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Giuliano · 01-05-2005, 05:51 AM

Quote: Originally Posted by Jackboot

how about more info about LVDS than just the acronym for us dummies here?

LVDS stands for Low Voltage Differential Signalling, and is one of the two commonly used LCD communication types, with the other being called TTL/CMOS.

LVDS and TTL/CMOS are most often used in laptops, where a direct digital connection to the LCD is required.

TTL/CMOS is the more common of the two signalling technologies, but it has some limitations, such as short cable length, and high number of pins/wires, often numbering in the 30-40 pin count.

As a result, LCD's with TTL/CMOS technologies cannot be very far from their controller, which is why you see LCD's like the Lilliput/Xenarc models with VGA controller boards.

LCD panels are not like analog glass-tube monitors - LCD's have a native physical resolution, and perform best only at that resolution, such as 640x480 or 800x600, or even the difficult to obtain 800x480 of widescreen LCD's.

VGA controller boards get around this limit by scaling down (or up) your PC's analog VGA signal to whatever physical resolution the LCD is capable of, which results in a blurry picture.

In addition, the process of conversion from digital to analog (VGA video port), and then back from analog (VGA LCD controller) back to digital (LCD itself) can lead to signal degredation and a fuzzy picture, because analog transmissions can easily be affected by EMI (electromagnetic interference).

TTL/CMOS wiring uses 1 wire for each bit of color resolution that the LCD is capable of - so if you have an 18-bit TTL/CMOS LCD capable of 262k colors, you have (at least) 18 wires to transmit signals on, not including power and ground lines, etc.. that many number of wires, and the method of signalling, can cause crosstalk (interference) problems in longer cables.

Because of this, TTL/CMOS data cables can not be longer than 6 or 12 inches, due to the interference over long lines.

LVDS solves this by transmitting the three color signals (Red, Green, Blue) on 6 wires, or 3 differential pairs. Because the signal is differential, or the difference between the signal on one wire and another, data can be transmitted farther than TTL/CMOS can, up to 12 meters with proper (shielded?) cabling.

The reason for LVDS's newfound popularity is simple - there are now Mini-ITX boards on the market that have LVDS transmitters on-board or as an option, and can easily drive the proper LCD's with the right cabling and knowledge.

Previously, in order to use a TTL/CMOS or LVDS LCD panel, you either had to have a VGA controller card attached to the LCD, a PCI LCD controller card attached to the PC, or you had to purchase a special "embedded" type of motherboard, usually in non-PC form factors such as PC/104 or boards the shape and size of a 5 1/4" drive.

Quote: Originally Posted by Yuriy

LVDS as in laptop LCDs? There have been a lot of laptop installs (including some of my own) but I doubt anyone actually connected something like that to a custom PC, the controller prices are simply horrid.

See, that's the point - you can now buy MiniITX motherboards with LVDS controllers built in (such as the Commell LV-670/671 P4 series), or as an option board (some Via Epia models).

The motherboards take care of all the LCD specific timing issues, and backlighting control, making it easier to use LCDs with these boards.

However, it won't work with just any LVDS LCD panel - the LCD panel has to support a specific resolution, color depth, and channeling (single/dual) such as 800x600 18-bit Single Channel, or 1280x1024 24-bit Dual Channel, and the video timing parameters for those LCD types must be supported by the motherboard's system bios for them to work.

This is why non-standard LCD sizes, such as the ever popular 7" widescreen 800x480 LCD's are not currently easily supported - it's because the motherboard manufacturers have not tested them and included the timing parameter set in their bios.

And that's even assuming you can locate and purchase a 7" widescreen LVDS panel - I've tried, and I can locate them easily enough, but it's next to impossible to buy one from a retailer or distributor, unless you want to buy tens of thousands at once.

The easy availability and standard resolution support of 4:3 aspect ratio LVDS LCDs make the possibility of an all-digital display solution that much more appealing, which is why I'm working on fitting a 8.4" 4:3 high-resolution screen in my WRX instead of a 7" widescreen Liliput or Xenarc.

01-05-2005, 05:51 AM	#4
Giuliano Maximum Bitrate Join Date: Feb 2004 Posts: 749 My Photos: ()	Quote: Originally Posted by Jackboot how about more info about LVDS than just the acronym for us dummies here? LVDS stands for Low Voltage Differential Signalling, and is one of the two commonly used LCD communication types, with the other being called TTL/CMOS. LVDS and TTL/CMOS are most often used in laptops, where a direct digital connection to the LCD is required. TTL/CMOS is the more common of the two signalling technologies, but it has some limitations, such as short cable length, and high number of pins/wires, often numbering in the 30-40 pin count. As a result, LCD's with TTL/CMOS technologies cannot be very far from their controller, which is why you see LCD's like the Lilliput/Xenarc models with VGA controller boards. LCD panels are not like analog glass-tube monitors - LCD's have a native physical resolution, and perform best only at that resolution, such as 640x480 or 800x600, or even the difficult to obtain 800x480 of widescreen LCD's. VGA controller boards get around this limit by scaling down (or up) your PC's analog VGA signal to whatever physical resolution the LCD is capable of, which results in a blurry picture. In addition, the process of conversion from digital to analog (VGA video port), and then back from analog (VGA LCD controller) back to digital (LCD itself) can lead to signal degredation and a fuzzy picture, because analog transmissions can easily be affected by EMI (electromagnetic interference). TTL/CMOS wiring uses 1 wire for each bit of color resolution that the LCD is capable of - so if you have an 18-bit TTL/CMOS LCD capable of 262k colors, you have (at least) 18 wires to transmit signals on, not including power and ground lines, etc.. that many number of wires, and the method of signalling, can cause crosstalk (interference) problems in longer cables. Because of this, TTL/CMOS data cables can not be longer than 6 or 12 inches, due to the interference over long lines. LVDS solves this by transmitting the three color signals (Red, Green, Blue) on 6 wires, or 3 differential pairs. Because the signal is differential, or the difference between the signal on one wire and another, data can be transmitted farther than TTL/CMOS can, up to 12 meters with proper (shielded?) cabling. The reason for LVDS's newfound popularity is simple - there are now Mini-ITX boards on the market that have LVDS transmitters on-board or as an option, and can easily drive the proper LCD's with the right cabling and knowledge. Previously, in order to use a TTL/CMOS or LVDS LCD panel, you either had to have a VGA controller card attached to the LCD, a PCI LCD controller card attached to the PC, or you had to purchase a special "embedded" type of motherboard, usually in non-PC form factors such as PC/104 or boards the shape and size of a 5 1/4" drive. Quote: Originally Posted by Yuriy LVDS as in laptop LCDs? There have been a lot of laptop installs (including some of my own) but I doubt anyone actually connected something like that to a custom PC, the controller prices are simply horrid. See, that's the point - you can now buy MiniITX motherboards with LVDS controllers built in (such as the Commell LV-670/671 P4 series), or as an option board (some Via Epia models). The motherboards take care of all the LCD specific timing issues, and backlighting control, making it easier to use LCDs with these boards. However, it won't work with just any LVDS LCD panel - the LCD panel has to support a specific resolution, color depth, and channeling (single/dual) such as 800x600 18-bit Single Channel, or 1280x1024 24-bit Dual Channel, and the video timing parameters for those LCD types must be supported by the motherboard's system bios for them to work. This is why non-standard LCD sizes, such as the ever popular 7" widescreen 800x480 LCD's are not currently easily supported - it's because the motherboard manufacturers have not tested them and included the timing parameter set in their bios. And that's even assuming you can locate and purchase a 7" widescreen LVDS panel - I've tried, and I can locate them easily enough, but it's next to impossible to buy one from a retailer or distributor, unless you want to buy tens of thousands at once. The easy availability and standard resolution support of 4:3 aspect ratio LVDS LCDs make the possibility of an all-digital display solution that much more appealing, which is why I'm working on fitting a 8.4" 4:3 high-resolution screen in my WRX instead of a 7" widescreen Liliput or Xenarc.