Patent ID: 7928936

Claim:
A method of compensating for changes in the threshold voltage of the drive transistor of an OLED drive circuit, comprising: a) providing the drive transistor with a first electrode, a second electrode, and a gate electrode; b) connecting a first voltage source to the first electrode of the drive transistor, and an OLED device to the second electrode of the drive transistor and to a second voltage source; c) providing a test voltage to the gate electrode of the drive transistor and connecting to the OLED drive circuit a test circuit that includes an adjustable current mirror that is set to provide a predetermined drive current through the drive transistor and the OLED device and causes the voltage applied to the current mirror to be at a first test level when the drive transistor and the OLED device are not degraded by aging conditions, and storing the first test level; d) providing a test voltage to the gate electrode of the drive transistor and connecting the test circuit to the OLED device to produce a second test level after the drive transistor and the OLED device have aged, and storing the second test level; and e) using the first and second test levels to calculate a change in the voltage applied to the gate electrode of the drive transistor to compensate for aging of the drive transistor.