Spectre Netlisting Multiple Instance Resistors

Hi Kevin,

The best way to achieve this is to have a Schematic PCell which takes care of producing the series or parallel connected structure and that then means that everything will behave, albeit with an extra level of hierarchy (of course, PCell Designer would help with that ). It would also be possible to write a custom netlist procedure for the spectre netlister to write multiple instances into the netlist (as the approach for the CDL netlister you link to proposes), but there's a downside with that since annotation and probing of currents etc becomes problematic because there's nothing for the tools to know that there is a one to many mapping from the schematic device to what ends up in the netlist (and hence the simulation results). Given a choice, I'd definitely go for the Schematic PCell approach.

There are a few netlist procedure examples (for example here - one I picked somewhat at random), but I don't think there are any articles that show doing this to create multiple instances (although it wouldn't be hard using the documented nl functions), even though I don't think it's the best approach.

Regards,

Andrew

I found an easy way to fix this but I'm having an LVS issue with the linked procedure due to the way the instance creation handles the instance term order. This doesn't seem to be controlled by the port order property in the symbol or the term order specified in the in the base CDF. However it creates an issue because the default ordering is the alphanumeric sorting default first sorted by pin type. It's easy enough to modify the script to get the right terminal but I'd rather force the instance to have the terminal order I want as it seems a little dangerous to leave that to chance. To be specific what I'm referring to is this property:

schView = dbOpenCellViewByType("kbu_edatrial" "lvs_check" "schematic" "" "r")
inst=nth(1 schView~>instances)             ;This is an instance of the customized resistor

If I request inst~>instTerms~>name it shows the default alphanumeric ordering (B MINUS PLUS) and inst is what gets passed to the function ansCdlGetSegmentConnections. Is there a way to control this instance order? If I open the properties in the schematic it shows the order I want in the system menu (PLUS MINUS B). The pin order in the symbol shows MINUS PLUS B so that doesn't seem to control the ordering on instances.

I found an easy way to fix this but I'm having an LVS issue with the linked procedure due to the way the instance creation handles the instance term order. This doesn't seem to be controlled by the port order property in the symbol or the term order specified in the in the base CDF. However it creates an issue because the default ordering is the alphanumeric sorting default first sorted by pin type. It's easy enough to modify the script to get the right terminal but I'd rather force the instance to have the terminal order I want as it seems a little dangerous to leave that to chance. To be specific what I'm referring to is this property:

schView = dbOpenCellViewByType("kbu_edatrial" "lvs_check" "schematic" "" "r")
inst=nth(1 schView~>instances)             ;This is an instance of the customized resistor

If I request inst~>instTerms~>name it shows the default alphanumeric ordering (B MINUS PLUS) and inst is what gets passed to the function ansCdlGetSegmentConnections. Is there a way to control this instance order? If I open the properties in the schematic it shows the order I want in the system menu (PLUS MINUS B). The pin order in the symbol shows MINUS PLUS B so that doesn't seem to control the ordering on instances.

Sorry I should have specified the pin types to make this more clear:

So B gets placed first because it is type 'input' and then MINUS and PLUS follow with the alphanumeric sorting.

I found a SKILL function that makes it easy to build the netlist the way I want without caring what the instance terms look like. Maybe this would be an improvement to the existing solution?

procedure(ansCdlGetSegmentConnections( inst connectionPairs iterSeg iterMult
 numSegments multiplicityFactor 
 segmentConnType netCount )

let( ( pairList )
 ;For series connections the procedure varies depending on which segment
 ;is being processed. In all cases the bulk connection remains the same.
 if( "series" == segmentConnType
 then 
 cond( 
 ;For the first segment the plus connection remains the same as in the schematic and
 ;the minus connection gets a new net name sNet with the netCount appended to it.
 ( (1 == iterSeg )
 pairList = list(
 car(setof(x connectionPairs car(x)=="PLUS"))
 list( caar(setof(x connectionPairs car(x)=="MINUS")) sprintf( nil "%s_sNet_%d" inst~>name netCount) )
 list( caar(setof(x connectionPairs car(x)=="B")) cadar(setof(x connectionPairs car(x)=="B")) )
 )
 )
 ;For the last segment the minus connection remains the same as in the schematic
 ;and the plus connection gets connected to the previously processed segment.
 ( ( iterSeg == numSegments )
 pairList = list(
 list( caar(setof(x connectionPairs car(x)=="PLUS")) sprintf( nil "%s_sNet_%d" inst~>name netCount-1) )
 car(setof(x connectionPairs car(x)=="MINUS"))
 list( caar(setof(x connectionPairs car(x)=="B")) cadar(setof(x connectionPairs car(x)=="B")) )
 )
 ) 
 ;For intermediate segments the plus connection gets connected to the previously processed
 ;segment and the minus connection gets a new net name with the netCount appended to it.
 (t
 pairList = list(
 list( caar(setof(x connectionPairs car(x)=="PLUS")) sprintf( nil "%s_sNet_%d" inst~>name netCount-1) )
 list( caar(setof(x connectionPairs car(x)=="MINUS")) sprintf( nil "%s_sNet_%d" inst~>name netCount) )
 list( caar(setof(x connectionPairs car(x)=="B")) cadar(setof(x connectionPairs car(x)=="B")) )
 )
 ) 
 ) 
 ;For parallel connections the terminals are identical to the schematic for all parts
 else 
 pairList = list(
 list( caar(setof(x connectionPairs car(x)=="PLUS")) cadar(setof(x connectionPairs car(x)=="PLUS")) )
 list( caar(setof(x connectionPairs car(x)=="MINUS")) cadar(setof(x connectionPairs car(x)=="MINUS")) )
 list( caar(setof(x connectionPairs car(x)=="B")) cadar(setof(x connectionPairs car(x)=="B")) )
 )
 )
 ;Return the list of connections for this segment
 pairList 
 ) 
 )