Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2000-01-20
2002-01-01
Gandhi, Jayprakash N. (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S800000, C361S802000, C439S607070, C174S034000, C385S092000
Reexamination Certificate
active
06335869
ABSTRACT:
THE FIELD OF THE INVENTION
This invention relates to the simple fabrication of removable electronic interface modules for connecting fiber optic communication or signal lines to a computer and, more specifically, to the shielding that forms a part of the module for collecting and suppressing the electromagnetic radiation generated and radiated by electronic components of the module.
BACKGROUND OF THE INVENTION
Computers increasingly are being connected to communications lines and other devices or networks with the computers performing as servers to the peripherally connected computers or devices. The volume of data sent and received by the computer serving as a server of a network is such that the networks are advantageously constructed using fiber optic lines in order to increase the throughput of data.
Fiber optic lines and the associated fiber optic signals require transceivers to convert the optical light pulse signals to electronic signals which are usable by the computer. Such a transceiver includes a transmitter optical subassembly and a receiver optical subassembly to send and receive the optical signals.
Industry standards have been established to define the physical parameters of the said devices and, particularly, the overall interface. This permits the interconnection of different devices manufactured by different manufacturers without the use of physical adapters.
Since about 1990, the fiber optic industry has been using a so-called “SC duplex fiber optic connector system” as the optical fiber connector interface on the front of fiber optic transceivers. The physical separation between the transmitter optical subassembly and receiver optical subassembly (TOSA and ROSA, respectively) for the SC duplex connector is approximately 12.7 mm. However, the industry is now converting to the so-called “Small Form Factor optical connectors” and associated “Small Form Factor optical transceiver.” In the so-called Small Form Factor optical connectors, the separation between the transmitter optical subassembly and receiver optical subassembly is established at approximately 6.25 mm, less than half the separation of the prior SC duplex connector. The Small Form Factor (SFF) standard establishes a module enclosure, having a 9.8 mm height and a width of 13.5 mm, and allows a minimum of 24 transceivers arranged across a standard rack opening. The reduction in size from the former SC duplex connector standard to the Small Form Factor standard requires both substantial redevelopment and redesign.
Moreover, the Small Form Factor optical fiber connector interface has been adopted as a standardized removable module. The module may be connected to a module interface on the host circuit board of a computer. The transmitter optical subassembly/receiver optical subassembly in the module of the Small Form Factor optical fiber connector interface, the processor, and all long conductors of the transmitter optical subassembly and receiver optical subassembly, individually and collectively, radiate electromagnetic radiation and create electromagnetic interference for other electronic devices and components which are exposed to the electromagnetic radiation.
The use of a separate removable module containing a variety of electronic devices requires that the module be easily and inexpensively assembled and that the module further provide its own electromagnetic radiation shielding. Due to the size constraints placed on the interface modules, the shielding must be small but at the same time efficient in collection and grounding of the collected electromagnetic radiation.
OBJECTS OF THE INVENTION
It is an object of the invention to enclose to the greatest degree possible within an electromagnetic radiation shield, an optical signal interface while permitting connection with a host electronic circuit board and fiber optic connectors carrying optical data signals.
It is another object of the invention to interconnect with grounding connections the several elements of electromagnetic radiation shields during assembly fabrication operations.
It is another object of the invention to collect and suppress electromagnetic radiation emanating from electronic components and conductors of a removable optical transceiver interface module.
SUMMARY OF THE INVENTION
A module for interfacing communication line or lines to the main system of the computer is designed to be removable. In order to provide the removability factor, the module must contain sufficient electronic circuitry to convert signals between optical fiber conveyed light pulses and electrical digital signals or vice-versa. This conversion requires at least a laser driver, post amplifier, and supporting circuitry as well as transmitter optical subassembly and a receiver optical subassembly which comprise light generating and light sensitive electronic devices, respectively. The operation of the electronics causes radiation of electromagnetic energy which may cause interference, if not suppressed, with nearby electromagnetic radiation sensitive equipment and components.
An easily removable module is advantageously assembled on a chassis which is molded plastic, preferably, selected for its durability and insulative characteristics. The chassis has an open channel structure for a portion of its length, and a duplex port receiving end for accepting fiber optic conductor connectors. The chassis is formed to include positioning surfaces against which an electronic circuit board is positioned, and a pair of locating pins or projections define the position of the electronic circuit board relative to the chassis.
In areas lacking additional stabilization, the walls of the chassis are formed thinly enough that the walls may be deflected to permit snap-in positioning of the circuit board within the chassis and allow retention latches to be forced out of the path of a circuit board once inserted into the chassis.
Once assembled, the chassis then is substantially enclosed with shielding to suppress the escape of electromagnetic radiation. The shield is fabricated of electrically conducting sheet metal, such as thin metal plate stock, and formed into a channel shape. The channel shaped shield is provided with edge tabs. Each edge tab may be bent to form spring contacts which contact and electrically ground to a bracket or frame member; additionally, tabs may be bent over walls of the chassis to retain the shielding in its desired position. A separate shielding member is positionable on the chassis and retainable by bending or crimping of the edge tabs as contact between the separate shield and the edge tabs establishes grounding electrical contact therebetween. The emissions of electromagnetic radiation from the duplex port end of the chassis are reduced and modified by extending a shield member between the transmitter optical subassembly/receiver optical subassembly, bridging the separate shield and the channel shaped shield to reduce the size of the effective opening to attenuate the electromagnetic radiation passing through the duplex port end of the chassis.
However, it is known that an aperture will attenuate electromagnetic radiation waves when the aperture is less than ½ of the wavelength &lgr; to be attenuated (i.e., length of aperture>{fraction (
1
/
2
)}&lgr;). Moreover, the smaller the aperture, the greater the attenuation of the electromagnetic radiation waves. The attenuation of electromagnetic radiation waves due to passage through an aperture can be determined using the following formula:
S=
20 log(&lgr;/2L),
where
S=the shielding effectiveness of the aperture (in decibels);
&lgr;=the wavelength of the electromagnetic radiation; and
L=the maximum linear length of the aperture (in meters).
Moreover, the wavelength &lgr; can be determined by dividing the velocity of the electromagnetic radiation wave (i.e., the wave speed, which is approximately 3×10
8
m/sec
2
) by the frequency of the electromagnetic radiation emissions.
Thus as the operational frequency (and hence, speed) of an electrical device increases
Branch Scott M.
Gaio David Peter
Hogan William K.
Gandhi Jayprakash N.
Letson Laurence R.
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