AD7785

Rev. 0 | Page 12 of 32

INTERNAL REFERENCE

Table 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)