AD7708 Analog Devices, AD7708 Datasheet - Page 20

• Manufacturer Part Number: AD7708
• Description: 16-Bit 8/10-Channel, Low Voltage, Low Power, Sigma Delta ADC
• Manufacturer: Analog Devices

Specifications of AD7708

• Resolution (bits): 16bit
• # Chan: 10
• Sample Rate: n/a
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: (2Vref/PGA Gain) p-p
• Adc Architecture: Sigma-Delta
• Pkg Type: SOIC,SOP

ADC NOISE PERFORMANCE CHOP DISABLED
(CHOP = 1)
Tables VII to X show the output rms noise and output peak-to-
peak resolution in bits (rounded to the nearest 0.5 LSB) for
some typical output update rates. The numbers are typical and
generated at a differential input voltage of 0 V. The output update
rate is selected via the SF7–SF0 bits in the Filter Register. It is
important to note that the peak-to-peak resolution figures represent
the resolution for which there will be no code flicker within a
six-sigma limit. The output noise comes from two sources. The
first is the electrical noise in the semiconductor devices (device
noise) used in the implementation of the modulator. Secondly,
AD7708/AD7718
–180
–200
–100
–120
–140
–160
–100
–120
–140
–160
–180
–200
–20
–40
–60
–80
–20
–40
–60
–80
0
0
0
0
SF = 75
OUTPUT DATA RATE = 54.6Hz
SETTLING TIME = 55ms
INPUT BANDWIDTH = 14.3Hz
50Hz REJECTION = –62.5dB, 50Hz 1Hz REJECTION = –57dB
60Hz REJECTION = –63dB, 60Hz 1Hz REJECTION = –60dB
SF = 68
OUTPUT DATA RATE = 60.2Hz
SETTLING TIME = 49.8ms
INPUT BANDWIDTH = 15.5Hz
50Hz REJECTION = –43dB, 50Hz 1Hz REJECTION = –40dB
60Hz REJECTION = –147dB, 60Hz 1Hz REJECTION = –101dB
10
10
20
20
30
30
FREQUENCY – Hz
FREQUENCY – Hz
40
40
50
50
60
60
70
70
80
80
90
90
100
100
when the analog input is converted into the digital domain,
quantization noise is added. The device noise is at a low level
and is independent of frequency. The quantization noise starts
at an even lower level but rises rapidly with increasing frequency
to become the dominant noise source. The numbers in the
tables are given for the bipolar input ranges. For the unipolar
ranges the rms noise numbers will be the same as the bipolar
range, but the peak-to-peak resolution is now based on half the
signal range which effectively means losing 1 bit of resolution.
–180
–200
–100
–120
–140
–160
–180
–200
–100
–120
–140
–160
–20
–40
–60
–80
–20
–40
–60
–80
0
0
0
0
SF = 151
OUTPUT DATA RATE = 27.12Hz
SETTLING TIME = 110ms
INPUT BANDWIDTH = 27.12Hz
50Hz REJECTION = –65.4dB, 50Hz 1Hz REJECTION = –60dB
60Hz REJECTION = –63dB, 60Hz 1Hz REJECTION = –60dB
SF = 255
OUTPUT DATA RATE = 16.06Hz
SETTLING TIME = 186ms
INPUT BANDWIDTH = 4.21Hz
50Hz REJECTION = –87dB, 50Hz 1Hz REJECTION = –77dB
60Hz REJECTION = –72dB, 60Hz 1Hz REJECTION = –68dB
10
10
20
20
30
30
FREQUENCY – Hz
FREQUENCY – Hz
40
40
50
50
60
60
70
70
80
80
90
90
100
100