U.S. patent application number 09/354014 was filed with the patent office on 2001-11-22 for electromagnetic interference blocking power bus bar.
Invention is credited to CHERNISKI, ANDREW MICHAEL, NELSON, GERALD J..
Application Number | 20010043126 09/354014 |
Document ID | / |
Family ID | 23391538 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010043126 |
Kind Code |
A1 |
CHERNISKI, ANDREW MICHAEL ;
et al. |
November 22, 2001 |
ELECTROMAGNETIC INTERFERENCE BLOCKING POWER BUS BAR
Abstract
An apparatus and a method of electrically filtering unwanted
noise signals between a computer sub-system and a power sub-system
is disclosed. The computer sub-system and the power sub-system are
housed within an electrically conducting housing which includes a
partition between the computer sub-system and the power sub-system.
The apparatus includes a bus bar connected between the power
sub-system and the computer sub-system for providing direct current
energy between the power sub-system and the computer sub-system. A
dielectric material encompasses the bus bar. An electrically
conducting material encompasses the dielectric material and is
connected to the electrically conducting housing. A virtual
capacitor is thereby formed between the bus bar and the housing,
providing a path of least resistance for the unwanted noise
signals.
Inventors: |
CHERNISKI, ANDREW MICHAEL;
(RESCUE, CA) ; NELSON, GERALD J.; (ROSEVILLE,
CA) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD
INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Family ID: |
23391538 |
Appl. No.: |
09/354014 |
Filed: |
July 15, 1999 |
Current U.S.
Class: |
333/12 ;
333/182 |
Current CPC
Class: |
H03H 1/0007
20130101 |
Class at
Publication: |
333/12 ;
333/182 |
International
Class: |
H03H 007/00 |
Claims
What is claimed is:
1. A system comprising: a power sub-system; an electrical component
sub-system; a bus bar connected between the power sub-system and
the electrical component sub-system, the bus bar providing power
signals between the power sub-system and the electrical component
sub-system; a dielectric material encompassing the bus bar; an
electrically conducting material encompassing the dielectric
material; and an electrically conducting housing electrically
connected to the electrically conducting material.
2. The system of claim 1, wherein the system is a computer
system.
3. An apparatus for providing direct current energy between a
sub-system and a computer sub-system and for electrically filtering
alternating current between the power sub-system and the computer
sub-system, the power subsystem and computer sub-system housed
within an electrically conducting housing which includes a
partition between the power sub-system and the computer sub-system,
the apparatus comprising: a bus bar connected between the power
sub-system and the computer sub-system, the bus bar providing
direct current energy between the power sub-system and the computer
sub-system; a dielectric material encompassing the bus bar; and an
electrically conducting material encompassing the dielectric
material and connected to the electrically conducting housing.
4. The apparatus of claim 3, wherein the bus bar connected between
the power sub-system and the computer sub-system further comprises
a copper alloy bus bar having a rectangular structure.
5. The apparatus of claim 3, wherein the dielectric material
encompassing the bus bar further comprises a Mylar tape dielectric
encompassing the bus bar.
6. The apparatus of claim 3, wherein the electrically conducting
material encompassing the dielectric material further comprises a
copper foil material encompassing the dielectric material and
connected to the electrically connecting housing.
7. The apparatus of claim 3, wherein the electrically conducting
material encompassing the dielectric material protrudes through an
aperture in the partition and is electrically connected to the
partition via a conductive gasket which completely fills the
aperture in the partition surrounding the electrically conducting
material.
8. The apparatus of claim 3, wherein a capacitor formed by the
dielectric material positioned between the bus bar and the
electrically conducting material has a capacitance of greater than
1500 picofarrods.
9. The apparatus of claim 8, wherein the capacitor operates at a
frequency greater than 200 megahertz.
10. A system for filtering unwanted noise between a computer
sub-system and a power sub-system, the system comprising: a bus bar
connected between the power sub-system and the computer sub-system,
for providing direct current signals between the power sub-system
and the computer sub-system; a dielectric material encompassing the
bus bar; an electrically conducting material encompassing the
dielectric material; an electrically conducting housing which
encompasses the computer subsystem and the power sub-system and
which includes an electrically conduction partition between the
power sub-system and the computer sub-system, the bus bar, the
dielectric, and the electrically conducting material penetrating
the partition via an aperture in the partition; and an electrically
conductive gasket positioned between the electrically conductive
material and the electrically conducting partition, thereby
electrically and mechanically sealing the aperture in the
partition.
11. The apparatus of claim 10, wherein the bus bar connected
between the power sub-system and the computer sub-system further
comprises a copper alloy bus bar having a rectangular
structure.
12. The apparatus of claim 10, wherein the dielectric material
encompassing the bus bar further comprises a Mylar tape dielectric
encompassing the bus bar.
13. The apparatus of claim 10, wherein the electrically conducting
material encompassing the dielectric material further comprises a
copper foil material encompassing the dielectric material.
14. The apparatus of claim 10, wherein a capacitor formed by the
dielectric material positioned between the bus bar and the
electrically conducting material has a capacitance of greater than
1500 picofarrods.
15. The apparatus of claim 14, wherein the capacitor operates at a
frequency greater than 200 megahertz.
16. A system for filtering unwanted noise between a computer
sub-system and a power sub-system, the system comprising: a first
electrically conducting material in electrical connection with an
electrically conducting housing; a second electrically conducting
material in electrical connection with the electrically conducting
housing; a first outer dielectric material positioned adjacent the
first electrically conducting material; a second outer dielectric
material positioned adjacent the second electrically conducting
material; a plurality of bus bars positioned between the first and
second outer dielectric materials connecting the power sub-system
and the computer sub-system for providing direct current signals
between the power sub-system and the computer sub-system; and at
least one inner dielectric material positioned between each pair of
bus bars.
17. The system of claim 16, wherein each of the plurality of bus
bars is formed from a copper material formed in a rectangular
structure.
18. The system of claim 16, wherein the first inner dielectric
material and the first and second outer dielectric materials is
formed from a Mylar material.
19. The system of claim 16, wherein the first and second
electrically conducting material is formed from a copper foil
material.
20. A method of filtering unwanted noise on a bus bar between a
computer sub-system and a power sub-system, the bus bar providing
power from the power sub-system to the computer sub-system, the
method comprising: encompassing the bus bar with a dielectric
material; encompassing the dielectric material with an electrically
conducting material; and enclosing the electrically conducting
material within an electrically conducting housing, wherein the
electrically conducting material is in electrical connection with
the housing.
21. The method of claim 20, wherein the step of encompassing the
bus bar with the dielectric material further comprises:
encompassing a copper material having a rectangular structure with
a dielectric material.
22. The method of claim 20, wherein the step of encompassing the
bus bar with the dielectric material further comprises:
encompassing the bus bar with a Mylar tape material.
23. The method of claim 20, wherein the step of encompassing the
dielectric material with an electrically conducting material
further comprises: encompassing the dielectric material with a
copper foil material.
24. The method of claim 23 and further comprising: positioning the
electrically conducting material through an aperture in a partition
of a housing, the partition physically isolating the computer
sub-system from the power sub-system.
25. The method of claim 24 and further comprising: forming a
conductive gasket within the aperture of the partition, thereby
electrically connecting the electrically conducting material with
the housing.
26. The method of claim 20 and further comprising: forming a
capacitor between the bus bar and the housing having a capacitance
of greater than 1500 picofarrods.
27. The method of claim 20 and further comprising: forming a
capacitor between the bus bar and the housing operating at a
frequency of greater than 200 megahertz.
Description
THE FIELD OF THE INVENTION
[0001] The present invention relates generally to the suppression
of electromagnetic interference within an electrical system, and
more particularly to the suppression of high frequency
electromagnetic noise signals transmitted between a sub-system and
a power sub-system within an overall system, such as a computer
system.
BACKGROUND OF THE INVENTION
[0002] The present invention applies to any electrical or
electronic system such as computer system. To those skilled in the
art of computer hardware technology, it is understood that computer
systems include a power source subsystem and a computer sub-system.
The computer sub-system includes all hardware components other than
those included in the power source sub-system. The two sub-systems
are typically physically separated within a housing by a partition.
A bus bar, known to those in this field, forms a conduit for DC
power from the power source sub-system to the computer sub-system.
The bus bar usually carries a large amount of current to the
computer sub-system in order for the computer sub-system to
properly operate.
[0003] A specific problem with prior art computer systems is that
electromagnetic interference (EMI), which can further be described
as a high frequency alternating current noise signal originating in
the computer subsystem, is transmitted via the bus bar from the
computer sub-system to the power source sub-system. Thus, it has
become a priority to electrically isolate the power source
sub-system from the computer sub-system, thereby preventing
unwanted EMI signals from reaching the power source sub-system. In
this application, electrical isolation as used here is defined as
radio frequency (RF) isolation only. It is neither practical nor
desirable to include direct current (DC) isolation in this
definition. One way of electrically isolating the power source
sub-system from the computer sub-system is by providing an RF
electrical path from the computer sub-system to another location
(other than the power source sub-system) having less RF impedance
than either the power source sub-system or the computer sub-system.
As is well known in the art, electrical current will follow a path
of least resistance. A related problem is found in commercial
server applications configured with multiple bus bars, with some of
the bus bars having high current and low voltage drop requirements.
In this type of commercial server configuration, each bus bar
provides a conduit for unwanted EMI signals.
[0004] Conventional solutions for the above-discussed EMI related
problems typically include some type of a feed-through filter. One
specific solution that has been developed is the utilization of a
lead-type capacitor, which is a capacitor having a plurality of
leads for connection to circuitry external to the capacitor. This
solution connects the lead-type capacitor between the bus bar and
the housing enclosing the computer sub-system and the power source
subsystem. Thus, unwanted EMI signals are bypassed through the
lead-type capacitor into the housing, rather than transmitted to
the power source. However, the disadvantage of using a lead-type
capacitor in this configuration is that lead-type capacitors are
not adequate RF solutions because of the parasitic inductance that
is unavoidably associated with these type of components.
Specifically, lead-type capacitors will not work at frequencies
greater than 100 megahertz. Therefore, lead-type capacitors will
not properly suppress RF EMI signals greater than 100
megahertz.
[0005] A second specific solution to the above-discussed problem is
the use of a feed-through capacitor. A feed-through capacitor,
while physically capable of suppressing EMI signals, is not a
viable solution because it is an expensive component and is
expensive to incorporate into a computer system. Feed-through
capacitors have the appearance in general of a stud or a bolt such
that it is necessary to bore holes in the computer housing and
provide attachment on both sides of the feed-through capacitor.
These interface connections on either side of the feed-through
capacitor become problematic because the connections produce a
large DC impedance. It becomes a logistical problem to insure that
a DC connection is provided through the feed-through capacitor.
Additionally, feed-through capacitors are formed from extremely
high dielectric ceramics, which are very brittle. The ceramic can
fracture and cause a short inside of the capacitor. In extreme
examples, the capacitor can heat up and start on fire.
[0006] Thus, there is a need for an apparatus and a method for
preventing EMI noise signals from escaping a computer sub-system
and entering a power source sub-system via a traditional bus bar.
It is desirous to have an apparatus and a method which will be
reliable, inexpensive in its components, and inexpensive to
implement.
SUMMARY OF THE INVENTION
[0007] The apparatus of the present invention includes a bus bar
connected between the power sub-system and the computer sub-system
for providing direct current signals between the power sub-system
and the computer sub-system. A dielectric material encompasses the
bus bar, while an electrically conducting material encompasses the
dielectric material and is connected to the electrically conducting
housing. Any electromagnetic interference from the computer
subsystem will be transmitted to the electrically conducting
housing and returned to the portion of the housing surrounding the
computer sub-system via a virtual capacitor formed by the
dielectric material positioned between the bus bar and the
electrically conducting material.
[0008] In one embodiment of the present invention, the bus bar is
formed from a copper alloy material in a rectangular shape, the
dielectric material is formed from a Mylar composition, and the
electrically conducting material is a copper foil material.
Additionally, due to the materials used and the configuration of
the capacitor, the capacitor has a capacitance of greater than 1500
picofarrods and operate at a frequency of greater than 200
megahertz.
[0009] In another embodiment of the present invention, multiple bus
bars are utilized between the power sub-system and the computer
sub-system. Each bus bar is separated from each adjacent bus bar by
either a single dielectric layer or a combination of a single
electrically conducting layer positioned between two dielectric
layers. Therefore, the present invention encompasses suppressing
EMI signals from one or more bus bars.
[0010] One aspect of the present invention is the formation of an
aperture within a partition of the housing. The partition creates
two sub-housings, one sub-housing for the power sub-system and one
sub-housing for the computer sub-system. The capacitor formed from
the dielectric material located between the bus bar and the
electrically conducting material is positioned such that it
protrudes through the aperture in the partition. A conductive
gasket electrically connects the electrically conducting material
to the housing by sealing the aperture around the electrically
conducting material.
[0011] In yet another embodiment of the present invention, a method
of filtering the electromagnetic interference signal between a
computer sub-system and a power sub-system is disclosed. The method
includes encompassing the bus bar with a dielectric material. The
dielectric material is then encompassed within an electrically
conducting material. The electrically conducting material is in
electrical connection with an electrically conducting housing. A
virtual capacitor is thereby formed between the bus bar and the
housing, providing a path of least resistance for the unwanted
noise signals.
[0012] The present invention provides an apparatus and a method
which provides a solution for the problem of electromagnetic
interference signals, which are a high frequency alternating
current noise signals, escaping a computer sub-system enclosure and
entering a power source sub-system enclosure. The apparatus
electrically suppresses or filters unwanted EMI signals between a
computer sub-system and a power sub-system, thereby preventing
unwanted noise signals to be transmitted between the computer
sub-system and the power sub-system. An electrically conducting
housing encompasses both the computer sub-system and the power
sub-system, and includes a partition between the computer
sub-system and the power sub-system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIGS. 1, 2A, and 2B are sectional views of a prior art
computer system.
[0014] FIG. 3 is a sectional view of a portion of a bus bar
incorporating the present invention.
[0015] FIG. 4 is a sectional view of a bus bar shown protruding
through an aperture within a housing partition incorporating the
present invention.
[0016] FIG. 5 is a sectional view of an alternative embodiment of
the present invention showing a plurality of bus bars.
[0017] FIG. 6 is a sectional view of a second alternative
embodiment of the present invention showing a plurality of bus
bars.
[0018] FIG. 7 is a sectional end view of the second alternate
embodiment incorporating the present invention.
[0019] FIG. 8 is a graphical representation of the attenuation of
electromagnetic interference through use of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] In the following detailed description of the preferred
embodiments, reference is made to the accompanying drawings which
form a part hereof, and which illustrate specific embodiments in
which the present invention may be practiced. Throughout the
drawings, identical numerals refer to similar or identical parts.
It is to be understood that other embodiments may be utilized and
structural or logical changes may be made without departing from
the scope of the present invention. The following detailed
description, therefore, is not to be taken in a limiting sense, and
the scope of the present invention is defined by the appended
claims.
[0021] The present invention applies to any electrical or
electronic system. However, for clarity sake, the present
application will specifically address a computer system. The
present invention addresses the issue of preventing electromagnetic
interference (EMI) from escaping a computer system enclosure and
interfering with a power source. A common method in aiding in the
suppression of EMI signals, also known as radio frequency (RF)
alternating current noise signals, includes the segregation of a
power source sub-system from a computer sub-system via a physical
partition. This partition reduces the size of the critical
containment vessel of the computer sub-system to the portion that
surrounds the system board and the inputs/outputs. The power source
enclosure can be designed with much less electromagnetic
containment requirements. Power segregation is especially useful
when multiple power sources must be considered as in telecom
applications where a 48-volt direct current line must be available
along with a conventional power line. Furthermore, the necessity to
restrict cooling vent openings in the power subsystem is
eliminated.
[0022] The process of electrically isolating the power source
sub-system from the computer sub-system, and thereby preventing the
transmittal of EMI signals, is a critical issue. FIG. 1 illustrates
a cross section view of computer system 50. Computer system 50
includes power source sub-system 52 and computer sub-system 54.
Power source sub-system 52 is housed within power source domain 62
and computer sub-system 54 is housed within computer domain 64.
Both sub-systems are enclosed within housing 56 and are physically
separated from each other by partition 58. Housing 56 and partition
58 are formed from an electrically conducting material.
[0023] Present computer designs separate power source domain 62
from computer domain 64 with partition 58. As shown in FIG. 1, bus
bar 60 forms a conduit for DC power between power source sub-system
52 and computer subsystem 54. Typically, bus bar 60 provides
relatively large currents at low voltages for powering various
electrical components, such as electronic components 57 and 59,
within computer sub-system 54. FIG. 1 illustrates a prior art low
performance system where no provision for bypassing EMI noise
signal is used.
[0024] One problem with the present design of computer hardware
systems is preventing unwanted electromagnetic interference (EMI)
signals from escaping computer sub-system 54 housed within computer
domain 64. Transmission of EMI signals, which are RF alternating
current noise signals, to power source sub-system 52 housed within
power source domain 62 can limit the overall performance of
computer system 50. Thus, it is desirous to confine EMI signals
within computer domain 54 and block EMI signals from entering power
source domain 62.
[0025] It is understood by those in the art that preventing EMI
signal transmission from computer sub-system 54 through partition
58 into power source domain 62 is necessary in order for computer
system 50 to comply with regulatory emissions requirements.
Therefore, a filtering configuration is necessary to filter the
unwanted EMI signals, thereby preventing the unwanted signal from
entering power source sub-system 52. In prior art systems where no
filtering is done between internal domains, alternate approaches
are used such as line cord filtering or other techniques.
[0026] Conventional solutions have also utilized the placement of
an actual capacitor between bus bar 60 and housing 56 or partition
58. Conventional designs, such as those discussed in the Background
section the present application, have utilized either a
feed-through capacitor or a lead-type capacitor.
[0027] FIGS. 2A and 2B show sectional views incorporating two prior
art solutions. As shown in FIGS. 2A and 2B, power source sub-system
52 is housed within power source domain 62, while computer
sub-system 54 is housed within computer domain 64. Bus bar 60
electrically interconnects power source sub-system 52 and computer
sub-system 54. Partition 58 has aperture 66 through which bus bar
60 is positioned. Capacitor 68A, shown in FIG. 2A, is a
feed-through capacitor and is connected to partition 58 and bus bar
60. Capacitor 68B, shown in FIG. 2B, is a lead-type capacitor and
is connected between bus bar 60 and housing 56. As shown in FIG.
2B, when lead-type capacitors are used, they usually reside on the
system printed circuit board or in the power system assembly.
[0028] Lead-type capacitors and feed-through capacitors each have
several disadvantages. Lead-type capacitors are not adequate
solutions due to their inadequacy at high frequencies. The
parasitic inductance associated with the leads of a lead-type
capacitor does not permit this type of capacitor to properly
operate at high frequencies. Therefore, lead-type capacitors will
not properly suppress high frequency EMI signals.
[0029] While feed-through capacitors will properly operate at the
necessary frequencies, these individual components are both
expensive and expensive to mount within computer 50. A feed-through
capacitor has the general appearance of a stud or a bolt. A hole
must be boared through partition 58 and bus bar 60 attached to the
terminals of the feed-through capacitor. Also, the interface
connections on either side of the feed-through capacitor becomes
problematic because these connections represent high DC impedances.
Therefore, there becomes a logistical problem to getting a DC
connection to go through a feed-through capacitor having the
necessary requirements. Also, in order to operate in the high
current range necessary for the types of computer systems that are
currently being manufactured, the actual size of a feed-through
capacitor becomes quite large. Additionally, feed-through
capacitors are formed from extremely high dielectric ceramics,
which are very brittle. The ceramic can fracture and cause a short
inside of the capacitor. In extreme examples, the capacitor can
heat up and start on fire.
[0030] The present invention provides a filtered bus bar which
transmits necessary current between power source sub-system 52 and
computer subsystem 54, while preventing unwanted EMI signals from
being transmitted to power source sub-system 52 from computer
sub-system 54. The present invention does not utilize an actual
capacitive device which must be mounted to both partition 58 and
bus bar 60, but rather a virtual capacitor is formed between
partition 58 and bus bar 60.
[0031] FIG. 3 is a sectional view showing the basic concept of the
present invention. FIG. 3 is a sectional view of a portion of bus
bar 60 for connecting to power source sub-system 52 in the
direction of arrow A and connecting to computer sub-system 54 in
the direction of arrow B. It is understood that bus bar 60 is
formed from an electrically conducting material, thereby permitting
power signals to be transmitted from power source sub-system 52 to
computer sub-system 54. As shown in FIG. 3, bus bar 60 has
dielectric material 70 positioned above and below bus bar 60. In
reality, dielectric material 70 would surround and encompass bus
bar 60. Also shown in FIG. 3 is electrically conducting material 72
positioned above and below dielectric material 70. It is also
understood that electrically conducting material 72 would surround
and encompass dielectric material 70. Therefore, a virtual
capacitor is formed having electrically conducting layers 60 and 72
separated by dielectric material 70.
[0032] In one embodiment, bus bar 60 of the present invention is
formed having a rectangular structure, a width in the range of
approximately 0.50 to 1.00 inches, and a thickness in the range of
approximately 0.025 to 0.150 inches. In one embodiment, bus bar 60
is formed from a copper material. It is understood, however, that
any material having the ability to transmit electrical signals may
be utilized for bus bar 60. Bus bar 60 is immediately surrounded by
a dielectric or insulating material having a relatively thin
cross-section, such as in the range of approximately 0.00050 to
0.0010 inches. In one embodiment, dielectric 70 is formed from
Mylar tape. In another embodiment, dielectric 70 is formed from
Kapton tape. It is understood, however, that any material having
dielectric qualities may be utilized for dielectric 70.
[0033] Completely surrounding and encompassing dielectric 70 is
electrically conducting material 72. In one embodiment,
electrically conducting material 72 is formed from a copper foil
material. It is understood, however, that any material having
electrically conducting qualities may be utilized for material 70.
Bus bar 60, dielectric material 70, and electrically conducting
material 72 form a virtual and distributed capacitor over the
length of bus bar 60 which is encompassed by dielectric material 70
and electrically conducting material 72. The length of bus bar 60
which is encompassed within dielectric material 70 and electrically
conducting material 72 may vary and can be predetermined in order
to achieve a desired capacitance, depending upon the EMI signals
produced within computer sub-system 54. Alternatively stated, with
the knowledge of the specific components used within computer
sub-system 54, the amount of EMI noise can be calculated. Thus, the
capacitance necessary to filter the EMI noise can be calculated and
a virtual capacitance meeting this criteria can be designed. As a
default, bus bar 60 can be encompassed within dielectric material
70 and electrically conducting material 172 the entire length
between power source subsystem 52 and computer sub-system 54.
[0034] FIG. 4 is a sectional view showing the connection between
partition 58 and bus bar 60. Bus bar 60 is interconnected between
power source sub-system 52 and computer sub-system 54 in the
directions shown by arrows A and B, respectively. Bus bar 60, along
with dielectric material 70 and electrically conducting material 72
are positioned within aperture 66 of partition 58. Conductive
gasket 74 physically and electrically seals aperture 66 such that
bus bar 60 is in electrical connection with partition 58.
Conductive gasket 74 is formed from any type of electrically
conducting material and is configured such that it is in direct
contact with partition 58 at all points around aperture 66 and at
all points around electrically conducting material 72. Bus bar 60
physically penetrates aperture 66, but there is no visible opening
that is not filled by conductive gasket 74. Thus, bus bar 60 is
connected to partition 58 in a low impedance configuration such
that it provides a high frequency solution to the problem of EMI
signals.
[0035] While FIG. 4 shows bus bar 60 in electrical connection with
partition 58, it is understood by those in the art that bus bar 60
can be connected to housing 56 or partition 58 at various
locations. The greater the number of electrical connections, the
lower each individual impedance path. In other words, by providing
various alternate paths between bus bar 60 and housing 56, the
impedance within a single path is smaller because multiple parallel
paths are available. The present invention, as described with
reference to FIGS. 3 and 4, disclose a virtual capacitor which has
a capacitance in each alternate path of greater than approximately
1500 picofarrods and operates at a frequency of greater than 200
megahertz and preferably up to 3.0 gigahertz.
[0036] The embodiment of the present invention shown in FIGS. 3 and
4 disclose a high frequency virtual capacitor where one plate,
which is electrically conducting material 72, is intimately
connected to a return path which is partition 58 and housing 56,
while the second plate of the virtual capacitor is bus bar 60 which
normally transmits unwanted EMI noise signals from the computer
sub-system 54 to power system 52. However, the EMI signals will
follow the path of least impedance. Therefore, since the impedance
through the virtual capacitor to housing 56 has less impedance than
that of bus bar 60 and the power source sub-system 52, the high
frequency EMI signals will follow the path through the virtual
capacitor to housing 56. The EMI signals will then harmlessly
return through housing 56 back to its source and never reach power
source sub-system 52.
[0037] Computer system 50 of FIGS. 3 and 4 shows a singular bus bar
interconnected between power source sub-system 52 and computer
sub-system 54. However, multiple bus bars are sometimes utilized in
present day computer systems. Therefore, FIG. 5 shows a
cross-sectional view of a portion of computer system 100 in which
multiple bus bars are interconnected between a power source
sub-system and a computer sub-system. Computer system 100, as shown
in FIG. 5, includes bus bars 102 and 104, dielectric materials 106,
108, and 110, electrically conducting materials 112 and 114,
conductive gasket 116, and partition 120. Bus bars 102 and 104
would be connected to a power source sub-system and a computer
sub-system similar to those shown in FIGS. 3 and 4 as directed by
arrows A and B, respectively.
[0038] While only two bus bars, bus bars 102 and 104, are shown in
FIG. 5, it is understood by those in the art that multiple bus bars
could be stacked upon each other having a dielectric material, such
as dielectric material 106 positioned between each pair of bus
bars. In this embodiment, one of the filtered bus bars could carry
a DC potential, which may be a variety of voltages, for example 5.0
volts or 3.3 volts. A second filter bus bar could carry another DC
voltage, while a third filtered bus bar could carry a ground
return. Regardless of the number of stacked bus bars, the concept
of a virtual capacitor formed along the length of the bus bars is
still desirable and applicable. Once again, one or more virtual and
distributed capacitors are formed between each bus bar and
partition 120, thereby providing a path of least resistance for
high frequency EMI signals.
[0039] FIG. 6 is a sectional view showing a second alternate
embodiment of the present invention. The sectional view shown in
FIG. 6 is similar to the sectional view shown in FIG. 5, except
that instead of having a single dielectric material, such as
dielectric material 106 positioned between each pairs of bus bars,
two dielectric materials, shown in FIG. 6 as dielectric materials
106 and 122, separated by an electrically conducting material, such
as electrically conducting material 124, are positioned between
each pair of bus bars. Once again, with the concept shown in FIG.
6, the entire structure operates as a distributed capacitor which
will filter unwanted EMI noise signals through a housing, rather
than transmitting unwanted EMI noise signals to the power source
sub-system. While only two bus bars are shown in FIG. 6, it is
understood by those in the art that multiple bus bars could be
stacked upon each other having two dielectric materials separated
by an electrically conducting material positioned between each bus
bar.
[0040] FIG. 7 is a sectional end view of the second alternate
embodiment shown in FIG. 6. The end view of FIG. 7 includes bus
bars 102 and 104, dielectric materials 106, 108, 110, and 122,
electrically conducting materials 112, 114 and 124, conductive
gasket 116, and partition 120. As shown in FIG. 7, dielectric
materials 106 and 110 encompass bus bar 102, while dielectric
materials 108 and 122 encompass bus bar 104. Also, electrically
conducting materials 112, 114 and 124 extend horizontally further
than any other layers and encompass all other layers. These three
electrically conducting materials are then rolled in a serpentine
or coil configuration. Also shown in FIG. 7, conductive gasket 116
completely closes a previously formed aperture in partition 120
through which the multi-layered design penetrates.
[0041] FIG. 8 is a graphical representation showing the attenuation
of unwanted EMI noise signals versus a spectrum of operating
frequencies. Due to the configuration of the present invention, the
attenuation of noise signals is great at certain frequencies, such
as indicated at 130 and 132. FIG. 8 also shows dips in attenuation
as indicated at 134 and 136. However, as can be seen from the
graphical representation of FIG. 8, the dips in attenuation are of
incredibly short durations as compared to the portions of the graph
having good attenuation. Thus, the graphical representation of FIG.
8 illustrates that the design shown in FIGS. 3 through 7 provides
acceptable attenuation for the desired application.
[0042] The present invention provides a solution to the problem of
EMI signals escaping a computer sub-system and entering a power
source sub-system. A virtual capacitor is created between a bus bar
and a housing of the computer system. The virtual capacitor does
not suffer from the shortcomings of prior art designs.
Specifically, the present invention is capable of operating at high
frequencies and is more reliable and cost efficient than prior art
designs.
[0043] Although specific embodiments have been illustrated and
described herein for purposes of description of the preferred
embodiments, it will be appreciated by those of ordinary skill in
the art that a wide variety of alternate and/or equivalent
implementations calculated to achieve the same purposes may be
substituted for the specific embodiments shown and described
without departing from the scope of the present invention. Those
with skill in electromechanical, electrical, and computer arts will
readily appreciate that the present invention may be implemented in
a wide variety of embodiments. This application is intended to
cover any adaptations or variations of the preferred embodiments
discussed herein. Therefore, it is manifestly intended that this
invention be limited only by the appended claims and the
equivalents thereof.
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