When there are multiple digital / analog function blocks in the PCB, why should the digital / analog
The reason for separating the digital / analog ground is because the digital circuit will generate noise in the power and ground when the high and low potentials are switched. The size of the noise is related to the speed and current of the signal.
If the ground plane is not divided and the noise generated by the digital area circuit is large and the analog area circuit is very close, even if the digital and analog signals do not cross, the analog signal will still be disturbed by ground noise. In other words, the digital-analog ground non-division method can only be used when the analog circuit area is far from the digital circuit area that generates large noise.
Another method is to ensure that the digital / analog signal is separated and the digital / analog signal traces do not cross each other. The entire PCB board is not divided, and the digital / analog signal is connected to this ground plane.
The requirement for digital-to-analog signal traces not to cross is because the return current path of the faster digital signal will try to flow back to the source of the digital signal along the ground near the bottom of the trace. If the digital-to-analog signal is routed, Cross, the noise caused by the return current will appear in the analog circuit area.