Patent Application
20080173465
Embodiments of the invention relate to electronic wiring and cabling employed to conduct signals from point to point. Such embodiments fall under the category of wired interconnect components.
Interconnect has largely been considered a passive element in any system, providing sufficient but non-ideal connectivity between different parts of the system. In that manner, a prior art twisted wire pair, whose cross-section is illustrated in
Additionally, electromagnetic coupling between wires, both near to, and at a distance from a signal wire contributes to distorting the signal conducted by the wire. Such undesirable coupling of signal energy, called ‘crosstalk’, takes two principal forms, capacitive and inductive. Capacitive coupling as the term indicates occurs due to the finite capacitance present between a signal wire and a coupling neighboring wire. Inductive coupling occurs due to the magnetic fields created by currents flowing in neighboring or distant wires that creates corresponding electro-motive force in the wire carrying the signal of interest. Both coupling phenomena lead to the addition of noise into a signal, degrading signal integrity and thereby increasing the probability of erroneous registration of the signal in a receiver system. Means of minimizing this degradation are therefore of much importance to communications systems employing wires to transmit signals.
The prior art twisted wire pair as well as standardized cables such as Cat-5e, Cat-6 (different categories) addresses such concerns of electromagnetic coupling. A wire pair consists of two individual wires coupled strongly and placed close to each other providing a means for ‘differential signaling’, a technique whereby a signal and its complement are transmitted simultaneously and the corresponding symbol recognized as the difference between the two electrical quantities received. Differential signaling largely eliminates concerns with any differences in ground or reference potentials between the communicating systems. Additionally, differential signaling makes it possible to employ high-gain amplifiers to recover an attenuated signal as long as the polarity relationship between individual signals of the differential pair is maintained. Thus, for example, a 1V swing binary, differential signal, with an effective difference between the two wires of 0.5V, may still be recognized correctly despite 10× attenuation down to 50 mV by a differential amplifier, provided that the polarity relationship between the true and complementary individual signals is maintained. Any distant-source noise that couples electro-magnetically into this wire pair couples in very much the same manner into both wires, thereby retaining the difference signal the same, and causing no significant degradation in signal integrity as long as the receiver differential amplifier is capable of rejecting this ‘common-mode’ noise. But a wire pair lying adjacent to another wire pair may not see such a benefit, such as in a flat-tape cable where signal wires as arranged in a bonded fashion adjacent to each other. This problem is effectively addressed by twisting the wires of the wire pair around each other. Over a sufficient length, because of the twist, the coupled noise from any adjacent signal wire sums out to be the same on both individual wires of a twisted wire pair, thus again rendering such noise ‘common-mode’. As an additional enhancement, standard cables such as Cat-5e also offset the twists of wire pairs with respect to each other, starting with a low twist rate for one wire pair and tightening the twist rate for other included wire pairs in the cable assembly.
Twisted wire pairs also cancel out electromagnetic emissions from the signal wires, diminishing electromagnetic interference (EMI) with other systems. Perhaps the very first instance of such a brilliant application of this prior art is the twisting of the wires providing alternating current electricity to lamps and other electrical systems in buildings, minimizing the noise heard in entertainment radio devices. Additionally, twisted wires remain physically close, albeit somewhat inadequately, as a consequence of the intertwining of the wires, thus maintaining relative uniformity in their impedance and good coupling to each other.
Due to the reasons discussed, twisted wire pairs are very commonly employed for electrical signaling within electronic system boxes as well as between these boxes, such as between computers, and from video content players and high-definition displays. But as the volume of data exchanged continues to grow, some of the deficiencies of twisted wire pairs manifest themselves as limitations. A key such limitation is intra-pair skew, or the inequality in the total effective length of one wire with respect to the other in a wire pair. This asymmetry arises because of the independent manner in which the two wires are tensed and twisted with each other. The inequality typically increases with increasing length of the wire pair. In electrical terms, any such inequality in length gives rise to a delay difference between the traveling true and complement signal transitions in binary signaling, transforming part of the differential signal into a common-mode signal. For example, if the effective delay difference at the end of a long length of a wire pair is an inch, this will correspond to approximately 100 ps or more of delay difference at the end of the wire pair depending upon the insulator electrical characteristics. If a true and complement signal (a rising edge and a falling edge for voltage signals, for example) were to be launched simultaneously at the transmitter end on this wire pair, they would be offset at the receiver end of the wire pair by about 100 ps, potentially rendering the signals the same for 100 ps at the beginning of the symbol period and similarly for 100 ps at the end of the symbol period. In other words, 200 ps of the symbol information in certain symbol sequences is transformed from differential to common-mode, and if the receiver further requires at least 200 ps of differential signal for correct recognition with low error, the maximum bit-rate that may be transmitted on this wire pair, even with signals of high signal-to-noise ratio, would be approximately 1/(400 ps) or 2.5 Gbps. The duration of differential signal transformed to common-mode also leads to electromagnetic emissions from the wire pair. Intra-pair skew in twisted wire pairs is hence a severe limitation to link performance, as studies in the industry have indicated as well [Ref. 4].
Additionally, twisted wire pairs are also prone to impedance discontinuities that arise due to the physical separation of the wires of the wire pair that may arise due to assembly errors. As the frequency of data transmission through wire pairs increases, these impedance discontinuities become more significant and impact signal integrity. Attempts to correct such problems include very tight twisting as is done in improved cabling solutions in the industry [Ref. 5]. Such designs further increase effective electrical lengths of the twisted wire pairs, increasing inter-pair (between wire pairs) skew and thereby increasing synchronization challenges between signals flowing in wire pairs within a cable assembly. Inter-pair skew is a problem usually addressed by realignment circuits in receiver systems. Typical values of inter-pair skew in Cat-5e cables resulting from twist offset are more than 1 nS per 10 meters of length.
Twisted wire pairs also occupy about 4 times the physical volume of a single wire and lead to bulkier and relatively inflexible cable assemblies.
As the definition and quality of 2-D images and audio in multimedia transmission increases, there is a need for significantly higher data rates and correspondingly high frequencies of operation of such links as defined in the High Definition Multimedia Interface (HDMI) specification [1]. In view of the varied and significant limitations in prior art twisted wire pairs and cable assemblies, there is a need to improve upon wire pair construction and cable architecture for such links.
The invention implements flattened conducting wires coated with insulation that are bonded to each other, providing approximately rectangular cross-sections and flat surfaces for the transport of charge through the wires. Flat wire pairs are then placed such that adjacent wire pairs are oriented orthogonally to each other to minimize crosstalk and render crosstalk common-mode. Flat wire pairs are also shielded for additional cross-talk minimization as well as near-field EMI minimization. A cable consisting of multiple flat wire pairs may also be shielded in its external jacket that maintains cable structure. Through these enhancements, the invention cable architecture eliminates intra-pair skew while substantially reducing signal loss due to skin-effect. Because the wire pairs are untwisted, inter-pair skew is also largely eliminated.
A prior art twisted wire pair (TWP) cross-section is illustrated in
A principal aspect of TWP's is the twist introduced into the wire pair along its length. This twist entwines both wires with each other and has significant advantages for the wire pair as well as the cable assembly. Not only does the twist cancel emissions through magnetic cancellation from the wire pair when a signal is transmitted ‘differentially’ through the wire pair, it also renders any noise introduced into the wires ‘common-mode’, or common to both wires. Additionally, by varying the rate of twist between wire pairs inside a cable assembly, noise coupled from one wire pair into an adjacent one is also diminished substantially provided the cable is of sufficient length. With these important advantages, twisted wire pairs may be used in unshielded fashion; Category 5 and 6 cables as defined by the TIA/EIA standards employ both unshielded twisted pair (UTP) and shielded twisted pair (STP) architectures.
Nevertheless, prior art wire pair twist introduces a significant disadvantage in the variation of the effective lengths between the two wires of the pair. This occurs because the wires are twisted independently around each other with mechanical limitations of the machinery determining the symmetry of the twist. In the extreme example, one can imagine one of the wires twisted around the other which is held straight. While such an extreme imbalance in twist is highly unlikely, prior art twisted wire pairs do suffer from a variance in the length of one wire with respect to the other, and this variance may accumulate over the length of the cable. A significant disparity in the effective length of one wire with respect to the other in a TWP leads to what is called ‘intra-pair-skew’ that becomes a key data rate limiting factor at high data rates. For example, an inch of difference in length between the two wires of a pair over a length of cable can lead to as much as 100 picoseconds of intra-pair skew, leading to approximately twice the duration being lost in the width of the received differential signal ‘EYE’. This is because the positive pulse traveling on one line suffers a shift with respect to the negative pulse traveling on the companion line, thereby reducing the duration for which these pulses appear to be opposite to each other at the receiver. Reference publication [Ref 4] details the negative impact of twisted pair imbalance.
Intra-pair length variance and the associated intra-pair skew are effectively eliminated in the invention flat wire pair architecture illustrated in
Because the two insulated wires are bonded together, they are the same in physical or electrical length over any wire pair length. It will hence be evident to one skilled in the art that there is negligible variance in length or in other words, ‘intra-pair skew’ between the two wires of the flat wire pair. Additionally, both flat wires are covered with the same insulation material using identical processes and process control, and are bonded to each other on their flat surfaces, leading to a structure that maintains the separation and insulation characteristics between the two conducting wires of the wire pair over the length of the wire pair. This construction ensures that the impedance presented by the flat wire pair remains essentially constant over the entire length of the wire pair without a need for any other control mechanism as employed by prior art taught in [7] and [8]. It is important to note that prior art by Siekierka [8] teaches of an adhesively bonded wire pair architecture that is intended to provide the same benefit as that of the flat wire pair. The distinction between this prior art and the invention is that the invention provides a flat, and therefore substantially increased surface area for adhesive or thermally induced cohesive bonding, thereby providing a very robust bond between the wires of the wire pair. In contrast, as may be seen in
Another important advantage of the flat wire construction is the flat, smooth surfaces of the conducting wires, leading to significantly reduced skin-effect signal loss as detailed in utility application Ser. No. 11/654168. This facilitates significantly higher data communication frequencies for the flat wire pair.
The invention cable architecture therefore obviates any need for twisting of wire pairs, while ensuring that crosstalk is minimized and rendered harmless. This benefit allows for the use of the shielded flat wire pair in untwisted form for any length necessary without incurring any of the consequences such as intra-pair or inter-pair skew or impedance variations of twisted wire pairs.
It is important to note that the orthogonality between adjacent flat wire pairs must be maintained throughout the length of the cable to ensure maximal benefit. This may be accomplished by close-fitting external jackets and conductive sheaths that provide an approximately square cross section to an entire cable assembly as illustrated in
Although specific embodiments are illustrated and described herein, any component arrangement configured to achieve the same purposes and advantages may be substituted in place of the specific embodiments disclosed. This disclosure is intended to cover any and all adaptations or variations of the embodiments of the invention provided herein. All the descriptions provided in the specification have been made in an illustrative sense and should in no manner be interpreted in any restrictive sense. The scope, of various embodiments of the invention whether described or not, includes any other applications in which the structures, concepts and methods of the invention may be applied. The scope of the various embodiments of the invention should therefore be determined with reference to the appended claims, along with the full range of equivalents to which such claims are entitled. Similarly, the abstract of this disclosure, provided in compliance with 37 CFR §1.72(b), is submitted with the understanding that it will not be interpreted to be limiting the scope or meaning of the claims made herein. While various concepts and methods of the invention are grouped together into a single ‘best-mode’ implementation in the detailed description, it should be appreciated that inventive subject matter lies in less than all features of any disclosed embodiment, and as the claims incorporated herein indicate, each claim is to viewed as standing on its own as a preferred embodiment of the invention.
This application is a continuation of U.S. utility patent application Ser. No. 11/654168, entitled “Shielded flat pair cable with integrated resonant filter compensation”, the specification and claims of which are fully incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11654168 | Jan 2007 | US |
| Child | 11713778 | US |
