SBASAK4B March 2023 – April 2024 ADS127L21
PRODUCTION DATA
For selected data rates, the sinc3 and sinc4 filters offer the option of a cascade sinc1 filter section. Compared to a single-stage sinc3 or sinc4 filter, cascading the sinc1 filter shortens latency time when operated at the same data rate. However, sinc3 and sinc4 filters provide greater rejection of 50Hz and 60Hz interference signals because of the wide frequency-rejection range at the data rate frequency. When operated in cascade mode, the OSR of the sinc3 or sinc4 stage is fixed at 32 (OSR = A). The decimation of the sinc1 stage (OSR = B) determines the output data rate. The first stage of the cascade filter is programmable to sinc3 or sinc4. Table 7-17 summarizes the cascade filter characteristics.
MODE | fCLK (MHz) |
OSR (A × B)(1) | DATA RATE (SPS) |
–3dB FREQUENCY (Hz) | LATENCY TIME (μs) | |
---|---|---|---|---|---|---|
SINC3 + SINC1 | SINC4 + SINC1 | |||||
Mid speed | 12.8 | 13334 (32 × 417) | 480 | 212 | 2097 | 2102 |
Mid speed | 12.8 | 16000 (32 × 500) | 400 | 177 | 2512 | 2517 |
Max speed | 32.768 | 26656 (32 × 833) | 614 | 271 | 1632 | 1634 |
High speed | 25.6 | 480 | 212 | 2089 | 2091 | |
Low speed | 3.2 | 60 | 26.5 | 16708 | 16728 | |
Max speed | 32.768 | 32000 (32 × 1000) | 512 | 226 | 1958 | 1960 |
High speed | 25.6 | 400 | 177 | 2506 | 2509 | |
Low speed | 3.2 | 50 | 22.1 | 20048 | 20068 | |
Mid speed | 12.8 | 48000 (32 × 1500) | 133 | 58.9 | 7512 | 7517 |
Mid speed | 12.8 | 80000 (32 × 2500) | 80 | 35.4 | 12512 | 12517 |
Max speed | 32.768 | 96000 (32 × 3000) | 170.6 | 75.4 | 5864 | 5866 |
High speed | 25.6 | 133.3 | 58.9 | 7506 | 7508 | |
Low speed | 3.2 | 16.7 | 7.37 | 60048 | 60068 | |
Max speed | 32.768 | 160000 (32 × 5000) | 102.4 | 45.3 | 9770 | 9772 |
High speed | 25.6 | 80 | 35.4 | 12506 | 12508 | |
Low speed | 3.2 | 10 | 4.42 | 100047 | 100067 |
Figure 7-26 illustrates the frequency response of the sinc1 cascade mode filter with the first stage in sinc4 mode for OSR = 26656 and 32000. These OSR values represent fDATA = 50SPS and 60SPS in low-speed mode operation. Nulls in the frequency response occur at n · fDATA, n = 1, 2, 3, and so on. At the null frequencies, the filter has zero gain. Assuming no ADC clock frequency error, the normal-mode rejection is 34dB (typical) over a ±2% signal frequency variation at the filter null frequencies.