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Design007-Aug2018

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58 DESIGN007 MAGAZINE I AUGUST 2018 Article by Chang Fei Yee KEYSIGHT TECHNOLOGIES This article studies the impact of dielec- tric thickness on crosstalk for transmission lines in single-ended and differential mode on outer (microstrip) and inner (stripline) PCB layers. Crosstalk analysis is performed in 2D simulation and S-parameters are subsequently observed. Introduction to Crosstalk Crosstalk is an unintentional electromagnetic (EM) field coupling between transmission lines on a PCB. This phenomenon becomes a major culprit in signal integrity (SI), contributing to the rise of bit error occurrence in data com- munications and electromagnetic interference (EMI). With the existence of mutual inductance and capacitance between two adjacent trans- mission lines on a PCB, crosstalk has become more severe due to the shorter signal rise/fall times at today's higher data speed rates. With reference to Equation 1, crosstalk can be minimized by routing the PCB traces fur- ther apart and reducing the dielectric thickness between PCB trace and reference plane [1, 2] . We will observe how a PCB's dielectric thick- ness affects the signal crosstalk. All crosstalk analyses are carried out in 2D simulation using Mentor's HyperLynx. Equation 1: D = Spacing between PCB traces H = Dielectric thickness between PCB trace and reference plane Analysis of Crosstalk in 2D Simulation In this study, eight 2D transmission line models in single-ended and differential mode on outer (microstrip) and inner (stripline) PCB layers are constructed based on varying PCB dielectric thickness. Figure 1 depicts the cross- talk simulation topology for each transmission line model (i.e., single-ended mode) listed in Table 1. The transmitting and receiving ends of

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