AFBR-810BZ datasheet(6/48 Pages) AVAGO

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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

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.

ASIC A

ASIC B

FO Rx

TP4

TP3

Fiber Optic Link

FO Tx

TP2

TP1

Fiber

Figure 6. Fiber Optic Link

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