Design PCB consideration for mixed sig

Discussion in 'General Electronics Chat' started by aamirali, Dec 4, 2012.

  1. aamirali

    Thread Starter Member

    Feb 2, 2012
    In MCU, I have analog & digital ground. But both are powered from same 7805 regulator.How to design pcb so that there is min interference b/w two ground.
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    A very good way is to use what is called a "star" ground because of the appearance of the connection. Pick a place near the 7805 like where the output cap joins the ground, and bring *every* component ground on a separate trace back to that point.

    Have too many wires there? Then divide the circuit into sub circuits, and lead each section back to the star.

    Still to many? Divide the circuit into analog and digital sections, connect each section to a ground, then lead these two wires back to the 7805.

    What is most useful here is to imagine what currents are flowing in what traces. Say you have a clock signal, an image of that will be going thru ground. The longer the trace the more voltage will appear across the trace, but if you connect past the trace you don't get any bounce.