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low voltage differential signalling (LVDS)

Low Voltage Differential Signaling (LVDS) can be described with the simple phrase"gigabit with milliwatts". LVDS is a protocol for display interfaces based on an initiative of Texas Instruments and National Semiconductor and standardized by the Visual Interface Consortium International (VICI), as well as ANSI and TIA/ EIA

Via LVDS, which forms a physical layer for digital graphics data, the data is transmitted differentially with a significantly reduced signal level. Compared to the Local Multipoint Distribution Service( LMDS), the LVDS method is characterized by improved noise immunity over long cable lengths and extremely low power consumption.

LVDS interface with differential transmission

LVDS interface with differential transmission

These advantages are due to the current limitation of the driver to 3 mA and the differential signal for transmission. The current control has the advantages that short-circuited transmission lines do not lead to overload and that there is extremely low electromagnetic interference( EMI). The differential amplifiers at the receiving end amplify the relatively low signal levels, which can be as low as 20 mV, to standard logic levels. With LVDS, the switching levels are reduced to 300 mV, which on the one hand reduces the interference and on the other hand increases the switching speed.

LVDS for high-speed transmissions

Comparison of the digital interfaces DisplayPort, LVDS, DVI and HDMI

Comparison of the digital interfaces DisplayPort, LVDS, DVI and HDMI

Via LVDS, the three serialized color signals R, G, B with the horizontal and vertical synchronization as well as the clock signal are transmitted. Each color signal is transmitted as a differential signal via a twisted pair of conductors. With a color resolution of 6 bits per color signal, i.e. 18 bits for RGB, and 3 bits for the synchronization characters, 21 bits are transmitted over three data channels with each clock signal. With a clock frequency of 50 MHz and serialization of 7:1, this results in a data rate of 350 MHz per channel or 1.050 Gbit/s for the three channels. With a higher color resolution and four transmission channels, the data rate increases accordingly.

LVDS is suitable for high-speed data transfer with data rates of over 655 Mbit/s per channel. A theoretical maximum of 1.923 Gbit/s is specified. LVDS can be used directly on and between printed circuit boards, modules, racks or LCD displays. It is used in stackable hubs, ATM switches, flat panel displays and servers, peripherals such as printers and digital copiers, high-resolution displays in industrial applications and flat panel displays in automotive applications, among others. With LVDS, resolutions up to 2,048 x 1,536 pixels are possible, at a refresh rate of 60 Hz. The LVDS protocol is transmitted between the computer and the display via the FPD link.

As transmission media, LVDS can use twisted copper cables with a maximum line length of 10 m or lines on a printed circuit board. As interface LVDS uses OpenLDI (Open LVDS Digital Interface) a 36- pin Sub-D connector or MDR connector. OpenLDI supports high graphics resolutions of Ultra-XGA( UXGA) and higher and a color depth of 24 bits, resulting in a data throughput of over 5 Gbps. For notebooks, LVDS technology has been replaced by Embedded DisplayPort( eDP).

Englisch: low voltage differential signalling - LVDS
Updated at: 16.11.2018
#Words: 492
Links: gigabit, protocol, display, American national standards institute (ANSI), telecommunications industry association (TIA)
Translations: DE

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