Tom McDonough’s scientific contributions

Vias can introduce impedance discontinuity, slow down signal edge rate, add jitter and reduce eye openings, and cause data misinterpretation by the receiver in high-speed channel. This paper presents the design and optimization of differential vias for high-speed serial ATA connection at the data rate of 6 Gb/s. First, differential vias on a specific stackup were modeled in the 3D full-wave solver HFSS. Second, via mechanical design parameters, including via stub length, antipad radius, capture pad radius, barrel radius, and spacing, were swept to study their impacts on impedance discontinuity using TDR impedance determined by simulation. Third, importance of differential via optimization was highlighted by case studies of two PCB transmission line connections with nominal and optimized differential vias respectively.

The speeds of computers need to increase. A limitation to increasing this speed is the layout design of printed circuit boards (PCB's). One of the critical limiting factors of the PCB is the orientation of differential capacitors with respect to one another. This paper determines the optimal orientation of these capacitors in order to reduce the return loss (DS11) from crosstalk as the speeds of computers rise to 20 GHz.

High-speed data transmission can suffer significant degradation after the signal has passed through a long transmission path. Proper design of PCB differential transmission pairs is one of the most important steps in creating a reliable serial ATA link. Based on a typical Intel 8-layer stackup, a design of 100 Omega microstrip and stripline differential pairs using empirical formulas and a 3D full-wave field solver is outlined in this paper.

This paper presents a systematic methodology to design a tunable inductor for potential applications of contactless couplers. The design applies the Ansoft software tool HFSS (High Frequency Structure Simulator) in conjunction with Microsoft Visual C++ programming to optimize an inductor's dimensions, e.g., number of trace turns, diameter of the wire, and diameter of the ferrite core. The proposed methodology was successfully applied to design a 200nH inductor at the frequency of 300 MHz.