Designing a custom Apalis SOM carrier based on the Ixora Reference schemaitc1.0 and Apalis Carrier Board Design Guide. The MXM3 SOM connector defines the area at pin numbers 303-321 for analog ADC, Touch and audio ports along with the related analog Vcc power and AGND. The Apalis Design Guide Figure 51 depicts the AGND pins directly connected to the regular GND plane, despite the AVcc LDO regulator referred to AGND in the same figure. The Ixora carrier 1.0 schematic shows the MXM connector X1A AGND pins 303,304,308 and 313 tied to AGND, The bead L21 is on another page near the AVcc LDO IC8 with a note that states the bead should be located close to the MXM connector AGND pins.
Is the direct connection to GND in fig 51 of the board design guide really a typo? According to the TK1 SOM datasheet, the AGND SOM pins are tied directly to the internal GND, thus rendering the external GND separation useless and possibly risky for EMI. Generally, great care is required when defining separate ground regions in a mixed-signal design, and is often discouraged by chip producers in order to avoid creating ground current loops that could generate EMI and other problems.