Low voltage differential signaling, or LVDS, is an electrical signaling system that can run at very high speeds over cheap, twisted-pair copper cables. It was introduced in 1994, and has since become very popular in computers, where it forms part of very high-speed networks and computer buses. It has been suggested that Unshielded twisted pair be merged into this article or section. ... 1994 (MCMXCIV) was a common year starting on Saturday of the Gregorian calendar, and was designated as the International Year of the Family and the International Year of the Sport and the Olympic Ideal by United Nations. ... A BlueGene supercomputer cabinet. ... RJ-45 patchcord of the type commonly used to connect network devices. ... In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers and typically is controlled by device driver software. ...

Differential vs. single-ended signaling

LVDS is a differential signaling system, which means that it transmits two different voltages which are compared at the receiver. LVDS uses this difference in voltage between the two wires to encode the information. The transmitter injects a small current, nominally 3.5 milliamperes, into one wire or the other, depending on the logic level to be sent. The current passes through a resistor of about 100 to 120 Ω (matched to the characteristic impedance of the cable) at the receiving end, then returns in the opposite direction along the other wire. From Ohm's law, the voltage difference across the resistor is therefore about 350 millivolts. The receiver senses the polarity of this voltage to determine the logic level. This type of signalling is called a current loop. It has been suggested that this article or section be merged into Low voltage differential signaling. ... Current can be measured by a galvanometer, via the deflection of a magnetic needle in the magnetic field created by the current. ... The characteristic impedance of a uniform transmission line is the ratio of the amplitudes of a single pair of voltage and current waves propagating along the line in the absence of reflections. ... Ohms law states that, in an electrical circuit, the current passing through a conductor is directly proportional to the potential difference applied across them provided all physical conditions are kept constant. ... Josephson junction array chip developed by NIST as a standard volt. ... A current loop describes two different electrical signalling schemes. ...

The small amplitude of the signal and the tight electric- and magnetic-field coupling between the two wires reduces the amount of radiated electromagnetic noise. Amplitude is a nonnegative scalar measure of a waves magnitude of oscillation, that is, magnitude of the maximum disturbance in the medium during one wave cycle. ...

The low common-mode voltage (the average of the voltages on the two wires) of about 1.25 V allows LVDS to be used with a wide range of integrated circuits with power supply voltages down to 2.5 V or lower. The low differential voltage, about 350 mV as stated above, causes LVDS to consume very little power compared to other systems. For example, the static power dissipation in the LVDS load resistor is 1.2 mW, compared to the 90 mW dissipated by the load resistor for an RS-422 signal. Without a load resistor the whole wire has to be loaded and unloaded for every bit of data. Using high frequencies and a load resistor so that a single bit only covers a part of the wire (while traveling near light speed) is more power efficient. EIA-422 (formerly RS-422) is a serial data communication protocol which specifies 4-wire, full-duplex, differential line, multi-drop communications. ...

LVDS is not the only differential signaling system in use. See Differential signaling for a list of other differential signalling systems. LVDS is currently the only scheme that combines low power dissipation with high speed. It has been suggested that this article or section be merged into Low voltage differential signaling. ...

Applications

LVDS only became popular in the latter half of the 1990s. Before that, computers were too slow to make use of such fast data rates, and the need to run twice as many wires for the same amount of data outweighed the speed benefits. Yet multimedia and supercomputer users, both of whom needed to move large amounts of data over links several meters long (from a disk drive to a workstation, for instance) maintained a widespread interest in LVDS. This article or section does not cite its references or sources. ... A supercomputer is a computer that leads the world in terms of processing capacity, particularly speed of calculation, at the time of its introduction. ... Disk Drive is the afternoon show on CBC Radio Two. ... Sun SPARCstation 1+, 25mhz RISC processor from early 1990s A workstation, such as a Unix workstation, RISC workstation or engineering workstation, is a high-end technical computing desktop microcomputer designed primarily to be used by one person at a time, but can also be accessed remotely by other users when...

Two examples of LVDS use in computer buses come from HyperTransport and FireWire, both of which trace their ancestry back to the post-Futurebus work which also led to SCI. LVDS is supported in SCSI standards (Ultra-2 SCSI and later) to allow higher data rates and longer cable lengths. Serial ATA, RapidIO, and SpaceWire utilize LVDS to allow high speed data transfer. HyperTransport logo HyperTransport (HT), formerly known as Lightning Data Transport (LDT), is a bidirectional serial/parallel high-bandwidth, low-latency computer bus that was introduced on April 2, 2001 [1]. The HyperTransport Technology Consortium is in charge of promoting and developing HyperTransport technology. ... The 6-pin and 4-pin FireWire Connectors FireWire is a proprietary name of Apple Computer for the IEEE 1394 interface. ... Futurebus (IEEE 896) is a computer bus standard, intended to replace all local bus connections in a computer, including the CPU, memory, plug-in cards and even, to some extent, LAN links between machines. ... SCI, for Scalable Coherent Interconnect, is a high-speed computer bus that supports a variety of topologies, speeds and connection systems. ... This article or section does not cite its references or sources. ... This article or section does not cite its references or sources. ... The RapidIOâ„¢ architecture is a high-performance, packet-switched, interconnect technology for interconnecting chips on a circuit board and circuit boards using a backplane. ... SpaceWire is a spacecraft communication network based on the signaling system for IEEE 1355. ...

LVDS can also transport video data from graphics adapters to computer monitors, particularly flat panels, using the Flat Panel Display Link (FPD-Link) or OpenLDI standards. These standards allow a maximum pixel clock of 112 MHz, which suffices for a display resolution of 1400 x 1050 (SXGA+) at 60 Hz refresh. A dual link can boost the maximum display resolution to 2048 x 1536 (QXGA) at 60 Hz. FPD-Link works with cable lengths up to about 5 m, and LDI extends this to about 10 m. A GeForce 4 4200-based graphics card A graphics card or video card is a component of a computer which is designed to convert a logical representation of an image stored in memory to a signal that can be used as input for a display medium, most often a monitor... Nineteen inch (48 cm) CRT computer monitor A computer display, monitor or screen is a computer peripheral device capable of showing still or moving images generated by a computer and processed by a graphics card. ... Flat Panel Display Link (FPD-Link) is a high-speed interface connecting the output of a video card in a laptop computer to the display panel. ... OpenLDI is a high-bandwidth digital interface standard for connecting high-resolution flat panel LCD monitors to computers. ... SXGA+ stands for Super eXtended Graphics Array and is a computer display standard. ... The QXGA display standard and its derivatives are relatively new (as of 2005) resolution standards in display technology. ...

SerDes (Serializer/Deserializer)

LVDS is often used for serial data transmission, which involves sending data bit-by-bit down a single wire (as opposed to parallel transmission, in which several bits, usually in multiples of eight, are sent down many wires at once). Its high speed, and its use of in-channel synchronisation, makes it possible to send serial data faster than could be done with a parallel bus, and using fewer wires. The device for converting between serial and parallel data is called a serializer/deserializer, abbreviated to SerDes. A SERializer/DESerializer (SERDES) is a device used in high speed communications. ... This article needs to be cleaned up to conform to a higher standard of quality. ... In computing, a parallel port is an interface from a computer system where data is transferred in or out in parallel, that is, on more than one wire. ...

Multipoint LVDS

When serial data transmission is not fast enough, data can be transmitted in parallel form using an LVDS pair for each bit or even byte (as in PCI Express). This system is called bus LVDS, or BLVDS. Standard LVDS transmitters are designed for point-to-point links, but multipoint bus systems can be made using modified LVDS transmitters with high-current outputs that can drive multiple termination resistors. Bus LVDS and LVDM (by TI) are de facto multipoint LVDS standards. Multipoint LVDS (MLVDS) is the TIA standard (TIA-899) that has evolved and is used in AdvancedTCA for some clock distribution. PCI Express (formerly known as 3GIO for 3rd Generation I/O, not to be mistaken with PCI-X) is an implementation of the PCI computer bus that uses existing PCI programming concepts and communications standards, but bases it on a much faster serial communications system. ... In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers and typically is controlled by device driver software. ... Texas Instruments (NYSE: TXN), better known in the electronics industry (and popularly) as TI, is an American company based in Dallas, Texas, USA, renowned for developing and commercializing semiconductor and computer technology. ... The Telecommunications Industry Association (TIA) is the leading trade association for the information and communications technology (ICT) industry, with 600 member companies that manufacture or supply the products and services used in global communications across all technology platforms. ... Advanced Telecommunications Computing Architecture is the largest specification effort in the history of the PCI Industrial Computers Manufacturers Group (PICMG), with more than 100 companies participating. ...

MLVDS has two types of receivers. Type-1 are nearly compatible with LVDS and use a 0 Volt threshold. Type-2 use a 100mV threshold to handle in a consistent way various errors such as open and short circuits. For MLVDS: Open circuit can mean:- In electronics, where there is nothing connected to a load and no current can flow. ... For alternate meanings see Short circuit (disambiguation) A short circuit (sometimes known as simply a short) is a fault whereby electricity moves through a circuit in an unintended path, usually due to a connection forming where none was expected. ...

SCI-LVD

The present form of LVDS was preceded by an earlier attempt, SCI-LVD, which was a subset of the Scalable Coherent Interconnect (SCI) specified in the IEEE 1596.3 standard. It was designed for interconnecting multiprocessing systems. SCI, for Scalable Coherent Interconnect, is a high-speed computer bus that supports a variety of topologies, speeds and connection systems. ... The Institute of Electrical and Electronics Engineers or IEEE (pronounced as eye-triple-e) is an international non-profit, professional organization for the advancement of technology related to electricity. ... Multiprocessing is traditionally known as the use of multiple concurrent processes in a system as opposed to a single process at any one instant. ...

Standards

The ANSI/TIA/EIA-644-A (published in 2001) standard defines LVDS. This recommends a maximum data rate of 655 Mbit/s over twisted-pair copper wire, but predicts a possible speed of over 1.9 Gbit/s for an ideal transmission medium. The American National Standards Institute or ANSI (pronounced an-see) is a nonprofit organization that oversees the development of standards for products, services, processes and systems in the United States. ... The Telecommunications Industry Association (TIA) is the leading trade association for the information and communications technology (ICT) industry, with 600 member companies that manufacture or supply the products and services used in global communications across all technology platforms. ... The Electronic Industries Alliance (EIA, until 1997 Electronic Industries Association) is a trade organization for electronics manufacturers in the United States. ...

External links

• Introduction to LVDS
• LVDS tutorial

References

• An Overview of LVDS Technology, National Semiconductor, AN-971, July 1998.
• LVDS Owner's Manual, National Semiconductor, 3rd Edition, 2004