DIGITAL-DRIVE ELECTROLUMINESCENT DISPLAY WITH AGING COMPENSATION
First Claim
1. A method of compensating for variations in characteristics of an electroluminescent (EL) emitter in an EL subpixel, comprising:
- (a) providing the EL subpixel having a drive transistor, the EL emitter, and a readout transistor, wherein the drive transistor has 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) connecting the EL emitter to the second electrode of the drive transistor;
(d) providing a second voltage source connected to the EL emitter;
(e) connecting the first electrode of the readout transistor to the second electrode of the drive transistor;
(f) providing a current source and a third switch for selectively connecting the current source to the second electrode of the readout transistor, wherein the current source provides a selected test current to the EL emitter;
(g) providing a voltage measurement circuit connected to the second electrode of the readout transistor;
(h) opening the first switch, closing the third switch, and in response to the voltage measurement circuit measuring the voltage at the second electrode of the readout transistor to provide a first emitter-voltage signal;
(i) using the first emitter-voltage signal to provide an aging signal representative of characteristics of the EL emitter;
(j) receiving an input signal;
(k) using the aging signal and the input signal to produce a compensated drive signal; and
(l) providing a selected drive voltage to the gate electrode of the drive transistor for a selected on-time corresponding to the compensated drive signal, wherein the selected drive voltage causes the drive transistor to operate in a linear region during the selected on-time, to compensate for variations in characteristics of the EL emitter.
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Abstract
An electroluminescent (EL) subpixel driven by a digital-drive scheme has a readout transistor driven by a current source when the drive transistor is non-conducting. This produces an emitter-voltage signal from which an aging signal representing the efficiency of the EL emitter can be computed. The aging signal is used to determine the loss in current of the subpixel when active, and an input signal is adjusted to provide increased on-time to compensate for voltage rise and efficiency loss of the EL emitter. Variations due to temperature can also be compensated for.
52 Citations
19 Claims
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1. A method of compensating for variations in characteristics of an electroluminescent (EL) emitter in an EL subpixel, comprising:
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(a) providing the EL subpixel having a drive transistor, the EL emitter, and a readout transistor, wherein the drive transistor has 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) connecting the EL emitter to the second electrode of the drive transistor; (d) providing a second voltage source connected to the EL emitter; (e) connecting the first electrode of the readout transistor to the second electrode of the drive transistor; (f) providing a current source and a third switch for selectively connecting the current source to the second electrode of the readout transistor, wherein the current source provides a selected test current to the EL emitter; (g) providing a voltage measurement circuit connected to the second electrode of the readout transistor; (h) opening the first switch, closing the third switch, and in response to the voltage measurement circuit measuring the voltage at the second electrode of the readout transistor to provide a first emitter-voltage signal; (i) using the first emitter-voltage signal to provide an aging signal representative of characteristics of the EL emitter; (j) receiving an input signal; (k) using the aging signal and the input signal to produce a compensated drive signal; and (l) providing a selected drive voltage to the gate electrode of the drive transistor for a selected on-time corresponding to the compensated drive signal, wherein the selected drive voltage causes the drive transistor to operate in a linear region during the selected on-time, to compensate for variations in characteristics of the EL emitter. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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Specification