Confusing symbol on schematic files

Thread Starter

abc14

Joined Oct 15, 2017
123
Hi Guys,


Probably a very basic question I have seen this strange symbol very often on schematics but don't really understand what is it for.

1594131839044.png
 

Irving

Joined Jan 30, 2016
815
And if it's really critical both traces should be the same length, so every left turn should ideally be matched by a right turn, if not possible use the absolute minimum possible spacing between the tracks.
 

andrewmm

Joined Feb 25, 2011
399
Route them as diff pairs, as in properties of these tracks should match each other ?
Tracks on a pcb have an impedance defined by how they are arranged above / below a ground reference.

For "slow" speed logic, the impedance matters little. as speed increases, the tracks behave more as a component, having an impedance. The impedance depends upon the track size, its closeness to a reference and the Er of the PCB.

https://www.signalintegrityjournal.com/blogs/12-fundamentals/post/1665-what-is-differential-impedance-and-why-do-we-care

https://www.multi-circuit-boards.eu/en/pcb-design-aid/impedance-calculation.html


One way of routing signals is differential.

where two signals are sent, as one side goes up in voltgae, the other goes down. At the receiver, that difference is then taken , thus any interference that's common to both tracks is minimised.

Differential signals tend to be close to each other, and relatively far from a reference. Thus these have a differential impedance.

Dr Johnson is "the" expert
http://www.sigcon.com/Pubs/news/2_30.htm


As the signal speed goes up, they behave more like RF, and things like anti pads, ground return vias track electrical length matching become more critical.

I'd suggest you get a book on high speed PCB tracking.

these might help in mean time.

https://www.nxp.com/docs/en/application-note/AN2536.pdf

https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/an/an224.pdf

https://www.analog.com/en/analog-dialogue/articles/high-speed-printed-circuit-board-layout.html
 

Thread Starter

abc14

Joined Oct 15, 2017
123
Hi routed by differential pairs using Eagle's differential routing as follows, I had to make a slight modifications to include the resistors on the tracks. But Hopefully its still good ?


1594642960592.png
 

Irving

Joined Jan 30, 2016
815
I would have turned resistors 90deg so you can get them closer to connector. Take out that 90deg bend in the lower set & try to follow the same route as the upper ones, maybe drop them down a bit. Is pin allocation on connector a given? If not swap pins on upper tracks for easier routing.
 

Thread Starter

abc14

Joined Oct 15, 2017
123
I would have turned resistors 90deg so you can get them closer to connector. Take out that 90deg bend in the lower set & try to follow the same route as the upper ones, maybe drop them down a bit. Is pin allocation on connector a given? If not swap pins on upper tracks for easier routing.

I have improved a bit, I don't think you can change pins on connector, its a standard RJ45 HR911105A connector.



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