Measuring ultra-low impedances (20 micro-ohm) is a challenge for any power distribution network (PDN) design engineer. The 2-port shunt-through measurement is the standard method for measuring milliohm impedances up to very high frequencies (GHz). Unfortunately, this measurement includes an undesirable ground loop related to the instrument grounds and test setup cabling. The ground loop introduces significant errors if proper care is not taken. This application note shows how to measure as low as 20 μΩ using the Picotest J2102A as a ground loop breaker.
After reviewing the differential impedance as well as the even or common mode, let’s now dive into the physical parameters of a differential pair.
aDuring PCB West, we met with Geoffrey Hazelett to discuss one of the most important PCB topics: impedance. Vice President Sales at Polar Instruments, he also explained the importance of understanding electromagnetic models, solutions of Maxwell’s equations in a two or three-dimensional environment, etc., and shared some insight on PI’s tools.
We previously quickly discussed signal reflection in our PCB Transmission Line series. This is an in-depth article about this very important topic that PCB designers should master. The first thing to remember is that reflections in transmission lines occur due to impedance discontinuity.
A transmission line should have a uniform characteristic impedance. Any variation or discontinuities to the impedance causes signal reflection and distortion. Continue reading “How Impedance Discontinuities Affect Signal Integrity”