Analog Devices AD7194 Manual page 49

0
–10
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–30
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–100
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–120
0
Figure 63. Filter Response for Average + Decimate Filter
(Sinc
Figure 64 shows the filter response when FS[9:0] is set to 5 and
the post filter averages by 16. In this case, the output data rate is
equal to 53.33 Hz when the first filter notch is placed at 60 Hz.
The rejection at 60 Hz ± 0.5 Hz is equal to 40 dB minimum.
0
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0
Figure 64. Filter Response for Average + Decimate Filter
(Sinc
Simultaneous 50 Hz/60 Hz rejection is achieved when FS[9:0] is
set to 30 and the postfilter averages by 16. The output data rate
is equal to 8.9 Hz, whereas the rejection at 50 Hz ± 0.5 Hz and
60 Hz ± 0.5 Hz is 42 dB typically.
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30 60 90 120
FREQUENCY (Hz)
3
Filter, FS[9:0] = 6, Average by 16)
30 60 90 120
FREQUENCY (Hz)
3
Filter, FS[9:0] = 5, Average by 16)
0
–10
–20
–30
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–60
–70
–80
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–100
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–120
15 0 0
Figure 65. Filter Response for Average + Decimate Filter
Simultaneous 50 Hz and 60 Hz rejection is also achieved by
using an FS word of 96 and averaging by 16, which places a
notch at 50 Hz. Setting the REJ60 bit to 1 places a notch at
60 Hz (see Figure 66). The output data rate is reduced to
2.78 Hz with this configuration, but the rejection is improved
to 94 dB typically at 50 Hz ± 1 Hz and 60 Hz ± 1 Hz.
0
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–20
–30
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150
–110
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0
Figure 66. Filter Response for Average + Decimate Filter
Rev. 0 | Page 49 of 56
30 60 90
FREQUENCY (Hz)
3
(Sinc Filter, FS[9:0] = 30, Average by 16)
30 60 90
FREQUENCY (Hz)
3
(Sinc Filter, FS[9:0] = 96, Average by 16)
AD7194
120 15 0
120 150