Frequency-dependent characterization of bulk and ceramic bypass capacitors

Abstract

Power distribution networks (PDN) use various kinds of capacitors to create the required impedance profile and to suppress noise. The simple model of bypass capacitors is a series R-L-C network with frequency independent parameters. The paper gives measured data for various bulk and ceramic capacitors, showing the extraction procedure and frequency dependent data of all three parameters. Various physical contributors to the frequency dependencies are identified. From low frequencies up to SRF (series resonance frequency), capacitance can drop as much as 60%. Inductance should be measured in a small PCB fixture with planes, vias and pads representing the intended application. The added inductance due to the capacitor body is shown to be fairly independent of via length connecting to the nearest planes.