FPD-Link
Encyclopedia
Flat Panel Display Link by National Semiconductor is a high-speed interface connecting the output of a video controller in a laptop
computer, computer monitor or LCD television set to the display panel. Most laptops, LCD computer monitors and LCD TVs use this interface internally. (Laptops produced before around 1995 and some devices with much lower display resolutions use a TTL
or CMOS
voltage interfaces instead.) However, DisplayPort
is currently in the process of replacing FPD-Link as an internal interface.
FPD-Link uses LVDS
, and it was the first large-scale application of the LVDS signaling standard. It uses LVDS on one twisted pair
in order to transmit a clock signal, and on the three or more remaining wire pairs it uses LVDS to transmit video data at a bit rate that is seven times the frequency of the clock signal. Since one of those bits indicates whether or not the other six bits transmitted in the clock cycle period needed to be inverted in order to maintain DC balance, each twisted pair other than the clock pair effectively transmits six bits per pair per clock cycle. Since FPD-Link was the first use of LVDS, many display engineers use the terms FPD-Link and LVDS synonymously.
FPD-Link II is a newer version of FPD-Link. The FPD-Link II enhancement embeds the clock signal in the data signal and therefore uses only one differential pair to transmit both the clock and data.
More recently, FPD-Link III embeds bidirectional communications between the source and destination on the one differential pair of FPD-Link II.
There is another display interface which uses LVDS: OpenLDI
. It is based on FPD-Link, but allows longer cable lengths, and is a rarely used method to connect external display panels to computers. Modern stand-alone LCD
display panels for desktop computers use a completely different interface such as DVI
.
Laptop
A laptop, also called a notebook, is a personal computer for mobile use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device and speakers into a single unit...
computer, computer monitor or LCD television set to the display panel. Most laptops, LCD computer monitors and LCD TVs use this interface internally. (Laptops produced before around 1995 and some devices with much lower display resolutions use a TTL
Transistor-transistor logic
Transistor–transistor logic is a class of digital circuits built from bipolar junction transistors and resistors. It is called transistor–transistor logic because both the logic gating function and the amplifying function are performed by transistors .TTL is notable for being a widespread...
or CMOS
CMOS
Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
voltage interfaces instead.) However, DisplayPort
DisplayPort
DisplayPort is a digital display interface standard produced by the Video Electronics Standards Association . The specification defines a royalty-free digital interconnect for audio and video. The interface is primarily used to connect a video source to a display device such as a computer monitor...
is currently in the process of replacing FPD-Link as an internal interface.
FPD-Link uses LVDS
Low voltage differential signaling
Low-voltage differential signaling, or LVDS, is an electrical digital signaling system that can run at very high speeds over inexpensive 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...
, and it was the first large-scale application of the LVDS signaling standard. It uses LVDS on one twisted pair
Twisted pair
Twisted pair cabling is a type of wiring in which two conductors are twisted together for the purposes of canceling out electromagnetic interference from external sources; for instance, electromagnetic radiation from unshielded twisted pair cables, and crosstalk between neighboring pairs...
in order to transmit a clock signal, and on the three or more remaining wire pairs it uses LVDS to transmit video data at a bit rate that is seven times the frequency of the clock signal. Since one of those bits indicates whether or not the other six bits transmitted in the clock cycle period needed to be inverted in order to maintain DC balance, each twisted pair other than the clock pair effectively transmits six bits per pair per clock cycle. Since FPD-Link was the first use of LVDS, many display engineers use the terms FPD-Link and LVDS synonymously.
FPD-Link II is a newer version of FPD-Link. The FPD-Link II enhancement embeds the clock signal in the data signal and therefore uses only one differential pair to transmit both the clock and data.
More recently, FPD-Link III embeds bidirectional communications between the source and destination on the one differential pair of FPD-Link II.
Other systems
Automotive infotainment displays are another application that started using FPD-Link. Now many of the infotainment applications are using FPD-Link II to take advantage of the benefits provided by the embedded clock signal; one being the reduce cable size and weight due to the single wire pair for all the data and the clock.There is another display interface which uses LVDS: OpenLDI
OpenLDI
OpenLDI is a high-bandwidth digital interface standard for connecting flat panel LCD monitors to computers. While it is virtually unknown in standalone displays, it has a strong basis in the interconnect for internal displays, as in laptops. OpenLDI is based on the de-facto FPD-Link specification...
. It is based on FPD-Link, but allows longer cable lengths, and is a rarely used method to connect external display panels to computers. Modern stand-alone LCD
Liquid crystal display
A liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....
display panels for desktop computers use a completely different interface such as DVI
Digital Visual Interface
The Digital Visual Interface is a video interface standard covering the transmission of video between a source device and a display device. The DVI standard has achieved widespread acceptance in the PC industry, both in desktop PCs and monitors...
.