Tech Insights: Transparent TVs

CES last month had LG and Samsung showing off their latest Transparent TVs to the world. Despite being in the limelight for a few years, the underlying mechanics never cease to amaze. How do these TVs achieve transparency? Where are all the wires?

LG relies on Organic LED (OLED) tech for its transparent displays. OLED displays have organic layers responsible for light emission between two transparent electrodes. Electrodes made of metals are usually opaque. Enter the star of the show: Indium Tin Oxide (ITO), a transparent Conductive Oxide. What makes something opaque is the fact that the incoming light is reflected or absorbed completely. The light we see has photon energies between 1.6 & 3.2eV. ITO has a large bandgap of more than 3.5eV, which means it just allows light to pass through. With high Tin doping in Indium Oxide, it becomes conductive with low resistivity, making ITO an ideal choice for electrodes balancing optical transparency and electrical conductivity.

Constructing the display involves taking glass as a substrate, depositing a layer of ITO, and adding multiple organic materials (hydrocarbon-based) on top. These organic layers emit light when an electric current passes through them. The structure is completed with another electrode made of an ultra-thin Magnesium and Silver layer, achieving an impressive 70% transparency. To preserve organic layers from water/oxygen, they are sealed with an encapsulant.

Now we need transparent display drivers below them. For that, we use Thin Film Transistors (TFT) made of a material called Transparent Amorphous Oxide Semiconductors (TAOS). Deposited on a glass substrate (not silicon), all layers of a transparent TFT consist of transparent oxides. These transistors regulate brightness beneath each pixel by turning ON and OFF. Optical filters for RGB on each sub-pixel complete the one full pixel. Multiply this process over a rectangular space, and voila, you have a Transparent TV.

PS: Hopefully, this hasn’t offended any material engg. aficionados. I might have made a few broad statements. ????

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Back to Basics: What does p in 1080p stand for?

Yesterday I was doing some research into display drivers for a project and got to learn about how the TV displays evolved. One of the things I learned was contrary to popular belief, it’s not pixels – it stands for “progressive.” Let me explain.

The “1080” part of 1080p stands for the number of pixels in the vertical direction of your display. It can be 720, 1440, 2160, etc. When you are trying to display something on a screen(called “scanning” the screen), there are 2 ways of doing it. Interlaced scan and Progressive scan. In an interlaced scan, the image to be displayed is divided into two fields, and only half of the lines are shown at a time. The first field includes the odd-numbered lines(1,3,5,..,1079), and the second field includes the even-numbered lines(2,4,6,…,1080). These fields are then displayed alternately to create a complete frame. Meaning, that at a single time, only half the screen is refreshed to a newer image. This was done in the olden days of CRT Displays to show higher-quality images on screen with only half the bandwidth. It reduced the transmission rate needed for videos. But this has drawbacks for fast-moving scenes, you may observe some stripes/artifacts in the screens for these videos.

Now Progressive scans, on the other hand, displays or “scans” every 1080 lines one by one, top to bottom, and refreshes every pixel on the screen at the same time. That means full bandwidth is needed to show a frame. Progressive scan provides a smoother, faster, and more detailed image, making it a preferred choice for modern displays. You don’t find interlaced formats that much these days.

Now you know what “p” means. Who knew pixels could be so progressive? ????

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