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AR# 40278

Virtex-6 - GTX Duty Cycle Distortion (DCD) Constraint for REFCLK

Description

The Virtex-6 GTX Transceiver Reference Clock duty cycle specification is 45-55% as shown in Table 21 of the Virtex-6 FPGA Data Sheet for DC and Switching Characteristics. It was 40-60% for the Virtex-5 GTX Transceiver Reference Clock. Why is the Duty Cycle Distortion (DCD) more conservative for Virtex-6 FPGA?

Solution

If the reference clock has too much distortion, then it manifests itself as a modulation in the output of the PLL.
Most of the oscillators on the market for the SerDes-type applications have tighter Duty Cycle Distortion (DCD) specifications.
AR# 40278
Date Created 08/02/2011
Last Updated 12/15/2012
Status Active
Type General Article
Devices
  • Virtex-6 LXT
  • Virtex-6 SXT