Analysis and minimization of crosstalk in high-speed microstrip transmission lines

In printed circuits employing high-speed digital circuits, the interconnects can be considered as transmission lines. The dispersion effects in signals transmitted via such interconnects are of importance in crosstalk phenomena inasmuch as the amount of interline coupling (or crosstalk) in a symmetric, coupled microstrip version of interconnect depends on the difference between the frequency-dependent propagation constants pertinent to even and odd modes of lines. This dissertation is concerned with the studies on the distortion and coupling of transient signals propagating in a symmetric, coupled and lossy (dispersive) microstrip transmission lines. Both time as well as frequency domain characteristics are analyzed and relevant mathematical expressions are obtained vis-a-vis pulse signals on signal lines and coupling on sense lines. Fourier transform technique (FT) and spectral domain approach (SDA) are the methods used in the studies pursued. Specifically, an optimization technique to minimize crosstalk in multilayered, multitrace microstrip lines is developed. Typical simulation results are finished which indicate the feasibility of achieving a crosstalk reduction by 76% at a given distance of 40 mm from the source-end excited with a 25 picosecond gaussian pulse by optimization of the geometry of the structure appropriately. This technique is a new strategy for optimal design of high-speed, digital interconnections on a printed circuit board (PCB). The anomalous behavior of the crosstalk versus the pulse-width of a high-speed digital signal in a closely-spaced, parallel coupled microstrip line is presented. It is shown that depending on the pulse-width of a pulse signal, the space between two lines must be beyond a certain limit for a given strip-width (w) and strip-thickness (h) so that crosstalk can be reduced by spacing lines away. The relevant analysis indicates plausible reasons which cause the said anomalous characteristics of crosstalk. A transient signal propagating on a multilayered, coupled microstrip line with lossy substrates is characterized. Relevant computational algorithm is presented. The Cole-Cole diagrams depicting the odd and even mode complex permittivity versus frequency are evolved. The concept of Cole-Cole representation is applied to analyze crosstalk in a microstrip line. Typical simulations show some very interesting and useful results. This study is the first of its kind and has not been done earlier. Lastly, relevant to above research, logical inferences and conclusions are enumerated and the scope for future research is presented.