Datasheet

Frequency(Hz)
Gain(dB)
0
-50
-100
-150
0 10 20 30 40 50 60 70 80 90 100
(a)
Frequency(Hz)
(b)
Gain(dB)
-50
-100
-150
494846 47 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64
DataRate=10SPS
DataRate=10SPS
ADS1131
SBAS449C –JULY 2009–REVISED OCTOBER 2013 www.ti.com
FREQUENCY RESPONSE
The ADS1131 uses a sinc
4
digital filter with the
frequency response. The frequency response repeats
at multiples of the modulator sampling frequency of
76.8kHz. The overall response is that of a low-pass
filter with a –3dB cutoff frequency of 3.32Hz with the
SPEED pin tied low (10SPS data rate) and 11.64Hz
with the SPEED pin tied high (80SPS data rate).
To help see the response at lower frequencies,
Figure 4(a) illustrates the nominal response out to
100Hz, when the data rate = 10SPS. Notice that
signals at multiples of 10Hz are rejected, and
therefore simultaneous rejection of 50Hz and 60Hz is
achieved.
The benefit of using a sinc
4
filter is that every
frequency notch has four zeros on the same location.
This response, combined with the low drift internal
oscillator, provides an excellent normal-mode
rejection of line-cycle interference.
Figure 4(b) zooms in on the 50Hz and 60Hz notches
with the SPEED pin tied low (10SPS data rate).
Figure 4. Nominal Frequency Response Out To
100Hz
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