HFBR-53A3VEM HP [Agilent(Hewlett-Packard)], HFBR-53A3VEM Datasheet - Page 4

• Manufacturer Part Number: HFBR-53A3VEM
• Description: 3.3 V 1 x 9 Fiber Optic Transceivers for Fibre Channel for Fibre Channel
• Manufacturer: HP [Agilent(Hewlett-Packard)]

APPLICATION SUPPORT
Optical Power Budget and Link
Penalties
The worst-case Optical Power
Budget (OPB) in dB for a fiber-
optic link is determined by the
difference between the minimum
transmitter output optical power
(dBm avg) and the lowest
receiver sensitivity (dBm avg).
This OPB provides the necessary
optical signal range to establish a
working fiber-optic link. The OPB
is allocated for the fiber-optic
cable length and the corre-
sponding link penalties. For
proper link performance, all
penalties that affect the link
performance must be accounted
for within the link optical power
budget.
Data Line Interconnections
Agilent’s HFBR-53A3VEM/FM
fiber-optic transceiver is designed
for compatible PECL signals. The
transmitter inputs are internally
ac-coupled to the laser driver
circuit from the transmitter input
pins (pins 7, 8). The transmitter
driver circuit for the laser light
source is an ac-coupled circuit.
This circuit regulates the output
optical power. The regulated light
output will maintain a constant
output optical power provided
the data pattern is reasonably
balanced in duty factor. If the
data duty factor has long, con-
tinuous state times (low or high
data duty factor), then the output
optical power will gradually
change its average output optical
power level to its pre-set value.
4
The receiver section is internally
ac-coupled between the pre-
amplifier and the post-amplifier
stages. The actual Data and Data-
bar outputs of the post-amplifier
are ac-coupled to their respective
output pins (pins 2, 3). Signal
Detect is a single-ended, TTL
output signal that is dc-coupled
to pin 4 of the module. Signal
Detect should not be ac-coupled
externally to the follow-on
circuits because of its infrequent
state changes.
Caution should be taken to
account for the proper intercon-
nection between the supporting
Physical Layer integrated circuits
and this HFBR-53A3VEM/FM
transceiver. Figure 3 illustrates a
recommended interface circuit
for interconnecting to a dc PECL
compatible fiber-optic
transceiver.
Eye Safety Circuit
For an optical transmitter device
to be eye-safe in the event of a
single fault failure, the transmit-
ter must either maintain normal,
eye-safe operation or be disabled.
In the HFBR-53A3VEM/FM there
are three key elements to the
laser driver safety circuitry: a
monitor diode, a window detector
circuit, and direct control of the
laser bias. The window detection
circuit monitors the average
optical power using the monitor
diode. If a fault occurs such that
the transmitter DC regulation
circuit cannot maintain the preset
bias conditions for the laser
emitter within
transmitter will automatically be
disabled. Once this has occurred,
only an electrical power reset will
allow an attempted turn-on of the
transmitter.
20%, the
Signal Detect
The Signal Detect circuit provides
a TTL low output signal when the
optical link is broken or when the
transmitter is off. The Signal
Detect threshold is set to
transition from a high to low state
between the minimum receiver
input optional power and –30 dBm
avg. input optical power
indicating a definite optical fault
(e.g., unplugged connector for the
receiver or transmitter, broken
fiber, or failed far-end transmitter
or data source). A Signal Detect
indicating a working link is
functional when receiving
encoded 8B/10B characters. The
Signal Detect does not detect
receiver data error or error-rate.
Data errors are determined by
signal processing following the
transceiver.
Electromagnetic Interference (EMI)
One of a circuit board designer’s
foremost concerns is the control
of electromagnetic emissions
from electronic equipment.
Success in controlling generated
Electromagnetic Interference
(EMI) enables the designer to
pass a governmental agency’s
EMI regulatory standard; and
more importantly, it reduces the
possibility of interference to
neighboring equipment. The EMI
performance of an enclosure
using these transceivers is
dependent on the chassis design.
Agilent encourages using
standard RF suppression
practices and avoiding poorly
EMI-sealed enclosures.