ADS1291_14 Datasheet, PDF (24/75 Pages) Texas Instruments – Power, 2-Channel, 24-Bit Analog Front-End for Biopotential Measurements

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.
0
0
-20
-40
-60
-80
-100
-120
-140
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Normalized Frequency (f_IN/f_DR)
Figure 26. Sinc Filter Frequency Response
-0.5
-1
-1.5
-2
-2.5
-3
0
0.05 0.1 0.15 0.2 0.25 0.3 0.35
Normalized Frequency (f_IN/f_DR)
Figure 27. Sinc Filter Roll-Off
0
DR[2:0] = 000
-20
DR[2:0] = 110
-40
-60
-80
-100
-120
-140
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
Normalized Frequency (f_IN/f_MOD)
Figure 28. Transfer Function of On-Chip
Decimation Filters Until f_MOD / 2
0
DR[2:0] = 000
-20
DR[2:0] = 110
-40
-60
-80
-100
-120
-140
0
0.01 0.02 0.03 0.04 0.05 0.06 0.07
Normalized Frequency (f_IN/f_MOD)
Figure 29. Transfer Function of On-Chip
Decimation Filters Until f_MOD / 16
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