High Speed PCB Design Considerations
by Lattice Semiconductor
The backplane is the physical interconnection where typically all electrical modules of a system converge. Complex systems rely on the wires, traces, and connectors of the backplane to handle large amounts of data at high speed. The communication between the various backplane modules depends on the inherent electrical characteristics such as impedance, capacitance, and inductance derived from connectors, trace lengths, vias, and termination, to name a few. An extremely important factor in designing a distributed-load high-performance backplane, is a basic understanding of the design practices used to ensure good signal integrity.
This technical note examines some basic differences in interconnection topologies. It describes the various issues that should be considered while designing a backplane and focuses on the critical aspects of point-to-point transmission lines that are run through a backplane. These aspects include PCB line structure, vias, device packaging and backplane connectors. A PCB design checklist is provided to aid the designer. Some frequency specific discussion and guidelines are given. This document also discusses Lattice Semiconductor's FPGA product line and its SERDES high-speed backplane interfaces. These provide high speed serial streams through CML differential buffers.