Data Sheet

AD7798/AD7799

Rev. B | Page 11 of 28

AD7799

Table 7 shows the AD7799 output rms noise for some update

rates and gain settings. The numbers given are for the bipolar

input range with a 2.5 V reference. These numbers are typical

and are generated with a differential input voltage of 0 V. Table 8

shows the effective resolution, and the output peak-to-peak

resolution is given in parentheses. Note that the effective

resolution is calculated using the rms noise, whereas the

peak-to-peak resolution is based on peak-to-peak noise. The

peak-to-peak 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 for the AD7799 Using a 2.5 V Reference

Update Rate

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 Hz

0.64

0.6

0.185

0.097

0.075

0.035

0.027

0.027

8.33 Hz

1.04

0.96

0.269

0.165

0.108

0.048

0.037

0.040

16.7 Hz

1.55

1.45

0.433

0.258

0.176

0.085

0.065

0.065

33.2 Hz

2.3

2.13

0.647

0.364

0.24

0.118

0.097

0.094

62 Hz

2.95

2.85

0.952

0.586

0.361

0.178

0.133

0.134

123 Hz

4.89

4.74

1.356

0.785

0.521

0.265

0.192

0.192

242 Hz

11.76

9.5

3.797

2.054

1.027

0.476

0.326

0.308

470 Hz

11.33

9.44

3.132

1.773

1.107

0.5

0.413

0.374

Table 8. Typical Resolution (Bits) vs. Gain and Output Update Rate for the AD7799 Using a 2.5 V Reference

Update Rate

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 Hz

23 (20.5)

22 (19.5)

22.5 (20)

22.5 (20)

22 (19.5)

22 (19.5)

21.5 (19)

20.5 (18)

8.33 Hz

22 (19.5)

21.5 (19)

22 (19.5)

22 (19.5)

21.5 (19)

21.5 (19)

21 (18.5)

20 (17.5)

16.7 Hz

21.5 (19)

20.5 (18)

21.5 (19)

21 (18.5)

21 (18.5)

21 (18.5)

20 (17.5)

19 (16.5)

33.3 Hz

21 (18.5)

20 (17.5)

21 (18.5)

20.5 (18)

20.5 (18)

20.5 (18)

19.5 (17)

18.5 (16)

62 Hz

20.5 (18)

19.5 (17)

20.5 (18)

20 (17.5)

19.5 (17)

19.5 (17)

19 (16.5)

18 (15.5)

123 Hz

20 (17.5)

19 (16.5)

20 (17.5)

19.5 (17)

19 (16.5)

19 (16.5)

18.5 (16)

17.5 (15)

242 Hz

18.5 (16)

18 (15.5)

18.5 (16)

18 (15.5)

18 (15.5)

18.5 (16)

18 (15.5)

17 (14.5)

470 Hz

18.5 (16)

18 (15.5)

18.5 (16)

18.5 (16)

18 (15.5)

18.5 (16)

17.5 (15)

16.5 (14)