8.1.1 Digital Filter Usage

The modulator generates a bitstream 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). Equation 2 shows a sinc³-type filter, which is a very simple filter, built with minimal effort and hardware:

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 oversampling ratio (OSR) of 256 and an output word width of 16 bits.

An example code for implementing a sinc³ filter in an FPGA is discussed in the Combining the ADS1202 with an FPGA Digital Filter for Current Measurement in Motor Control Applications application note, available for download at www.ti.com.