ASD1194 datasheet(23/76 Pages) TI

23 / 76 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

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

× tDR to settle. The

fourth DRDY pulse is settled data. 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 23 and Figure 24 show the filter transfer function until fMOD/2 and fMOD/16,

respectively, at different data rates. Figure 25 shows the transfer function extended until 4

× fMOD. It can be seen

that the passband of the ADS1194/6/8 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 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 fMOD/2

Decimation Filters Until fMOD/16

Figure 25. Transfer Function of On-Chip Decimation Filters

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

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