Comment 12 for bug 593988

http://<email address hidden>/msg02746.html

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On Aug 26, 2013 5:15 AM, "lkcl" <email address hidden> wrote:

> On Mon, Aug 26, 2013 at 7:17 AM, jean-pierre charras
> <email address hidden> wrote:
> > Le 25/08/2013 23:30, lkcl a écrit :
> >> On Sun, Aug 25, 2013 at 5:15 PM, Lorenzo Marcantonio
> >> <email address hidden> wrote:
> >>> On Sun, Aug 25, 2013 at 02:42:22PM -0000, lkcl wrote:
> >>>> we *need* differential pairs in kicad, otherwise it will be necessary
> to
> >>>> go back to using proprietary software such as ORCAD and PADS.
> >>>
> >>> As Dick would say contributions are welcome...
> >>
> >> yehh i knowww... *sigh*. in c++ it's a bit heavy-going. i'll see
> >> what i can do in python,
> >
> > What is needed is an algorithm able to route differential pairs.
>
> except for vias (which need to be laid down also in pairs, so you
> need to violate the differential-track-separation for as short a
> track-length as possible whilst also ensuring that the vias are laid
> symmetrically) i think you'll find that treating a differential pair
> as "a track of width (2 x single-track + separation-distance)" should
> be absolutely fine as a first approximation.
>
> the layout systems i've used they allow flipping between the pairs:
> the cursor lays one of them and the other follows like a ghost, and
> you can choose which of the pair is the ghost. however i'd say it was
> much more intuitive to have the pair treated as if they were a single
> (wide) track, with the cursor tracking the mid-point between the two
> tracks.
>
> joining at the end to a pad-pair is a little strange: often because
> of going round corners one track will be slightly longer than another.
> the layout systems i've used will compensate for this right at the
> end by joining one of the tracks directly to one of the pad pair then
> "circling" the other track round the other one for a bit until the
> length is compensated for and _then_ bringing it in.
>
> i'd say that as a first iteration the joining should be done by hand,
> and even the via layout done by hand. just the differential pair
> routing (as if a single track) would be immensely helpful, even if
> it's only allowed to be on a single layer.
>
>
> >> although a priority right now is having a
> >> track-length measurer (i'm doing DDR3 tracks.... *by hand*. mad.
> >> completely mad)
> >
> > Is the track length displayed (since years) on the bottom of the frame
> > not working ?
>
> ah thank you! it took a while to find that, because it's
> context-sensitive. now i know what i'm looking for i've spotted it.
>
> l.
>
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> https://bugs.launchpad.net/bugs/593988
>
> Title:
> Differential pair track layout tool.
>
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