Determining your optimum geometry, plus two methods for providing data to the fabricator.

Controlling impedance (resistance) is almost a given with today’s technology. One day we are adding a wireless option to a common object and calling it the Internet of Things. The next day we’re simply keeping up with the competition on processing the code. The trend is toward a greater percentage of the connections falling under the domain of impedance control.

Controlled impedance has two main branches: Single-ended transmission lines are the backbone of RF technology, while differential pairs do the heavy lifting for digital circuits. We’ll start with the single-ended lines. They have a start and an end point. The signal is sent one way on the transmission line, and the circuit is completed over the adjacent ground plane.

The main factor influencing impedance is the width of the trace relative to the thickness of the dielectric material between the trace and the ground plane – or planes – used as a reference. What is a reference? It is usually a metal plane with zero volts – “ground” but can have a few volts of its own, either positive or negative relative to what’s happening on the trace itself.

Keeping some margin on the table increases the chances of immediate success and leaves a little bit for later.

There are many more ways to constrain a PCB layout than when I started my journey as a semi-intelligent designer. Guardrails were put in place to smooth transition into fabrication once the layout is completed. The other thrust of newer rules concerns the shrinking timing budget of our digital interfaces, particularly the memory banks.

We have so many aspects we can control that it can be tempting to disable or ignore some of them. That is a completely rational choice to make. New features take time to learn and implement. It may not be so easy to get everyone on board for a new feature or a whole new iteration of the software.

I remember getting buy-in to move up to a different whole number revision of the ECAD tools by reminding the team we didn’t have to use any of the new features and could go on using the tool exactly as before. It’s easy to get comfortable with what you have if that gets the job done to everyone’s satisfaction.

What we do is observed by many of the people around us. A narrow focus ends with the various EEs and your management team. Truly satisfying everyone takes a much wider view of the situation. Who is watching? Practically the whole company – and then some.