afbr-820bz Avago Technologies, afbr-820bz Datasheet - Page 6

• Manufacturer Part Number: afbr-820bz
• Description: Twelve-channel Transmitter And Receiver Pluggable, Parallel-fiber-optic Modules
• Manufacturer: Avago Technologies

Link Model and Reference Channel
Performance specifications for the AFBR-810 Transmitter
and AFBR-820 Receiver are based on a reference channel
model. A reference channel model provides the basis for
inter-operability between independently produced trans-
mitter and receiver modules. The reference model used for
the AFBR-810 Transmitter and AFBR-820 Receiver is based
on the industry standard 10GbE link model (10GEPBud3_
1_16a.xls available at the IEEE P802.3ae 10Gb/s Ethernet
Task Force Serial PMD Documents website http://www.
ieee802.org/3/ae/public/adhoc/serial_pmd/documents/).
As shown in Figure 6, a channel for a fiber optic link
comprises a transmitter, receiver and cable plant with
inputs at test point TP1 and outputs at test point TP4.
The test points TP1 and TP4 coincide with the compliance
points defined in Figure 3. The cable plant here assumes
a point to point link and does not include any inline
connectors.
A reference channel permits the effect of various channel
attributes to be referred to different points in the channel
and accumulated. For example, in the GbE (All_1250.
xls available at the IEEE website http://grouper.ieee.
org/groups/802/3/10G_study/public/email_attach/All_
1250.xls) and 10 GbE models all signal impairments are
captured and translated into power penalties. Also, the
effect of transmitter and fiber attributes are also captured
and referred to TP3 to define stressed receiver test criteria.
Similarly, all effects upstream of TP4 can be captured and
referred to TP4 and combined at this point into a figure of
merit. Since the signal at TP4 is electrical and not optical
there are advantages for this.
To ensure inter-operability among independently pro-
duced transmitters and receivers, definition of acceptable
devices is required. This can be accomplished on an indi-
vidual parameter basis by setting min/max limits or with
aggregates of attributes by establishing a figure of merit.
Referring again to the 10GbE link model, the entity ‘margin
at target distance’ is an aggregate figure of merit of all link
attributes. There a set of link attributes will yield a specific
Figure 6. Fiber Optic Link
6
ASIC A
TP1
FO Tx
TP2
Fiber Optic Link
Fiber
link margin and a worst case set of link attributes can be
defined for a minimum level of performance. Instead of
placing a maximum or minimum limit on each attribute, it
is possible to allow elements in the set to shift (i.e. tradeoff
with others within the set) as long as the desired margin
is achieved. Further, if ‘margin at target distance’ can be
translated into eye opening at TP4, the aggregate figure
of merit is directly measurable. To preserve independence
for transmitter, receiver and fibers, it is required that trans-
mitter attributes only trade-off with other transmitter at-
tributes and, similarly, receiver attributes can only trade-
off with other receiver attributes.
In this data sheet, a minimum eye width at TP4 for a
specified maximum BER is the figure of merit used to
define acceptable link performance. Additional inputs and
calculations have been added to the 10GbE link model to
calculate eye closure and the effects of all impairments are
referred to TP4 and combined as elements of eye closure.
The minimum eye width at TP4 is included in tables,
Transmitter Optical Characteristics and Receiver Electri-
cal Characteristics, as minimum “Reference Link Output
Eye Width’ . The Recommended Operating Conditions table
and those for transmitter and receiver characteristics provide
the necessary attributes to define the worst case set for the
reference channel. Various elements of this worst case set
are labeled ‘Informative’ and are allowed to range outside
the maximum or minimum limit for the individual element
when there is a compensating improvement in others of the
worst case subset. Transmitter attribute tradeoffs are limited
to the transmitter subset and receiver tradeoffs are limited to
the receiver subset.
The following two tables summarizes the practical trade-
offs between different informative transmitter param-
eters, as well as different informative receiver parameters,
respectively. Although the wavelength and spectral width
can also trade off with each other, they are not included
here for interoperability reason.
TP3
FO Rx
TP4
ASIC B