While trying to reduce the overall noise level on some boards I’ve been working with, I was looking for a reliable way to first measure the noise level and figure out how best to address the problem.  If you can’t measure or visualize it, it’s hard to fully understand it and reliably fix it!   Looking for a solution to measure the quality of the GND planes, etc., I came across this helpful appnote from Analog Devices: Measuring Ground Noise.  They present a relatively straight-forward setup based on an AD620 instrumentation amplifier that can be used to characterize the GND plane on your boards.  The article is worth reading simply because it brings up something a lot of people don’t think about doing boards design: GND.  Particularly with high-speed design (anything greater than a few MHz), or with switching-mode power supplies, etc.,  it’s important to think about the return paths on your boards in addition to the signal transmission lines and part placement.  Howard Johnson’s High Speed Digital Design is probably the best book (that I know of!) on the subject, but I haven’t seen very many circuits showing how you can measure noise on the gnd plane, so I thought it was worth sharing the above PDF.