The modulator generates a bit stream that is processed by a digital filter to obtain a digital word similar to a conversion result of a conventional analog-to-digital converter (ADC). A very simple filter, built with minimal effort and hardware, is a sinc3-type filter, as shown in Equation 2:
This filter provides the best output performance at the lowest hardware size (count of digital gates) for a second-order modulator. All the characterization in this document is also done with a sinc3 filter with an over-sampling ratio (OSR) of 256 and an output word width of 16 bits.
An example code for an implementation of a sinc3 filter in an FPGA, see the application note Combining ADS1202 with FPGA Digital Filter for Current Measurement in Motor Control Applications (SBAA094), available for download at www.ti.com.