Do the analog and digital portions need different power supplies?

[Emma Frost]

I'm trying to design a pcb that connects the input of the DAC to a nucleo board with an stm32 and the output connected to a RF mixer. I have a 3.3v regulator, 5v regulator, and a 1.8 v regulator. In the below circuit diagram. it looks like the analog and digital power supplies even for the same voltage are different and isolated from each other. Is this a necessity? If so, how can I achieve this on a circuit that has only one input (12V) and I'm using tutuapp vidmate different voltage regulators for different circuit components. Thanks for your input.

[grayb]

Very interesting post!