Patent ID: 7463222

Claim:
An active matrix electroluminescent display device comprising an array of display pixels, each pixel comprising: an electroluminescent display element ( 2 ); a drive transistor ( 22 ) connected between a power supply line ( 26 ) and the display element ( 2 ) for driving a current through the display element ( 2 ); a storage capacitor ( 24 ) for storing a voltage to be used for addressing the drive transistor; a discharge photodiode ( 27 ) for discharging the storage capacitor ( 24 ) in dependence on the light output of the display element; and circuit elements for changing an input data voltage applied to the pixel by an amount corresponding to the threshold voltage of the drive transistor, and for applying the changed data voltage between the gate and the source of the drive transistor ( 22 ), wherein the circuit elements comprise a second photodiode ( 30 ) and a second storage capacitor ( 32 ),.wherein the second photodiode ( 30 ) is connected between the gate of the drive transistor ( 22 ) and one terminal of the second storage capacitor ( 32 ), and the discharge photodiode ( 27 ) is connected between the one terminal and the power supply line ( 26 ).