AD7739

Rev. 0 | Page 10 of 32

OUTPUT NOISE AND RESOLUTION SPECIFICATION

The AD7739 can be operated with chopping enabled or

disabled, allowing the ADC to be programmed to optimize

either the offset drift performance or the throughput rate and

channel switching time. Noise tables for these two primary

modes of operation are outlined below for a selection of output

rates and settling times.

The AD7739 noise performance depends on the selected

chopping mode, the filter word (FW) value, and the selected

analog input range. The AD7739 noise will not vary

significantly with MCLK frequency.

CHOPPING ENABLED

The first mode, in which the AD7739 is configured with

chopping enabled (CHOP = 1), provides very low noise with

lower output rates.

Table 4 to Table 6 show the –3 dB frequencies and typical

performance versus the channel conversion time and equivalent

output data rate, respectively.

Table 4 shows the typical output rms noise. Table 5 shows the

typical effective resolution based on rms noise. Table 6 shows

the typical output peak-to-peak resolution, representing values

for which there will be no code flicker within a 6-sigma limit.

The peak-to-peak resolutions are not calculated based on rms

noise but on peak-to-peak noise.

These typical numbers are generated from 4096 data samples

acquired in continuous conversion mode with an analog input

voltage set to 0 V and MCLK = 6.144 MHz. The conversion

time is selected via the channel conversion time register.

Table 4. Typical Output RMS Noise in µV vs. Conversion Time and Input Range with Chopping Enabled

Input Range / RMS Noise (µV)

FW

Conversion

Time

Register

Conversion

Time

(µs)

Output Data

Rate

(Hz)

–3 dB

Frequency

(Hz)

±2.5 V, +2.5 V

±1.25 V, +1.25 V, ±0.625 V, +0.625 V

127

0xFF

2689

372

200

1.8

1.1

46

0xAE

1001

999

500

2.7

1.7

17

0x91

397

2519

1325

4.8

2.7

10

0x8A

251

3982

2209

9.3

4.7

9

0x89

230

4342

2450

10.8

6.3

2

0x82

84

11838

9500

600

460

Table 5. Typical Effective Resolution in Bits vs. Conversion Time and Input Range with Chopping Enabled

Input Range / Effective Resolution (Bits)

FW

Conversion

Time

Register

Conversion

Time

(µs)

Output Data

Rate

(Hz)

–3 dB

Frequency

(Hz)

±2.5 V

+2.5 V

±1.25 V

+1.25 V ±0.625 V +0.625 V

127

0xFF

2689

372

200

21.4

20.4

21.2

20.2

20.2

19.2

46

0xAE

1001

999

500

20.8

19.8

20.5

19.5

19.5

18.5

17

0x91

397

2519

1325

20.0

19.0

19.8

18.8

18.8

17.8

10

0x8A

251

3982

2209

19.0

18.0

19.0

18.0

18.0

17.0

9

0x89

230

4342

2450

18.8

17.8

18.6

17.6

17.6

16.6

2

0x82

84

11838

9500

12.9

11.9

12.4

11.4

11.4

10.4

Table 6. Typical Peak-to-Peak Resolution in Bits vs. Conversion Time and Input Range with Chopping Enabled

Input Range / Peak-to-Peak Resolution (Bits)

FW

Conversion

Time

Register

Conversion

Time

(µs)

Output Data

Rate

(Hz)

–3 dB

Frequency

(Hz)

±2.5 V

+2.5 V

±1.25 V

+1.25 V ±0.625 V +0.625 V

127

0xFF

2689

372

200

18.6

17.6

18.3

17.3

17.3

16.3

46

0xAE

1001

999

500

17.9

16.9

17.6

16.6

16.6

15.6

17

0x91

397

2519

1325

17.1

16.1

16.9

15.9

15.9

14.9

10

0x8A

251

3982

2209

16.2

15.2

16.2

15.2

15.2

14.2

9

0x89

230

4342

2450

16.0

15.0

15.8

14.8

14.8

13.8

2

0x82

84

11838

9500

10.7

9.7

9.7

8.7

8.7

7.7