I would like to implement a LED Matrix circuit like this one, where the LED matrix enclosed within the blue dots will be on a seperate PCB than the rest of the circuit.
Since this will be a multiboard design, I am confused whether ground lines should be passed between the matrix board and the main board to protect against EMI and signal integrity as suggested very well by the answers here and here.
If the boards don't share ground at all, then the return paths will flow directly between the shift registers and the mcu in the ground plane of the main board (not the matrix board). Which of course, will not stop the system from operating but will create huge current loops.
1) Is a very high speed multiplexing of the leds in the array considered "high frequency" in terms of its currents so that the return currents choose the path of least impedance underneath the rows and columns?
2) Should a ground trace per signal (in this case per row, or per column) be added in the connectors bewteen matrix board and main board?
EDIT: The design will be adjusted so that instead of a shift register, two multiplexer's will be used to switch between rows and columns and select a certain LED. Probably the ADG704 because of low Ton=20ns. This hopefully clarifies what range of frequencies I expect the system to operate at.