Apparatus and method for evaluating organic EL display

A method for evaluating an organic EL display comprised of an array of pixels in which each pixel is connected to a respective one of a plurality of signal lines and to a respective one of a plurality of selection lines, in which each pixel includes a switch circuit, a constant current circuit and an organic EL element, with the switch circuit being operative to connect the signal line for the pixel to the constant current circuit when the selection line for the pixel is suitably energized, and in which the constant current circuit includes a capacitor which is charged and discharged based on a voltage on the signal line for the pixel when the selection line for the pixel is suitably energized, the capacitor supplying a constant current to the organic EL elements, according to a charge stored in the capacitor;

• the method comprising the steps of:
• generating test voltages;
• supplying the test voltages to the signal lines and the selection lines according to a sequence in which only one signal line and one selection line are simultaneously energized, whereby the organic EL elements are energized one at a time;
• detecting a first current flowing to the organic EL element in a pixel when the capacitor in the pixel is charged and a second current flowing to the organic EL element in the pixel when the capacitor in the pixel is discharged;
• and
• detecting defects in each pixel based on a difference between the first and second currents.

An organic EL display which comprises:

• an array of pixels in which each pixel is connected to a respective one of a plurality of signal lines and to a respective one of a plurality of selection lines,
• each pixel including:
• an organic EL element;
• a switch circuit operative to connect the signal line for the pixel to the constant current circuit when the selection line for the pixel is energized;
• a constant current circuit which includes a capacitor which is charged and discharged based on a voltage on the signal line for the pixel when the selection line for the pixel is energized, the capacitor supplying a constant current to the organic EL elements, according to a charge stored in the capacitor;
• and
• a testing subsystem comprised of:
• a test voltage generation circuit which generates test signals;
• a control circuit that controls the test voltage generation circuit to supply the test signals to the signal lines and selection lines to energize the organic EL elements of the pixels one at a time;
• a current detection circuit which is operative to detect a first current flowing to the energized organic EL element when the capacitor in the pixel has been charged and to detect a second current flowing to the energized organic EL element when the capacitor in the pixel has been discharged;
• and
• a defect decision circuit which identifies a pixel as defective based on a difference between the first and second currents.

An apparatus for evaluating an organic EL display which comprises:

• an array of pixels in which each pixel is connected to respective one of a plurality of signal lines and to a respective one of a plurality of selection lines, in which each pixel includes a switch circuit, a constant current circuit and an organic EL element, with the switch circuit being operative to connect the signal line for the pixel to the constant current circuit when the selection line for the pixel is suitably energized, and in which the constant current circuit includes a capacitor which is charged and discharged based on a voltage on the signal line for the pixel when the selection line for the pixel is suitably energized, the capacitor supplying a constant current to the organic EL elements, according to a charge stored in the capacitor, the apparatus being comprised of:
• a test voltage generation circuit which generates test signals;
• a delivery circuit that delivers the test signals to the signal lines and selection lines to energize the organic EL elements of the pixels;
• a current detection circuit which is operative to detect a first current flowing in an energized organic El element when the capacitor in the pixel has been charged and to detect a second current flowing in the energized organic EL element when the capacitor in the pixel has been discharged;
• and
• a defect decision circuit which identifies a pixel as detective based on a difference between the first and second currents.