• SMA Connector Layout

    greg07/18/2019 at 03:44 0 comments

    SMA connectors are quite common for high speed interconnect in applications like this and you would think there would be plenty of app notes or examples to copy, but I was surprised how difficult it was to find a suitable reference to copy.  I did find some information online to point me in the right direction.  One issue I wanted to address was the fact that the pad for the signal pin is significantly wider than the trace width for a 50 Ohm trace.  This article by Dr.  Howard Johnson describes some techniques to deal with this ( http://www.sigcon.com/Pubs/edn/TaperedTransitions.htm ) I'm not going to go full tapered, but I did round the pad and cut away a little off the plane below to reduce the effect of the transition. 

  • The Tool

    greg07/18/2019 at 03:11 0 comments

    The lazy engineer in me has become a little too dependent on upverter and they have recently hosed me with their major system update that left several of my projects stranded, so I am finally making the long overdue effort to wean myself off and switch to KiCad.  

    One of the techniques I want to use is curved traces which should make the impedance more consistent, especially since I won't necessarily be able to hit it perfectly.  I discovered that KiCad does not support curved traces, but fortunately Seth Hillbrand presented a technique to work around this at KiCon.  It is a bit of a kludge and a little painful but usable for the number of corners I need.  It sounds like real support for curved traces is coming to KiCad, so we shouldn't need to do this much longer.

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  • Project goals and strategy

    greg07/18/2019 at 03:05 0 comments

    The purpose of this project is to build a USB Type-C breakout board to facilitate the evaluation of boards designed to utilize the super speed differential pairs.  This is intended to be a cost effective alternative to the commercial breakout boards.  To keep this accessible to makers, I am designing this to be fabricated at OSHPARK to see what performance I can get with there standard 4 layer stackup.  I'm designing the board to be as small as possible to keep the price down and the traces short.  It should be a little easier to keep the traces short and matched now that vertical plugs are available ( https://www.digikey.com/product-detail/en/jae-electronics/DX07VN24WA2C1568/670-3103-ND/9695489 )  I don't have access to 3D field solvers, nor the time or patience to use them, so I will take be using my best engineering judgement, over-design a little and use every rule of thumb I can find.