The assignee for this patent, patent number 8624805, is
Reporters obtained the following quote from the background information supplied by the inventors: "The present invention relates to calibration of current variations in the pixels/sub-pixels of an active matrix organic light-emitting diode (AMOLED) display caused by non-uniformity of thin-film transistors (TFTs) in the sub-pixels.
"An OLED display is generally comprised of an array of organic light emitting diodes (hereafter referred to as 'OLED diodes') that have carbon-based films deposited between two charged electrodes. Generally one electrode is comprised of a transparent conductor, for example, indium tin oxide (ITO). Generally, the organic material films are comprised of a hole-injection layer, a hole-transport layer, an emissive layer and an electron-transport layer. When voltage is applied to the OLED diode, the injected positive and negative charges recombine in the emissive layer and transduce electrical energy to light energy. Unlike liquid crystal displays (LCDs) that require backlighting, OLED displays are self-emissive devices--they emit light rather than modulate transmitted or reflected light. Accordingly, OLEDs are brighter, thinner, faster and lighter than LCDs, and use less power, offer higher contrast and are cheaper to manufacture.
"An OLED display typically includes a plurality of OLED diodes arranged in a matrix form including a plurality of rows and a plurality of columns, with the intersection of each row and each column forming a pixel of the OLED display. An OLED display is generally activated by way of a current driving method that relies on either a passive-matrix (PM) scheme or an active-matrix (AM) scheme.
"In a passive matrix OLED (PM OLED) display, a matrix of electrically-conducting rows and columns forms a two-dimensional array of picture elements called pixels. Sandwiched between the orthogonal column and row lines are thin films of organic material of the OLEDs that are activated to emit light when current is applied to the designated row and column lines. The brightness of each pixel is proportional to the amount of current applied to the OLED diodes of the pixel. While PM OLEDs are fairly simple structures to design and fabricate, they demand relatively expensive, current-sourced drive electronics to operate effectively and are limited as to the number of lines because only one line can be on at a time and therefore the PM OLED must have instantaneous brightness equal to the desired average brightness times the number of lines. Thus, PM OLED displays are typically limited to under 100 lines. In addition, their power consumption is significantly higher than that required by an active-matrix OLED. PM OLED displays are most practical in alpha-numeric displays rather than higher resolution graphic displays.
"An active-matrix OLED (AMOLED) display is comprised of OLED pixels (that are each comprised of
In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventor's summary information for this patent: "According to various embodiments of the present invention, sub-pixel current in an AMOLED display is forced to converge to a desired level regardless of the source of pixel current error. This is accomplished by forcing pixel transistor current of each sub-pixel to converge to a value such that the pixel transistor current matches a predetermined target current that is established using an analog feedback control circuit, in order to correct
"The OLED sub-pixels have a so-called 3T cell structure including three TFTs, one TFT for connecting the data line to the storage capacitor in the OLED sub-pixel, another TFT (the pixel transistor) for driving the OLED diode in each sub-pixel, and still another TFT for connecting the OLED diode anode to the data line of the AMOLED panel so that the pixel transistor current can be measured for
"For Mura correction, an average RGB value corresponding to a target current is loaded onto the column digital-to-analog converters (DACs) driving the data lines of the AMOLED panel. Any deviation of the pixel transistor current from the target current causes
"The present invention has the advantage that the pixel transistor current is forced to converge to the desired current level simply by setting the predetermined target current, regardless of the cause of variations, inaccuracies, or non-uniformity in the sub-pixels.
For more information, see this patent: McCreary,
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