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FPD-Link

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Flat Panel Display Link (FPD-Link) is the original high-speed video interface created in 1996 by National Semiconductor (now the Silicon Valley Analog entity within Texas Instruments). It connects the output from a Video Display Processor (VDP) in a laptop, tablet computer, flat-panel monitor, or LCD TV to the display panel's timing controller. Most laptops, tablets, flat-panel monitors, and TVs use this interface internally. (Pre 1996 laptops and devices with lower display resolutions use a TTL or CMOS interface instead.) Internal DisplayPort intended to replace FPD-Link as an internal interface, but has not done so due to its high cost.

FPD-Link was the first large-scale application of the LVDS signaling standard. Since it was the first use of LVDS, many display engineers use the terms FPD-Link and LVDS synonymously. FPD-Link uses LVDS to transmit a clock signal on one twisted pair, and video data on three or more additional pairs. FPD-Link serializes seven video data bits per clock cycle into each of the twisted pair channels. Therefore, the bit rate is 7 times the frequency of the clock signal. For example, if the clock signal is 50 MHz, then the streaming video data rate will be 350 Mbps per twisted pair.

An FPD-Link interface with 3 data channels and 1 clock (3D+C) then reduces the 21-bit input down to 3D+C, which is perfect for 6-bits per Red, Green, and Blue (RGB) colors plus 3 video control bits. A 4D+C FPD-Link interface serializes 28-bits, which is 8-bits per RGB plus 4 video control bits. A 5D+C FPD-Link interface serializes 35-bits, which is 10-bits per RGB and 5 control bits.

FPD-Link II is an improved version of FPD-Link, and designed specifically for automotive infotainment and camera interface applications. FPD-Link II embeds the clock signal in the data signal and therefore uses only one differential pair to transmit both the clock and data.

FPD-Link III is the latest and greatest infotainment and camera interface standard. It embeds a bidirectional communication channel between the source and destination on the same differential pair. This channel transfers control signals between source and destination in addition to clock and the streaming video data.

Automotive and other system applications

Automotive infotainment displays for navigation systems started using FPD-Link in 2001. BMW was one of the first OEMs to use FPD-Link in their cars. Today many infotainment and driver assist applications are using FPD-Link II and FPD-Link III to benefit from the embedded clock and control signals. One of the main benefits is the reduced cable size and weight due to the single wire pair for all the data and clock signals.

There is another display interface based on FPD-Link, which is OpenLDI. Sometimes these two terms are used interchangeably. It enables longer cable lengths because of a built-in DC balance scheme to reduce the affects of Inter Symbol Interference (ISI). In the Open LDI version of this LVDS interface, one of the seven serialized bits indicates whether the coding scheme needs to invert the other six bits transmitted in the clock period to maintain DC balance. Therefore, each twisted pair other than the clock pair effectively transmits six bits per clock cycle. However, OpenLDI lost the video-transfer standards competition to DVI in the early twenty first century, and today stand-alone LCD display panels for desktop computers typically use DVI for the video transfer.

See also


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