8
Data Line Interconnections
Avago Technologies’ AFCT-5943xxZ ber-optic trans-
ceivers are designed to couple to +3.3 V PECL signals.
The transmitter driver circuit regulates the output
optical power. The regulated light output will maintain
a constant output optical power provided the data
pattern is balanced in duty cycle. If the data duty cycle
has long, continuous state times (low or high data duty
cycle), then the output optical power will gradually
change its average output optical power level to its pre-
set value.
The AFCT-5943xxZ has a transmit disable function
which is a single-ended +3.3 V TTL input which is dc-
coupled to pin 8.
The receiver section is internally ac-coupled between
the pre amplier and the post-amplier stages. The Data
and Data-bar outputs of the post-amplier are inter-
nally biased and ac-coupled to their respective output
pins (pins 4, 5).
Signal Detect is a single-ended, +3.3 V TTL compatible
output signal that is dc-coupled to pin 3 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 in-
tercon-nection between the supporting Physical Layer
integrated circuits and these transceivers. Figure 6 il-
lustrates a recommended interface circuit for intercon-
necting to a +3.3 V dc PECL ber-optic transceiver.
Power Supply Filtering and Ground Planes
It is important to exercise care in circuit board layout to
achieve optimum performance from these transceivers.
Figure 6 shows the power supply circuit which complies
with the small form factor multisource agreement. It is
further recommended that a continuous ground plane
be provided in the circuit board directly under the
transceiver to provide a low inductance ground for sig-
nal return current. This recommendation is in keeping
with good high frequency board layout practices.
Package footprint and front panel considerations
The Avago Technologies transceivers comply with the
circuit board “Common Transceiver Footprint” hole
pattern dened in the current multisource agreement
which dened the 2 x 5 package style. This drawing
is reproduced in Figure 7 with the addition of ANSI
Y14.5M compliant dimensioning to be used as a guide
in the mechanical layout of your circuit board. Figure 8
shows the front panel dimensions associated with such
a layout.
Eye Safety Circuit
For an optical transmitter device to be eye-safe in the
event of a single fault failure, the transmit-ter must ei-
ther maintain eye-safe operation or be disabled.
The AFCT-5943xxZ is intrinsically eye safe and does not
require shut down circuitry.
Signal Detect
The Signal Detect circuit provides a deasserted output
signal when the optical link is broken (or when the
remote transmitter is OFF). The Signal Detect thresh-
old is set to transition from a high to low state be-
tween the minimum receiver input optical power and
-35 dBm avg. input optical power indicating a denite
optical fault (e.g. unplugged connector for the receiver
or transmitter, broken ber, or failed far-end transmit-
ter or data source). The Signal Detect does not detect
receiver data error or error-rate. Data errors can be
determined by signal processing oered by upstream
PHY ICs.
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. Avago Technologies
has designed the AFCT-5943xxZ to provide good EMI
performance. The EMI performance of a chassis is de-
pendent on physical design and features which help im-
prove EMI suppression. Avago Technologies encourages
using standard RF suppression practices and avoiding
poorly EMI-sealed enclosures.
Avago Technologies’ OC-48 LC transceivers (AFCT-
5943xxZ) have nose shields which provide a convenient
chassis connection to the nose of the transceiver. This
nose shield and the underlying metalization (except
‘G’ options) improve system EMI performance by eec-
tively closing o the LC aperture. The recommended
transceiver position, PCB layout and panel opening for
both devices are the same, making them mechanically
drop-in compatible. Figure 8 shows the recommended
positioning of the transceivers with respect to the PCB
and faceplate.
