(PCB)How Do Ground Planes Work?

Discussion in 'Homework Help' started by naf456, Dec 12, 2012.

  1. naf456

    Thread Starter New Member

    May 24, 2012
    7
    0
    Hi, Nathan here.
    In my PCB development lesson we are building a voltage buffer which creates a stable flow of electricity to some logic circuits.
    We were going through grounding the input supply voltage and the output to the ground plane on are PCB (the copper area that aren't going to be milled out for the circuit)

    How does this work? How does connecting the circuit to the copper plane of the board get rid of fault current/ground the circuit? - it's not connected to earth in anyway?

    I'm not sure how earthing works.

    another example is a guitar - on my guitar , all the earths are soldered to one of the tone pots - how does this connect to earth? / how does it work?

    Thanks for your time.
    Nathan.
     
  2. tshuck

    Well-Known Member

    Oct 18, 2012
    3,531
    675
    Occasionally, we refer to what should be called a common as ground. Ground sounds nicer, so we say it. Really this is a common - a point which all other voltages are in reference to on your circuit(which may very well be much higher than earth ground). To clear up the confusion, a little, we usually say earth ground when referring to a circuit that has a reference to the earth(usually through a building's grounding).

    The ground plane - again, common unless it's specifically connected to earth ground - is useful in many circuits. It helps with RF circuits, heatsinking, ground loops, among other uses. Because copper is not a superconductor, it has a resistance associated with it, so a common connected trough a single copper trace will actually create a new voltage reference for anything using this common point as a reference. the problem comes when the circuits using the true common and the circuit using the other common connect. Since there is a voltage difference in the commons and a resistor, albeit a small one, formed from the copper trace, current will flow in simply using the commons! Bad news for a battery powered circuit! By creating a ground plane, the resistance of the copper drops considerably. This won't eliminate ground loops, but will minimize their influence on a circuit.
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,003
    3,232
    tusuck beat me to it but here's my take anyway.

    You are confusing "earth" ground with circuit ground. The circuit ground is just the common connection in the circuit where all the voltages are referenced. It may or may not be connected to "earth".

    Ideally the circuit ground should have no fluctuations in its voltage due to any currents through it (called ground bounce). This fluctuation problem voltage becomes worse for high current, high frequency, or fast rise-time signals. The best way to minimize these fluctuations on a PCB is to use one or more ground planes, as this has much lower resistive and inductive impedance as compared to a single wire or trace. Such planes are sometimes also used to distribute power for the same reason, to minimize voltage fluctuations.
     
  4. tshuck

    Well-Known Member

    Oct 18, 2012
    3,531
    675
    ...been a while since someone called me that!:p
     
  5. #12

    Expert

    Nov 30, 2010
    16,278
    6,791
    You never know about the really old guys like crutschow and audioguru. Sometimes they exhibit a sense of humor.
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,003
    3,232
    Sorry for the typo. :p
     
  7. naf456

    Thread Starter New Member

    May 24, 2012
    7
    0
    Ahh, it's been bugging me for ages, cheers.
     
Loading...