Xilinx Virtex-4 RocketIO User Manual page 238

Chapter 9: Methodology Overview
frequency component in a coded stream is the longest run length allowed by the encoding
scheme.
Large value capacitors have larger body sizes, which can introduce sufficient shunt
capacitance and series inductance to filter the edges of the signal. A 0402 capacitor is
preferred for higher data rates, whereas 0603 capacitors are acceptable for lower data rates.
To improve performance, use smaller capacitor values in applications with higher data
rates. If the value is too small, the capacitor charges quickly and develops voltage across it
during long runs of consecutive zeros or ones, resulting in common mode voltage drift. A
larger capacitor value has less common mode voltage drift for the same run length due to
the larger RC time constant. Choosing capacitors with values much higher than required
can introduce more surge currents during board hot-swaps. Such surge currents can stress
MGT circuits.
238 www.xilinx.com Virtex-4 RocketIO MGT User Guide
UG076 (v4.1) November 2, 2008
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