Fixture-free measurement technique for PDN discrete components

Ceramic capacitors are small in body size and have good high frequency performance. They are widely used in electronic designs, including RF impedance matching, DC blocking, and as decoupling capacitors in a Power Distribution Network (PDN). It is essential to accurately characterize the capacitor behavior over a broad frequency band to achieve successful system design and validation. The capacitor characterization/modeling method that is widely used in industry requires fabrication of a test board [1-4]. Then a de-embedding process is applied to get the impedance of the capacitor. This paper describes a fixture-free measurement based capacitor modeling methodology, which is low cost and can quickly provide results. The method consists of two major steps, measurement of the capacitor under test, and postprocessing of the measured data to produce a capacitor model. In the measurement step a two-port measurement has been applied rather than one-port measurement because of better noise immunity and port impedance match. The impact of probing locations on the resulting capacitor model was investigated, concluding that the probes should be placed close together at the center of the capacitor. The postprocessing of the measured capacitor impedance is done to generate single-, dual-, and multiple-branch equivalent circuit models along with S-parameter models. This capacitor modeling process has been performed on capacitors used in PCB design. Results for a small-sized 01005 capacitor, a reverse geometry 0204 capacitor, and a special high Equivalent Series Resistance (ESR) capacitor are shown as examples in this paper. Finally, a PDN measurement versus simulation comparison is shown to demonstrate how using capacitor models generated with the fixture-free method improves correlation. This method can also be applied to the characterization of other 2-port components, such as discrete filters and resistors.