Datasheet

Data Sheet AD7193
Rev. D | Page 45 of 56
Simultaneous 50 Hz and 60 Hz rejection is obtained when
FS[9:0] is set to 480 (master clock = 4.92 MHz), as shown in
Figure 42. The output data rate is 10 Hz when zero latency is
disabled and 3.3 Hz when zero latency is enabled. The sinc
3
filter has rejection of 100 dB minimum at 50 Hz ± 1 Hz and
60 Hz ± 1 Hz.
–120
–110
–100
–90
–80
–70
–60
–50
–40
–30
–20
–10
0
0
30
60
90
120
150
FREQUENCY
(Hz)
FIL
TER GAIN (dB)
08367-038
Figure 42. Sinc
3
Filter Response (FS[9:0] = 480)
Simultaneous 50 Hz/60 Hz rejection is also achieved using the
REJ60 bit in the mode register. When FS[9:0] is programmed to
96 and the REJ60 bit is set to 1, notches are placed at both 50 Hz
and 60 Hz for a stable 4.92 MHz master clock. Figure 43 shows
the frequency response of the sinc
3
filter with this configuration.
Assuming a stable clock, the rejection at 50 Hz/60 Hz (±1 Hz) is
in excess of 67 dB minimum.
–120
–
110
–100
–90
–80
–70
–60
–50
–40
–30
–20
–10
0
0 25 50 75 100 125 150
FREQUENC
Y (Hz)
FILTER GAIN (dB)
08367-039
Figure 43. Sinc
3
Filter Response (FS[9:0] = 96, REJ60 = 1)
CHOP ENABLED (SINC
4
FILTER)
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 are then inverted, 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.
SINC
3
/SINC
4
POST FILTERMODULATOR
ADC
CHOP
08367-040
Figure 44. Chop Enabled
Output Data Rate and Settling Time (Sinc
4
Chop Enabled)
For the sinc
4
filter, the output data rate is equal to
f
ADC
= f
CLK
/(4 × 1024 × FS[9:0])
where:
f
ADC
is the output data rate.
f
CLK
is the master clock (4.92 MHz nominal).
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 1.17 Hz to 1200 Hz. The settling time is
equal to
t
SETTLE
= 2/f
ADC
Table 32 gives some examples of FS[9:0] values and the
corresponding output data rates and settling times.
Table 32. Examples of Output Data Rates and the
Corresponding Settling Time
FS[9:0] Output Data Rate (Hz) Settling Time (ms)
96 12.5 160
80 15 133