Patent ID: 7859501

Claim:
A method of compensating for changes in characteristics of an OLED drive circuit, comprising: a. providing a drive transistor with a first electrode, a second electrode, and a gate electrode; b. providing a first voltage source and a first switch for selectively connecting the first voltage source to the first electrode of the drive transistor; c. providing an OLED device connected to the second electrode of the drive transistor, and a second voltage source and a second switch for selectively connecting the OLED device to the second voltage source; d. connecting the first electrode of a readout transistor to the second electrode of the drive transistor; e. providing a current source and a third switch for selectively connecting the current source to the second electrode of the readout transistor; f. providing a current sink and a fourth switch for selectively connecting the current sink to the second electrode of the readout transistor; g. providing a test voltage to the gate electrode of the drive transistor and providing a voltage measurement circuit connected to the second electrode of the readout transistor; h. closing the first and fourth switches, and opening the second and third switches and using the voltage measurement circuit to measure the voltage at the second electrode of the readout transistor to provide a first signal representative of characteristics of the drive transistor; i. opening the first and fourth switches, and closing the second and third switches and using the voltage measurement circuit to measure the voltage at the second electrode of the readout transistor to provide a second signal representative of characteristics of the OLED device; and j. using the first and second signals to compensate for changes in characteristics of the OLED drive circuit.