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AR# 37016

Virtex-6 FPGA GTX Transceiver - What value of external AC coupling capacitor is required?

Description

Most applications that use the Virtex-6 GTX Transceiver require the use of an external AC coupling capacitor. This Answer Record discusses the acceptable values for this capacitor.

Solution

The Virtex-6 FPGA Data Sheet notes that the typical value for the AC coupling capacitor is 100 nF.This is a good guideline for the line rates supported by the GTX Transceiver, but does not preclude the use of other values depending on the application. For example, PCIe recommends a capacitor in the range of 75-200 nF and the GTX User's Guide has use cases that recommend 10 nF. In the end, it is up to the board designer to understand the requirements based on the line rate and transition density in determining the capacitor to use.
AR# 37016
Date Created 07/27/2010
Last Updated 01/28/2013
Status Active
Type General Article
Devices
  • Virtex-6 SXT
  • Virtex-6 CXT
  • Virtex-6 HXT
  • Virtex-6 LXT