Crosstalk

For other uses, seeCrosstalk (disambiguation).

Not to be confused withSpill (audio).

Inelectronics,crosstalkis a phenomenon by which asignaltransmitted on onecircuitorchannelof atransmission systemcreates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesiredcapacitive,inductive,orconductive couplingfrom one circuit or channel to another.

Where the electric, magnetic, or traveling fields of two electric signals overlap, theelectromagnetic interferencecreated causes crosstalk. For example, crosstalk can comprise magnetic fields that induce a smaller signal in neighboring wires.

In electrical circuits sharing a common signal return path, electrical impedance in the return path createscommon impedance couplingbetween the signals, resulting in crosstalk.

Crosstalk is a significant issue instructured cabling,audio electronics,integrated circuit design,wireless communicationand othercommunications systems.

In cabling

In structured cabling, crosstalk refers toelectromagnetic interferencefrom one unshieldedtwisted pairto another twisted pair, normally running in parallel. Signals traveling through adjacent pairs of wire create magnetic fields that interact with each other, inducing interference in the neighboring pair. The pair causing the interference is called thedisturbing pair,while the pair experiencing the interference is thedisturbed pair.

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 asnear endbecause 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.

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).The Superior Modular Products White paperstates 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 bandwidth in excess of 100 MHz (Category 5 cablebandwidth) make consideration of PSNEXT more important asGigabit EthernetthroughCat 6uses 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.

Equal level far end crosstalk (ELFEXT)

ELFEXT measures the FEXT with attenuation compensation.

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.

In audio

Instereoaudio reproduction, crosstalk can refer to signal leakage across from one program channel to another, reducing channel separation andstereo 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 programs or material.

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 from one channel to another. TheIndependent Broadcasting Authoritypublished aweighting curvefor 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.

Good crosstalk performance for a stereo system is not difficult to achieve in today'sdigital audiosystems, though it is hard to keep below the desired figure of -30 dBor so onvinyl recordingsandFM radio.

Other examples

Intelecommunicationortelephony,crosstalk is often distinguishable as pieces of speech orin-band signalingtones leaking from other people's connections.If the connection is analog,twisted paircabling can often be used to reduce crosstalk. Alternatively, the signals can be converted to digital form, which is typically less susceptible to crosstalk.

Inwireless communication,crosstalk is often denotedco-channel interference,and is related toadjacent-channel interference.

Inintegrated 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. Seesignal integrityfor tools used to measure and prevent this problem, andsubstrate couplingfor a discussion of crosstalk conveyed through theintegrated circuitsubstrate. There are a wide variety of repair solutions, with increased spacing, wire re-ordering, and shielding being the most common.

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

Instereoscopic 3D displays,crosstalk refers to the incomplete isolation of the left and right image channels so that one bleeds into the other - like adouble exposure,which produces aghostingeffect.

See also

• Attenuation-to-crosstalk ratio
• Audio system measurements
• Print-through
• Signal integrity
• Signal-to-interference ratio(SIR orS/I), also known ascarrier-to-interference ratio(CIR orC/I)
• Substrate coupling
• Unger model

References

This article incorporatespublic domain materialfromFederal Standard 1037C.General Services Administration.Archived fromthe originalon 2022-01-22.(in support ofMIL-STD-188).

External links

• Crosstalk: Overview and Modes (ppt)at theWayback Machine(archived 2012-03-18)
• Minimizing Crosstalk in Wiring and Cabling