Q. What is the benefit of the post filters versus the standard sinc filters?
A. In industrial applications, many customers require 50/60 Hz rejection but require the minimum settling time. Ideally, customers would like a settling time of 20 ms i.e. the customer could sequence through multiple channels with each channel producing a valid conversion in 20 ms. This is difficult to achieve while still attaining good 50/60 Hz rejection.
The post filters offer a compromise between these 2 parameters. A standard sinc3 filter has a settling time of 60 ms when operating at an output data rate of 50 sps while offering sim 50/60 Hz rejection. The rejection at 50/60 Hz is 66 dB. The post filters can operate at an output data rate of 25 sps, with the settling time being approximately equal to 40 ms. The 50/60 Hz rejection is 62 dB. So, the rejection is a little worse than the sinc filter. However, it is still at an acceptable level for industrial applications and the settling time is 50% less.