An area‐ratio gray‐scale method to achieve image uniformity in TFT‐LEPDs

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Abstract
Abstract— An area‐ratio gray‐scale method (ARG) has been developed for low‐temperature‐polysilicon thin‐film‐transistor‐driven light‐emitting‐polymer displays (LTPS TFT‐LEPDs). A pixel consists of plural sub‐pixels, which are controlled to be in either an on‐state or off‐state. The gray scale is acquired by selecting the number of the on‐state sub‐pixels, that is, the ratio of the light‐emitting area. One advantage of the ARG is to improve image uniformity. In the on‐state, since TFT resistance is negligible, the current is determined by the LEP diode resistance. Therefore, the TFT characteristic deviation has no effect on the current. Moreover, the dimensions of each sub‐pixel are the same, and the shapes of the sub‐pixel are circular in order to improve their uniformity. As a result, the image becomes uniform. Another advantage of the ARG is to achieve digital operation, which makes interfacing easy. A digital‐analog converter (DAC) automatically exists in the sub‐pixel and the naked eye.