JAJSHV4C January 2014 – August 2019 ADS1283
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 fMOD (fCLK / 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, and is set by the DR[2:0] register bits, as shown in Table 7.
DR[2:0] REGISTER | DECIMATION RATIO (N) | DATA RATE (SPS) |
---|---|---|
000 | 128 | 8,000 |
001 | 64 | 16,000 |
010 | 32 | 32,000 |
011 | 16 | 64,000 |
100 | 8 | 128,000 |
Equation 9 shows the scaled Z-domain transfer function of the sinc filter.
where
Equation 10 shows the frequency domain transfer function of the sinc filter.
where
The sinc filter has notches (or zeros) that occur at the output data rate and multiples thereof. At these frequencies, the filter has zero gain. Figure 36 shows the frequency response of the sinc filter and Figure 37 shows the roll-off of the sinc filter.