Koninklijke Philips Corporation N.v.

Tpo Hong Kong Holding Limited

Koninklijke Electronics N.v.

Jurgen J L Hoppenbrouwers

Nijs Cornelis Van Der Vaart

David Andrew Fish

Roel Van Woudenberg

Alan G Knapp

Franciscus P M Budzelaar

Mark Johnathan Childs

Wilhelmus H M Van Beek

Martin J J Jak

In an active matrix electroluminescent display device, comprising an array of display pixels, each pixel comprises an electroluminescent display element, active matrix circuitry including at least one drive transistor for driving a current through the display element, means for determining an overall brightness level of an image to be displayed in a frame period, means for controlling the at least one drive transistor of each pixel in dependence on, (1) a respective input signal providing a drive level for the pixel, and (2) the overall brightness level. The novel arrangement is capable of controlling the pixels to limit the maximum currents drawn by the pixels, thereby limiting cross-talk effects resulting from voltage drops along row or column conductors. If an image is bright, the pixel drive levels across the image, or at least part of the image, can be reduced, so that the maximum brightness is reduced.

System and method for determining an overall brightness level of an image to be displayed in a frame period in electroluminescent display devices

In an active matrix electroluminescent display, a plurality of rows of pixels are illuminated, defining at least two bands of rows separated by a non-illuminated band. The bands of rows of pixels scroll in the column direction over time, and at most 75% of the rows are illuminated at any point in time. This method is in essence a double bar scrolling method. By scrolling two bars, the required peak brightness is reduced as the effective overall duty cycle is increased. However, the period of illumination can still remain short, so that motion perception remains improved. The scrolling speed can be halved for the same frame rate or else the frame rate can be increased to reduce flicker.

Electroluminescent display devices

In an active matrix electroluminescent display device, an overall brightness level of an image to be displayed in a frame period is determined. A drive transistor of each pixel is controlled in dependence on an input drive signal for the pixel and on the overall brightness level, for example using a signal processor () to vary the pixel drive signals. This arrangement can control the pixels to limit the maximum currents drawn by the pixels, thereby limiting the cross talk effects resulting from voltage drops along row or column conductors. If an image is bright, the pixel drive levels across the image (or at least a part of the image) can be reduced, so that the maximum brightness is reduced.

Control of current supplied by a transistor to a pixel in an electroluminescent display device

A color electroluminescent, EL, display device comprising an array of pixels () each comprising sub-pixels () of two or more colors (R, G, B). For at least one of the colors (R, G, B), the pixel () comprises a first sub-pixel (R, G, B) comprising a first EL material and a second sub-pixel (R, G, B) comprising a second EL material. The first EL material is of higher lifetime than the second EL material; the second EL material has better color points and/or better color rendition properties than the first EL material. In some embodiments a pixel comprises two red sub-pixels (R, R), two green subpixels (G, G) and two blue sub-pixels (BL, Bc), one sub-pixel of each color (R, G, B) comprising relatively high lifetime EL material and the other sub pixel of each color (R, G, B) comprising relatively good color points EL material. In other embodiments a pixel comprises two blue sub-pixels (B, B) but only one red sub-pixel and one green sub-pixel.

Colour electroluminescent display device and its driving method

Growing community of inventors

Eindhoven, Netherlands

Jurgen J L Hoppenbrouwers