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60 DESIGN007 MAGAZINE I AUGUST 2018 the aggressor line are assigned as port P1 and P2. respectively, while the transmitting and receiving ends of the victim line are assigned as port P3 and P4, respectively. The coupled spacing and length between the aggressor and victim are set triple the trace width and 3 inches, respectively. These four transmission line models are created with medium-loss substrate material (i.e., 3.6 Dk and 0.01 Df). Each model has a trace thickness of .0012". Model 1A is set as microstrip, with a substrate thickness .003" and trace width .007" to achieve a charac- teristic impedance of 45.1 ohms. Meanwhile, model 1B has the same parameter setting as 1A except the substrate thickness is increased to .004" to achieve a characteristic impedance of 53.7 ohms. The substrate thickness of model 1B is increased by not more than .001" versus model 1A to limit the trace impedance of both models to within ±10% tolerance of the nomi- nal 50 ohms. The interest of this study is on varying substrate thickness, hence the other parameters of both model 1A and 1B shall remain the same. On the other hand, model 2A in Table 1 is set as a symmetrically centered stripline, with a trace width of .005" and a substrate thick- ness of .005" between the trace and upper/ lower reference plane, to achieve characteristic impedance of 45.7 ohms. Meanwhile, model 2B has the same parameter setting as 2A except substrate thickness between trace and upper/ lower reference plane is increased to .007", to help achieve characteristic impedance of 54.8 ohms (i.e., within ±10% tolerance of the nominal 50 ohms). By field solving the four-port simulation topology depicted in Figure 1, the S41 param- eter that represents far-end crosstalk of the transmission line models in Table 1 are plot- ted in Figure 2 (from 1MHz to 30GHz). Most data communication protocols in embedded systems are source synchronous, where high- speed signals propagate in the same direction at any one time. We are concerned about the ratio of induced noise at the victim's receiv- ing end to the injected signal at the adjacent aggressor's transmitting end (i.e., S41 param- eter). A more severe crosstalk is indicated by smaller absolute value in dB. With reference to Figure 2, across the wide- band up to 30GHz, the S41 for model 1A is about 3dB lower than 1B. Similarly, the S41 for model 2A is at least 8dB lower versus 2B. This result indicates that for both microstrip and stripline in single-ended mode, a thinner Figure 1: Crosstalk simulation topology for transmission line models listed in Table 1. Table 1: 2D transmission lines in single-ended mode for varying dielectric thicknesses modeled.