Datasheet

AD7785
Rev. 0 | Page 12 of 32
INTERNAL REFERENCE
Tabl e 7 shows the output rms noise of the AD7785 for some of
the update rates and gain settings. The numbers given are for
the bipolar input range with the internal 1.17 V reference. These
numbers are typical and are generated with a differential input
voltage of 0 V.
Table 8 shows the effective resolution, with the
output peak-to-peak (p-p) resolution given in parentheses. It is
important to note that the effective resolution is calculated
using the rms noise, while the p-p resolution is calculated based
on p-p noise. The p-p resolution represents the resolution for
which there is no code flicker. These numbers are typical and
are rounded to the nearest LSB.
Table 7. Output RMS Noise (μV) vs. Gain and Output Update Rate Using the Internal Reference
Update Rate (Hz) Gain of 1 Gain of 2 Gain of 4 Gain of 8 Gain of 16 Gain of 32 Gain of 64 Gain of 128
4.17 0.81 0.67 0.32 0.2 0.13 0.065 0.04 0.039
8.33 1.18 1.11 0.41 0.25 0.16 0.078 0.058 0.059
16.7 1.96 1.72 0.55 0.36 0.25 0.11 0.088 0.088
33.2 2.99 2.48 0.83 0.48 0.33 0.17 0.13 0.12
62 3.6 3.25 1.03 0.65 0.46 0.2 0.15 0.15
123 5.83 5.01 1.69 0.96 0.67 0.32 0.25 0.26
242 11.22 8.64 2.69 1.9 1.04 0.45 0.35 0.34
470 12.46 10.58 4.58 2 1.27 0.63 0.50 0.49
Table 8. Typical Resolution (Bits) vs. Gain and Output Update Rate Using the Internal Reference
Update Rate (Hz) Gain of 1 Gain of 2 Gain of 4 Gain of 8 Gain of 16 Gain of 32 Gain of 64 Gain of 128
4.17 20 (19) 20.5 (18) 20 (18.5) 20.5 (18) 20 (17.5) 20 (17.5) 20 (17.5) 19 (16.5)
8.33 20 (18.5) 20 (17.5) 20.5 (18) 20 (17.5) 20 (17.5) 20 (17.5) 19 (16.5) 18 (15.5)
16.7 20 (17.5) 19.5 (17) 20 (17.5) 19.5 (17) 19 (16.5) 19.5 (17) 18.5 (16) 17.5 (15)
33.2 19.5 (17) 19 (16.5) 19.5 (17) 19 (16.5) 19 (16.5) 18.5 (16) 18 (15.5) 17 (14.5)
62 19.5 (17) 18.5 (16) 19 (16.5) 19 (16.5) 18.5 (16) 18.5 (16) 18 (15.5) 17 (14.5)
123 18.5 (16) 18 (15.5) 18.5 (16) 18 (15.5) 17.5 (15) 18 (15.5) 17 (14.5) 16 (13.5)
242 17.5 (15) 17 (14.5) 17.5 (15) 17 (14.5) 17 (14.5) 17.5 (15) 16.5 (14) 15.5 (13)
470 17.5 (15) 17 (14.5) 17 (14.5) 17 (14.5) 17 (14.5) 17 (14.5) 16 (13.5) 15 (12.5)