Investigation On The Crosstalk Over Lossless And Lossy Substrate Of Printed Circuit Boards

With the coming of digital age,electromagnetic compatibility (EMC) is agrowing critical problem with electronic devices using the higher frequency,higher integration densities and more sharp signal rise-time. How to make thediversified electronic devices operation reliably in complicated and worseningelectromagnetic environment has spurred a lot of interest in recent years. Theelectromagnetic compatibility of printed circuit boards (PCB), which is thenecessary for electronic devices, can influence the performance of the devicesgreatly, so the electromagnetic compatibility investigation on PCB is a matterof great urgency.In this paper the EMC problems such as the electromagnetic interferencesuppression and optimization effectiveness of guard lines for victim lines andthe antenna effectiveness of PCB traces are investigated and the theoreticalmodels for analysis are extracted. The finite difference time domain (FDTD)method has been used to simulate the situation and the approach ofappropriate placement of guard lines is obtained. The contributions done inthis paper are as follows: 1. The FDTD models suitable for analysis of microstrip circuits areestablished,these models include various aspects such as 3-dimensionanisotropic perfectly matched layer(PML) absorbing boundary condition, theFDTD simulation of lumped element, the subgridding method and the nearzone to far zone transformation for radiation computation. 2. Under the assumption that conductor and medium are all lossless,influence of the parameters of guard lines on crosstalk between coupledmicrostrip lines is investigated, such as the diameter, spacing of via holes, theseparation between guard line and signal line and the permittivity of substratemedium. The larger diameter, the shorter separation between guard line andsignal line, and the smaller permeability, the lower the crosstalk. The spacingof via holes has little effect on crosstalk reduction but if the via spacing is toolarge resonance may occur in operation frequency. However, the resonancecan be avoided by ensuring that the spacing between the adjacent vias is lessthan half wavelength of the highest operation frequency component of thesignals in the aggressor lines. 3. The crosstalk suppression effectiveness of the height, length and thestart location of guard lines is investigated. The higher via holes, longer theguard line, the lower the crosstalk. The start location of guard lines hassignificant effect on near-end crosstalk and to reduce the crosstalk the guardlines should start from near-end.