nadst2@unix.cis.pitt.edu (Nilanjan Adhikari) (06/28/90)
I posted the following article in the rec.photo newsgroup. I am posting it here too, hoping for some theoretical input as well as any in-life experiences (personal or commercial) of netters about the ubiquitous lcd panels. Has anybody seen lcd's die of old age ? What's the longest one has seen an lcd panel to work ? ========================================================================= >Then again, there's the likelihood of having to replace the LCD screen >after it's about five years old. (LCD's have an unfortunate tendency >to degrade after some period of time...newer ones are better in this >respect, but they'll eventually die.) > The above is something I heard/read several times about, including at least once in the Modern Photography. This is something expected in theory, having to do with dc leakage or something ( I may be wrong, being too lazy to go read about it ). I am curious, how much of it has been proven correct in real life ? I know of lcd's rated for about 50,000 hours. I presume that is for continuous use. That is equivalent to about 5.5 years. This may be applicable to watches and such. But how about lcd's subject to only intermittent use, like those in cameras, calculators etc. ? I have a casio calculator from 1980, which is doing fine even today, after seeing me through 10 years of moderate use. It seems rather surprising that manufacturers would put in things supposed to die in only 5 years or so in such durable things ( for amateurs ) as cameras. How many 36 exp. rolls of film would an average amateur shoot in 5 years, -- 100 ? , 200 ? In the same magazine ( Mod Photo ), I also read that average amateur cameras should have a life of at least 30000 shots (833 rolls ). Where average life of a model is about 2--3 years these days, how could one expect to find replacement lcd panel(s) for a given camera after 5--10 years ? Does anyone out there have a real life experience of lcd's dying of age in cameras or calculators, or even in watches ? I think Ricoh introduced lcd panels in their cameras in early 80's ( if not even earlier). Awaiting some informative discussion...
r91400@memqa.uucp (Michael C. Grant) (06/28/90)
In article <25269@unix.cis.pitt.edu>, nadst2@unix.cis.pitt.edu (Nilanjan Adhikari) writes: > The above is something I heard/read several times about, including at least > once in the Modern Photography. This is something expected in theory, having > to do with dc leakage or something ( I may be wrong, being too lazy to go read > about it ). I am curious, how much of it has been proven correct in real life ? LCD is difficult to work with, because it must be driven by an AC voltage, or else it will quickly degrade. The diagram below illustrates how a pixel in a typical LCD setup is driven. Cnt --+---+ + 'Osc' is a square wave (say, 60Hz) |XOR|---(Cnt XOR Osc)-----(CELL) and Cnt is 0 when the pixel is to Osc---+--+---+ | - be off, and 1 when it is to be on. | | The resulting voltage difference +------------------------------+ across the terminals of the pixel is, IN THE PERFECT CASE, 0 when Cnt=0, and a square wave (at twice Osc's amplitude) when Cnt=1 (try it!) The problem is that no XOR gates (or square waves) are perfect, and some DC potential is applied to the cell. So, the potential across the cell isn't quite 0 when Cnt=0, and isn't quite 2*Osc when Cnt=1. Sure, this DC potential is quite small, but I assume that it is enough to cause the degredation of the cells over a long period of time. Michael C. Grant
mmm@cup.portal.com (Mark Robert Thorson) (06/28/90)
I heard the mechanism of failure is destruction of the cholesterol molecules in the liquid crystals by exposure to UV light. I don't know if that's true or not ... that's just what I was told once.
irwin@m.cs.uiuc.edu (06/29/90)
Eleven years ago, my wife and I purchased a matching set of men's/women's watches, made by Seiko. They are quartz LCD watches. Both of ours are still going strong after 11 years of use. If the watch dies before I do, I will let you know :-) Al Irwin irwin@m.cs.uiuc.edu
forbes@aries.scs.uiuc.edu (Jeff Forbes) (06/29/90)
In article <3922@memqa.uucp> r91400@memqa.uucp (Michael C. Grant) writes: >LCD is difficult to work with, because it must be driven by an AC voltage, >or else it will quickly degrade. >.... > Sure, this DC potential is quite small, but I assume that it is >enough to cause the degredation of the cells over a long period of time. What is the failure mode for LCD displays? The liquid crystal certainly won't degrade due to a DC voltage being applied, all they do is line up with the field. Jeff Forbes Factotum of Od
henry@zoo.toronto.edu (Henry Spencer) (06/29/90)
In article <3922@memqa.uucp> r91400@memqa.uucp (Michael C. Grant) writes: > The problem is that no XOR gates (or square waves) are perfect, and >some DC potential is applied to the cell... However, 4000-series CMOS gates are pretty close to perfect for this. :-) Still, the point is valid: even the slightest DC offset will eventually degrade the LCD. Basically, it causes electrolytic reactions of various kinds, as I recall. With a perfectly symmetrical AC wave, e.g. square wave, reactions during one half of a cycle reverse themselves (you hope) in the other half. -- "Either NFS must be scrapped or NFS | Henry Spencer at U of Toronto Zoology must be changed." -John K. Ousterhout | henry@zoo.toronto.edu utzoo!henry
cgordon@vpnet.chi.il.us (Gordon Hlavenka) (06/30/90)
>What's the longest one has seen an lcd panel to work ?
I've got an old Radio Shack calculator from back when LCD was cutting edge
stuff (for the Shack, anyway). This calculator has been abused, and left in
direct sun on auto dashboards for I-don't-know-how-long-but-it's-long, and I
haven't seen any evidence of fading...
----------------------------------------------------------
Gordon S. Hlavenka cgordon@vpnet.chi.il.us
Disclaimer: He's lyingnadst2@unix.cis.pitt.edu (Nilanjan Adhikari) (06/30/90)
In article <1990Jun29.150402.6752@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes: >However, 4000-series CMOS gates are pretty close to perfect for this. :-) >Still, the point is valid: even the slightest DC offset will eventually >degrade the LCD. Basically, it causes electrolytic reactions of various >kinds, as I recall. With a perfectly symmetrical AC wave, e.g. square >wave, reactions during one half of a cycle reverse themselves (you hope) >in the other half. >-- It appears that the degradation requires a dc field to be present. Does that mean that for intermittently used lcd's (like those in a camera or a calculator), the degradation is practically of no concern ? Do lcd's deteriorate over time anyway, whether or not they are turned on ? I came to know that Canon warns about a possible degradation of the lcd panels in their EOS series cameras after about five years.
phil@pepsi.amd.com (Phil Ngai) (06/30/90)
In article <3922@memqa.uucp> r91400@memqa.uucp (Michael C. Grant) writes: | The problem is that no XOR gates (or square waves) are perfect, and |some DC potential is applied to the cell. So, the potential across the cell |isn't quite 0 when Cnt=0, and isn't quite 2*Osc when Cnt=1. I guess a series capacitor would be too easy. -- Phil Ngai, phil@amd.com {uunet,decwrl,ucbvax}!amdcad!phil PALASM 90: it's not the same old PALASM any more!
henry@zoo.toronto.edu (Henry Spencer) (07/01/90)
In article <25522@unix.cis.pitt.edu> nadst2@unix.cis.pitt.edu (Nilanjan Adhikari) writes: >>Still, the point is valid: even the slightest DC offset will eventually >>degrade the LCD. Basically, it causes electrolytic reactions... > > It appears that the degradation requires a dc field to be present. >Does that mean that for intermittently used lcd's (like those in a >camera or a calculator), the degradation is practically of no concern ? I would worry about long-term degradation in almost any device involving chemicals in solution. Effects that normally don't even rate mention can get significant when you leave the thing to sit for five years. However, I believe it's true that LCDs don't degrade *much* when powered down. -- "Either NFS must be scrapped or NFS | Henry Spencer at U of Toronto Zoology must be changed." -John K. Ousterhout | henry@zoo.toronto.edu utzoo!henry
ISW@cup.portal.com (Isaac S Wingfield) (07/01/90)
In article <1990Jun29.150402.6752@zoo.toronto.edu> henry@zoo.toronto.edu (Henr Spencer) writes: >However, 4000-series CMOS gates are pretty close to perfect for this. :-) >Still, the point is valid: even the slightest DC offset will eventually >degrade the LCD. Basically, it causes electrolytic reactions of various >kinds, as I recall. With a perfectly symmetrical AC wave, e.g. square >wave, reactions during one half of a cycle reverse themselves (you hope) >in the other half. If memory serves, it's simple electroplating that's the problem. Any voltage will cause one or the other of the tim oxide electrodes to migrate, but if the waveform is perfectly symmetrical, equal amounts move each way. With any DC component, however, eventually one electrode will vanish. Isaac isw@cup.portal.com
jimc@isc-br.ISC-BR.COM (Jim Cathey) (07/03/90)
In article <25522@unix.cis.pitt.edu> nadst2@unix.cis.pitt.edu (Nilanjan Adhikari) writes: > It appears that the degradation requires a dc field to be present. >Does that mean that for intermittently used lcd's (like those in a >camera or a calculator), the degradation is practically of no concern ? >Do lcd's deteriorate over time anyway, whether or not they are turned >on ? I came to know that Canon warns about a possible degradation of >the lcd panels in their EOS series cameras after about five years. In the case of EOS cameras, the LCD is powered up all the time there is a battery in the calculator, so there really isn't any 'intermittent' use. Of course, it might depend on just how clever the designer of the driver circuitry is. Does anyone know the exact circuit details for the common watch and camera type LCD's? Are off segments merely in-phase AC signals and on segments out-of-phase, or does an off segment have zero potential placed upon it? If it's the phase switch kind of circuit, then slight differences in the drivers can result in an average (albeit low) DC potential. If it's completely decoupled then what about microcurrents induced capacitively? Of course, I'm not convinced that the 5-year specified life is due to inevitable DC degradation effects and isn't something more like chemical decomposition -- or maybe even a combination? Or maybe just CYA specsmanship 'cause no one's done an extensive test lately?