Date: Mon, 14 Jan 2002 09:53:04 +0800 From: Raymond <[EMAIL PROTECTED]> Subject: Re: [LIB] Amorphous LCD vs. LTPS Crystaline LCD vs. TFT
At 12:37 PM 13/01/2002 -0800, you wrote: >Date: Sun, 13 Jan 2002 20:30:57 +0000 >From: "Eugene Hsu" <[EMAIL PROTECTED]> >Subject: Amorphous LCD vs. LTPS Crystaline LCD vs. TFT > >Hmmm.... sorry for this long message.... > >Does anyone know of a good LCD-industry access or LCD discussion board. It has been >a while since I took physical electronics, and I can't fine enough information to >satiate my curiosity. If you're interested in pouring through periodicals then magazines like IEEE Spectrum and the like are worth looking through at your local university library ... or if you've already got access just look it up in their online index. >I was shopping around for a 17" LCD with TV inputs, and I came across the two Samsung >Models 170MP and 171MP. There are a few feature differences listed, but a question >arose since the 170MP was listed as TFT-LCD and the 171MP was listed as A-Si LCD. I >need to ask, "Is this not the same technolgy? Does A-Si LCD = TFT-LCD, or not?" Hehe they're talking about different things. A-Si talks about Amorphous Silicon, a process where silicon is deposited in thin layers onto a substrate by the use of a gas plasma (amongst other things). The alternative is crystalline or polycristalline silicon, neither of which in traditional forms is suitable for this purpose. TFT simply means the display contains thin film transistors to do the switching - each pixel element (of which there are 3 per pixel) is controlled by its own transistor(s). Now the only mass technology (apart from Toshiba's LTPS) that can do TFTs is gas plasma deposition which creates amorphous silicon! I think the REAL question would not be if A-Si == TFT-LCD but rather if a panel ADVERTISED as A-Si == one ADVERTISED as TFT-LCD. AFAIK (and someone correct me if I'm wrong) ALL LCD panels made of A-Si except for Toshiba's LTPS but only SOME are TFT. If a panel uses A-Si as its selling point then chances are thats because it ain't a TFT so marketing can't slap a TFT badge on it. Of coures, it still boils down to how it looks ... a decent passive screen might still beat a poor TFT. See further down for more though ... >I remember the old days when people spoke of Active matrix (transistor on every >pixel) vs Passive Matrix (transistors on edges, so dual-scan was added at some time >to improve response). The Toshiba spec seems to indicate that this LTPS technology >is another way of having transistors in the LCD. >*ponder* TFT == Active Matrix ... I'm not really familiar with this LTPS stuff but if what I hear is correct, its their (polycrystalline) silicon-on-polymer and silicon-on-glass technology (yes there can be 2 'poly's there) ... its currently used in their Portege range AFAIK. Certainly if something USED LTPS then it'd make a song-and-dance about it (for one thing its another acronym for the marketing bods) so if it DOESN'T put 'LTPS' in lights you can be pretty sure it doesn't have it. >The brightness level and view angle are greater for the 171MP, but it seems so too is >the power requirement, which would indicate that perhaps the same LCD components are >the same (LCD's block light when aligned right?), but the light producing elements >draw greater current... or am I completely off track? Its possible yes ... one sure way of finding out if a panel is a TFT or not though is to load up a test pattern consisting of a black screen with a white box in the middle that covers about 1/3 of the screen (or inverse). There should be no 'shadow' cross on the background on a TFT. If you confine the box to one half of the screen, on a dual-scan the 'shadow' should only affect that half of the screen. Another test is to run an animation or game and see how bad the ghosting is. On a good TFT (note, not necessarily a NEW one, my old Tecra 500CDT from 1995 has a damn good screen with almost no ghosting) the ghosting should be barely noticeable (perhaps as much as one would expect on a TV), on a passive screen the ghosting should be quite noticeable. >Well the cost of the 171MP is greater (runs about $1300), so I am probably going to >pick up the 170MP (a local store has it for $700-800.00 vs the $1000.00 I see on the >internet). Does anyone have one of these? Not me ... thats curious though ... perhaps the 171 IS a TFT but for some reason the marketing spin doctors decided that since everyone was advertising TFT they'd do something different *shrug* ... just run those tests I just mentioned and it'll tell them apart. >Since everything ends up going back to Toshiba, further reading found these: > >TOSHIBA INTRODUCES WORLD'S SMALLEST LOW-TEMPERATURE POLY-SILICON TFT LCD WITH XGA >RESOLUTION >http://www.toshiba.com/taec/press/to-055.shtml > >LCD Frequently Asked Questions >http://www.toshiba.com/taec/main/faq/lcd_faq.html > >It seems that Toshiba in 1999 had the 1024x768 LTPS-TFT displays in a 6.3 inch >format, and at the time it was claiming that the technology was better than >amorpheous silicon. I do wish that my 70CT had greater resolution, so I wonder >whether we could replace our screens with the LTM06C310 or its modern equivalent. >*further pondering* I can't say I've seen one of these LTPS panels ... the article DOES have a point that polycrystalline silicon has better conductivity than amorphous silicon. However, amorphous silicon is significantly more 'predictable' if you like ... the crystals in polycrystalline silicon have a habit of forming in the wrong places and 'shorting out' things. Thats why the best solar cells are made from single-crystal silicon wafers (what used to be the round disk type) as opposed to the polycrystalline silicon wafers (the ones where you can see the variety of crystals). I'm guessing Toshiba has either found a way around this crystal unpredictability or they've done something else to negate the problem. I'd imagine there'd be a significant premium for LTPS at the moment given that only one company is making them plus no doubt there will be 'issues' to iron out just as there were when LCDs first came out. I've not seen one of the new Porteges with an LTPS panel either but I have heard them described as being 'fuzzier' than normal TFTs .... its probably a case of 'see it for yourself' though. Almost certainly their circuit driver technology will be different so I don't like the chances of being able to swap our panels out for one of these. - Raymond --- /~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\ | | "Does fuzzy logic tickle?" | | ___ | "My HDD has no reverse. How do I backup?" | | /__/ +-------------------------------------------| | / \ a y b o t | [EMAIL PROTECTED] | | | HTTP://www.raybot.net | | ICQ: 31756092 | Need help? 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