Analog, RF & amp; EMCconsiderations in printed wiring board design

Abstract

Recent advances in digital and analog technologies have presented new challenges to the design of Printed Wiring Boards (PWBs). As clock frequencies approach the L-Band region, digital designers are now faced with considerations that were once only viewed as analog/RF concerns. These considerations include dielectric loss, skin effects and impedance matching. High dynamic range analog components also present unique challenges concerning noise immunity and stability. The presentation covers the construction of PWBs including topics related to stack-up (one layer, two layer and multi-layer), copper weight, copper roughness and material selection. In discussing material selection, both electrical properties (permittivity, loss tangent, resistivity, voltage breakdown, etc.) and mechanical properties (glass transition temperature, thermal conductivity, coefficient of expansion, etc.) are covered. Although rigid PWBs are the main focus, flex PWBs are also reviewed. In regard to signal distribution on PWBs, various single-ended routing options, which are implemented both in micro-strip and strip-line, are examined. In addition, various edgecoupled and broadside-coupled differential structures are presented. These differential structures can also be implemented in both micro-strip and strip-line. Signal integrity issues involving impedance matching, coupling and dispersion are presented, along with potential solutions to these issues. Lastly, power distribution and grounding considerations are explored. Besides reviewing the inductance, capacitance and resistance of power/ground planes, the power handing capability of traces is also reviewed. Guidelines are discussed for selecting and connecting local power decoupling components. Throughout the lecture, sample calculations, simulation results and empirical data are presented as reference to reinforce the concepts covered. Several physical PWB samples are also distributed for viewing, to further supplement the lecture. This presentation is intended for analog/RF, EMC and digital engineers.