XAPP1252 (v1.3) April 12, 2019 1
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Summary
Burst-mode clock data recovery (BCDR) is a term describing a deterministic clock and data
recovery (CDR) method that can obtain symbol lock in a very short time. Without
augmentation, digital CDR methods, based on a bang-bang phase detector like the native CDR
circuit used by GTH and GTY transceivers, exceed the required lock times required by passive
optical network (PON) applications.
This application note describes how to implement a BCDR quick-lock circuit to provide fast and
bounded lock times to augment the native CDR circuit used by GTH and GTY transceivers in
Virtex® UltraScale™, Kintex® UltraScale, Virtex UltraScale+™, and Kintex UltraScale+ devices.
The BCDR quick-lock circuit is appropriate for use with PONs using the NG-PON2 or the
10G-EPON standard.
You can download the reference design files for this application note from the Xilinx® website.
For detailed information about the design files, see Reference Design.
Introduction
In a PON, the upstream transmission uses time division multiplexing and is shared among many
customers. In the upstream direction, the phase relationship between customers transmitting
back to the central office is random. This requires a CDR circuit that can acquire symbol lock
quickly and deterministically. To support PON applications, the GTH and GTY transceiver CDR
circuit can be augmented by implementing a BCDR quick-lock circuit.
Application Note: Virtex UltraScale, Virtex UltraScale+,
Kintex UltraScale, Kintex UltraScale+ Devices
XAPP1252 (v1.3) April 12, 2019
Burst-Mode Clock Data Recovery with
GTH and GTY Transceivers
Author: Edward Lee and Caleb Leung
Introduction
XAPP1252 (v1.3) April 12, 2019 2
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NG-PON2 Network Overview
Figure 1 shows the NG-PON2 architecture during downstream transmission.
The optical line terminal (OLT) transmits data using four wavelengths which are multiplexed into
a single optical stream. The aggregate downstream bandwidth is 39.8 Gb/s. The passive optical
splitter replicates the data stream to each optical network unit (ONU) connected to it. The
downstream data is continuous, and none of the ONU receivers are operating in burst mode.
Each ONU receives the same data, but only a fraction of that data, defined as a slot, can be
decoded by a specific ONU. Each ONU is equipped with a wavelength-tunable transmitter and
receiver. The transmitter can be tuned to any of the four upstream wavelengths and the receiver
can be tuned to any of the four downstream wavelengths.
Figure 2 shows the NG-PON2 architecture for upstream transmission.
X-Ref Target - Figure 1
Figure 1: NG-PON2 Downstream Transmission Architecture
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Figure 2: NG-PON2 Upstream Transmission Architecture
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