Calibrating the 2-Port Probe for Low Impedance PDN Measurements
May 18, 2021
Benjamin Dannan and Steve Sandler
"High speed printed circuit board (PCB) design requires well designed power delivery networks (PDN) to support today's FPGAs or custom mixed-signal ASICs. The PDN contains important impedance information that can offer the designer insight into how a system will react to dynamic currents. The PDN is the transmission line connecting the voltage regulator module (VRM) and the load, making the VRM a good starting point for a successful PDN design.
Vendor information for a VRM’s output impedance is not always provided, and when it is provided it may not be accurate. Further, measuring ultra-low impedance on multiple VRMs, or a multi-topology DC-DC regulator, is a challenge for many design engineers. The 2-port shunt-through measurement is the gold standard for measuring a VRM’s output impedance in the milliOhm and sub-milliOhm region ; however, it is not always possible to make these measurements without including dedicated RF connectors on the PCB or device under test (DUT). Therefore, when a designer makes these types of measurements with a vector network analyzer (VNA), the method of connecting the DUT requires attention to detail to ensure inductance is minimized to allow an accurate measurement..."
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