AD7194 Analog Devices, AD7194 Datasheet - Page 45

• Manufacturer Part Number: AD7194
• Description: 8-Channel, 4.8 kHz, Ultralow Noise, 24-Bit Sigma-Delta ADC with PGA
• Manufacturer: Analog Devices

Specifications of AD7194

• Resolution (bits): 24bit
• # Chan: 8
• Sample Rate: n/a
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (2Vref/PGA Gain) p-p
• Adc Architecture: Sigma-Delta
• Pkg Type: CSP

CHOP ENABLED (SINC
With chop enabled, the ADC offset and offset drift are
minimized. The analog input pins are continuously swapped.
With the analog input pins connected in one direction, the
settling time of the sinc filter is allowed and a conversion is
recorded. The analog input pins invert and another settled
conversion is obtained. Subsequent conversions are averaged
to minimize the offset. This continuous swapping of the analog
input pins and the averaging of subsequent conversions means
that the offset drift is also minimized. With chop enabled, the
resolution increases by 0.5 bits. Using the sinc
enabled is suitable for output data rates up to 320 Hz.
Output Data Rate and Settling Time (Sinc
Enabled)
For the sinc
where:
f
f
FS[9:0] is the decimal equivalent of Bit FS9 to Bit FS0 in the
mode register.
The value of FS[9:0] can be varied from 1 to 1023. This results
in an output data rate of 1.56 Hz to 1600 Hz. The settling time
is equal to
Table 33. Examples of Output Data Rates and the
Corresponding Settling Time (Chop Enabled, Sinc
FS[9:0]
96
80
When a channel change occurs, the modulator and filter are
reset. The complete settling time is required to generate the first
conversion after the channel change. Subsequent conversions on
this channel occur at 1/f
ADC
CLK
CONVERSIONS
is the master clock (4.92 MHz nominal).
is the output data rate.
f
t
ADC
SETTLE
CHANNEL
= f
CHOP
= 2/f
CLK
Output Data Rate (Hz)
16.7
20
3
Figure 49. Channel Change (Sinc
Figure 48. Chop Enabled (Sinc
filter, the output data rate is equal to
/(3 × 1024 × FS[9:0])
CH A
ADC
CHANNEL A
MODULATOR
CH A CH A
ADC
.
3
FILTER)
ADC
SINC
3
/SINC
1/
3
CH B
Chop Enabled)
f
CHANNEL B
3
ADC
4
Chop Enable)
Settling Time (ms)
120
100
CH B
POST FILTER
3
3
filter with chop
CH B
Chop
CH B
3
Filter)
CH B
Rev. 0 | Page 45 of 56
If conversions are performed on a single channel and a step
change occurs, the ADC does not detect the change in analog
input; therefore, it continues to output conversions at the
programmed output data rate. However, it is at least two
conversions later before the output data accurately reflects
the analog input. If the step change occurs while the ADC is
processing a conversion, then the ADC takes three conversions
after the step change to generate a fully settled result.
The cutoff frequency f
50 Hz/60 Hz Rejection (Sinc
When FS[9:0] is set to 96 and chopping is enabled, the filter
response shown in Figure 51 is obtained. The output data rate
is equal to 16.7 Hz for a 4.92 MHz master clock. The chopping
introduces notches at odd integer multiples of f
notches due to the sinc filter is addition to the notches intro-
duced by the chopping means that simultaneous 50 Hz and
60 Hz rejection is achieved for an output data rate of 16.7 Hz.
The rejection at 50 Hz/60 Hz ± 1 Hz is typically 53 dB,
assuming a stable master clock.
Figure 50. Asynchronous Step Change in Analog Input (Sinc
f
3dB
–100
–110
–120
–10
–20
–30
–40
–50
–60
–70
–80
–90
Figure 51. Sinc
ANALOG
0
OUTPUT
= 0.24 × f
0
INPUT
ADC
25
ADC
3
Filter Response (FS[9:0] = 96, Chop Enabled)
3dB
1/
f
50
is equal to
ADC
FREQUENCY (Hz)
3
Chop Enabled)
75
100
SETTLED
FULLY
ADC
125
3
/2. The
Chop Enabled)
AD7194
150