There was a rapid change in image display technology within the last few years. Nowadays CRTs are history, flatpanels substitute them everywhere. Even in the broadcast industry.
Different technologies dominate the market;
Plasma - a self-lighting principle - mostly used for large screens;
TFT-LCDs - a concept that always needs a backlight - most common in the display industry for tiny up to huge screens;
OLED; - another self-light-emitting principle - up-coming technology for small and larger displays in any industry.
OLED stands for “organic light emitting diode” and physically it’s like an array of extremely small LEDs. Does this technology have the power to conquer the broadcast monitor market?
In general the answer has to be yes. LEDs themselves are used widely for outdoor displays and illuminate large screens such as The Strip in Las Vegas, the replay at the Wimbledon Grand Slam or are used as stage background in show events all over the world.
Standard LEDs are physically too big to make small displays possible. During the last years the display industry, headed by Samsung, CMEL and others, have developed valuable and cost effective materials and manufacturing technologies allowing to print light emitting organic substrate onto glass or plastic foil. This opens new opportunities for designing displays to be used in telecommunication, industrial appliance or digital signage.
In the middle of last century the physical effect that organic material emits light by applying high-voltage was found at the University of Nancy, France. The phenomena was called electroluminescence; it’s the recombination of electrons and positive holes injected onto the organic layer material through the different levels of energy between anode and cathode creating lights of certain wavelength in the visible region.
It took another 30 years until scientists at Eastman Kodak invented the first diode device, which uses a two-layer structure with separate hole transporting and electron transporting layers such that recombination and light emission occurred in the middle of the organic layer. With this the era of OLED begins.
Today OLEDs are mostly made of a polymer dye consisting of derivatives of poly-phenylene vinylene (PPV), while the anode and cathode are typically indium tin oxide (ITO) and aluminium respectively. Other materials may also be used in between these layers to increase the efficiency of the device. The cells can illuminate according to the organic materials all wavelength so that a full color display can be realized. As a self-light emitting diode, these cells have a high level of brightness and color purity.
In the beginning of this technology the device life time was an issue, especially the blue colored organic materials which have had the shortest life. Improvements have increased the life time of an RGB cell sustaining 400 cd/m2 of luminance for over 60.000 h nowadays. Another hurdle was intrusion of water into displays that can cause damage or destroy the organic materials. Therefore, improved sealing processes are important for practical manufacturing and may limit the longevity of more flexible displays.
As like LCD, two different types of OLED are available:
Passive matrix OLED (PMOLED) [cell phones, PDAs, ...] see graphic -passive matrix-
Active matrix OLED (AMOLED) [monitors, TV, signs, ...] see graphic -active matrix-
The passive matrix devices are simple to manufacture, but have a high power assumption and lower light output.
The active matrixes are more complicated to manufacture, but have a low power consumption and are possible to make in larger sizes and high resolution. That is what we need for monitor application.
The broadcast and video market, in some cases, still has problems accepting flatpanels and to switch-off their tubes finally. But the fact of the matter is that CRTs are obsolete now so something else, e.g. LCD or OLED has to used.
Advantage key facts to substitute with OLED are;
Self-lighting, not using a backlight system
Lower power consumption as LCD,
Temperature independent response time of less than 50 s,
Contrast ratio better than 100.000:1,
No viewing angle limitation,
Wide color gamut,
Better outdoor readability
At the beginning of 2008 the first samples of OLED equipped monitors were introduced to the broadcast market. In Japan Sony announced the OLED viewfinder HDVF-EL100 for their studio cameras. It’s an 11 inch widescreen monitor with half-HD resolution, designed to check colormetry, focus and more camera settings. At the BVE'09 show in London TAMUZ presented its prototype of a 7.6” OLED equipped portable monitor OCM 107W HD which was launched at NAB'09 as reselling product, outfitted with HDSDI, HDMI, analog composite and component inputs. At the same NAB exhibition Marshall Electronics announced its competing model V-OL761.
Both monitors were designed as portable and battery powered device. The resolution of that 7.6” screen is 800x480 pixel, so that 16:9 footage produces a small unused black area at top and bottom. Comparing to similar LCD equipped monitors the black is dramatically deeper, as video signal black at 0 Volts generates no light at the OLED. Measuring contrast under laboratory circumstances is nearly impossible due to the limitations of the measurement devices. LCD panels deal with the issue of response time in a range of some milliseconds, OLEDs are much faster and operating in the range of nanoseconds. A little disadvantage is a tailing effect when high-contrast images are displayed over a longer period (e.g. OSD menu over video for a couple of minutes), known as streaking on CRTs.
Using the OLED monitors outdoors, the user must not worry about the temperature, the unit works equally well in the cold of winter as in the bright sun of a dessert. The power consumption during operation is not easy to estimate, video footage with mostly dark scenarios draws less power than high-bright footage. Each pixel of the OLED screen produces the emitted light itself and there is no dependence from the geometrical position within the panel so the displayed image should be very homogeneously.
Not much experience using this young technology in broadcast has been collected, but all signs indicate that the advantages over the conventional LCD technology outweigh and OLED will become very successful.