Measure PDN on a budget

by Steve Sandler, Picotest, EDN, Mar 18 2014

Focus:
Designing high-speed digital systems requires attention to the design of the power distribution network (PDN) that feeds power to the microcontrollers and FPGAs. An important aspect of designing a PDN is measuring its impedance in the frequency domain. For those new to this measurement, this short article discusses what impedance levels and frequency ranges are typically measured and what instruments are required to make the impedance measurements. Specifically, vector network analyzers or VNAs are required, and here the article discusses the dynamic range and bandwidth requirements for measuring PDN impedance. With that as background, the author describes the measurement capabilities of two low-cost VNAs, the Bode 100 from Omicron Lab and the S5048 from Copper Mountain Technologies. Together, these VNAs allow measurement of PDN impedances up to 4.8 GHz, which according to the author’s informal poll, covers the majority of PDN impedance measurements that engineers are making today.

What you’ll learn:

• How to understand instrument requirements for measuring the impedance of a power distribution network (PDN)
• How to make PDN impedance measurements inexpensively using low-cost vector network analyzers (VNAs)

Notes:
For more detailed instructions on how to make the PDN measurements, see the Troubleshooting Distributed Power Systems videos parts 2 and 3, in particular, which can be accessed at http://www.how2power.com/videos/index.php .

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