Datasheet

0
20
40
60
80
100
120
140
-
-
-
-
-
-
-
Normalized Frequency (f /f )
IN MOD
Gain (dB)
0.05 0.10 0.50.15 0.2 0.25 0.3 0.35 0.4 0.45
DR[2:0] = 000
DR[2:0] = 110
0
20
40
60
80
100
120
140
-
-
-
-
-
-
-
Normalized Frequency (f /f )
IN MOD
Gain (dB)
0.010 0.070.02 0.03 0.04 0.05 0.06
DR[2:0] = 110
DR[2:0] = 000
0
-20
-40
-60
-80
-100
-120
-140
Normalized Frequency (f /f )
IN DR
Gain (dB)
1 20 3 4 50.5 4.53.52.51.5
0
0.5
1
1.5
2
2.5
3
-
-
-
-
-
-
Normalized Frequency (f /f )
IN DR
Gain (dB)
0.05 0.10 0.15 0.350.2 0.25 0.3
ADS1291
ADS1292
ADS1292R
SBAS502B –DECEMBER 2011–REVISED SEPTEMBER 2012 www.ti.com
The sinc filter has notches (or zeroes) that occur at the output data rate and multiples thereof. At these
frequencies, the filter has infinite attenuation. Figure 26 shows the sinc filter frequency response and Figure 27
shows the sinc filter roll-off. With a step change at input, the filter takes 3 t
DR
to settle. After a START signal
rising edge, the filter takes t
SETTLE
time to give the first data output. The filter settling times at various data rates
are discussed in the START subsection of the SPI Interface section. Figure 28 and Figure 29 show the filter
transfer function until f
MOD
/ 2 and f
MOD
/ 16, respectively, at different data rates. Figure 30 shows the transfer
function extended until 4 f
MOD
. It can be seen that the ADS1291, ADS1292, and ADS1292R passband repeats
itself at every f
MOD
. The input R-C anti-aliasing filters in the system should be chosen such that any interference
in frequencies around multiples of f
MOD
are attenuated sufficiently.
Figure 26. Sinc Filter Frequency Response Figure 27. Sinc Filter Roll-Off
Figure 28. Transfer Function of On-Chip Figure 29. Transfer Function of On-Chip
Decimation Filters Until f
MOD
/ 2 Decimation Filters Until f
MOD
/ 16
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Product Folder Links: ADS1291 ADS1292 ADS1292R