value in figure 12 from the datasheet (for 1MSPS)?

I would like to understand how ENOB value is correctly calculated during a normal ADC selection process. For this particular ADC I have a "calculated value" of ENOB = 11.66, but can't figure it out how is calculated.

Any help is appreciated! Many thanks in advance!

  • +1
    TI__Mastermind 24940 points

    Hello, 

    I would like to share the following video (power point available for download):  Statistics Behind Error Analysis of ADC System, this documentation can help understand what values to use for system design, such as typical vs maximum/minimum. 

    From there, it is suggested to use typical values when doing calculations. In your case, it would be 72dB SINAD. in Figure 12, it provides a more detailed look at SINAD performance , but if you notice, only one VDD value seems to be at ~70dB across the frequency spectrum. If you are not using this VDD=2.35V  specific value (note that VDD=2.7V performs at ~72dB), then I suggest you use 72dB. 

    Regards

    Cynthia

  • 0 in reply to Cynthia
    Prodigy 20 points

    Thanks Cynthia! Looks like I overlooked somehow the calculations with the typical SINAD=72dB. The calculation is correct. Your explanation helped me a lot to pay attention for the details in case of further and future ENOB calculations.