Question on Modeling multiple ground regions with mentor calibre

[abcyin]

Hi, all,

I'd like to analyse the substrate noise coupling with mentor calibre, which supports this function as "modeling multiple ground regions", but the calibre user manual doesn't tell me how to make it, so could anyone has this kind of experience on how to extract this parasitics with this software? any suggestions are welcome.

Thanks in advance,
abcyin

 

[slizak]

When you say "how to make it", what exactly are you referring to, the layout? The basic SVRF file? I checked the "Modeling Multiple Ground Regions" section and it is pretty clear about what rules you need to add to your already-existing file. And the run would be just the same as usual (well, assuming you do parasitic extraction modes other than -rc).

The parasitics to the different substrate regions show up as coupled capacitance between the net and the region; that is why you need to mark the regions and add those layers to the CONNECT statement. (Like it says in the manual -- "The steps result in ground regions "above" a global ground. When you extract, intrinsic capacitance goes to the named ground regions; grounded coupled capacitance goes to the global ground.")

-Sam.

 

[abcyin]

Thanks very much for your kind reply,

I am using Calibre PEX to extract the parasitics, I am not sure about how to "mark the regions and add those layers to the CONNECT statement" as you said.
For example in my layout, there are two grounds named GND_1 and GND_2, should I use the CONNECT statement like:
CONNECT GND_1 GND_2

And what about the "PEX GROUND LAYER" statement and "PEX EXTRACT FLOATING NETS" statement? how to add them into the rule file? could you please give me an example?

thanks in advacne,
abcyin

 

[slizak]

I am using Calibre PEX to extract the parasitics, I am not sure about how to "mark the regions and add those layers to the CONNECT statement" as you said.
For example in my layout, there are two grounds named GND_1 and GND_2, should I use the CONNECT statement like:
CONNECT GND_1 GND_2

To mark the regions, in the layout there should be some layers (GND_1 and GND_2, presumably) that will have polygons indicating the different ground regions. If there are various layers/names (happens frequently with IP), you can collect them in an SVRF LAYER statement -- just be sure not to mix ones at different levels.

For the connection, somewhere in the SVRF file(s) there should be a CONNECT statement already, or xRC won't run. (Nor will LVS, for that matter.) The CONNECT statement defines the electrical connectivity. Normally ground layers aren't listed, but the way xRC models the multiple ground regions separately is by treating them as a type of conductor at the bottom level, just above true ground.

And what about the "PEX GROUND LAYER" statement and "PEX EXTRACT FLOATING NETS" statement? how to add them into the rule file? could you please give me an example?

If you have access to the SVRF file (some places restrict end-users to the GUI interface), just add PEX GROUND LAYER GND_1 GND_2 somewhere near the rest of the parasitics rules. A good bet is to find where the parasitic extraction rules are included (typically "INCLUDE rules.R" and/or "INCLUDE rules.C" -- those are the default file names), and add the statement near there so you can be sure of being in the right combination of #IFDEF and other control logic that most places add to the rule file.

If you are in the GUI, you add them in the PEX Options pane. (This is hidden by default; you can make it visible with Setup > PEX Options.) Go to Netlist, then look for the Format tab. There should be a field, "Ground layer name", where you add the layers that indicate the different ground regions.

PEX Extract Floating Nets is optional. If you only care about the parts of the ground regions that interact with signals, you don't need this. Same if you just want "not otherwise accounted for" to be treated as ground -- that is the default behavior. If you use this statement, you'll also be getting nets for all your fill in the netlist, which causes really long run times. Also, if there is text on the ground regions, they won't be treated as "floating nets" anyhow. All these disclaimers aside, the statement would probably look like PEX EXTRACT FLOATING NETS REDUCED or PEX EXTRACT FLOATING NETS ALL. ("Reduced" will only include them if they affect signal nets; "ALL" makes sure to put them in the netlist even if they do nothing. **broken link removed** in the SVRF manual attempt to show this schematically.) Notice this statement does not take layer names -- everything not a signal net gets the same treatment. In the GUI, look for "Extract floating nets" in the same tab as "Ground layer name".

Good luck with all this. Oh, and the instructions also assume you are using a relatively current version of Calibre. I think the GUI added the fields in 2009 or 2010, and the SVRF statements were created 2007.2 and 2008-ish. There are some technotes on SupportNet still about how to do it for the old versions, but the one I found assumes your parasitic rules are unencrypted.

-Sam.