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		Introduction by Luc Bureller, 3LCD Epson Branded Projector Business Manager 3LCD – A Brand is Born The Hearth of 3LCD: PolySilicon (HTPS) Coming to Grips with 3LCD (HTPS) Advantages of 3LCD in different applications Epson Projects the Future at IFA New 3LCD Projectors from Epson Conclusion by Gérard Lefebvre, Cleverdis President & Founder

by Richard Barnes,
Editor in Chief

We have entered the digital era. An era when digital convergence and the use of digital displays has become part of daily life, whether at the office, outdoors, or in the home. But does digital living make us all happier?…

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	STEPHAN HARTMANN Senior Manager LCD, Marketing Engineering and Sales EEG (Epson Europe Electronics GmbH) Stefan Hartmann has studied telecommunication in Germany and partly in Australia. After joining EPSON in the year 1995, Stefan Hartmann was responsible for the technical support of European customers for Microcontrollers, LCD Driver/ Controllers and different types of LCD Modules for several years in, various positions. Over the years, his focus was shifting more and more to EPSON's HTPS-LCDs for projectors. Today Stefan Hartmann holds the position of a Senior Manager for Display Products and focuses his work on EPSON's product line of HTp-Si TFT-LCD's used in 3LCDbased front – and rear – projection systems.

Cleverdis: What is HTPS?

Stefan Hartmann: This term stands for High Temperature Polysilicon. LCD displays are made up of two glass plates between which the liquid crystal is sandwiched. In difference to Passive Matrix LCD's, Active Matrix LCD’s have an additional small transistor on each single pixel, which leads to contrast and speed improvements of the display. During the HTPS production, the amorphous silicon sputtered onto a special glass substrate is then melted at more than one thousand degrees Celsius in order grow the silicon grains and thus to increase the electron mobility. This leads to a higher switching speed of the on glass electronics and thus higher integration possibilities allowing us to achieve XGA resolution on a glass with 0.6” diagonal size. In our newest factory we perform this process on 12 inch glass wafers.

What are the basic principles of a 3LCD engine, and how is it different from single chip technologies?

S.H.: Just like in other projector technologies, we use a very powerful lamp to generate white light. In most cases it is an ultra high pressure lamp (UHP) which generates the white light, which is then separated by using a dichroic mirror into its red, green and blue colour components rather than filtering it as is done in some other technologies. This means we have a theoretically loss-free system in this case because of the separation of the light beam as opposed to filtering; and, then, the three separate colour beams are guided by mirrors onto three monochrome HTPS panels which modulate the light separately and simultaneously for the different colour compounds green, red and blue. After this light modulation, the three colours are then recombined inside a prism which then passes the remodulated image through optics onto the screen.

The fact that we use this ‘recombiner’ prism to put together the three colours means that the eye, and thus the brain, receives the full colour image, as opposed to single chip technologies which use time sequential colour systems. We don’t need the human brain, or eye, to do the work of integrating the colour image which makes our images more smooth and gentle on the eyes.

So the human eye doesn’t have any work to do, the image has already been processed?

S.H.: Exactly right. In a single chip system, the human eye is receiving only one colour at any given time. In addition, because the single chip system uses colour filtering, it is less efficient and thus the brightness suffers. To boost brightness, single chip manufacturers may use white segments in the colour filter in addition to the red, green and blue, which again compromises the colour depth, thus the number of grey scales they have. Once the image is received by the human eye, the brain normally reacts slowly enough to integrate these time-sequential colours into one single colour image. But sometimes, depending on the scene shown, the human eye is fast enough to recognise this difference and this is what creates the so called “rainbow” effect.

Where can we mostly notice the “rainbow effect”?

S.H.: When you have a dark background and white or grey object moving in front of it quickly, the edge of this moving object is not in a consistent position from picture to picture. So the red, green and blue colours are in different positions. This moving object will appear as if it has a rainbow behind it. A more neutral term would be ‘colour break-up’.

What are some of the other advantages of 3LCD?

S.H.: Other advantages of 3LCD are, of course depending on the actual setup, less power consumption, or higher light output, so more brightness. The images are also more “natural”.

Due to the fact that we have red, green and blue light valves to modulate the three light beams continuously, we have, on each single light valve, 10 or 12 bit resolution to produce grey scale, so you have 3 x 10 (or 12) bit resolution, whereas a single chip system does this time sequentially which means so the gradients are not as good. It means that, esp. compared with single-chip systems using so called “white segments” in the colour wheel, the colour depth and colour (grey shade-) reproduction of our 3 chip system is outstanding – this is the natural image component.

Could you tell us about the differences between LCOS and “normal” 3LCD?

S.H.: Liquid crystal material is used in both these technologies, filled between two substrates. 3LCD HTPS technology uses a transmissive LCD panel which means we have two glass plates while LCOS replaces one of the two glass plates with a silicon chip which makes it a purely reflective technology. In a LCOS system, you have to separate incoming and outgoing light, for which polarising beam splitters are used, adding some additional complexity to the system. In other words, when you send the light to the LCOS chip, it comes back the same way. So you have to differentiate between this 2 parts before projecting the modulated part of the light out through the projection lens.

What is a Micro-Lens array and how does this improve image quality?

S.H.: The micro-lens array is a small array of tiny lenses that sit on top of the LCD panels. In other words, there is a small lens on top of each single pixel, focusing the light onto the actual opening of the pixel – the actual area in use.
We have certain aperture ratio on the transmissive HTPS-panel, which means that a part of the actual pixel area can be used to transmit light, and another part is used for the electronics to drive this pixel. This is what people call the grid, because it blocks some light. The micro lens actually focuses the light only onto the usable area, meaning you gain brightness by adding a micro-lens to the HTPS panel. The visibility of the grid is also reduced by this technique.

The micro-lens array requires smaller lamps which in-turn means lower power consumption. Is this a selling point?

S.H.: It really depends on which market you address. There are certain markets that are very brightness driven and for these markets I would rather add a micro-lens. Other markets where brightness is less critical, are usually not applying this additional lens-array which obviously adds costs.

© Epson

Is this helped by the new generation D4 panel?

S.H.: Newer technologies enable us to shrink the electronics on each single pixel, therefore increasing the aperture ratio. Consequently it allows us as well to reduce panel sizes such as the recently announced 0.6 XGA inch panel, whereas before, the smallest XGA panel was 0.7 inches. Shrinking the panel, the pixel pitch is reduced accordingly (size of each pixel), but using newer panel technologies, the aperture ratio remains the same or is getting even larger.
Using new technologies, we are thus able to shrink the whole panel giving us a production cost advantage.

We sometimes hear arguments about how to calculate the total cost of ownership (TCO) of a front projector system. What factors do you think should be taken into account when calculating TCO of projection systems, and how does 3LCD stand up?

S.H.: The important thing when considering TCO is not just the unit itself, but also, very importantly, the elements that need to be replaced occasionally. This is one of the big advantages of HTPS technology, because the projectors are able to use smaller lamps for the same brightness levels. This in turn means that the lamps are cheaper and last longer. As lamps are one of the major cost considerations when calculating TCO, this really tips the scales for people who use projectors regularly.