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.

Hi,

The formula in calculating the effective resolution is:

Effective resolution = log2(FS input voltage range/ADC RMS noise), thus,

Effective resolution = log2(5x2/9.7uVrms) =

19.98 bitsUsing the same noise and reference values above, the p-p resolution is

17.26 bitssince the effective resolution is always 2.72 bits higher than the p-p resolution unless you are limited by the data output word. At the four slowest data rate settings, the ADC noise level is low enough that the effective resolution is better than 24 bits if it were to output more than 24 bits of data.Thanks,

Jellenie