[PCB_FORUM] Re: Diff pair Constraints and CM
- From: "Austin Franklin" <austin@xxxxxxxxxxxx>
- To: <icu-pcb-forum@xxxxxxxxxxxxx>
- Date: Thu, 10 Mar 2005 19:13:12 -0500
Hi Kevin,
I think the diff pair constraints work in the CM best if you have the 600
series tool that has automatic impedance adjustment for different layers.
I'm still not sure that necessarily works well either...as fabricators like
to give you the trace/space, not have you determine them.
Regards,
Austin
> -----Original Message-----
> From: Kevin McCowan [mailto:kmccowan@xxxxxxxxxxxxxx]
> Sent: Thursday, March 10, 2005 5:13 PM
> To: icu-pcb-forum@xxxxxxxxxxxxx
> Subject: [PCB_FORUM] Re: Diff pair Constraints and CM
>
>
> Well, I guess I opened a can of worms, didn't I?
> What I have done to circumvent this issue is to
> get a stackup that has the same width and space for
> all internal layers and not allow the pairs on the
> outside of the board where it is difficult to get
> them the same.
> I agree with everyone (and it seems like it was everyone!)
> as to how to do them with different rules on different
> layers. I just found my way to allow me to use the diff
> pair constraints.
> Sorry for any confusion.
>
> Kevin
>
> Austin Franklin wrote:
> > Hi Andrew,
> >
> >
> >>This is not necessarily true for diff pair stuff, when you have
> >>different widths and spacing for different layers. For instance, outer
> >>layers tend to have different spacing characteristics than inner layers
> >>(not always.. but for the point of illustration).
> >
> >
> > I just did things this way...
> >
> >
> >>In this case, you would NOT enter the values in the Electrical
> >>constraints/Diff pair area, but back in Physical constraints, where
> >>we're all used to doing it. The important thing here is that you would
> >>simply leave those entries blank in the Electrical constraints/Diff pair
> >>setup.
> >
> >
> > Ah, this I did not do. I'll review what I did based on this,
> thanks! Which
> > takes precedence? If I enter it in the EC/DP set-up, and I
> have an outer
> > layer value set different in PC, which value will it use for the outer
> > layers?
> >
> > Regards,
> >
> > Austin
> >
> >
> >
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