kicad-developers team mailing list archive

[Dick Hollenbeck <dick@xxxxxxxxxxx>]

On 04/16/2014 03:40 PM, Pierre Parent wrote:
> Hi,
> 
> Well, someone reported to me that he could ran a board only in slower DDR 
> timing because he did not do any  length matching.
> 
> Also olimex has done length matching in their board olinuxino maxi (enclosed 
> image), and we can find plenty of design guidelines about DDR(2,3) routing 
> speaking of length matching. Eagle and Altium include length matching tool. So 
> I'm not an expert but it is probably not just a joke when it comes to Ram 
> (don't know about USB).
> 
> Pierre.

I once used the microwave tool to generate a delay line for a clock signal, this was to
generate a fixed delay in a DDR RAM circuit on that one line only.  (This was 5-6 years
ago.  We still make that board.)  The output was a module, and I dropped that module onto
the board after I got it to be the correct length.

It did its job, but I think there was always a DRC error, because I did not put it into
the schematic.

Again, your tool will be useful.  Matching the data and address lines in a DDR design is
the big need these days.

We're asking the electrons to do more in less time, but they seem lazy.


Dick





> 
> 
> 
> Le mercredi 16 avril 2014, 22:01:06 Lorenzo Marcantonio a écrit :
>> On Wed, Apr 16, 2014 at 08:33:45PM +0200, Pierre Parent wrote:
>>> I've sent to production my first length matched board, here is a picture!
>>> I
>>> hope it will work!
>>
>> I did a board which contained an USB high speed hub (and an USB camera,
>> too). Didn't measure the impedance or looked at the eye pattern (no
>> equipment :P) but it worked. Luckily both TVS and common mode chokes
>> where designed to work with it, so no big meandering to do...
>>
>> So it should work your too.
>>
>>
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