v23818-c18-l47 Finisar Corporation., v23818-c18-l47 Datasheet - Page 13

• Manufacturer Part Number: v23818-c18-l47
• Description: Small Form Factor Single Mode 1310 Nm Multirate Up To 155 Mbit/s Transceiver 2x5 Pinning With Lc? Connector
• Manufacturer: Finisar Corporation.

V23818-C18-Lxx, V23818-C18-L4xx Product Specification – August 2004
EMI Recommendations
To avoid electromagnetic radiation exceeding the required limits please take note of the
following recommendations.
When high speed components are found on a PCB (multiplexers, clock recoveries etc.)
any opening of the chassis may produce radiation also at chassis slots other than that of
the device itself. Thus every mechanical opening or aperture should be as small as
possible.
On the board itself every data connection should be an impedance matched line (e.g.
strip line, coplanar strip line). Data, Datanot should be routed symmetrically, vias should
be avoided. A terminating resistor of 100
should be placed at the end of each matched
line. An alternative termination can be provided with a 50
resistor at each (D, Dn). In
DC coupled systems a thevenin equivalent 50
resistance can be achieved as follows:
V
V
V
V
for 3.3 V: 125
to
and 82
to
, for 5 V: 82
to
and 125
to
at Data
CC
EE
CC
EE
and Datanot. Please consider whether there is an internal termination inside an IC or a
transceiver.
In certain cases signal GND is the most harmful source of radiation. Connecting chassis
GND and signal GND at the plate/ bezel/ chassis rear e.g. by means of a fiber optic
transceiver may result in a large amount of radiation. Even a capacitive coupling
between signal GND and chassis may be harmful if it is too close to an opening or an
aperture.
If a separation of signal GND and chassis GND is not planned, it is strongly
recommended to provide a proper contact between signal GND and chassis GND at
every location where possible. This concept is designed to avoid hotspots. Hotspots are
places of highest radiation which could be generated if only a few connections between
signal and chassis GND exist. Compensation currents would concentrate at these
connections, causing radiation.
By use of Gigabit switching components in a design, the return path of the RF current
must also be considered. Thus a split GND plane of Tx and Rx portion may result in
severe EMI problems.
A recommendation is to connect the housing leads to signal GND. However, in certain
applications it may improve EMI performance by connecting them to chassis GND.
The cutout should be sized so that all contact springs make good contact with the face
plate.
Please consider that the PCB may behave like a waveguide. With an
of 4, the
r
wavelength of the harmonics inside the PCB will be half of that in free space. In this
scenario even the smallest PCBs may have unexpected resonances.
© Finisar Corporation August 20, 2004 Rev. C
Page 13