[PCB_FORUM] Re: Using an "Electrical CSET" vs a "Constraint Set" for diff pairs...

 

 

 

Gerry Meier, Sr. PCB Designer

Freedom CAD Services. Inc

Voice: (256)776-7470 or (603) 864-1350

Email:gerry.meier@xxxxxxxxxxxxxx

visit us at http://www.freedomcad.com

 

 

________________________________

From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Austin Franklin
Sent: Wednesday, March 26, 2008 2:52 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Using an "Electrical CSET" vs a "Constraint
Set" for diff pairs...

 

Hi Gary,

 

> I'm not sure how to handle a different trace width and spacing within
the pair for inner layers as opposed to outer layers.

 

I use Setup/Constraints and under "Physical (lines/vias) rule set" I use
"Set values..." and create a new Constraint Set Name, and set the values
for each layer there.  Close that, then use "Attach property, nets..."
and assign the attribute "NET_PHYSICAL_TYPE" to all the nets I want to
control with this constraint.

 

That's the only way to do different trace width/gap on different layers
that I know of in Allegro 15.2.  Is that what you were asking?

 

Unfortunately, I don't always have the luxury of having the same
width/gap for inner and outer layers.

 

Regards,

 

Austin

        -----Original Message-----
        From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx]On Behalf Of Macindoe, Gary
        Sent: Wednesday, March 26, 2008 1:18 PM
        To: icu-pcb-forum@xxxxxxxxxxxxx
        Subject: [PCB_FORUM] Re: Using an "Electrical CSET" vs a
"Constraint Set" for diff pairs...

        Hey Austin,

         

        You know, I've wondered about that. Luckily I haven't had to
deal with it yet.

        One reason is that lately I only have top and bottom as routing
layers.

        I think the last time I had inner layers, the stack-up was
designed to have the trace widths/spaces the same for inner and outer
for all impedances.

         

        Here's how I handle it now for only outer routing layers, on
15.5.1:

         

        -          I set up the diff pairs using Logic -> Assign
Differential Pair, Auto Generate

         

        -          I set the trace width, spacing etc. for the pairs in
CM

         

        -          I create a Spacing Constraint Set for each impedance
(i.e. "90DIFF" for USB) with the "Line To Line" set to the spacing
required pair to pair

         

        I'm not sure how to handle a different trace width and spacing
within the pair for inner layers as opposed to outer layers.

         

        I would suggest, if you can, to design the stack-up to have the
widths and spacings the same for outer and inner.

        That's the easy way out!

         

        Maybe setting up constraints, including diff pairs, is easier in
16, I hope so.

         

        Good luck, I'm curious to see if anyone has the solution to
this.

         

          

        Gary E. MacIndoe
        PCB Design Engineer
        Fort Collins, Colorado

        amd.com

        gary.macindoe@xxxxxxxxxxxxxxxxxxxx Message-----
        From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Austin Franklin
        Sent: Wednesday, March 26, 2008 12:39 PM
        To: icu-pcb-forum@xxxxxxxxxxxxx
        Subject: [PCB_FORUM] Using an "Electrical CSET" vs a "Constraint
Set" for diff pairs...

         

        Hi,

         

        There appear to be two ways to get the diff pair spacing and
gap, but only

        one allows differing them by layer.  Setting up an "Electrical
CSET" only

        seems to allow one overall (as in for all layers) space/gap.
But, the

        advantage of using the ECSET is you can assign it to a net or
multiple nets

        using the Constraints Manager spreadsheet using a pulldown menu.

         

        Or, I can setup a "Constraint Set" and select each layer's
space/gap...but I

        then have to attach this as a property to each and every net
manually by

        selecting the nets and attaching this Constraint Set name as a

        NET_PHYSICAL_TYPE attribute.

         

        I prefer the Constraint Set, since it gives me the per layer
control...but

        the thing that seems to be missing, is the ability to assign a
given

        Constraint Set to the nets using the Constraint Manager
spreadsheet.

         

        I'm on 15.2.  Am I missing something?  If not, has this improved
on 15.7 or

        16?

         

        Regards,

         

        Austin

         

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