Electrical connectors – With circuit conductors and safety grounding provision – Grounding to conductive sheath of cable
Reexamination Certificate
2000-11-28
2002-07-02
Patel, Tulsidas (Department: 2839)
Electrical connectors
With circuit conductors and safety grounding provision
Grounding to conductive sheath of cable
C174S1170FF
Reexamination Certificate
active
06413103
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates generally to portable computing devices. More particularly, the present invention relates to an apparatus for reducing electromagnetic interference (EMI) noise emitted from a portable computing device.
2. Description of the Related Art
Advances in technology have enabled the size of personal computers to decrease. As a result, the use of portable computers such as notebook, or laptop, computers and notepad computers is rapidly increasing. The portability of notebook computers and notepad computers enables a user to keep his or her computer readily accessible such that computing resources are effectively always at hand. By way of example, a notebook computer running on a battery pack enables a user to access computational resources without the need for external sources of electricity.
Many portable computers are configured such that a display screen of the computer pivots, or rotates, with respect to the base of the computer.
FIG. 1
is a diagrammatic representation of a portable computer or, more specifically, a notebook computer. A notebook computer
102
generally includes a display section
106
and a base section
110
. Display section
106
typically includes a display screen
114
, while base section
110
often includes an input/output device such as a keyboard
118
, and houses a central processing unit and memory devices (not shown).
In general, within notebook computer
102
, circuitry associated with base section
110
must be electrically coupled to circuitry associated with display section
106
. As such, within notebook computer
102
, a cable mechanism (not shown) is often used to facilitate the transfer of signals, e.g., signals associated with low voltage differential signaling (LVDS), between base section
110
and display section
106
.
In order to maintain a relatively small size for notebook computer
102
, relatively thin, or low-profile, cable mechanisms are typically used to facilitate the transfer of LVDS signals within notebook computer
102
. For many portable computing devices, a flexible circuit such as a polyemide flexible circuit may be used due to its flexible characteristics and low profile. However, a polyemide flexible circuit does not have any inherent electromagetic compatibility (EMC) shielding within it. As a result, electromagnetic interference (EMI) emissions, such as emissions which may be in the range of approximately 100 megaHertz (MHz) to approximately 1000 MHz, generally result from the LVDS signals associated with a polyemide flexible circuit with no shielding.
EMI is typically characterized as electromagnetic emissions from a device, e.g., notebook computer
102
, which have the tendency to interfere with the operation of another device or system. By way of example, EMI emissions from notebook computer
102
may interfere at relatively close range with FM radio reception, television reception, controls on an aircraft such as a rudder control, and operations of a cellular telephone. EMI emissions may result from an LVDS signal, as a cable mechanism which carries an LVDS signal acts as a noisy antenna which picks up EMI noise in base section
110
and pipes the EMI noise out of notebook computer
102
.
As will be understood by those skilled in the art, a section of notebook computer
102
that is particularly susceptible to emitting EMI is a “junction”
130
between base section
110
and display section
106
which effectively separates base section
110
and display section
106
. A small gap (not shown) is often a part of junction
130
, and acts as an “emissions point” that is characterized by a relatively large amount of irradiated EMI emissions. Typically, the emissions point is located at approximately the area through which a cable mechanism that transfers signals between base section
110
and display section
106
passes.
A cable mechanism which serves as a conduit between base section
110
and display section
106
generally has a higher level of EMI emissions than other cable mechanisms that may be associated with notebook computer
102
. This higher level of EMI emissions is due, at least in part, to the fact that the cable mechanism between base section
110
and display section
106
has a substantially vertical orientation while LVDS signals are being transferred between base section
110
and display section
106
. In other words, the fact that at least part of the cable mechanism or flexible circuit, i.e., the part in display section
106
, is oriented along a y-axis
134
during the operation of notebook computer
102
typically provides increased EMI emissions relative to other cables within notebook computer
102
.
In order to lower the amount of EMI emissions associated with cable mechanisms such as a flexible circuit, ferrite may be added in proximity to the emissions point or junction
130
associated with notebook computer
102
. The ferrite effectively absorbs energy, and blocks at least some EMI emissions. Hence, the use of a ferrite block or wrapping may provide at least some EMC shielding. While the use of ferrite has been observed as being relatively effective, ferrite blocks often have a high profile, i.e., ferrite blocks often have at least one physical dimension such as a thickness which is large with respect to the dimensions of notebook computer
102
. In other words, ferrite blocks generally occupy more space than is acceptable within notebook computer
102
. Additionally, ferrite blocks are relatively expensive, and may cause undesirable pooling, or visible swirls, in the liquid crystal displays which are often associated with display section
106
.
Therefore, what is needed is a low profile, relatively inexpensive cable mechanism for transferring LVDS signals without producing significant EMI emissions within a portable computing device.
SUMMARY OF THE INVENTION
The present invention relates to a cable which enables electromagnetic interference emissions to be reduced. According to one aspect of the present invention, a cable includes a first coaxial cable component, a second coaxial cable component, and a grounding plate. The first coaxial cable component has a first end and a second end, and includes a first shield. The second coaxial cable component also has a first end and a second end, and includes a second shield. The grounding plate is arranged to be conductively coupled, e.g., electrically coupled, to the first shield and the second shield, and is offset from the first end of the first coaxial cable component, the second end of the first coaxial cable component, the first end of the second coaxial cable component, and the second end of the second coaxial cable component. In one embodiment, the grounding plate is also arranged to contact a ground source.
In another embodiment, the cable includes a first connector that is coupled to the first end of the first coaxial cable component. The first connector is also coupled to the first end of the second coaxial cable component. In such an embodiment, the first connector may include a grounding shield that is arranged to be conductively coupled to the first shield at the first end of the first coaxial cable component and to the second shield at the first end of the second coaxial cable component.
A cable which enables contact to be made between a grounding plate and a ground source provides for the transmission of low voltage differential signals while being relatively immune to noise, reducing the emission of electromagnetic interference. Reducing the emission of electromagnetic interference enables a device, e.g., a portable computing device, which uses the cable to operate without significantly affective the performance of other devices in proximity to the cable.
According to another aspect of the present invention, a computing system includes a base portion, a display portion, and a cable assembly. The base portion includes a central processing unit and a first receptacle, while the display portion includes a display screen, a second receptacle, and a first
Kriege Michael
Merz Nicholas G. L.
Apple Computer Inc.
Beyer Weaver & Thomas LLP
Patel Tulsidas
LandOfFree
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