ADS1274
ADS1278
www.ti.com
SBAS367–JUNE 2007
High-Resolution Mode
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
The oversampling ratio is 128 in High-Resolution
mode. Figure 62 shows the frequency response in
High-Resolution mode normalized to fDATA. Figure 63
shows the passband ripple, and the transition from
passband to stop band is shown in Figure 64. The
overall frequency response repeats at multiples of the
modulator frequency fMOD (128 × fDATA), as shown in
Figure 65. The stop band of the ADS1274/78
provides 100dB attenuation of frequencies that begin
just beyond the passband and continue out to fMOD
.
Placing an antialiasing, low-pass filter in front of the
ADS1274/78 inputs is recommended to limit possible
high-amplitude out-of-band signals and noise. Often,
a simple RC filter is sufficient. Table 3 lists the image
rejection versus external filter order.
0.45
0.47
0.49
0.51
0.53
0.55
Normalized Input Frequency (fIN/fDATA
)
Figure 64. Transition Band Response for
High-Resolution mode
0
-20
20
0
-40
-20
-40
-60
-80
-60
-80
-100
-120
-140
-100
-120
-140
-160
0
0.25
0.50
0.75
1
Normalized Input Frequency (fIN/fDATA
)
0
32
64
96
128
Normalized Input Frequency (fIN/fDATA
)
Figure 62. Frequency Response for
High-Resolution Mode
Figure 65. Frequency Response Out to fMOD for
High-Resolution Mode
0.02
0
-0.02
-0.04
-0.06
-0.08
-0.10
0
0.1
0.2
0.3
0.4
0.5
0.6
Normalized Input Frequency (fIN/fDATA
)
Figure 63. Passband Response for
High-Resolution Mode
23
Copyright © 2007, Texas Instruments Incorporated
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