ADS1294 datasheet(29/88 Pages) TI

29 / 88 page

100

120

140

NormalizedFrequency(f /f

)

IN DR

1.0

2.0

3.0

4.0

5.0

0.5

4.5

3.5

2.5

1.5

0.5

1.0

1.5

2.0

2.5

3.0

NormalizedFrequency(f /f

)

IN DR

0.05

0.10

0.15

0.35

0.20

0.25

0.30

100

120

140

NormalizedFrequency(f /f

)

IN MOD

0.05 0.10

0.50

0.15 0.20 0.25 0.30 0.35 0.40 0.45

DR[2:0]=110

DR[2:0]=000

100

120

140

NormalizedFrequency(f /f

)

IN MOD

0.01

0.07

0.02

0.03

0.04

0.05

0.06

DR[2:0]=000

DR[2:0]=110

110

130

NormalizedFrequency(f /f

)

IN MOD

0.5

4.0

1.0

1.5

2.0

2.5

3.0

3.5

DR[2:0]=110

DR[2:0]=000

ADS1294, ADS1294R

ADS1296, ADS1296R

ADS1298, ADS1298R

www.ti.com

SBAS459H

– JANUARY 2010 – REVISED OCTOBER 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 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

× tDR to settle. After a

rising edge of the START signal, the filter takes tSETTLE 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 fMOD/2 and fMOD/16, respectively, at different data rates. Figure 34

shows the transfer function extended until 4

× fMOD. It can be seen that the passband of the ADS129x repeats

itself at every fMOD. The input R-C anti-aliasing filters in the system should be chosen such that any interference

in frequencies around multiples of fMOD 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 fMOD/2

Decimation Filters Until fMOD/16

Figure 34. Transfer Function of On-Chip Decimation Filters

Until 4fMOD for DR[2:0] = 000 and DR[2:0] = 110

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ADS1294 Datasheet(PDF) 29 Page - Texas Instruments

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