AD7732
Rev. A | Page 10 of 32
OUTPUT NOISE AND RESOLUTION SPECIFICATION
The AD7732 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 AD7732 noise performance depends on the selected
chopping mode, the filter word (FW) value, and the selected
analog input range. The AD7732 noise will not vary
significantly with MCLK frequency.
Chopping Enabled
The first mode, in which the AD7732 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
