Bringing Local Dimming to Small Displays

By Ken Werner

As you read this, I am driving from my home in Connecticut to Research Triangle Park in North Carolina. The distance is nearly 600 miles (960 km).

The last time I made that drive was when I was in graduate school at Chapel Hill. Then, I routinely did the trip non-stop. I’m a bit older now, so I spent last night in the charming historic district of Fredericksburg, Virginia. (Note to self: Radar detectors are illegal in Virginia.)

Does this have anything to do with display technology, except that my Uniden radar detector has a nice alphanumeric OLED display? Well, it’s a bit of a stretch, but here it is.

Auto manufacturers love the high contrast and saturated colors of OLEDs, but they don’t like the high cost relative to LCDs, and they remain concerned about burn-in, lifetime, and the fact that many OLED materials are not yet stable over the temperature range required for automotive applications.

If you could make small LCDs with local dimming that were thin enough and had enough dimming zones, you would have a display that could bridge the image-quality gap between conventional LCDs and OLEDs, and with the predictable behavior and relatively low cost LCDs deliver. This would be of great interest to automotive OEMs and Tier 1 suppliers, as well as makers of semi-premium smartphones and larger displays, as well. But the conventional approach of using individually packaged LEDs for the full-matrix backlight would result in a small display that is far too thick and does not have enough zones.

MiniLED to the Rescue

The solution was shown all over the show floor at SID Display Week. That solution is the miniLED backlight, Confusingly, most manufacturers were calling LCDs with miniLED backlights “miniLED displays.” Unlike microLED displays, which do use small LED chips as the display elements, “miniLED displays” are LCDs with miniLED backlights. My colleague, Bob Raikes, mentioned miniLEDs in his DD on Tuesday (MicroLED May Drive You Mad). Let’s talk about them in a bit more detail here.

At Display Week, Tianma received a “best in show” award for its 6.46″ HDR LTPS LCD miniLED smartphone display prototype, with peak brightness above 1000 cd/m² and maximum local contrast over 3,000,000:1. The display also features 10-bit output and DCI-P3 color gamut, said Tianma. “These features [enable] the LTPS LCD to better compete at OLED performance levels.” Tianma expects the display to be in production by the end of 2019.

BOE showed a 27″ UHD LCD with miniLED backlight unit. BOE did not reveal the number of zones, but did say the luminance was 600 cd/m², contrast ratio 1 million to 1, and the color gamut 99% DCI-P3. The module thickness was 8mm. A 5.99″ miniLED-lit LCD intended for smartphones had 1080 x 2160 pixels, 450 cd/m², CR of 180,000:1 and a gamut of 100% NTSC. The border was only 0.5mm on three sides and 1.4mm on the bottom edge.

thumb BOE 5.99 inch MiniLED LCDAmong the miniLED-backlit LCDs at SID Display Week was this 5.99″ smart phone panel from BOE. (Photo: Ken Werner)

AUO showed miniLED backlt displays for gaming monitors, gaming notebook PCs, and VR headsets. The company’s 27 UHD 4K gaming monitor display had144Hz refresh rate, local dimming, and 1000 cd/m² luminance.

A 6″ in-cell touch panel had a module thickness of only 1.1mm, and a 2″ LTPS display for VR applications featured a pixel density of 1000 ppi and 1024 dimming zones.

JDI, had an alternative approach: the laser backlight. The company showed a 17.3″ 8K panel with 510 ppi and a gamut of 97% of BT.2020. More on that to come.- Ken Werner

Ken Werner is Principal of Nutmeg Consultants, specializing in the display industry, manufacturing, technology, and applications, including mobile devices, automotive, and television. He consults for attorneys, investment analysts, and companies re-positioning themselves within the display industry or using displays in their products. He is the 2017 recipient of the Society for Information Display’s Lewis and Beatrice Winner Award. You can reach him at [email protected]