V23818-K15-L37 Datasheet, PDF (18/24 Pages) Infineon Technologies AG – Small Form Factor Single Mode 1300 nm 1.0625 Gbit/s Fibre Channel 1.25 Gigabit Ethernet Transceiver 2x5/2x10 Pinning with LC Connector

V23818-K15-Lxx
EMI-Recommendations
EMI-Recommendations
To avoid electromagnetic radiation exceeding the required limits please take note of the
following recommendations.
When Gigabit switching 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 Ω should be placed at the end of each matched
line. An alternative termination can be provided with a 50 Ω resistor at each (D, Dn). In
DC coupled systems a thevenin equivalent 50 Ω resistance can be achieved as follows:
for 3.3 V: 125 Ω to V_CC and 82 Ω to V_EE, for 5 V: 82 Ω to V_CC and 125 Ω to V_EE at Data
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 ε_r of 4, the
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.
Data Sheet
18
2003-03-21