I was reviewing the schematic of a motor driver board and noticed that the digital and analog grounds are tied together with a 3.9 ohm 1/4 watt resistor. I am still trying to find the gerber files to see how the ground plains are laid out, but does anyone know why this would be done instead of using a 0-ohm resistor or just connecting them in the copper?
My first thought was that it was an attempt at some sort of noise suppression but this doesn't seem like something that would be very effective at doing that. Feel free to speculate, because for now I'm at a loss.
EDIT: The analog ground feeds back to a 24V supply off the board and the digital ground feeds back to a 5V supply off the board. At each of the power connectors there are several decoupling capacitors. However the resistor is by noneof the connectors and the respective capacitors.