AD7734

Rev. 0 | Page 10 of 32

OUTPUT NOISE AND RESOLUTION SPECIFICATION

The AD7734 can be operated with chopping enabled or

disabled, allowing the ADC to be programmed to either

optimize the throughput rate and channel switching time or to

optimize the offset drift performance. Noise tables for these two

primary modes of operation are outlined below for a selection

of output rates and settling times.

The AD7734 noise performance depends on the selected

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

analog input range. The AD7734 noise will not vary

significantly with MCLK frequency.

Chopping Enabled

The first mode, in which the AD7734 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

FW

Conversion Time

Register

Conversion Time

(µs)

Output Data Rate

(Hz)

–3 dB Frequency

(Hz)

RMS Noise

(µV)

127

FFh

2686

372

200

9.6

46

AEh

999

1001

520

15.5

22

96h

499

2005

1040

22.7

17

91h

395

2534

1300

26.1

8

88h

207

4826

2500

39.2

6

86h

166

6041

3100

46.0

2

82h

82

12166

6300

120.0

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)

±10 V

0 V to +10 V

±5 V

0 V to +5 V

127

FFh

2686

372

200

21.0

20.0

20.0

19.0

46

AEh

999

1001

520

20.3

19.3

19.3

18.3

22

96h

499

2005

1040

19.7

18.7

18.7

17.7

17

91h

395

2534

1300

19.5

18.5

18.5

17.5

8

88h

207

4826

2500

19.0

18.0

18.0

17.0

6

86h

166

6041

3100

18.7

17.7

17.7

16.7

2

82h

82

12166

6300

17.3

16.3

16.3

15.3

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)

±10 V

0 V to +10 V

±5 V

0 V to +5 V

127

FFh

2686

372

200

18.1

17.1

17.1

16.1

46

AEh

999

1001

520

17.4

16.4

16.4

15.4

22

96h

499

2005

1040

16.9

15.9

15.9

14.9

17

91h

395

2534

1300

16.7

15.7

15.7

14.7

8

88h

207

4826

2500

16.2

15.2

15.2

14.2

6

86h

166

6041

3100

15.8

14.8

14.8

13.8

2

82h

82

12166

6300

15.0

13.4

13.4

12.4