HFBR-53A3VEMZ Datasheet, PDF (4/13 Pages) AVAGO TECHNOLOGIES LIMITED – RoHS Compliant 3.3 V 1 x 9 Fiber Optic Transceivers for Fibre Channel

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 corres­ponding 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
Avago’s HFBR-53A3VEMZ/VFMZ 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 transmit-
ter 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,
con­tinuo­ us 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.
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 inter-
con­nec­tion between the supporting Physical Layer
integrated circuits and this HFBR-53A3VEMZ/VFMZ trans-
ceiver. 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 trans­mit­ter must either
maintain normal, eye-safe operation or be disabled.
In the HFBR-53A3VEMZ/VFMZ 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 ±20%, the transmitter will automatically be
disabled. Once this has occurred, only an electrical power
reset will allow an attempted turn-on of the transmitter.
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 Electro-
magnetic Interference (EMI) enables the designer to pass
a governmental agency’s EMI regulatory standard; and
more importantly, it reduces the possibility of interfer-
ence to neighboring equipment. The EMI performance
of an enclosure using these transceivers is dependent on
the chassis design. Avago encourages using standard RF
suppression practices and avoiding poorly EMI-sealed
enclosures.
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