ZHCSGA6A February 2017 – June 2017 ADS114S06 , ADS114S08
PRODUCTION DATA.
The low-pass nature of the sinc3 filter establishes the overall frequency response. The frequency response is given by Equation 8:
where
The sinc3 filter offers simultaneous 50-Hz and 60-Hz line cycle rejection at data rates of 2.5 SPS, 5 SPS, and 10 SPS. The sinc3 filter offers only 50-Hz rejection at data rates of 16.6 SPS and 50 SPS, and only 60-Hz rejection at data rates of 20 SPS and 60 SPS. The sinc3 digital filter response scales with the data rate and has notches at multiples of the data rate. Figure 69 shows the sinc3 digital filter frequency response normalized to the data rate. As an example, Figure 70 shows the frequency response when the data rate is set to 10 SPS, and Figure 71 illustrates a close-up of the filter rejection of 50-Hz and 60-Hz line frequencies. For more detailed frequency response plots, download the ADS1x4S0x design calculator from www.ti.com.
Table 14 gives the bandwidth of the sinc3 filter for each data rate.
Frequency normalized to data rate, sinc3 filter |
fCLK = 4.096 MHz, sinc3 filter |
fCLK = 4.096 MHz, sinc3 filter |
NOMINAL DATA RATE (SPS)(1) | –3-dB BANDWIDTH (Hz)(1) |
---|---|
2.5 | 0.65 |
5 | 1.3 |
10 | 2.6 |
16.6 | 4.4 |
20 | 5.2 |
50 | 13.1 |
60 | 15.7 |
100 | 26.2 |
200 | 52.3 |
400 | 105 |
800 | 209 |
1000 | 262 |
2000 | 523 |
4000 | 1046 |
As mentioned in the previous section, filter notches and output data rate scale proportionally with the clock frequency and the internal oscillator can change frequency with temperature.