Design of Extreme Connector Stacking in PCI Express Interface

This paper describes the electrical architecture and design of the PCI express interface in the Blade Centertrade (J.E. Hughes et al., 2000) system. A comprehensive electrical design methodology, including accurate and detailed modeling and simulation of the complete design space, is required in order to achieve the speeds required by this interface, while using low-cost printed circuit board materials. In this paper, some of the obstacles and solutions to support 2.5 Gb/s to 5 Gb/s data transmission over multiple boards and multiple connector technologies are highlighted. Pre-layout analysis was performed to predict the interconnect performance for relatively long trace lengths in FR-4 material across four connectors in order to satisfy the PCI express design requirements and guarantee the overall performance objective of the system. Signal integrity affects (including frequency dependent losses, inter-symbol-interference (ISI), crosstalk, impedance discontinuities, via and pad capacitance effects and skew) were integrally analyzed across the complete design space. The solution provided was stack connector arrangements integrated into the PCI express link. The benefit was greater density, but a product that could be customized. This paper concludes the correlation between a post route simulation result and lab measurements. The correlation of simulation results with hardware measurements provided a high confidence in the simulation methodology, which could be relied upon in developing the broader set of PCB based design guidelines.