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Monochrome TFT for cars, industrial products

With full-colour TFT LCD display panels becoming ever more ubiquitous, the concept of a monochrome TFT panel might seem like a retrograde step. The concept does, however, have some significant advantages for products in the industrial and automotive sectors, according to Varitronix. You can have a display with wide viewing angle, fast response time and very good extended temperature stability that offers a very high contrast image—and, as it is a monochrome unit, the drive circuitry will be much less complex. Varitronix has manufactured a demonstration 2.8-in. panel but, based on initial customer feedback, may go to production with a 3.5-in. diagonal panel. The company sees the idea as a“next-step” product from its own ISTN panels. The company says that in terms of the panel itself, you will save little if any cost relative to a colour panel—the material and processing content is similar— but your system cost could be much lower because the drive and interconnect cost will be reduced: drive requirements will be similar to that of an STN monochrome panel. Many automotive and industrial instrumentation projects, the company says, have no requirement for full colour, making monochrome TFT a high-performance alternative to DSTN and other passivedisplay technologies. You can expect a contrast ratio of approximately 1000:1, and other parameters are similar to those of full-colour TFT (viewing angles and operating temperatures). Mono TFT also improves the sunlight readability of the display over full-colour TFT. With a transmission ratio in excess of 20% there is potential to reduce the brightness or even eliminate the backlightto save power.

Varitronix has also been addressing the sunlight-viewability parameter using another approach, employing index matching between the protective glass placed over the LCD (liquid-crystal-display) panel and the front glass surface of the panel itself. In a conventional structure there is an air gap in this position and light is refl ected from each of the air-glass interfaces—the front and back of the protective glass and the front surface of the panel. By the rules of optics, if you reduce the change in the optical refractive index at each of these surfaces, the refl ection will also be lower. Therefore, Varitronix fi lls that gap with an optical adhesive whose refractive index closely matches the glass itself. Refl ections from the inner two interfaces are almost nearly eliminated, and the viewability in bright light improves. The principle, according to the company, is well-known but translating it to a volume-manufacturing operation has been diffi cult. Varitronix says it has now mastered the process for small panels, has demonstrated that it can do it at 10.4 in., and hopes soon to have a12-in. panel with the same feature.

Varitronix, www.varitronix.com.