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Defining power supply symbols

markbeck

I'm trying to do something which is common in BiPolar analog design, but not as much in CMOS design.  I'm trying to figure out how to create a symbol which will allow me to define a net's connectivity when placed upon that net. 

For example:
I have a schematic and symbol which have VCC and VEE defined as ports (Note: they are defined as ports to make power supply modeling easier).  To make the schematic more readable, I wish to place instance symbols which represent VCC and VEE inside the schematic which will connect those nets to the actual VCC and VEE power ports.

I know that it is possible, and I think that it was done in the past using netset, but I can't seem to find any information about netset which doesn't pertain to defining a global power and ground supply (something that I do NOT want).

Any ideas?
Mark

 

  •  Ok, I think that I figured out how to do what I was trying to do.

    1. Create the symbol
    2. Add a port
    3. Add a net expression on the port (e.g. vdd = vdd!)- the global name will be overridden...
    4. Then, in the CDF add the netSet (vdd = vdd)

    This appears to work the way that I wanted.

    The only issue that I see is when I instatiate the instance, there is a big error message, but once I do a check-n-save it works fine.

     Mark

  •  Hum... spoke a bit too soon. While this works in the schematic I'm running into an issue with netlisting. The stupid symbols are trying to be netlisted as instances.

     I set the nlAction=ignore in the CDF parameters, but they are still showing up.  I had to create a dummy spectre view just to keep the netliser happy, but they are showing up in the netlist.

    Setup:
    I have a library cell with a symbol and spectre view.
    In the CDF, I have set:
      Name        Prompt  Type    DefaultValue
      vdd            vdd        netSet vdd
      nlAction     nlAction string   ignore

    The netlist is being created, and the instances that have a vdd port on them do have vdd set in the netlist, so that part is working correctly.  Now I just need nlAction to work.

     Running IC6.1.5.504

    Any ideas?
    Mark

  • Ok, figured that last one out myself....

    The right way is to not create a spectre view, but to create a schematic view (which is just a copy of the symbol).  When I did this, it all worked as expected.

    Maybe I should emote less?

    Mark

  • Ok, while the above method worked, I was still getting warnings in the CIW when netlisting.

    I found that the nlAction = ignore needed to be added as a property to the schematic (It has no real effect inside the CDF parameters).  Then everything worked as desired (as far as I can tell today)

     sigh...

     

  •  So I'm back to mucking with this stuff again and I'm running into an issue:

    If I place one of the power supply symbols on a net, it works fine. However, if I also place a label on that net it overrides the netset property (probably by design). 

    Does anyone know if there is there a way to get the behavior that a global net has in winning (or at least complaining when doing a check ) over a label?  If I create a symbol with a ! name (e.g. vdd!), it will always complain if you try placing a label on that  net as well. However, if I do that on a netset net, it doesn't complain and blithely accepts the label's name.

    Mark

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