1.25 Gbps Single Mode SFF LC Transceiver
C-1x-1250(C)-FDFB-SLC2(4)
Printed Circuit Board Layout Consideration
A fiber-optic receiver employs a very high gain, wide bandwidth transimpedance amplifier. This amplifier detects and amplifies
signals that are only tens of nA in amplitude when the receiver is operating near it’s limit. Any unwanted signal current that couples into the
receiver circuitry causes a decrease in the receiver’s sensitivity and can also degrade the performance of the receiver’s signal detect (SD) circuit.
To minimize the coupling of unwanted noise into the receiver, careful attention must be given to the printed circuit board.
At a minimum, a double-sided printed circuit board(PCB) with a large component side ground plane beneath the transceiver must
be used. In applications that include many other high speed devices, a multi-layer PCB is highly recommended. This permits the placement of
power and ground on separate layers, wich allows them to be isolated from the signal lines. Multilayer construction also permits the routing of
signal traces away from high level, high speed sinal lines. To minimize the possibility of coupling noise into the receiver section, high level, high
speed signals such as transmitter inputs and clock lines should be routed as far away as possible from the receiver pins.
Noise that couples into the receiver through the power supply pins can also degrade performance. It is recommended that a pi filter
be used in both transmitter and receiver power supplies.
EMI and ESC Consideration
LuminentOIC transceivers offer a metalized plastic case and a special chassis grounding clip. As shown in the drawing, this clip connects
the module case to chassis ground then installs flush through the panel cutout. This way, the grounding clip brushes the edge of the cutout in
order to make a proper contact. The use of a grounding clip also provides increased electrostatic protection and helps reduce radiated emission
from the module or the host circuit board through the chassis faceplate. The attaching posts are at case potential and may be connected to chassis
ground. They should not be connected to circuit ground.
Plastic optical subassemblies are used to further reduce the possibility of radiated emission by eliminating the metal from the
transmitter and receiver diode housings, which extend into connector space. By providing a non-metal receptacle for the optical cable ferrule, the
gigabit speed RF electrical signal is isolated from the connector area thus preventing radiated energy leakage from these surfaces to the outside of
the panel.
LUMINENTOIC.COM
20550 Nordhoff St. • Chatsworth, CA 91311 • tel: 818.773.9044 • fax: 818.576.9486
9F, No 81, Shui Lee Rd. • Hsinchu, Taiwan, R.O.C. • tel: 886.3.5169222 • fax: 886.3.5169213
6
LUMNDS613-Oct2406
Rev. A.2
SOURCE [ SOURCE PHOTONICS, INC. ]
