flat CRT

They've been making them for years. I have two 20" IBM P260 monitors, and their screens are as flat as window glass.

They're probably not as common now, with the proliferation of flat panel displays all over the place.

Cheers! Rich

snipped-for-privacy@coolgroups.com wrote: > Why doesn't someone make a CRT tube that is almost > flat like an LCD monitor? I know the electrons > would have a sharper angle to travel, but isn't it > possible?

It's called Plasma.

GG

** Makes the tube and hence monitor *very* heavy.

The flat front glass must be many times thicker than a curved one.

Check out any flat faced TV set.

........ Phil

I guess by flat you mean not very thick front to back? A problem with the sharper angle is more demanding deflection circuitry, which would have to supply higher currents to get a stronger magnetic field, and problems maintaining geometry- it would be hard to keep the correct angle with the larger ratios between the distances to the center, the centers of the edges, and the corners.

-- john

If you mean thin, I hear that they are trying to manufacture a flat CRT by replacing the electron guns with an array of wires. So you'd have the brighness of CRT, with the discrete array of an LCD or plasma.

Conventional single-gun CRTs don't work well at extreme deflection angles. The color shadow mask is a big part of the problem.

The holy grail here is the field-emitter CRT, with a planar array of cold electron emitters just behind the phosphor-coated screen. Lots of techniques have been tried for the emitters - microtips, amorphous diamond, carbon nanotubes - but nothing practical so far.

Too bad LCDs are so slow; you could do a dynamite display with an lcd and sequential R-G-B backlighting from LEDs... less wasted light, 3x the resolution.

John

I'm looking at one right now !

It's so flat that I took a steel rule to it to check - and it's utterly flat !

Uh ?

You don't have a clue what you're talking about do you ?

Get yourself a Sony E500 or E530 and you may understand !

Graham

I think that by "flat" he means "thin", maybe.

Nobody seems to want CRTs any more; they take up too much space and use too much electricity.

John

OK, as other have already noted, presumably by "flat like and LCD monitor" you mean both flat AND thin. Flat- face CRTs obviously have been with us for quite some time.

There have been a number of attempts at flat/thin displays which work like a CRT. I'm going to have to disagree with an earlier response here - a plasma screen is NOT one of these. Color plasma displays are phosphor-based, emissive devices, like CRTs, but the operating principle is very different. In a plasma display, the phosphor is excited by UV radiation from a "plasma glow," which is most akin to what you see in a neon bulb (the main difference is that in an AC plasma panel, the electrodes are buried under an insulating layer, and the gas mixture is optimized for UV rather than visible light emission.

The class of display closest to a "true thin-flat CRT" are the "field-emission displays," or FEDs. These have also been called "cold-cathode" CRTs - they use phosphors, and the phosphors are excited by streams of electrons, but the electrons come from several different types of emitters, none of which requires a hot filament as does a conventional CRT cathode. One of the most promising FEDs right now is a thing called the SED, for "surface-conduction electron-emitted display," being developed by a joint venture of Toshiba and Canon.

Oh, and the "CRT based on an array of wire filaments" sort of thing that someone mentioned earlier was already done - and abandoned. In the late 1980s, Panasonic developed a (fairly) thin, flat CRT - a 14" example used a tube that was maybe 2-3" thick - which had a series of wires as cathodes rather than the usual single cathode of a conventional CRT. It worked OK, but really didn't provide much of an advantage over conventional type, was difficult to produce, and was never successfully made to support high resolutions.

These days, there's just very little reason for continuing development in this area, except for the FEDs. The other flat-panel display technologies have already been developed to the point of doing just about everything a CRT can do, and the costs of building them continue to drop. It makes more sense to continue to develop those rather than try to develop something completely new just for the purpose of having a "thin CRT."

Bob M.

"Bob Myers"

** One very famous one - the Sinclair FTV-1 (aka TV80) from 1984.

Similar design flat CRTs are found in some current "video door monitors".

...... Phil

Any idea when we are going to see mass produced OLED dispays of any worthwhile size?

Lifetime is still a problem. Seems that almost anything that emitts light progressively destroys itself; there must be a fundamental physical basis for this.

John

i'm no expert but ive been reading up on crt's most of the night, so im just passing on what i've read. Because of the high vacuum in the tube that crt's need to function properly, the tube structure needs to be strong to withstand the pressure difference. Older displays have the classic goldfish bowl type screen because this shape gives strength to the tube. Making the front of the screen flatter reduces the structural integrety of the screen so countermeasures must be employed to restore its stregnth - hence the very thick glass. And this is all without taking into account what effect on structure flattening the back of the tube.

Assuming that by "worthwhile size," you're meaning something like a monitor- or TV-sized panel (or at least something for a notebook PC), I wouldn't expect any significant volumes there until at least the end of the decade, if then. The material lifetimes are getting up to the point where they'd be practical (i.e., at least as good as a CRT), but the problem is that the OLED may not offer an attractive enough set of advantages - LCDs have become SO good, and there's a huge manufacturing infrastructure devoted to them already. OLEDs are just getting started, and the manufacturers (for most part, the same companies now making the LCDs) would have to have some pretty good reasons to make the huge investments it would take to put OLEDs on the same scale. They're starting out right now in such things as cell phones and digital cameras, and those sorts of products DO see some significant advantages from the OLED (thickness, weight, power), and being small displays they take a smaller investment to get into large-volume manufacturing.

Bob M.

I'm having a senior moment but I've seen a proto of such a thing (circa

1995) and can't remember the details. As I recall it used a (cold?) cathode per pixel approach. So a search at the US Patent Office web site might be helpful. I recall that there was research going on at Princeton (I think) on the phosphors required for the solution and it seemed the fundamental design concept was from a startup company in france. This was under consideration as an alternative to LCDs in laptop computers to give you an idea of it's mechanical properties. The general idea was to marry the best properties of a CRT with those of a LCD.

As I recall, the technical issues at that instant in time were non-trivial but not impossible to overcome in time. Although I'm overgeneralizing, it looked like a Beta vs VHS situation (where LCDs of that era were the VHS). LCD quality and manufacturing advances were improving at a rate that taking this technology to market a poor idea. In retrospect the improvements in LCDs exceeded what was predicted at that time.

Mike

Why not try to redesign the deflection mechanism instead of just improve on the original idea? (asking and not telling... I'm wondering about it)

Surely there might be a better way to delect the electrons so that one doesn't have to have such a high angle of deflection?

Some potential ideas(just making stuff up) could be: Using more then one beam at different angles, Use more specialized magnetic yokes, Use more then one beam at different positions(almost like just stacking crt units but contained in one unit), etc...

The last idea might seem plausable since we can do this now.

i.e., on has a grid

| | | | | | | |

----+-----+-----+-----+---- | | | | | | | |

----+-----+-----+-----+---- | | | | | | | |

where the + are "emitters". You are looking into the screen. The grid size could be small to large. if, say, each emitter(tube/beam) had no deflection control then one would bet a discrete set of pixels(like an LDC) but if you are able to add a way to deflect the electrons then the '+'s become fuzzy and can take up the whole box around them.

Ofcourse there are technical challenges but it might work. If, say, you are able to use a smaller tube where you could place an emitter every inch then you would could maybe use the only magnetic deflection idea buton a smaller scale. (not sure if it would scale down enough). I know there are a lot of technical problems with this idea but I'm just making up something.

My main point is that it seems no one has really modified the basic CRT idea since it was created(nothing drastic atleast). Instead someone finally used a totally different technology, which isn't a bad thing.

One could thing if the above idea could be implemented is that one could run the emitters in parallel and have amazing refresh rates. I think n^2 * that of a normal CRT, where n is the number of emitters. They might also be able to be made much thinner but the electronics to control everything would be more complicated.

anyways, Just an idea off the top of my head, Jon

That's actually in part the thinking behind the one-or-more-emitter-per- subpixel sorts of approaches, like the FEDs. If each electron source is responsible for only lighting up one little patch of color, there's no need to deflect OR focus the electrons from that source.

The CRT as it stands is a mass of design compromises. If the electron source is a hot cathode located a significant distance from the screen, then you need a very high anode voltage to get the electrons to the screen with sufficient energy so as to produce usable brightness. But such a high-velocity stream of electrons is relatively "stiff" - it also then requires a good deal of energy to deflect or otherwise manipulate (as in those processes used to focus the beam or to ensure proper color purity and convergence). That generally means you HAVE to use magnetic fields to do these jobs, but there's also a definite limit as to how finely you can control the shape and position of the coils that generate these fields, and the currents that control them. Putting the electron source closer to the screen, but leaving it as-is (hot cathode style) makes for even greater deflection angles to get the beam out to the corners (and as such the beam becomes much, much harder to control accurately). On the other hand, moving the source off-aixs (parking it to the side and bending the beam to hit the screen) is also an approach that's been used to shorten tube lengths, but it has similar problems re the accurate control of the beam.

The only way to deflect an electron beam outside of a magnetic field is to use an electric field (i.e., electrostatic deflection). This is what was used in the early oscilloscope tubes, but the length of those tubes relative to the screen size should be an indication that this sort of thing is even worse in terms of coping with large deflection angles. To use purely electrostatic control over the sorts of angles seen in even a conventional-design CRT would be impractical - it requires voltages that would be way too high to easily and accurately produce, distribute, and control (esp. without seeing HV breakdowns within the tube structure).

All of these have actually been tried in one form or another, with varying degrees of success. The precursor to "dual trace" oscilloscopes, for instance, was the "dual beam" tube, which actually DID have two or more independent electron guns, one for each trace to be produced. It's complicated to make, complicaed to adjust, and it's virtually impossible to get the guns to stay together in terms of brightness, cutoff, etc.. Some very specialized deflection yokes have also been introduced over the years, but again these are expensive, difficult to produce and align properly, and tend not to stay aligned/ adjusted once you get them to work in the first place. The "more than one beam at different angles" is basically how the common color CRT works, but that's also a nightmare in terms of the adjustments it needs.

And the bottom line to all of this is - why bother? What would a truly thin/flat but otherwise conventional CRT actually bring to the party that would be worth the effort at this point?

Bob M.

Of course they have. Electrostatic deflection, magnetic deflection, distributed deflection, meshes, shadow masks, PDA, alumized phosphors, phosphor stripes, dynamic focussing, ion traps, and many others.

You should really read up on the technology to understand its history and constraints. And do some of the math. Some seriously smart people have put thousands of man-years into CRT design, and I don't think they would have missed anything obvious.

John

Na, I don't care about it. There are more interesting things to do with my life. Thats why it was a question and I repreated several times that I'm basically just making things up. I'm sure there have been many smart people working on it but I think the problem that the crt hasn't had a major redesign creates some questions. Its hightly possible that the original idea is flawed and makes it very difficult to enhance apon or that there are econmic reasons why or there has been modification but they just didn't catch on.