Datasheet

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SBAS306F − NOVEMBER 2004 − REVISED OCTOBER 2007
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23
0
−
1
−
2
−
3
−
4
−
5
−
6
−
7
−
8
−
9
−
10
Normalized Input Frequency (f
IN
/f
DATA
)
Amplitude (dB)
0.45 0.47 0.49 0.51 0.53 0.55
Figure 56. Transition Band Response for
High-Speed and Low-Power Modes
20
0
−
20
−
40
−
60
−
80
−
100
−
120
−
140
−
160
Input Frequency (f
IN
/f
DATA
)
Gain (dB)
016324864
Figure 57. Frequency Response Out to f
MOD
for
High-Speed and Low-Power Modes
High-Resolution Mode
The oversampling ratio is 128 in High-Resolution mode.
Figure 58 shows the frequency response in
High-Resolution mode normalized to f
DATA
. Figure 59
shows the passband ripple, and the transition from
passband to stop band is illustrated in Figure 60. The
overall frequency response repeats at multiples of the
modulator frequency f
MOD
, (128 × f
DATA
), as shown in
Figure 61. The stop band of the ADS1271 provides 100dB
attenuation of frequencies that begin just beyond the
passband and continue out to f
MOD
. Placing an
antialiasing, low-pass filter in front of the ADS1271 inputs
is recommended to limit possible high-amplitude
out-of-band signals and noise.
0
−
20
−
40
−
60
−
80
−
100
−
120
−
140
0.50
Normalized Input Frequency (f
IN
/f
DATA
)
Amplitude (dB)
00.25 0.751
Figure 58. Frequency Response for
High-Resolution Mode
0.02
0
−
0.02
−
0.04
−
0.06
−
0.08
−
0.10
0.2
Normalized Input Frequency (f
IN
/f
DATA
)
Amplitude (dB)
0 0.1 0.3 0.4 0.5 0.6
Figure 59. Passband Response for
High-Resolution Mode