April 9, 2007 -- As field-programmable gate arrays have evolved into true programmable systems-on-chips, the task of designing the printed-circuit boards on which these chips are used has become more complex. Multimillion-gate densities, transceiver data rates above 6Gbps and other considerations affect the mechanical and electrical board-design efforts of system developers. The die, chip package and board form a closely coupled system in which careful pcb design is needed to fully realize the capabilities of an FPGA.

When using high-speed FPGAs in a design, it is important to consider several design issues both before and during board development. They include reducing system noise by filtering and evenly distributing sufficient power to all devices on the pc board; properly terminating signal lines to minimize reflections; minimizing crosstalk between board traces; reducing the effects of ground bounce and Vcc droop (also called Vcc sag); and properly matching impedances on high-speed signal lines.

By Joel Martinez. (Martinez is senior product marketing manager for high-density FPGA products at Altera Corp.)