Analog and digital ground for PCB layout.

Discussion in 'General Electronics Chat' started by vrvrao, Oct 31, 2012.

  1. vrvrao

    Thread Starter New Member

    Sep 17, 2012
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    0
    Hello,

    I am new with pcb layout and am using Eagle Cad.

    I have 6 (-15 v to 15 v ) sources from inverter output and i am using an opam to convert them in 6 ( 0 - 3 v) sources using LT1632 with an reference voltage of 5v and 24 V dc supply.


    I am attaching pic of my schematic , my issue is at bottom of pic around Con_in.

    I am stuck with problem of grounding i used a schottkey diode for 24 v dc source for dc grounding and 0.1uF for -15 v to 15v supply.

    Please let me know whether it is ok .
     
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  2. nigelwright7557

    Senior Member

    May 10, 2008
    487
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    Its vital you keep the power supply separate from the audio ground and only join them once at the star ground.
    The main problem comes from the power supply capacitors having very short but high current pulses on them, these can feed into the audio if you are not careful.
     
  3. crutschow

    Expert

    Mar 14, 2008
    12,981
    3,221
    It's always good to use a ground plane, if you can. But you should split the plane for analog and digital, and only connect them together at one point.
     
  4. vrvrao

    Thread Starter New Member

    Sep 17, 2012
    20
    0

    The Ground plane mentioned here, does it mean the polygon which we use, or a separte layer for ground.

    If it is a separate layer, do we need to mentioned at the time of sending layout to manufacturer or do weed to create a layer in eagle.

    Can you please let me know
     
  5. ScottWang

    Moderator

    Aug 23, 2012
    4,852
    767
  6. crutschow

    Expert

    Mar 14, 2008
    12,981
    3,221
    It's is indeed a separate (near) continuous layer of copper on the board which you create as a separate layer in Eagle. It is labeled as ground and all ground connections are automatically made to it by Eagle. The manufacturer just builds what is on the layout so you don't have to make any particular mention of that.

    I also like to flood the area between traces on other layers and use that as a ground also.
     
  7. vrvrao

    Thread Starter New Member

    Sep 17, 2012
    20
    0

    Thanks Crurschow,

    Sorry to ask this again, how can we define an individual layer for Ground, i have an eagle edition which allows 6 layers. I know how to use a polygon but i couldn't find, how can we define a layer for ground.

    Also,i have a doubt can we use different layers for different sources, as my ckt operates at high frequency i taught we can reduce some noise using this way.
     
  8. crutschow

    Expert

    Mar 14, 2008
    12,981
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    Sorry, I haven't worked with Eagle so don't know how they specify a layer to be ground, but I'm sure there is a way.

    Try an Eagle forum or their website for help.

    Edit: Not sure what you mean by "different sources". :confused:
     
  9. MrChips

    Moderator

    Oct 2, 2009
    12,418
    3,355
    You have to decide ahead of time how many layers you are creating.
    I have never made multi-layered board except double sided.
    When I need a ground plane (which is now every time) I make the entire bottom layer the ground plane. You draw a polygon on the bottom layer (blue) and name it GND, the same name as your GND in your schematic net.

    You can run traces and vias as you wish on the bottom layer and Eagle will take care of the flood. I set isolation to 0.016".
     
  10. vrvrao

    Thread Starter New Member

    Sep 17, 2012
    20
    0
    Thanks Crutschow,

    Different sources i mean , Digital and analog ( Ac or DC).

    To reduce the intereferenece between them, i was thinking to have separte layers for different sources with a ground layer in between.
     
  11. vrvrao

    Thread Starter New Member

    Sep 17, 2012
    20
    0
    Thanks MrChips,

    I never had experience with multi layer.For now i have done in the same way as u explanined above.

    But, there in an point raaised like wht about the mutual interference b/w two sources, then some one said like we can have differenet layers of sources with a ground layer in between, which will reduce interference.


    So, i want to know is it possible to do that way. It is , then i need any refference to do.
     
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