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OLEDs and such



 
 
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  #11  
Old May 29th 13, 06:00 PM posted to uk.tech.digital-tv
R. Mark Clayton
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Posts: 1,331
Default OLEDs and such


"Stephen" wrote in message
...

"Steve Thackery" wrote in message
...

Colleagues,

The ongoing progress of OLED displays led me to wonder something: does
anyone know why organic LEDs are considered suitable for making TV and
computer displays, but ordinary LEDs are not?

Presumably each pixel needs an RGB triplet whichever technology is
used. Each sub-pixel will require it's own drive current. This must
be the same basic requirement regardless of which type of LED is used.

The only thing that occurs to me is about the size. Is there a lower
size limit for a traditional LED, which does not apply to an OLED?

--
SteveT


As far as I know LCD displays have a transisitor in the corner of every
pixel. Why can't these be ordinary LEDs instead?


That's easy - LCD just get switched, whereas LED's have to be driven.


  #12  
Old May 29th 13, 06:03 PM posted to uk.tech.digital-tv
R. Mark Clayton
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Posts: 1,331
Default OLEDs and such


"Steve Thackery" wrote in message
...
Stephen Wolstenholme wrote:

There is no way to print LED on flat panels. They are much too big.


Indeed, but they don't "print" plasma displays, either.


Well they do - rather like CRT's - there are phosphors on the back of the
glass you look at.

I just
wondered why - if they can fabricate plasma displays at a competitive
price - they couldn't replace each plasma cell with an LED on a similar
scale. (I realise the drive electronics are different.)


A LED is a fabricated semiconductor device for a CRT, plasma screen the
electrons are delivered across a vacuum (or very thin ionised gas).

IMO plasma displays will get obviated by cool technology.


--
SteveT



  #13  
Old May 29th 13, 07:18 PM posted to uk.tech.digital-tv
Grimly Curmudgeon[_2_]
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Posts: 237
Default OLEDs and such

On Wed, 29 May 2013 14:52:04 +0100, "Rick" wrote:

A number of years ago I saw on TV a demonstration given by a British Company
of a flexible plastic TV screen, IIRC the (green) image was produced by some
kind of organic compound and was predicted would be in glorious colour
within a few years.
It was also said that this development would lead to TV displays which would
be able to be rolled up and might even become as disposable as newspapers,
does anyone else remember this, or know what happened?


I recall that and I've been waiting for the roll-out screen for the
last twenty years. Istr it showed promise, but short lifespan was a
real problem. I don't know if that was fixed or not, and I'd think if
it was a real world-beater only needing some R&D of a reasonable
level, somebody would have brought it out by now.
  #14  
Old May 29th 13, 07:27 PM posted to uk.tech.digital-tv
Steve Thackery[_2_]
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Posts: 2,552
Default OLEDs and such

R. Mark Clayton wrote:

Well they do - rather like CRT's - there are phosphors on the back of
the glass you look at.


They obviously print the phospors, but the zillions of little electron
guns aren't printed, are they? I would think they must be fabricated
using something more complex than printing, although I don't know for
sure. There's a picture of one he

http://en.wikipedia.org/wiki/File:Pl...omposition.svg

I've just found this:

"The first true all-LED flat panel television screen was possibly
developed, demonstrated and documented by James P. Mitchell in 1977.[1]
The modular, scalable display was initially designed with hundreds of
MV50 LEDs......."
https://en.wikipedia.org/wiki/LED_display

1977, eh? Mind you, it says it was monochrome only because they didn't
have blue LEDs for another decade.

Hmmm..... it still isn't clear to me why LEDs aren't used for TVs,
except possibly because it isn't possible to make them small enough.
They seem to be extensively used for very large, outdoor displays.


--
SteveT
  #15  
Old May 29th 13, 10:26 PM posted to uk.tech.digital-tv
R. Mark Clayton
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Posts: 1,331
Default OLEDs and such


"Steve Thackery" wrote in message
...
R. Mark Clayton wrote:

Well they do - rather like CRT's - there are phosphors on the back of
the glass you look at.


They obviously print the phospors, but the zillions of little electron
guns aren't printed, are they? I would think they must be fabricated
using something more complex than printing, although I don't know for
sure. There's a picture of one he

http://en.wikipedia.org/wiki/File:Pl...omposition.svg

I've just found this:

"The first true all-LED flat panel television screen was possibly
developed, demonstrated and documented by James P. Mitchell in 1977.[1]
The modular, scalable display was initially designed with hundreds of
MV50 LEDs......."
https://en.wikipedia.org/wiki/LED_display

1977, eh? Mind you, it says it was monochrome only because they didn't
have blue LEDs for another decade.


Something odd inthe history here as only the first two lines above are mine.

There were blue LEDs in ~1980, but they were 30 each retail - or was it
1990?


Hmmm..... it still isn't clear to me why LEDs aren't used for TVs,
except possibly because it isn't possible to make them small enough.


about 2mm is the smallest LED you can get and you need three for each pixel,
so 1920X1080 display would be ~6MX3M

They seem to be extensively used for very large, outdoor displays.


Correct and these cost $$$$$




--
SteveT



  #16  
Old May 29th 13, 11:27 PM posted to uk.tech.digital-tv
Steve Thackery[_2_]
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Posts: 2,552
Default OLEDs and such

R. Mark Clayton wrote:

about 2mm is the smallest LED you can get and you need three for each
pixel, so 1920X1080 display would be ~6MX3M


Ah, so we can be sure that is the limit? It's because we can't make
ordinary LEDs small enough for a domestic TV screen?

--
SteveT
  #17  
Old May 30th 13, 12:56 AM posted to uk.tech.digital-tv
Stephen
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Posts: 115
Default OLEDs and such


"R. Mark Clayton" wrote in message
...

"Stephen" wrote in message
...

"Steve Thackery" wrote in message
...

Colleagues,

The ongoing progress of OLED displays led me to wonder something: does
anyone know why organic LEDs are considered suitable for making TV and
computer displays, but ordinary LEDs are not?

Presumably each pixel needs an RGB triplet whichever technology is
used. Each sub-pixel will require it's own drive current. This must
be the same basic requirement regardless of which type of LED is used.

The only thing that occurs to me is about the size. Is there a lower
size limit for a traditional LED, which does not apply to an OLED?

--
SteveT


As far as I know LCD displays have a transisitor in the corner of every
pixel. Why can't these be ordinary LEDs instead?


That's easy - LCD just get switched, whereas LED's have to be driven.


Hmm. Although I thought the point of the transisitors was to allow more
drive to each pixel in the LCD. And I thought the brightness/darkness of an
LCD pixel was controlled by an analogue signal.

(I don't think they can be switched because the timing would be too
critical. Each pixel is only addressed for about a 10 nanoseconds per frame
in and HDTV, and you'd have to control the edge timing to within a 256th of
that, or 1/25th of a nanosecond. (Equivalent to handling frequencies of up
to 25 GHz in the display, which sounds unlikely to me.)


  #18  
Old May 30th 13, 01:02 AM posted to uk.tech.digital-tv
Stephen
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Posts: 115
Default OLEDs and such


"Steve Thackery" wrote in message
...
R. Mark Clayton wrote:

about 2mm is the smallest LED you can get and you need three for each
pixel, so 1920X1080 display would be ~6MX3M


Ah, so we can be sure that is the limit? It's because we can't make
ordinary LEDs small enough for a domestic TV screen?

--
SteveT


I don't know of any reason why you can't make an LED as small as you like,
the same as any other diode or transistor - it's a mystery to me too. And if
you did make a normal size TV from conventional LEDs, you would only need a
tiny output from each one. I estimate about 1 microAmp to each one, instead
of the typical 20 milliAmps or so.


  #19  
Old May 30th 13, 10:54 AM posted to uk.tech.digital-tv
Rick[_10_]
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Posts: 662
Default OLEDs and such



"Jim Lesurf" wrote in message
...
In article , Stephen

wrote:

"Steve Thackery" wrote in message
...

Colleagues,

The ongoing progress of OLED displays led me to wonder something: does
anyone know why organic LEDs are considered suitable for making TV and
computer displays, but ordinary LEDs are not?



As far as I know LCD displays have a transisitor in the corner of every
pixel. Why can't these be ordinary LEDs instead?


My vague and unreliable recollection is that it may be because the OLEDs
are more flexible and easier to stick to something like a glass surface in
a thin layer. LEDs tend to be more rigid crystalline and damaged by small
defects. So thermal and flexure effects can cause failure. However I'm not
sure of this as I'm trying to recall articles on the OLEDs I read years
ago!



One supposes that this is also a factor which might have to be taken into
consideration by manufacturers, I mean, think of all the ensuing lawsuits if
it turns out to be true.
http://news.in.msn.com/international/article.aspx?cp-documentid=253019725











  #20  
Old May 30th 13, 11:18 AM posted to uk.tech.digital-tv
Roderick Stewart[_3_]
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Posts: 2,159
Default OLEDs and such

On Thu, 30 May 2013 01:02:45 +0100, "Stephen"
wrote:


I don't know of any reason why you can't make an LED as small as you like,
the same as any other diode or transistor - it's a mystery to me too. And if
you did make a normal size TV from conventional LEDs, you would only need a
tiny output from each one. I estimate about 1 microAmp to each one, instead
of the typical 20 milliAmps or so.


Maybe the percentage yield isn't good enough yet when you have a lot
of them together in a situation where they all have to work?

Make a few million transistors on the same silicon wafer and you can
just throw away the ones that don't work and still have enough left to
sell at a profit, but if you have a few million semiconductor devices
fixed in an array during manufacture because every one of them has to
form part of a picture, you need 100% working or the whole thing has
to be thrown away.

Rod.
 




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