Datasheet

0
-20
-40
-60
-80
-100
-120
-140
NormalizedFrequency(f /f )
IN DR
Gain(dB)
1.0 2.00 3.0 4.0 5.00.5 4.53.52.51.5
0
0.5
1.0
1.5
2.0
2.5
3.0
-
-
-
-
-
-
NormalizedFrequency(f /f )
IN DR
Gain(dB)
0.05 0.100 0.15 0.350.20 0.25 0.30
0
20
40
60
80
100
120
140
-
-
-
-
-
-
-
NormalizedFrequency(f /f )
IN MOD
Gain(dB)
0.05 0.100 0.500.15 0.20 0.25 0.30 0.35 0.40 0.45
DR[2:0]=110
DR[2:0]=000
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]=000
DR[2:0]=110
10
10
30
50
70
90
110
130
-
-
-
-
-
-
-
NormalizedFrequency(f /f )
IN MOD
Gain(dB)
0.50 4.01.0 1.5 2.0 2.5 3.0 3.5
DR[2:0]=110DR[2:0]=000
ADS1294, ADS1294R
ADS1296, ADS1296R
ADS1298, ADS1298R
SBAS459I –JANUARY 2010–REVISED JANUARY 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 30 shows the frequency response of the sinc filter and
Figure 31 shows the roll-off of the sinc filter. With a step change at input, the filter takes 3 × t
DR
to settle. After a
rising edge of the START signal, the filter takes t
SETTLE
time to give the first data output. The settling time of the
filters at various data rates are discussed in the START subsection of the SPI Interface section. Figure 32 and
Figure 33 show the filter transfer function until f
MOD
/2 and f
MOD
/16, respectively, at different data rates. Figure 34
shows the transfer function extended until 4 × f
MOD
. It can be seen that the passband of the ADS129x 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 30. Sinc Filter Frequency Response Figure 31. Sinc Filter Roll-Off
Figure 32. Transfer Function of On-Chip Figure 33. Transfer Function of On-Chip
Decimation Filters Until f
MOD
/2 Decimation Filters Until f
MOD
/16
Figure 34. Transfer Function of On-Chip Decimation Filters
Until 4f
MOD
for DR[2:0] = 000 and DR[2:0] = 110
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Product Folder Link(s): ADS1294 ADS1294R ADS1296 ADS1296R ADS1298 ADS1298R