9.3.6.1.1 Low-Latency Filter Frequency Response
The low-latency 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 54 to Figure 68 show the frequency response of the low-latency filter for different data rates. Table 12 gives the bandwidth of the low-latency filter for each data rate.
Table 12. Low-Latency 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 |
718 |
2000 |
718 |
4000 |
718 |
(1) Valid for the internal oscillator or an external 4.096-MHz clock. Scales proportional with fCLK.
The low-latency 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. Note that 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.