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 Ground Plane split in PCB editor - Isolated ground plane creation 

Last post Mon, Jul 16 2012 12:39 PM by PCBdesigner100. 3 replies.
Started by PCBdesigner100 13 Jul 2012 12:14 PM. Topic has 3 replies and 4019 views
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  • Fri, Jul 13 2012 12:14 PM

    Ground Plane split in PCB editor - Isolated ground plane creation Reply
     I am new to PCB design. Designing a PCB which has isolated grounds. To create splitted ground I follow this procedure. 

    1. Run add line.
    2. In the Options tab, choose ANTI-ETCH class and the subclass where you want the split plane.
    3. In the Options tab, use the line width setting to control the clearance between the split planes.
    4. Add the line to indicate where the split is to occur. We suggest that the line endpoints extend
    beyond the ROUTE KEEPIN/ALL shape that is used as the basis for the split plane.
    5. Continue adding lines for the number of required split planes desired.
    6. Optional: run the split plane parameter command to indicate the fill style of the shapes on the split
    plane using split plane param.
    7. Run split plane create.
    The Create Split Plane dialog box appears.
    8. Enter the layer on which to create a split plane (should correspond to the layer chosen in step 2).
    9. Choose a Shape Type of dynamic or static.
    10. Click Create.
    The display centers on and highlights a shape and a net data browser appears requesting a net be
    assigned to the shape.
    11. Enter a net name you want associated with this shape.
    12. Continue net assignment for each shape that was created.
     
    But when I need any modification I dont know how to do it. I started with step 1 again. But it removes all past splits and starts with unspitted ground plane again. Please suggest how to modify the ground split or any other method to have the isolated ground plane.
     
    • Post Points: 35
  • Sat, Jul 14 2012 8:05 AM

    • oldmouldy
    • Top 10 Contributor
    • Joined on Tue, Jul 15 2008
    • Woking, Surrey
    • Posts 1,414
    • Points 24,150
    Re: Ground Plane split in PCB editor - Isolated ground plane creation Reply
    This method of dealing with shapes and splits is antiquated, take a look at the algroshapes.pdf in the doc\algroshapes directory of the installation and get the job done properly with positive dynamic shapes.
    • Post Points: 20
  • Sat, Jul 14 2012 7:57 PM

    Re: Ground Plane split in PCB editor - Isolated ground plane creation Reply
    Please consult the device manufacturer's data sheet for grounding guidelines. 

    Noise energy will always take the lowest impedance path back to the power source/regulator.  If an adjacent device sharing a signal net has a lower ground inductance path, the only way to prevent noise on signal lines is to improve ground fill coverage between vias/pins on the first device.  Keep anything that would increase the physical size of the current loop as small as possible.

    If you signficantly interrupt the ground plane under a high-speed net, you will increase the inductance(loop area) of the return path.  Periodically, a digital engineer asks me to isolate nets between domains.  The mixed-signal engineer adds small jumpers across this isolation to be cut..and restored during testing.  By the next rev, I have a single ground net again.

    Get familiar with Cadence's excellent return-path continuity DRC.   After all, you aren't using Mentor tools.

    High-voltage potential situations are really the only valid application for an isolated return net.  In aircraft equipment, devices that protect against lightning surges are intended to be robust and have their own return net to the air-frame ground (high-current ability and lowest impedance.)  

    • Post Points: 5
  • Mon, Jul 16 2012 12:39 PM

    Re: Ground Plane split in PCB editor - Isolated ground plane creation Reply
    Thanks a lot. It helped me.
    • Post Points: 5
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Started by PCBdesigner100 at 13 Jul 2012 12:14 PM. Topic has 3 replies.