System and methods for aging compensation in AMOLED displays
Methods and systems to provide baseline measurements for aging compensation for a display device are disclosed. An example display system has a plurality of active pixels and a reference pixel. Common input signals are provided to the reference pixel and the plurality of active pixels. The outputs of the reference pixel is measured and compared to the output of the active pixels to determine aging effects. The display system may also be tested applying a first known reference current to a current comparator with a second variable reference current and the output of a device under test such as one of the pixels. The variable reference current is adjusted until the second current and the output of the device under test is equivalent of the first current. The resulting current of the device under test is stored in a look up table for a baseline for aging measurements during the display system operation. The display system may also be tested to determine production flaws by determining anomalies such as short circuits in pixel components such as OLEDs and drive transistors.
1. A voltage-programmed display panel allowing measurement of effects on pixels in the panel, comprising:
a plurality of active pixels forming the display panel to display an image under an operating condition, the active pixels each being coupled to a supply line and a programming line for displaying images under said operating condition;
a reference pixel coupled to the supply line and the programming line, the reference pixel being coupled to said supply line and said programming line in a manner that said reference pixel has only a controlled condition independent of the operating condition; and
a controller coupled to each of the plurality of active pixels and reference pixel, the controller causing a test voltage to be applied to the plurality of active pixels and the reference pixel, the controller further comparing an output of the reference pixel in comparison with the output of one of the plurality of active pixels.
2. The system of claim 1 , wherein the active pixels and the reference pixel each include a drive transistor and an organic light emitting device coupled to the drive transistor.
3. The system of claim 1 , wherein the controller compensates a programming voltage to the one of the plurality of pixels based on the comparison of the output of the reference pixel with the output of the one of the plurality of active pixels.
4. The system of claim 1 , wherein the reference pixel is one of a plurality of reference pixels, and the controller determines whether the reference pixel is functioning, and if the reference pixel is not functioning, the test voltage is applied to another reference pixel of the plurality of reference pixels.
5. The system of claim 1 , wherein the panel has columns and rows of pixels, and the reference pixel is associated with a column of pixels.
6. The system of claim 5 , wherein output from the reference pixel and the one of a plurality of active pixels is an output current.
7. The system of claim 1 , wherein the reference pixel is associated with a row of pixels.
8. The system of claim 7 , further comprising a memory storing luminance curve data for the one of the plurality of active pixels, and wherein the controller compares the stored luminance curve data with the output from the reference pixel.
9. The system of claim 1 , wherein the controlled condition of the reference pixel is an un-aged condition, wherein the plurality of active pixels are affected by aging when displaying images.
10. The system of claim 1 , wherein the plurality of active pixels have an applied current level and wherein the reference pixel has an applied current level less than the current level of the plurality of active pixels.