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
ADS1231
www.ti.com SBAS414D –JULY 2009–REVISED OCTOBER 2013
FREQUENCY RESPONSE
The ADS1231 uses a sinc
4
digital filter with the
frequency response shown in Figure 17 for f
CLKIN
=
4.9152MHz. 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 17(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,
thus providing excellent normal-mode rejection of
line-cycle interference.
Figure 17(b) zooms in on the 50Hz and 60Hz notches
with the SPEED pin tied low (10SPS data rate).
The ADS1231 data rate and frequency response
scale directly with clock frequency. For example, if
f
CLKIN
increases from 4.9152MHz to 5.5296MHz when
the SPEED pin is tied high, the data rate increases
from 80SPS to 90SPS, while the notch also increases
from 80Hz to 90Hz. Note that these changes are only
possible when an external clock source is applied.
Figure 17. Nominal Frequency Response Out To
100Hz
Copyright © 2009–2013, Texas Instruments Incorporated Submit Documentation Feedback 11
Product Folder Links: ADS1231