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AR# 62527

UltraScale and UltraScale+ GTY and GTH: how to set the CDR to "lock to local reference clock"

Description

Some popular applications such as oversamplers require that the Clock Data Recovery (CDR) be locked to "local reference clock".

This means that the Phase Interpolator (PI) is frozen and should not be driven by the CDR.

Another request is that the equalization frequency response be as "flat" or transparent as possible.

It is not possible to bypass the Continuous Time Linear Equalizer (CTLE), however the following solution provides a preferred CTLE and AGC configuration.

Solution

For GTY and GTH transceivers, you can apply the setup below to have the CDR always locked to the local oscillator:

1) use LPM mode

  • RXLPMEN = 1b1

 2) CDR configuration

  • RXCDRHOLD = 1b1

  • RXCDROVRDEN = 1b0

3) LPM, CTLE configuration

  • RXLPMLFHOLD = does not matter

  • RXLPMLFKLOVRDEN = 1

  • RXDFELPM_KL_CFG0 = 0

  • RXLPMHFHOLD = does not matter

  • RXLPMHFOVRDEN = 1

  • RXLPM_KH_CFG0 = 0

 

Note: the LPM Gain Control (GC) is always fixed.

AR# 62527
Date 10/19/2018
Status Active
Type General Article
Devices
  • Virtex UltraScale
  • Kintex UltraScale
  • Virtex UltraScale+
  • Kintex UltraScale+
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