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With the multitude of signal integrity problems that can arise in real PCBs, how can the astute designer distinguish them all? Some problems are clearer than others, with specific signal integrity measurements being developed for testing and measuring particular aspects of signal behavior. One question that arises has to do with the appearance of a fluctuation in the output voltage on a banks of I/Os, known as simultaneous switching noise or...

An impedance matching network is important for power transfer and preventing reflections. Rather than looking at power transfer, voltages, and currents, RF engineers normally look at S-parameters to evaluate impedance matching circuits as 2-port networks. In particular, the relevant quantities for impedance matching are normally insertion loss and return loss, which can be calculated using S-parameters for a 2-port impedance matching network. Her...

Just like driver and receiver components connected to transmission lines, antennas need to be impedance matched to their feed lines. Some common matching schemes that also provide filtration are built as LC networks, where capacitors and inductors are placed as series and shunt elements in the antenna impedance matching network. With multi-band antennas, wideband antennas, or extremely narrow-band antennas, these networks can get quite...

With more devices running at faster edge rates and higher frequencies, power integrity can’t be considered separate from signal integrity. In any digital PCB design, the PDN needs to be carefully engineered to provide stable power with low transient ringing. The steps required in digital systems mirror those used in analog systems, but there are some exceptions in analog systems due to the very narrow analog signal bandwidth in these boards. Dig...

Anyone who has taken apart an old cell phone or designs IoT devices knows multiple communication capabilities are present in these designs, each requiring different antennas. The RF designer should already take precautions for interconnect isolation, but antenna isolation is just as important when modeling and designing wireless systems. The most basic antenna isolation technique simply requires placing antennas farther apart and designing the...

Crosstalk is a fundamental aspect of signal integrity, both in single-ended and differential trace. The spacing between signal lines with each routing configuration is defined using typical rules of thumb, which can be easily defined as design rules in your PCB design software. One rule of thumb for defining differential pair spacing between each trace is the “5S” rule, sometimes called the “5W” rule in application notes and other PCB design...

It every designer’s nightmare: you receive boards from your prototyping run, you power them up, and you suddenly find nothing works as expected. Even worse is a critical failure that causes a short, creating a beautiful plume of blue smoke and the familiar smell of burning plastics and resins. Where do you start when trying to locate problems in your new board? What tools do you need to investigate different types of failure? There isn’t always a...

Ever drive through a winding mountain pass? When I was a student, there was one back road that would wind back and forth as you ascended a small mountain. This style of paving roads is also used to route traces in PCBs. This routing style, called switchback routing, can be used for length matching/delay matching in replacement of, or alongside, other length tuning styles. With all the different length tuning and routing styles available in PCB...

Not all design rules are applicable in every situation, and they are often communicated without context. One particular rule for sizing traces is to always opt for wider traces when possible. Unlike many rules of thumb I’ve seen thrown about, this particular trace rule has some merit. However, when you need to control trace impedance and simultaneously reduce ringing, you need to carefully control the trace width to ensure transmission lines have...