ZHCSES1B March 2016 – October 2018 ADS1282-SP
PRODUCTION DATA.
The sinc filter is a variable decimation rate, fifth-order, low-pass filter. Data are supplied to this section of the filter from the modulator at the rate of ƒMOD (ƒCLK/4). The sinc filter attenuates the high-frequency noise of the modulator, then decimates the data stream into parallel data. The decimation rate affects the overall data rate of the converter; it is set by the DR[2:0] register bits, as shown in Table 5.
Equation 8 shows the scaled Z-domain transfer function of the sinc filter.
DR[2:0] REGISTER | DECIMATION RATIO (N) | SINC DATA RATE (SPS) |
---|---|---|
000 | 128 | 8000 |
001 | 64 | 16000 |
010 | 32 | 32000 |
011 | 16 | 64000 |
100 | 8 | 128000 |
Equation 9 shows the frequency domain transfer function of the sinc filter.
where
The sinc filter has notches (or zeroes) that occur at the output data rate and multiples thereof. At these frequencies, the filter has zero gain. Figure 37 shows the frequency response of the sinc filter and Figure 38 shows the roll-off of the sinc filter.