November 6, 2007

Shiny pixels at Qualcomm

CRT, LCD, TFT, OLED, EPD and DLP are just some of the many acronyms used for the techniques behind displays. There's an article in the November 2007 issue of Scientific American that presents a new acronym: IMOD. The IMOD displays are based on many small interferometric modulators, which bounce back light at different intensities. They don't need a backlight, which means power consumption is much lower, ever so important for portable applications. The viewing experience is also greatly enhanced I am sure. The electronic paper displays that I've seen don't use a back-light either and they're great. They read like paper. The e-ink pixels change intensities too slowly to show video though, while the IMOD technology is very fast. The whole technology reminds me of the, also MEMS-based, DLP from Texas Instruments. Within a few years, that technology quickly became prevalent in projectors, beating out LCD.

With better displays, video coding artefacts will only become more apparent. Is your video subsystem ready to capture and play the highest quality video?

3 comments:

Anonymous said...

What is the advantage of this technique compared to OLED?

Marco Jacobs said...

About IMOD Technology vs. OLED, from http://www.qualcomm.com/common/documents/white_papers/Competitive_Display_Technologies_White_Paper.pdf

Since IMOD components can be built on a subset of FPD fab lines, the IMOD display’s manufacturing costs are expected to ramp quickly downward as volume increases. OLEDs, on the other hand, require completely new fab facilities.

Perhaps the IMOD display’s greatest advantage over OLEDs, especially in the battery- powered, small-screen arena is that in order to be visible, the OLED must be powered continuously. OLEDs, then, typically consume around 200mW, compared to 10s of microwatts for IMOD displays without supplemental lighting (display in hold state showing static image).

OLEDs offer several advantages over LCDs. However, the technology has not gained a major foothold for several reasons. The cons will be discussed on the next page while the pros will be reviewed here. The basic OLED cell structure is comprised of a stack of thin organic layers that are sandwiched between a transparent anode and a metallic cathode. When a current passes between the cathode and anode, the organic compounds emit light (see Figure 8.) The obvious advantage is that OLEDs are like tiny light bulbs, so they don’t need a backlight or any other external light source. They’re less than one-third the bulk of a typical color LCD and about half the thickness of most black-and-white LCDs. The viewing angle is also wider, about 160 degrees. OLEDs also switch faster than LCD elements, producing a smoother animation. Once initial investments in new facilities are recouped, OLEDs can potentially compete at an equal or lower cost than incumbent LCDs.


Despite these advantages, OLEDs have experienced slow acceptance in the industry for a variety of reasons. First, they have a relatively short lifespan and as power/brightness is increased the life is reduced dramatically. This is especially true for the blues, which lose their color balance over time. Low manufacturing yields have also been a problem, keeping the cost of production relatively high. As OLEDs are susceptible to water and oxygen contamination, during manufacturing they need to be encapsulated and sealed against the elements adding significant cost and complexity. In addition, only low resolution OLED displays can use passive matrix backplanes and higher resolutions require active matrices, which need to be highly conductive since OLEDs are current driven. Typically, low temperature poly silicon (LTPS) backplanes are used which adds cost and complexity. These conductors are also highly reflective requiring the OLED designers to add a circular polarizer on the front of the display reducing the efficiency of the display and increasing the cost. Finally, as is the case with all emissive displays, OLED displays have poor readability in environments such as the bright outdoors.

Anonymous said...

It's a pritty pro IMOD article. The development of OLED is already much futher. The idea behind OLED is that they do can use the current LCD factories. That is currently only possible for smaller displays, so there is the problem for OLED. For the rest, it looks real good, espacialy the power part. But I have to see what the brightness will be.
Because both techniques aren't widely availible we have to see what the future will bring. But it is nice to see that there is so much development.