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Length matched lines in a PCB Take a look at two signal readouts on an oscilloscope, and you can see how length/timing mismatches between signal traces can improperly trigger downstream gates. The situation becomes worse when we look at the travel time for a master clock signal and the roundtrip time for sent/received data in different computer interfaces. SDRAM has solved this nicely by placing a clock in the slave device and sending a clock...

Do you know the transmission line critical length for these traces? Whether you are working with digital or analog signals, you’ll most likely need to match impedances between a source, transmission line, and load. The reason impedance matching is important in transmission lines is to ensure that a 5 V signal sent down the line is seen as a 5 V signal at the receiver. If you understand why transmission line matching is important, you can start...

The image above shows a snapshot of results from an EMC test under CISPR requirements (U.S. uses FCC certification requirements). This product is right at the edge of Class B limits on radiated emissions. We can see a very complicated resonance spectrum in this plot with a large number of sharp peaks superimposed on wide peaks at lower level. What causes all of this radiated noise? There a number of sources that can cause this type of emission...

Define a hierarchy for schematic designs In PCB design, organization is critical, and it takes a bit of experience to anticipate when you will need to use flat vs. hierarchical schematics. When I started working on one of my first projects, and as my design continued to grow in size and complexity, it quickly became obvious that I would never be able to fit all my components and connections into a single schematic, and it became extremely...

Signal integrity analysis and measurements go hand-in-hand I remember the first time I—back in my days of working with sensors—pumped nitrogen dioxide into a humid environmental chamber while evaluating a DUT. Over time, the surface of my copper leads slowly corroded as they sat unprotected in such a noxious environment. As my electronics experiment was living a double life as a chemistry experiment, I questioned whether to use a conformal...

We often write about signal integrity and power integrity around here, but there is one area where we sometimes fall short: test and measurement. Both aspects of building a new device are critical for ensuring your board will work as intended and meets stringent performance requirements. With advanced systems, the level of testing and measurements required to qualify a prototype for full-scale production spans far beyond using a multimeter. Pow...