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
ADS1194, ADS1196
ADS1198
www.ti.com SBAS471C –APRIL 2010– REVISED NOVEMBER 2011
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 21 shows the frequency response of the sinc filter and
Figure 22 shows the roll-off of the sinc filter. With a step change at input, the filter takes 3 × t
DR
to settle. The
fourth DRDY pulse is settled data. 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 23 and Figure 24 show the filter transfer function until f
MOD
/2 and f
MOD
/16,
respectively, at different data rates. Figure 25 shows the transfer function extended until 4 × f
MOD
. It can be seen
that the passband of the ADS1194/6/8 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 21. Sinc Filter Frequency Response Figure 22. Sinc Filter Roll-Off
Figure 23. Transfer Function of On-Chip Figure 24. Transfer Function of On-Chip
Decimation Filters Until f
MOD
/2 Decimation Filters Until f
MOD
/16
Figure 25. Transfer Function of On-Chip Decimation Filters
Until 4f
MOD
for DR[2:0] = 000 and DR[2:0] = 110
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