An Accurate Method For Measuring Capacitor ESL

Focus:

The equivalent series inductance (ESL) of chip capacitors is becoming an increasingly important parameter as bandwidths and switching frequencies rise in many high-performance systems. The stability and high-frequency dynamic performance of these systems is dependent, in part, on capacitor ESL. Manufacturers of ceramic and tantalum capacitors have been working hard to reduce the ESL of their components. However, system designers cannot simply rely on the capacitor vendors' published data for ESL, which is limited at best. It's important that designers be able to make their own ESL measurements. Yet, with values typically in the range of 1 nH to 5 nH, measuring the ESL of chip capacitors is not a trivial task. This article presents an ESL measurement method using a network analyzer in combination with an impedance adapter to measure the device impedance over frequency. This approach specifically addresses the issue of test-fixture parasitics, accurately measuring both the capacitance and inductance of the device under test. The procedure presented here for measuring ESL uses OMICRON Lab's Bode 100 network analyzer and B-SMC impedance adapter. Calibration and measurement procedures are described and test results are presented to verify the validity of the measurement setup and method. Finally, the author presents measurement results for a 1-uF ceramic chip capacitor, which is found to have an ESL of 730 pH.

What you’ll learn:

• How to measure ESL of chip capacitors using OMICRON Lab's Bode 100 network analyzer and B-SMC impedance adapter

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Author & Publication:

Steve Sandler, Picotest, Phoenix, Ariz., How2Power Today, Apr 29 2011

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