Video walls using multicolor LEDs are in demand, especially if the LED can be mounted using surfacemount technology. This technical article deals with the latest RGB LED package approaches for fullcolor indoor and outdoor displays, as well as technical considerations, which designers should take into account when designing these large full color displays.
There are different packages available in the market that can be used to build up a video wall using a surface mount approach.
For instance, PLCC-2 LEDs can be used to build up a mono-chromatic display or full-color display while one pixel is made from multiple LEDs. On the other hand, due to the size of a PLCC-2 LED, the pixel pitch of such a screen can be quite large. This might be acceptable in screens with a certain distance to the viewer, at least 10-15m.
In situations where the viewer is closer to the screen, like at a shopping mall, a finer resolution would be more favorable. To achieve smaller pixels, 3- in-1 RGB packages can be found in the market as well. The most popular 3-in-1 RGB packages are based on either a PLCC-4 or PLCC- 6 platform.
Avago released a new 3-in-1 RGB PLCC-4 LED (ASMT-QTB0). This PLCC-4 LED has highly reflective white package material, which provides a high extraction of light. Another feature required for a high contrast ratio is the black surface on the upper side of the LED.
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| Figure 1: The pixel pitch of the aforementioned PLCC-4 can go down to 8mm for high resolution video screens. |
The black surface needs to be non-reflective to absorb as much light as possible shining onto the screen from various sources, e.g. spot lights or the setting sun. The pixel pitch of the aforementioned PLCC-4 can go down to 8mm for high resolution video screens (Figure 1 above).
A completely black PLCC-4 leads to an even better increase of the contrast ratio. The visual performance and appearance of indoor full color screens can be improved tremendously using a LED with a completely black package.
Avago's ASMT-QTC0, for example, provides a very small pixel pitch down to 8mm. This makes the screen appear like an LCD display, but it can be designed much bigger compared to what can be done with current LCD technology.
Another popular package platform for full color video screens is a PLCC-6 LED which has 6 leads with an individual anode and cathode for each chip, like Avago's ASMT-YTB0. A high reflective white package enables good color mixing and high brightness performance. Because of the high brightness performance, it can be used in outdoor full-color screens as well.
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| Figure 2: For better product performance, the recommended pixel pitch is 10mm. |
The black surface helps to achieve a high contrast ratio in indoor and outdoor video walls. Additionally, the small package design enables a small pixel pitch to 8mm. For better product performance, the recommended pixel pitch is 10mm (Figure 2, above).
