Patent ID: 7696773
Filing Date: 2010-04-13
Classification: G09G

Abstract:
1. A method of determining characteristics of transistors and electroluminescent devices in an electroluminescent display, comprising: (a) providing an electroluminescent display having a two-dimensional array of electroluminescent devices arranged in rows and columns, wherein each electroluminescent device is driven by a drive circuit in response to a drive signal; (b) providing for pairs of electroluminescent devices a first drive circuit associated with the first electroluminescent device, a second drive circuit associated with the second electroluminescent device, and a single readout line, each drive circuit including a drive transistor having first, second, and gate electrodes, and a readout transistor having first, second, and gate electrodes, with each readout transistor of a pair being electrically connected to the readout line; (c) providing a first voltage source and a first switch for selectively connecting the first voltage source to the first electrodes of the drive transistors; (d) providing a second voltage source and a second switch for selectively connecting the electroluminescent devices to the second voltage source; (e) providing a current source and a third switch for selectively connecting the current source to the second electrode of the readout transistors; (f) providing a current sink and a fourth switch for selectively connecting the current sink to the second electrode of the readout transistors; (g) providing a test voltage source for turning the drive transistors on and off by applying potential to the gate electrodes of the drive transistors; (h) providing a voltage measurement circuit connected to the second electrode of the readout transistors; (i) sequentially testing the drive transistors of the first and second drive circuits by closing the first and fourth switches, opening the second and third switches, using the test voltage source to turn on the drive transistor of the first drive circuit and turn off the drive transistor of the second drive circuit, drawing a test current using the current sink, using the voltage measurement circuit to measure the voltage at the second electrode of the readout transistor of the first drive circuit to provide a first signal representative of characteristics of the drive transistor of the first drive circuit using the test voltage source to turn off the drive transistor of the first drive circuit and turn on the drive transistor of the second drive circuit, and using the voltage measurement circuit to measure the voltage at the second electrode of the readout transistor of the second drive circuit to provide a second signal representative of characteristics of the drive transistor of the second drive circuit, whereby the characteristics of each drive transistor are determined; and (j) simultaneously testing the first and second electroluminescent devices by opening the first and fourth switches, and closing the second and third switches, using the test voltage source to turn off both of the drive transistors, driving a test current using the current source, and using the voltage measurement circuit to measure the voltage at the second electrode of the readout transistors to provide a third signal representative of characteristics of the pair of electroluminescent devices, whereby the characteristics of both electroluminescent devices are determined.