AD7785

Rev. 0 | Page 11 of 32

OUTPUT NOISE AND RESOLUTION SPECIFICATIONS

EXTERNAL REFERENCE

Table 5 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 an external 2.5 V reference. These

numbers are typical and are generated with a differential input

voltage of 0 V. Table 6 shows the effective resolution, with the

output peak-to-peak (p-p) resolution shown in parentheses. It is

important to note that the effective resolution is calculated

using the rms noise, while the p-p resolution is based on the 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 5. Output RMS Noise (μV) vs. Gain and Output Update Rate Using an External 2.5 V 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

0.64

0.6

0.29

0.22

0.1

0.065

0.039

0.041

8.33

1.04

0.96

0.38

0.26

0.13

0.078

0.057

0.055

16.7

1.55

1.45

0.54

0.36

0.18

0.11

0.087

0.086

33.2

2.3

2.13

0.74

0.5

0.23

0.17

0.124

0.118

62

2.95

2.85

0.92

0.58

0.29

0.2

0.153

0.144

123

4.89

4.74

1.49

1

0.48

0.32

0.265

0.283

242

11.76

9.5

4.02

1.96

0.88

0.45

0.379

0.397

470

11.33

9.44

3.07

1.79

0.99

0.63

0.568

0.593

Table 6. Typical Resolution (Bits) vs. Gain and Output Update Rate Using an External 2.5 V 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 (20)

20 (19.5)

20 (19.5)

20 (19)

20 (19)

20 (18.5)

20 (18.5)

20 (17.5)

8.33

20 (19.5)

20 (19)

20 (19)

20 (18.5)

20 (18.5)

20 (18.5)

20 (18)

19.5 (17)

16.7

20 (19)

20 (18)

20 (18.5)

20 (18)

20 (18)

20 (18)

20 (17.5)

19 (16.5)

33.2

20 (18.5)

20 (17.5)

20 (18)

20 (17.5)

20 (18)

20 (17.5)

19 (16.5)

18.5 (16)

62

20 (18)

19.5 (17)

20 (18)

20 (17.5)

20 (17.5)

19.5 (17)

19 (16.5)

18 (15.5)

123

20 (17.5)

19 (16.5)

19.5 (17)

19 (16.5)

19.5 (17)

19 (16.5)

18 (15.5)

17 (14.5)

242

18.5 (16)

18 (15.5)

18 (15.5)

18 (15.5)

18.5 (16)

18.5 (16)

17.5 (15)

16.5 (14)

470

18.5 (16)

18 (15.5)

18.5 (16)

18.5 (16)

18 (15.5)

18 (15.5)

17 (14.5)

16 (13.5)