The AC coupled variant of the 5764 can sample in the first and second Nyquist zones (the DC coupled variant has a 400 MHz anti-alias filter in the hardware so it is limited to the first Nyquist zone only). Since the AC coupled variant does not have any filtering you will need to add an external filter if you want to block frequency content that is present in the first Nyquist zone from aliasing into the second Nyquist zone, or vise versa.
Note that the frequency response of the 5764 is not as flat in the second Nyquist zone, as can be seen in Figure 8 in the datasheet, so be aware of this for your application. Also note that there is a software property for the 5764 where you must select which Nyquist zone you are using. The ADC on this module is an interleaving ADC that has a built in algorithm to reduce interleaving spurs. If they wrong Nyquist zone of operation is selected large interleaving spurs will be present in the frequency spectrum. The default Nyquist zone of operation is the first Nyquist zone, so you must change this property if you plan to use this device in the second Nyquist zone.
