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Laptop Screen Signalling Interfaces - LVDS & EDP



Like a television requires a signal cable, so does a laptop or tablet screen. The cable for the LCD screen fitted to a computer, comes from the computer's motherboard (main board or logic board), and attaches to the back of the screen via a connector. The connectors come in different shapes and sizes, with different amounts of pin connections

Not only are the connectors and cables different, with different screen models, but the signalling type is also different. The signalling type, is, if you like the language the computer uses to talk to the screen, and therefore send the images you see to the display.

Signalling types differ not only in language but also in speed.

LVDS

655 Mbit/s (rates up to 1-3 Gbit/s possible)

Older LCD screens use LVDS signalling. Low Voltage Differential Signalling was introduced in 1994, and quickly became popular in laptop computers due to the high speed video that was achievable. Previously, the lower resolutions that computers used, such as VGA and SVGA, did not require such a high speed data transmission, however with the advent of XGA and WXGA onwards, a bigger bandwidth was required. 

LVDS operated at low power, as low as 1.2v, making it ideal for battery operated devices, such as a laptop computer, and could operate with cheaper quality twisted pair copper cables. It placed little demand on the power supply Because of this, it quickly became a standard for laptop display technology.

Although introduced in 1994 into the PC market, Apple had two years previously developed a signalling technology (BUS) called QuickRing, with the help of National Semi Conductor (NSC), for use in Macintosh computers.

EDP

8 Gbit/s per lane (rates up to 255.92 Gbit/s possible for a 4 - lane link)

eDP or Embedded Display Port, developed in 2006 by a consortium of industry leaders, and introduced by VESA in 2008, is a more modern signalling interface, that has become more popular with the laptop and tablet display industry since around 2013. Newer display panels use eDP signalling. 

eDP uses even less power than LVDS, enhancing battery life further and requires less wires, which is why usually eDP laptop screens and their connecting cables use have smaller connectors with less pins. Typical 40 PIN LVDS screens are reproduced in the eDP standard with smaller 30 PIN connectors.

eDP offers much higher signal bandwidth and allows for high refresh rates, colour depths and ultra high screen resolutions like UHD / 4K and higher.

Embedded Display Port (eDP) was developed by VESA, the Video Electronics Standards Association, the people who designed the original VGA standard for IBM computers, and thus promises better standardisation


This standardisation should make eDP screens more compatible with each other, but unfortunately reality doesn't agree with the design, and newer eDP screens seem to be less interchangeable than their older LVDS cousins, making supplying compatible replacements even more difficult than it was before.That of course is a good thing for us =)

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