Crosstalk

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In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, inductive, or conductive coupling from one circuit or channel to another.

Electronics physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter

Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter.

Signal varying physical quantity that conveys information

In signal processing, a signal is a function that conveys information about a phenomenon. In electronics and telecommunications, it refers to any time varying voltage, current or electromagnetic wave that carries information. A signal may also be defined as an observable change in a quantity.

Electronic circuit electrical circuit with active components such as transistors, valves and integrated circuits; electrical network that contains active electronic components, generally nonlinear and require complex design and analysis tools

An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow. To be referred to as electronic, rather than electrical, generally at least one active component must be present. The combination of components and wires allows various simple and complex operations to be performed: signals can be amplified, computations can be performed, and data can be moved from one place to another.

Contents

Crosstalk is a significant issue in structured cabling, audio electronics, integrated circuit design, wireless communication and other communications systems.

Structured cabling telecommunications cabling infrastructure

In telecommunications, structured cabling is building or campus cabling infrastructure that consists of a number of standardized smaller elements called subsystems.

Audio electronics implementation of electronic circuit designs to perform conversions of sound/pressure wave signals to electrical signals, or vice versa

Audio electronics is the implementation of electronic circuit designs to perform conversions of sound/pressure wave signals to electrical signals, or vice versa. Electronic circuits considered a part of audio electronics may also be designed to achieve certain signal processing operations, in order to make particular alterations to the signal while it is in the electrical form. Additionally, audio signals can be created synthetically through the generation of electric signals from electronic devices. Audio Electronics were traditionally designed with analog electric circuit techniques until advances in digital technologies were developed. Moreover, digital signals are able to be manipulated by computer software much the same way audio electronic devices would, due to its compatible digital nature. Both analog and digital design formats are still used today, and the use of one or the other largely depends on the application. The following is a partial list of audio-related circuits/techniques/devices:

Integrated circuit design Engineering process for electronic hardware

Integrated circuit design, or IC design, is a subset of electronics engineering, encompassing the particular logic and circuit design techniques required to design integrated circuits, or ICs. ICs consist of miniaturized electronic components built into an electrical network on a monolithic semiconductor substrate by photolithography.

In cabling

In structured cabling, crosstalk refers to electromagnetic interference from one unshielded twisted pair to another twisted pair, normally running in parallel. Signals traveling through adjacent pairs of wire interfere with each other. The pair causing the interference is called the “disturbing pair”, while the pair experiencing the interference is the “disturbed pair”.

Electromagnetic interference Disturbance generated in an electrical circuit due to external fields or sources of radio-frequency electromagnetic radiation

Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction. The disturbance may degrade the performance of the circuit or even stop it from functioning. In the case of a data path, these effects can range from an increase in error rate to a total loss of the data. Both man-made and natural sources generate changing electrical currents and voltages that can cause EMI: ignition systems, cellular network of mobile phones, lightning, solar flares, and auroras. EMI frequently affects AM radios. It can also affect mobile phones, FM radios, and televisions, as well as observations for radio astronomy and atmospheric science.

Twisted pair wiring in which two conductors of a circuit are twisted together to improve electromagnetic compatibility

Twisted pair cabling is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted balanced pair, a twisted pair reduces electromagnetic radiation from the pair and crosstalk between neighboring pairs and improves rejection of external electromagnetic interference. It was invented by Alexander Graham Bell.

Near end crosstalk (NEXT)
NEXT is a measure of the ability of a cable to reject crosstalk, so the higher the NEXT value, the greater the rejection of crosstalk at the local connection. It is referred to as Near End because the interference between the two signals in the cable is measured at the same end of the cable as the interfering transmitter. The NEXT value for a given cable type is generally expressed in decibels per feet or decibels per 1000 feet and varies with the frequency of transmission. General specifications for cabling (such as CAT 5) usually include the minimum NEXT values. [1]
Power sum near end crosstalk (PSNEXT)
PSNEXT is a NEXT measurement which includes the sum of crosstalk contributions from all adjacent pairs as an algebraic sum of the NEXT of the three wire pairs as they affect the fourth pair in a four-pair cable (e.g., Category 6 cable). [1] The Superior Modular Products White paper [2] states that the testing process for PSNEXT consists of measuring all pair-to-pair crosstalk combinations and then summing all of the values for each pair. The specification was developed to directly address the effect of transmissions on multiple adjacent pairs on the pair being tested and is relevant to all connecting hardware and associated communications cables.
Cabling bandwidths in excess of 100 MHz (Category 5 cable bandwidth) make consideration of PSNEXT more important as Gigabit Ethernet through Cat-6 uses all four wire pairs simultaneously and bidirectionally. The additional wire pair usage and growing bandwidth increases the need to keep NEXT in check.
Far end crosstalk (FEXT)
FEXT measures the interference between two pairs of a cable measured at the far end of the cable with respect to the interfering transmitter. [1]
Equal level far end crosstalk (ELFEXT)
ELFEXT measures the FEXT with attenuation compensation. [1]
Alien crosstalk (AXT)
AXT is interference caused by other cables routed close to the cable of interest as opposed to signals contained in the same cable. [3]

In audio

IBA Crosstalk weighting curve.svg

In stereo audio reproduction, crosstalk can refer to signal leaking across from one program channel to another, reducing channel separation and stereo imaging. Crosstalk between channels in mixing consoles, and between studio feeds is a much more noticeable problem, as these are likely to be carrying very different programmes or material.

Stereo imaging refers to the aspect of sound recording and reproduction concerning the perceived spatial locations of the sound source(s), both laterally and in depth. An image is considered to be good if the location of the performers can be clearly located; the image is considered to be poor if the location of the performers is difficult to locate. A well-made stereo recording, properly reproduced, can provide good imaging within the front quadrant; a well-made Ambisonic recording, properly reproduced, can offer good imaging all around the listener and even including height information.

Crosstalk is an electrical effect and can be quantified with a crosstalk measurement. Crosstalk measurements are made on audio systems to determine the amount of signal leaking across from one channel to another. The Independent Broadcasting Authority published a weighting curve for use in crosstalk measurement that gives due emphasis to the subjective audibility of different frequencies. In the absence of any international standards, this is still in use despite the demise of the IBA.[ citation needed ]

Independent Broadcasting Authority British television organisation

The Independent Broadcasting Authority (IBA) was the regulatory body in the United Kingdom for commercial television – and commercial and independent radio broadcasts. The IBA came into being when the Sound Broadcasting Act 1972 gave the Independent Television Authority responsibility for organising the new Independent Local Radio (ILR) stations. The Independent Television Commission formally replaced the IBA on 1 January 1991 in regulatory terms; however, the Authority itself was not officially dissolved until 2003.

A weighting curve is a graph of a set of factors, that are used to 'weight' measured values of a variable according to their importance in relation to some outcome. An important example is frequency weighting in sound level measurement where a specific set of weighting curves known as A, B, C and D weighting as defined in IEC 61672 are used. Unweighted measurements of sound pressure do not correspond to perceived loudness because the human ear is less sensitive at low and high frequencies, with the effect more pronounced at lower sound levels. The four curves are applied to the measured sound level, for example by the use of a weighting filter in a sound level meter, to arrive at readings of loudness in Phons or in decibels (dB) above the threshold of hearing..

Good crosstalk performance for a stereo system is not difficult to achieve in today's digital audio systems, though it was hard to keep below the desired figure of -30 dB[ citation needed ] or so on vinyl recordings and FM radio.

Digital audio technology that records, stores, and reproduces sound

Digital audio is sound that has been recorded in, or converted into, digital form. In digital audio, the sound wave of the audio signal is encoded as numerical samples in continuous sequence. For example, in CD audio, samples are taken 44100 times per second each with 16 bit sample depth. Digital audio is also the name for the entire technology of sound recording and reproduction using audio signals that have been encoded in digital form. Following significant advances in digital audio technology during the 1970s, it gradually replaced analog audio technology in many areas of audio engineering and telecommunications in the 1990s and 2000s.

Other examples

In telecommunication or telephony, crosstalk is often distinguishable as pieces of speech or in-band signaling tones leaking from other people's connections. [4] If the connection is analog, twisted pair cabling can often be used to reduce crosstalk. Alternatively, the signals can be converted to digital form, which is typically less susceptible to crosstalk.

In wireless communication, crosstalk is often denoted co-channel interference, and is related to adjacent-channel interference.[ clarification needed ]

In integrated circuit design, crosstalk normally refers to a signal affecting another nearby signal. Usually the coupling is capacitive, and to the nearest neighbor, but other forms of coupling and effects on signal further away are sometimes important, especially in analog designs. See signal integrity for tools used to measure and prevent this problem, and substrate coupling for a discussion of crosstalk conveyed through the integrated circuit substrate. There are a wide variety of repair solutions, with increased spacing, wire re-ordering, and shielding being the most common.

In full-field optical coherence tomography, "crosstalk" refers to the phenomenon that due to highly scattering objects, multiple scattered photons reach the image plane and generate coherent signal after traveling a pathlength that matches that of the sample depth within a coherence length.

In stereoscopic 3D displays, "crosstalk" refers to the incomplete isolation of the left and right image channels so that one leaks or bleeds into the other - like a double exposure, which produces a ghosting effect.

See also

Related Research Articles

In telecommunications and professional audio, a balanced line or balanced signal pair is a transmission line consisting of two conductors of the same type, each of which have equal impedances along their lengths and equal impedances to ground and to other circuits. The chief advantage of the balanced line format is good rejection of external noise when fed to a differential amplifier. Common forms of balanced line are twin-lead, used for radio frequency signals and twisted pair, used for lower frequencies. They are to be contrasted to unbalanced lines, such as coaxial cable, which is designed to have its return conductor connected to ground, or circuits whose return conductor actually is ground. Balanced and unbalanced circuits can be interconnected using a transformer called a balun.

Capacitive coupling

Capacitive coupling is the transfer of energy within an electrical network or between distant networks by means of displacement current between circuit(s) nodes, induced by the electric field. This coupling can have an intentional or accidental effect.

Electromagnetic compatibility

Electromagnetic compatibility (EMC) is the ability of electrical equipment and systems to function acceptably in their electromagnetic environment, by limiting the unintentional generation, propagation and reception of electromagnetic energy which may cause unwanted effects such as electromagnetic interference (EMI) or even physical damage in operational equipment. The goal of EMC is the correct operation of different equipment in a common electromagnetic environment. It is also the name given to the associated branch of electrical engineering.

Category 5 cable

Category 5 cable, commonly referred to as Cat 5, is a twisted pair cable for computer networks. Since 2001, the variant commonly in use is the Category 5e specification (Cat 5e). The cable standard provides performance of up to 100 MHz and is suitable for most varieties of Ethernet over twisted pair up to 1000BASE-T. Cat 5 is also used to carry other signals such as telephony and video.

Frequency-division multiplexing multiplexing dividing a comm medium into non-overlapping frequency bands, each carrying a separate signal

In telecommunications, frequency-division multiplexing (FDM) is a technique by which the total bandwidth available in a communication medium is divided into a series of non-overlapping frequency bands, each of which is used to carry a separate signal. This allows a single transmission medium such as a cable or optical fiber to be shared by multiple independent signals. Another use is to carry separate serial bits or segments of a higher rate signal in parallel.

Communication channel physical transmission medium such as a wire, or logical connection

A communication channel or simply channel refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking. A channel is used to convey an information signal, for example a digital bit stream, from one or several senders to one or several receivers. A channel has a certain capacity for transmitting information, often measured by its bandwidth in Hz or its data rate in bits per second.

Selectivity is a measure of the performance of a radio receiver to respond only to the radio signal it is tuned to and reject other signals nearby in frequency, such as another broadcast on an adjacent channel.

Balanced audio is a method of interconnecting audio equipment using balanced lines. This type of connection is very important in sound recording and production because it allows the use of long cables while reducing susceptibility to external noise caused by electromagnetic interference.

A subcarrier is a sideband of a radio frequency carrier wave, which is modulated to send additional information. Examples include the provision of colour in a black and white television system or the provision of stereo in a monophonic radio broadcast. There is no physical difference between a carrier and a subcarrier; the "sub" implies that it has been derived from a carrier, which has been amplitude modulated by a steady signal and has a constant frequency relation to it.

Differential signaling method for electrically transmitting information using two complementary signals

Differential signaling is a method for electrically transmitting information using two complementary signals. The technique sends the same electrical signal as a differential pair of signals, each in its own conductor. The pair of conductors can be wires or traces on a circuit board. The receiving circuit responds to the electrical difference between the two signals, rather than the difference between a single wire and ground. The opposite technique is called single-ended signalling. Differential pairs are usually found on printed circuit boards, in twisted-pair and ribbon cables, and in connectors.

Shielded cable electrical conductors enclosed by a conductive layer

A shielded cable or screened cable is an electrical cable of one or more insulated conductors enclosed by a common conductive layer. The shield may be composed of braided strands of copper, a non-braided spiral winding of copper tape, or a layer of conducting polymer. Usually this shield is covered with a jacket.

Grid dip oscillator

Grid dip oscillator (GDO), also called grid dip meter, gate dip meter, dip meter, or just dipper, is a type of electronic instrument that measures the resonant frequency of unconnected, nearby radio frequency circuits. It is a variable frequency oscillator that circulates a small-amplitude signal through an exposed coil, whose electromagnetic field can interact with adjacent circuitry. The oscillator loses power when its coil is near a circuit that resonates at the same frequency. A meter on the GDO registers the amplitude drop, or “dip”, hence the name.

Noise (electronics) random fluctuation in an electrical signal

In electronics, noise is an unwanted disturbance in an electrical signal. Noise generated by electronic devices varies greatly as it is produced by several different effects.

In an integrated circuit, a signal can couple from one node to another via the substrate. This phenomenon is referred to as substrate coupling or substrate noise coupling.

Video sender Device for transmitting audio and video signals wirelessly

A video sender is a device for transmitting domestic audio and video signals wirelessly from one location to another. It is most commonly used for sending the output of a source device, such as a satellite television decoder, to a television in another part of a property and provides an alternative to cable installations.

Copper cable certification

In copper twisted pair wire networks, copper cable certification is achieved through a thorough series of tests in accordance with Telecommunications Industry Association (TIA) or International Organization for Standardization (ISO) standards. These tests are done using a certification-testing tool, which provide pass or fail information. While certification can be performed by the owner of the network, certification is primarily done by datacom contractors. It is this certification that allows the contractors to warranty their work.

Oscilloscope type of electronic test instrument

An 'oscilloscope', previously called an 'oscillograph', and informally known as a scope or o-scope, CRO, or DSO, is a type of electronic test instrument that graphically displays varying signal voltages, usually as a two-dimensional plot of one or more signals as a function of time. Other signals can be converted to voltages and displayed.

Star quad cable

Star-quad cable is a four conductor cable that has a special quadrupole geometry that provides magnetic immunity when used in a balanced line. Four conductors are used to carry the two legs of the balanced line. All four conductors must be an equal distance from a common point. The four conductors are arranged in a four-pointed star. Opposite points of the star are connected together at each end of the cable to form each leg of the balanced circuit.

References

  1. 1 2 3 4 "Category 5 / 5E & Cat 6 Cabling Tutorial and FAQ's". lanshack.com. Archived from the original on 2013-01-17. Retrieved 2013-01-05.
  2. "Component Level PowerSum Compliance and RJ21X Connectivity Solutions (Superior Modular Products White paper)" (PDF). Archived from the original (PDF) on July 16, 2006. Retrieved 2008-09-13.
  3. Eliminating alien crosstalk, Communications News, February 2009, archived from the original on 2010-02-09
  4. "crosstalk (XT)". Federal Standard 1037C glossary. Retrieved 2018-03-26.

PD-icon.svg This article incorporates  public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188 ).