Electroluminescent display compensated analog transistor drive signal

Apparatus for providing an analog drive transistor control signal to the gate electrode of a drive transistor in a drive circuit that applies current to an EL device, the drive circuit including a voltage supply electrically connected to a first supply electrode of the drive transistor and the EL device electrically connected to a second supply electrode of the drive transistor, comprising:

• a) a measuring circuit for measuring the current passing through the first and second supply electrodes at first and second times to provide respective aging signals representing variations in the characteristics of the drive transistor and EL device caused by operation of the drive transistor and EL device over time, the measuring circuit including a memory for storing the measured current at the first time;
• b) means for providing a linear code value;
• c) a compensator for changing the linear code value in response to the aging signal to compensate for the variations in the characteristics of the drive transistor and EL device, wherein the compensator is adapted to calculate current change from the aging signal values at the first and second times, map current loss to threshold voltage shift, and add the mapped threshold voltage shift to the linear code value to provide a changed linear code value;
• and
• d) a source driver having a linear relationship of input code value to analog voltage for producing the analog drive transistor control signal in response to the changed linear code value for driving the gate electrode of the drive transistor.