Re: Beginner Question - July 26, 2002 - "After 15 years in the display industry, I think I can give a definative answer to all the posts here which say "can I stick my laptop screen onto my PC - can I just get the right pinout?" or "can I make my laptop screen accept NTSC or PAL video?"

NO! - not without some electronics!!

Your average TFT LCD panel needs to get 6 or 8 bits of TTL level digital data for each of 3 colours plus H & V syncs and a data enable and a clock to keep all these signals together.(plus a few grounds to be happy)

Your average PC VGA port gives out 3 ANALOGUE signals (Red, Green, Blue) and H & V syncs (again plus a few grounds to be happy)

In addition, the panel may have a different physical resolution to that being sent out by the VGA card.

SO

You need some electronics ("driver card" or "interface card" or "controller card") to do some conversions to both signal and/or resolution.

First an analogue to digital conversion (A/D) then perhaps a "scaling engine" to convert the output resolution to the physical resolution of the panel. A PLL (phase locked loop) or clock circuit is necessary to keep things happening together along with some memory (maybe as little as a single line of data on some cards, but a frame full at least on better cards). An OSD (On Screen Display) controller chip or chipset is necessary for the user to be able to set up image geometry and the like (height, width etc.) along with adjustments to the sampling phase and dot clock to get the image error free.

This then will provide the required signals for the panel and probably supply the power and control signals to the backlight invertor as well (on/off and brightness setting)

There in a nutshell is what a controller or interface card does and why it's needed. IF you have a "Video" signal (Composite or S-video, PAL or NTSC encoded) then it gets one step more complicated. You have to have a "video decoder" chipset before the A/D conversion in order to chnage the video signal into something the A/D can use (usually RGB analogue and H & V syncs.

The controller may be a bus mounted device (ie it sits in the PC on the PCI or AGP bus) or it may reside at the panel end of things - usually inside the case of a desktop LCD monitor.

More recently it has been noted that the conversion from a digital signal in your pc to an analogue one for VGA then back to digital for the panel is not the best way to do things. Consequently we have seen a few "standards" over the last few years which are entirely digital and replace the traditional VGA type system. First there was P&D "plug n display" which defined a system and connectors for taking a digital signal (via a suitable PCI bus card) straight to a panel mounted decoder card. Along with LVDS and TMDS these have been merged under the VESA standard of DVI - Digital Video Interconnect. Some graphics cards (from ATI and others) have this DVI connector on and many more DVI enabled desktop LCD monitors are on the market. Ultimately this should take over from the VGA type system.

Does this answer your question?" - Craig Shearstone