Method and apparatus for uniformity and brightness correction in an electroluminescent display

A method for reducing brightness uniformity variations in an active-matrix electroluminescent (EL) display employing amorphous silicon thin-film transistors, comprising the steps of:

• a) providing an active-matrix EL display having amorphous silicon thin-film transistors that drive a plurality of light-emitting elements responsive to an input signal that causes the light-emitting elements to emit light;
• b) deriving a first correction value from a measured or estimated current used or from a measured light output emitted by the light-emitting element in response to known image signals at a first time;
• c) identifying a plurality of predetermined groups of light-emitting elements, the plurality of predetermined light-emitting groups including all of the light-emitting elements in the EL display, wherein each predetermined group of light-emitting elements includes more than one light-emitting element;
• d) selecting one or more representative light-emitting elements for each predetermined group of light-emitting elements, wherein, in each predetermined group, the number of the representative light-emitting elements is fewer than the number of the light-emitting elements;
• e) measuring total representative current used by the representative light-emitting elements for each predetermined group of light-emitting element in response to known image signals at a second time;
• f) deriving an estimated second correction value from i) the first correction value, or the measured or estimated current used or the measured light output emitted by the light-emitting element in response to known image signals at the first time, and ii) the measured total representative currents for each individual light-emitting elements;
• and
• g) employing the estimated second correction value to correct image signals for the changes in the output of the light-emitting elements in each predetermined group and produce compensated image signals,
• wherein the method employs only a single measurement of the total representative current per each predetermined group, and
• the frequency of the measurements is tens of hours of use.