Retro CPC Dongle – Part 25

What’s wrong with this picture? (Impedance matching and other things)

It’s about time we talked about high speed signals, impedance matching and signal reflections.  Take a look at this picture:

(Very) close up view of the captured CPC screen

There is something clearly wrong with the image above, the pixels are all there and the colours are almost right, but what you’re seeing above isn’t what was sent from the FPGA. What I think I’m seeing here is signal trace length skew and signal reflections.

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Working with Surface Mount Components and BGAs

Surface mount PCBs (Part 2 –  BGAs)

In my first post I described the process of reliably soldering surface mount components to create sophisticated and high density PCBs.   Many of the really exciting components are only available in a Ball Grid Array (BGA) package.  Think of ARM processors, high density memory, and Field Programmable Gate Arrays (FPGA).  These complex devices can have too many connections to the silicon to use a traditional Small Outline Package (SOP) or Quad Flat Pack (QFP).   On high pin count QFPs the pins are so narrowly spaced that solder bridges are common and pins are far to easy to bend and damage. Ironically BGAs are easier to work with in this regard as they are intrinsically far more resistant to damage prior to mounting.

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Working with Surface Mount Components and BGAs

Surface mount PCBs (Part 1)

If you look at a circuit board today, you’ll see a beautiful array of surface mount chips and components, including very fine 0.5mm or even 0.4mm leaded devices and BGAs.  Some of these ‘exotic’ devices can contain really advanced technology such as high speed ARM microprocessors, flash and high capacity memory, and FPGAs.  If you’re like me, you’ve looked at these boards and wished that you could produce circuit boards of such fine detail at home, and build projects with these exciting technologies.  Well, I’m here to tell you that it’s not as difficult as it looks.

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