Note: Descriptions are shown in the official language in which they were submitted.
AE-363 PATENT
A HIGH IMPEDANCE ELECTRICAL CABLE AND
METHOD OF FORMING SAME
1 FIELD OF THE INVENTION
This invention relates generally to high impeded
electrical cable and also relates to a method of forming a
high impedance cable having conductors being spaced at a
given pitch.
BACKGROUND OF THE INVENTION
Flat multiconductor ribbon cable is used
extensively in the electronics industry, especially in the
computer field. Cable of this type typically includes a
plurality of electrical conductors arranged in side-by-side
spaced orientation. These conductors are surrounded by an
insulative casing which electrically isolates each of the
conductors.
Several factors affect the quality and reliability
of these cables. The size of each conductor, measured by
the cross-sectional area, dictates the amount of signal
current that each conductor can carry. The amount of signal
current carried is directly proportional to the size of the
conductor.
In addition, the impedance value of the cable is
related, in part, to the spacing between adjacent
conductors. In cables having similar dielectric constants,
the greater the space between adjacent conductors (i.e. the
more insulating mass therebetween) the greater the impedance
value of the cable.
It is desirable to construct a cable which is
capable of carrying high signal currents while also having
a high impedance value. Thus, cable having large conductors
and ample spacing between adjacent conductors would be
ideal. However, in the modern computer environment, a cable
assembly of this construction is not practical. In fact,
the current state of the computer industry is to require
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1 smaller cable, i.e. cable with conductors spaced at a
smaller pitch, while maintaining the high signal carrying
capabilities of the cable as well as the high impedance
value. However, when spacing conductors at a smaller pitch,
the insulating mass between facing surfaces of adjacent
conductors is reduced. This results in lowering the
impedance value of the cable. Side-by-side round
conductors, typically used in cables of this type, when
spaced at a small pitch, would result in the facing curved
surfaces of adjacent conductors being in close proximity.
This would cause the impedance value to be lowered beyond
tolerability.
The art has seen the use of rectangular conductors
in flat multiconductor cable assemblies which permit the
conductors to be placed on a smaller pitch while maintaining
more insulating mass between facing surfaces of adjacent
conductors. However, rectangular conductors are difficult
to form and are more expensive than conventional round
conductors. Further, in most computer applications, mass
cable termination to insulation displacing contacts of
electrical connectors is desired. Rectangular conductors
are inherently difficult to mass terminate in this matter.
It is therefore desirable to provide a flat multi-
conductor electrical cable which permits spacing of
electrical conductors at a reduced pitch while maintaining
a high degree of signal transmission and a high impedance
value.
SUMMARY OF THE INVENTION
It is an object of the present invention to
provide an improved multiconductor electrical cable.
It is a further object of the invention to form an
electrical cable where conductors may be spaced at a small
pitch while maintaining high signal carrying capabilities
and sufficient insulation between adjacent conductors.
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1 In the efficient attainment of these and other
objects, the present invention provides a method of forming
an electrical cable assembly including providing a plurality
of elongate electrical conductors having a substantially
circular cross-sectional shape. One of the conductors is
flattened along its length. The conductors are arranged so
that the flattened portion of the one conductor is facing an
adjacent conductor. An insulative casing is formed around
the connectors to place the connectors in electrical
isolation.
The present invention also provides an electrical
cable assembly including a plurality of elongate electrical
conductors and an insulative casing surrounding each of the
conductors. The conductors are arranged in side-by-side
transversely spaced orientation. The casing includes a
major planar surface. One of the conductors includes a flat
surface portion which faces an adjacent one of the plural
conductors. The one conductor further includes a curved
surface portion which faces the major planar surface to
provide mass termination capabilities.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows an extend of a conventional round
conductor of the type used in accordance with the present
invention.
Figure 2 shows schematically, the cross-sectional
shape of the conductor of Figure 1.
Figure 3 shows, partially in section and partially
schematically, a portion of a conventional flat
multiconductor cable including round conductors of the type
shown in Figure 1.
Figure 4 shows schematically, an electrical
conductor formed in accordance with the present invention.
Figure 5 shows, partially in section and partially
schematically, a portion of an electrical cable of the
present invention employing the conductor shown in Figure 4.
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1 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Figure 1 and 2, an electrical
conductor 10, used in accordance with the present invention
is shown. Conductor 10 is a solid round copper wire of
conventional construction used to transmit electrical
signals therealong. Conductor 10 has a major longitudianl
axis c and a circular cross-sectional shape as shown in
Figure 2.
Typical wire sizes used in accordance with the
present invention include American Wire Gage (AWG) sizes 26
through 30. Round conductors of these sizes have diameters
d of between .010 inches and .016 inches. The cross-
sectional areas of these conductors range between
approximately 100 and 250 circular mils. Electrical
resistance of a copper wire is inversely proportional to its
cross-sectional area. Therefore, larger wires will have
less resistance and can accordingly carry a greater amount
of electrical signal therealong.
Referring now to Figure 3, a plurality of
conductors 10 are arranged in an electrical cable assembly
12. Cable assembly 12 includes an electrically insulative
casing 14 formed of extruded plastic such as polyvinyl
chloride (PVC). Casing 14 is generally flat having an upper
planar surface 16 and a lower planar surface 18
substantially parallel thereto. While planar surfaces 16
and 18 are shown as flat, cable having undulating planar
surfaces may also be employed. Cables of this type are
commonly referred to as ribbon cables.
Conductors 10 are supported within casing 14 in
electrical isolation. Conductors 10 are spaced from one
another within casing 14 at a given pitch. Conductor pitch
is defined by the distance between center line c of adjacent
conductors 10. The pitch between conductors of flat ribbon
cable is critical as ribbon cable is designed to be mass
terminated to electrical connectors (not shown) having
insulation displacing contacts fixedly supported in an
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1 insulative housing. the pitch of the cable must match the
pitch of the connector. In Figure 3, the conductors are
spaced at a pitch of Pl. Since conductors 10 are of the
round variety, the actual space between facing surfaces of
adjacent conductors will be less than P1.
As shown in Figure 3, the distance between tangent
points T, and T2 of side-by-side conductors 10' and 10" is
S1, which is substantially less than P1. The impedance value
of an electrical cable is determined, in part, by the
special separation between facing surfaces of adjacent
conductors. As a mass of insulating material increases
between adjacent conductors, the impedance value of the
cable will correspondingly increase. Thus, as conductor
size is increased and/or the pitch between conductors is
decreased, the impedance value of the cable will drop.
The present invention provides a technique for
placing conductors at a closer pitch without either
decreasing conductor size or decreasing the impedance value
of the cable.
Referring to Figure 4, an electrical conductor
formed in accordance with the present invention is shown.
Conductor 20 is formed from a conventional solid round
conductor such as conductor 10 shown in Figure 1. The round
conductor 20 is passed through flattening rollers (not
shown) to form flat surfaces 21 along the length thereof.
The rollers are of the type conventionally used in the
metallic forming art to press flat surfaces on metallic
objects. Rollers capable of such function are commercially
available. Flat surfaces 21 may be placed on conductor 20
either simultaneously or by separate forming steps. As
shown in Figure 4, flat surfaces 21 are diametrically
opposed and substantially parallel to one another.
An important feature of the present invention is
that rather than cutting a flat surface on each diametrical
side of conductor 20, the conductor is actually flattened in
a manner such that opposed upper and lower rounded conductor
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1 surfaces 23 and 25 are outwardly deformed from their
original condition. Thus, the cross-sectional area of
conductor 20 does not change during formation. This permits
the conductor to carry the same amount of signal current as
was possible prior to the forming steps employed in the
present invention.
Additionally, upper and lower surfaces 23, 25 also
substantially maintain their rounded configuration. This
facilitates the ability to mass terminate cable assembly 22
(Fig. 5) with conventional electrical connectors having
insulation displacing contacts (not shown).
Referring to Figure 5, a cable assembly 22 of the
present invention is shown. Cable assembly 22 includes
insulative casing 24 similar to casing 14 shown in Figure 3.
Casing 24 includes upper and lower major planar surfaces 26
and 28 respectively which support therebetween conductors
20. Cable assembly 22 includes conductors 20 of the type
shown in Figure 4. Conductors 20 are arranged within casing
24 so that flattened surfaces 21 are substantially
perpendicular to major planar surfaces 26 and 28 and center
lines c line in a common plane. Rounded surfaces 23 and 25
face major surfaces 26 and 28 respectively. Cable assembly
22 is typically formed by extruding insulative casing 24
over conductors 20.
The conductors 20 of cable assembly 22 are spaced
at a pitch P, which is less than P2 the pitch of cable
assembly 12 (Fig. 3). Since each of conductors 20 includes
flattened surfaces 21, the distance S2 between facing
flattened surfaces 21 of adjacent conductors 20'and 20" is
not correspondingly reduced. Comparing cable assembly 12
shown in Figure 3, with cable assembly 22 of the present
invention shown in Figure 5, this feature is illustrated.
While the conductor pitch of the cable assembly 22 of the
present invention has been reduced from P1 to P2, the actual
spacing between facing surfaces of adjacent conductors
remains substantially the same. That is, Sl ~ S2.
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1 As the amount of insulating mass between facing
surfaces of adjacent conductors 20' and 20" remains the
same, the impedance value of cable assembly 22 would be
substantially similar to impedance value of cable assembly
12. Also, as mentioned above, since conductors 20 maintain
the same cross-sectional area as conductors 10, the signal
carrying capability of cable assembly 22 is not reduced.
The present invention, as shown in Figure 5,
employs multiple conductors, each identically formed to have
diametrically opposed flattened surfaces 21. However, it is
contemplated that conductors 20 may be formed to have only
one flattened surface. Also, it is contemplated that only
selected ones of conductors 20 may be formed to have one or
more flattened surfaces. This would permit the eable
assembly 22 to have selected different impedanee values as
between various pairs of conductors.
Various changes to the foregoing described and
shown structures would now be evident to those skilled in
the art. Aecordingly, the particularly disclosed scope of
the invention is set forth in the following claims.
