Datasheet
AD7193 Data Sheet
Rev. D | Page 46 of 56
When a channel change occurs, the modulator and filter 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
.
CHANNEL
CONVERSIONS
CHANNEL A
CH A CH A CH A CH BCH B CH B CH B
CHANNEL B
1/
f
ADC
CH B
0
8367-041
Figure 45. Channel Change (Sinc
4
Chop Enabled)
When 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, the ADC takes three conversions after
the step change to generate a fully settled result.
1/
f
ADC
ANALOG
INPUT
ADC
OUTPUT
FULLY
SETTLED
08367-042
Figure 46. Asynchronous Step Change in Analog Input (Sinc
4
Chop Enabled)
The cutoff frequency f
3dB
is equal to
f
3dB
= 0.24 × f
ADC
50 Hz/60 Hz Rejection (Sinc
4
Chop Enabled)
When FS[9:0] is set to 96 and chopping is enabled, the output
data rate is equal to 12.5 Hz for a 4.92 MHz master clock. The
filter response shown in Figure 47 is obtained. The chopping
introduces notches at odd integer multiples of f
ADC
/2. The notches
due to the sinc filter in addition to the notches introduced by
the chopping mean that simultaneous 50 Hz and 60 Hz rejection
is achieved for an output data rate of 12.5 Hz. The rejection at
50 Hz/60 Hz ± 1 Hz is typically 63 dB, assuming a stable
master clock.
–120
–110
–100
–90
–80
–70
–60
–50
–40
–30
–20
–10
0
0 25 50 75 100 125 150
FREQUENCY (Hz)
FILTER GAIN (dB)
0
8367-043
Figure 47. Sinc
4
Filter Response (FS[9:0] = 96, Chop Enabled)
The 50 Hz/60 Hz rejection can be improved by setting the
REJ60 bit in the mode register to 1. With FS[9:0] set to 96
and REJ60 set to 1, the filter response shown in Figure 48
is achieved. The output data rate is unchanged but the 50 Hz/
60 Hz (±1 Hz) rejection is increased to 83 dB typically.
–120
–110
–100
–90
–80
–70
–60
–50
–40
–30
–20
–10
0
0 255075100125150
FREQUENCY (Hz)
FILTER GAIN (dB)
08367-044
Figure 48. Sinc
4
Filter Response (FS[9:0] = 96, Chop Enabled, REJ60 = 1)