KiCad

high frequency tool

Asked by Alexandre Secchin de Melo

I need to make a PCB with DDR memory, so I have timing and impedance constraints. Does anybody know how to use the Kicad microwaves tools? What are the steps? I've not found anything in manual about it. When I try to use the tool "Create line to specified length for microwaves applications" (icon that resembles a serpentine) the result is a trace like a "u" letter and I don't know how to edit it.

Best regards,

Alexandre

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Lorenzo Marcantonio
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Best Lorenzo Marcantonio (l-marcantonio) said : 		#1

On Mon, Apr 01, 2013 at 10:55:57PM -0000, Alexandre Secchin de Melo wrote:
> I need to make a PCB with DDR memory, so I have timing and impedance constraints. Does anybody know how to use the Kicad microwaves tools? What are the steps? I've not found anything in manual about it. When I try to use the tool "Create line to specified length for microwaves applications" (icon that resembles a serpentine) the result is a trace like a "u" letter and I don't know how to edit it.

These are for another purpose, creating couplers and other passive
parasites in the GHz range (well, they could have some use if you
need to meander). There are currently no built-in tools for controlled
impedance routing other than 1) the calculator tool for knowing the size
and the spacing of the tracks and 2) the track length measurement shown
when selecting a track.

In short you have to do it yourself. IIRC you're lucky since DDR only
has one differential pair (the clock), so you mostly need to ensure that
all the tracks are of the same length (but there usually is a feedback
loop which should be exactly twice that...). Look in the datasheet of
your DDR controller for details.

It's very useful (nearly mandatory, I'd say) to define classes for the
controlled impedance tracks (especially for differential pairs, since
the clearance is mostly significant)

--
Lorenzo Marcantonio
Logos Srl

Revision history for this message
Alexandre Secchin de Melo (alexandresecchin) said : 		#2

Lorenzo, thank you so much for reply.

2013/4/2 Lorenzo Marcantonio <email address hidden>

> Your question #225645 on KiCad changed:
> https://answers.launchpad.net/kicad/+question/225645
>
> Status: Open => Answered
>
> Lorenzo Marcantonio proposed the following answer:
> On Mon, Apr 01, 2013 at 10:55:57PM -0000, Alexandre Secchin de Melo wrote:
> > I need to make a PCB with DDR memory, so I have timing and impedance
> constraints. Does anybody know how to use the Kicad microwaves tools? What
> are the steps? I've not found anything in manual about it. When I try to
> use the tool "Create line to specified length for microwaves applications"
> (icon that resembles a serpentine) the result is a trace like a "u" letter
> and I don't know how to edit it.
>
> These are for another purpose, creating couplers and other passive
> parasites in the GHz range (well, they could have some use if you
> need to meander). There are currently no built-in tools for controlled
> impedance routing other than 1) the calculator tool for knowing the size
> and the spacing of the tracks and 2) the track length measurement shown
> when selecting a track.
>
> In short you have to do it yourself. IIRC you're lucky since DDR only
> has one differential pair (the clock), so you mostly need to ensure that
> all the tracks are of the same length (but there usually is a feedback
> loop which should be exactly twice that...). Look in the datasheet of
> your DDR controller for details.
>
> It's very useful (nearly mandatory, I'd say) to define classes for the
> controlled impedance tracks (especially for differential pairs, since
> the clearance is mostly significant)
>
> --
> Lorenzo Marcantonio
> Logos Srl
>
> --
> If this answers your question, please go to the following page to let us
> know that it is solved:
> https://answers.launchpad.net/kicad/+question/225645/+confirm?answer_id=0
>
> If you still need help, you can reply to this email or go to the
> following page to enter your feedback:
> https://answers.launchpad.net/kicad/+question/225645
>
> You received this question notification because you asked the question.
>

Revision history for this message
Alexandre Secchin de Melo (alexandresecchin) said : 		#3

Thanks Lorenzo Marcantonio, that solved my question.