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Impedance Measurements Evaluating EMC Components with DC Bias Superimposed Application Note Table of Contents Introduction... 1 About Ferrite Beads ... 2 Impedance Measurements with a Vector Network Analyzer... 4 E5071C ENA Network Analyzer ... 5 Sample VBA Program and Measurement Steps ... 5 Fixture Compensation ... 8 Measurement Results Under Actual Operating Conditions ... 11 Selecting Bias Tees ... 13 Summary... 14 Introduction Recent developments in semiconductor and communications technologies have accelerated the expansion of digital technology applications to more and more fields including home electronics and automotive parts and accessories. Meanwhile, in order to cope with ever-increasing amounts of data, the demand for higher communication speeds has been increasing daily. In addition, developers are faced with stricter electromagnetic compatible (EMC) and noise control requirements and the increasingly complicated challenge of meeting today's standards and needs for power saving, low voltage design, smaller components, etc. EMC/noise control requirements will continue to become stricter and stricter. Using ferrite beads as an example, this application note gives an overview on how to correctly evaluate EMC components in a way that satisfies these strict requirements. It also introduces various EMC measurement solutions. About Ferrite Beads Figure 1 shows the equivalent circuit of a ferrite bead. Figure 2 shows the fre- quency characteristics of two different ferrite beads. Unlike ordinary inductors, Ferrite beads have high frequency components that are mainly resistive. Since resistive components absorb noise and turn it into heat, ferrite beads are primar- ily used to rectify signal waveforms or reduce high frequency noise in power or signal lines. Figure 1. Equivalent circuit of a ferrite bead Impedance () 1500 1200 900 1600 300 0 1 10 100 1000 Frequency (Hz) Figure 2. Examples of frequency ch