Equivalent mixed-mode characteristic impedances for differential signal vias

• Published in: 2009 IEEE International Symposium on Electromagnetic Compatibility pp. 74 - 79
• Main Authors: Siming Pan, Jun Fan
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.08.2009
• Subjects: Capacitance; Coupling circuits; differential via structures; equivalent mixed-mode characteristic impedances; Impedance; mode conversions; multi-conductor transmission line; multi-layer PCBs and packages; Multiconductor transmission lines; Packaging; Power transmission lines; Propagation constant; Signal design; signal integrity; Transmission line theory; Transmission lines
• ISBN: 9781424442669; 1424442664
• ISSN: 2158-110X; 2158-1118
• DOI: 10.1109/ISEMC.2009.5284632

Differential signal via structures in multi-layer printed circuit boards (PCBs) and packages are studied using an equivalent coupled multi-conductor transmission-line model. Thus, easy-to-understand transmission-line concepts, such as mixed-mode characteristic impedances and propagation constants, can be used to characterize the performance of differential signal via structures in a signal path. The closed-form expressions of per-unit-length parameters in the equivalent coupled multi-conductor transmission-line model are derived based on a physics-based via circuit model with parallel-plane impedances and via-plate capacitances. Mode conversions are discussed for different via structures. Effects of geometrical parameters on equivalent differential via impedances are studied in the paper as well. The proposed method provides a straightforward approach to design differential via structures for better signal integrity.