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Troubleshooting Distributed Power Systems (Part 4): Measuring Impedance Using Vector Network Analyzers (Two-Port Tests) Focus: In the previous installment in this video series, Sandler discussed the benefits of using VNAs to measure the impedance of devices encountered in distributed power systems, providing details on how to perform and interpret one-port measurements. In this video, the focus shifts to making and interpreting two-port impedance measurements, particularly those in which the device under test is connected “in shunt through†with the VNA ports. Shunt through, wideband measurements can be made from approximately 100 microohms to a few ohms. This is the measurement performed by designers for the power distribution network (PDN) assessment of VRMs and POLs. This technique may also be used to measure the impedances of batteries, dc-dc converters, EMI filters, and other functions. Setup requirements such as 4-wire connections, a common-mode transformer, dc blockers, and ac versus dc coupling are explained in this video. Also discussed is the use of a preamp to measure impedances below 1 milliohm. In addition, the video presents impedance measurement examples such as a POL output, a motherboard PDN and a 250-microohm resistor.
What you’ll learn: - How to understand the impedance measurement capabilities of VNAs in the two-port test configuration and what aspects of the test setup influence measurement accuracy
- How to measure the output impedance of a point of load regulator
- How to measure extremely low values of impedance
View the Source
Author & Publication: Steve Sandler, AEi Systems and Picotest, Phoenix, Ariz, How2Power Today, Sep 16 2013
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