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Difference of effective Resolution between equation and value in data sheet

Question asked by Jiwon.Lee on Aug 29, 2016
Latest reply on Aug 30, 2016 by JellenieR

Hi,

 

May I have the reason why these two values are different ?

1) Calculated Effective Resolution of AD7176-2 based on AN-615.

     SNR = 6.02N + 1.76 = 20log(peak-to-peak noise / full-scale input)

                                       = 20xlog(0.000066/5x2)    , Ext. REF = 5V

                                        =-103.609 dB

              N = (103.609 - 1.76)/6.02 = 16.918 Bits

2) Data from Table 6. shows 17.3 Bits with peak-to-peak noise 66uVrms

 

 

Question 1) Why these two values are different ? Is there any wrong calculation ?

 

Question 2) AD7176-2 is 24bits ADC, then How can we get 24.7, 24.8, 24.9 and 25.1 Bits Effective Resolution ?

 

Thanks a lot.

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