Finisar QSFP28 LR4 Application Note

100G QSFP28 LR4 and CWDM4 initialization Application Note Rev B

Introduction

The purpose of this application note is to document the recommended power-on initialization sequence of
Finisar's 100 Gigabit Ethernet QSFP28 LR4 and CWDM4 modules. At the time of writing this application
note, the affected part numbers are FTLC1151xDPL (25/28G) 10km LR4 and FTLC1152xGPL (25/28G)
2km CWDM4.
The CAUI-4 (4 X 25/28G) high speed signal that propagates from the host ASIC to the module's transmit
electrical input can be affected by ISI (inter symbol interference) when the electrical signal is transmitted
over long host trace lengths. The accumulation of ISI can distort the high speed signals, sufficient to
cause eye closure at the TP1a CAUI-4 input to the QSFP28 module.
Finisar's QSFP28 modules implement a transmit input equalizer function that is designed to compensate
the ISI and jitter, to provide an open eye to the transmit CDR (clock and data recovery). Equalization is a
signal processing technique that boosts the high frequency component of the signal and reduces ISI. This
function is called CTLE (Continuous Time Linear Equalization) and is implemented at the CDR on all 4
input lanes.
Finisar's QSFP28 modules have fixed programmable CTLE implementation.
For more details on the CTLE function please refer to the Appendix on page 5 of this application note.

How to use this Application Note

This application note outlines the default CTLE configuration type in QSFP 28 LR4 and CWDM4 modules
and explains how each CTLE method defines the power on sequencing of the module. This will allow the
host to determine which CTLE setting best suits their application.
Applicable Documents, Standards and MSA's
a. SFF-8636, QSFP28 100G Common Management Interface Rev 2.6, June 19
b. SFF-8679, QSFP28 QSFP28 4X Base Electrical Specification Rev 1.7 August 12
c. SFF-8024, SFF Committee Cross Reference, Rev 3.5, December 2
d. IEEE802.3bm D3p3
e. OIF-CEI-03.1 Common Electrical I/O (CEI) Electrical and Jitter Interoperability agreements for
6G+ bps, 11G+ bps and 25G+ bps I/O
f. OIF-CEI-28G-VSR Common Electrical Interface - 28G-VSR (CEI-28G-VSR)
Rev AN-2153 REV B
20-May-2016
Application Note AN-2153
©2016 Finisar Corporation AN-2153 REV B
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