9.3.6.1 Digital Filter Frequency Response
The digital filter provides many data rate options for rejecting 50-Hz and 60-Hz line cycle noise. At data rates of 2.5 SPS, 5 SPS, 10 SPS, and 20 SPS, the filter rejects both 50-Hz and 60-Hz line frequencies. At data rates of 16.6 SPS and 50 SPS, the filter has a notch at 50 Hz. At a 60-SPS data rate, the filter has a notch at 60 Hz.
For detailed frequency response plots showing line cycle noise rejection, download the ADS1x4S0x design calculator from www.ti.com.
Figure 47 to Figure 61 illustrate the frequency response of the digital filter for different data rates. Table 6 lists the bandwidth of the digital filter for each data rate.
Table 6. Digital Filter Bandwidth
NOMINAL DATA RATE (SPS)(1) |
–3-dB BANDWIDTH (Hz)(1) |
2.5 |
1.1 |
5 |
2.2 |
10 |
4.7 |
16.6 |
7.4 |
20 |
13.2 |
50 |
22.1 |
60 |
26.6 |
100 |
44.4 |
200 |
89.9 |
400 |
190 |
800 |
574 |
1000 |
717 |
2000 |
1434 |
4000 |
2868 |
(1) Valid for the internal oscillator or an external 4.096-MHz clock. Scales proportional with fCLK.
The digital filter notches and output data rate scale proportionally with the clock frequency. For example, a notch that appears at 20 Hz when using a 4.096-MHz clock appears at 10 Hz if a 2.048-MHz clock is used. The internal oscillator can vary over temperature as specified in the Electrical Characteristics table. The data rate, conversion time, and filter notches consequently vary by the same percentage. Consider using an external precision clock source if a digital filter notch at a specific frequency with a tighter tolerance is required.