LVDS system

The need for higher bandwidth is increasing and to meet to this demand, system designers are opting for differential signalling. This measure minimises power requirement, increases noise immunity and brings down Electromagnetic Interference (EMI)/Radio Frequency Interference (RFI) emissions. Low Voltage Differential Signalling (LVDS) is an electrical signalling system that has the ability to run at very high speeds over economical and twisted-pair copper wires. Being a differential signalling system, LVDS conducts two different voltages which are compared at the receiver. It has been well received in computer applications, where it constitutes a part of very high-speed networks. In the telecommunications and networking world, LVDS is one of the most popular standards for high-speed serial interconnects.

LVDS system provides very rapid data transmission, common-mode noise rejection and low power utilisation over a broad range of frequency. LVDS is defined by two industry standards: The American National Standards Institute/Telecommunications Industry Association/Electronic Industries Alliance–644-1995 (ANSI/TIA/EIA-644-1995) and IEEE 1596.3 SCI-LVDS. The ANSI/TIA/EIA-644 standard defines LVDS electrical specifications that include driver and receiver electrical characteristics. This standard does not encompass the functional specifications, interconnect, transmission medium characteristics or protocols because they are independent of application. This is a generic standard and is intended for multiple applications.

The other standard, the IEEE 1596.3 SCI-LVDS, is a subset of SCI (Scalable Coherent Interface). It is comparable to the ANSI/TIA/EIA-644 standard but is different in the proposed usage of the interface. Three configurations are used in LVDS applications – point-to-point, multi-point and multi-drop configurations. In point-to-point configuration, which is ideal for LVDS, there is one transmitter and one receiver. In multi-drop LVDS configuration, there is one transmitter and multiple receivers. Multi-point LVDS configurations feature multiple transmitters and receivers. LVDS is extensively used in the telecommunications sector in a range of applications such as routers, switches, add/drop multiplexers and hubs. It is also used in point–to–point, rack–to–rack and box–to–box network processors, among others.

The advantages with LVDS are that it is specified to be technology and process independent. It is EMI/RFI tolerant. As no transmission medium is defined in the standard, the medium can be customised to meet the specific requirements of the application. The typical LVDS voltage swing being 350 mV, the data transfer rate will be high and power consumption will be low. The LVDS Standard’s Working Group defined only the electrical characteristics. This makes LVDS a multipurpose interface standard and each application that uses LVDS can have a specific protocol and interconnect standard.


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