Original question:
The amplifier bandwidth was selected using trial-and-error simulation with amplifiers with different bandwidth. Beyond helping with amplifier bandwidth requirements, the charge bucket filter helps to minimize noise from the amplifier. The charge bucket filter is not a true antialiasing filter as its bandwidth is typically beyond the Nyquist frequency of the ADC. Nevertheless, it does help with some higher order alias signals. From a practical perspective this kind if filter is used in the vast majority of SAR drive. In the next revision of this content I would like to eliminate the slide you show. It is more important to realize that using the optimal filter for performance. The two pictures below show that both SNR and THD are impacted by the filter selection and there is an optimal filter value. I hope this helps.
Art
