Crosstalk

Signals in one channel affecting another

In electronics, crosstalk is a 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. Where the electric, magnetic, or traveling fields of two electric signals overlap, the electromagnetic interference created 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 creates between the signals, resulting in crosstalk. Crosstalk is a significant issue in structured cabling, audio electronics, integrated circuit design, wireless communication and other communications systems.

In stereo audio reproduction, crosstalk can refer to signal leakage 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 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. 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. Good crosstalk performance for a stereo system is not difficult to achieve in today's digital audio systems, though it is hard to keep below the desired figure of 30 dB or so on vinyl recordings and FM radio.

In telecommunication or telephony, crosstalk is often distinguishable as pieces of speech or in band signaling tones leaking from other people's connections. 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. 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 a 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 bleeds into the other like a double exposure, which produces a ghosting effect.