Method and apparatus for managing and uniformly maintaining pixel circuitry in a flat panel display
First Claim
1. A method for an emissive display, comprising:
- providing a driver transistor of an emissive pixel with a plurality of drive voltages;
measuring the current flowing through the emissive pixel as a result of providing each drive voltage to the driver transistor;
storing values associated with the drive voltages and the corresponding measured currents flowing through the emissive pixel in a look up table;
selecting desired current flow value through the emissive pixel;
using the look up table to determine the corresponding drive voltage value for the desired current flow value; and
providing the drive transistor with the drive voltage determined by using the look up table to cause the desired current to flow through the pixel.
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Accused Products
Abstract
The present invention describes a method and apparatus for measuring the voltage and current characteristics of the OLED pixel as it ages and correlating the measured data to the decrease in quantum efficiency and changes in OLED impedance over the life of the OLED, so that corrections can be made to the image drive system to prevent image sticking and color point drift. The method and apparatus of the present invention do not require any additional circuitry or changes in the display design. The circuitry of the present invention is implemented in the display driver integrated circuit (IC) chips. The basis of the invention is the luminance-current-voltage (LIV) curves which characterize the OLED materials over their life time. A series of these curves are stored in memory representing a OLED material at various ages. The apparatus of the present invention is used to measure driver voltages and currents for a pixel having an OLED, which measurements are then used to extract the voltage current curve for the OLED at any point in time. The extracted curve is compared to the aging curves stored in memory to determine the aging curve that best describes the measured present voltage current characteristic of the pixel. That aging curve is used to drive the pixel.
263 Citations
31 Claims
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1. A method for an emissive display, comprising:
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providing a driver transistor of an emissive pixel with a plurality of drive voltages;
measuring the current flowing through the emissive pixel as a result of providing each drive voltage to the driver transistor;
storing values associated with the drive voltages and the corresponding measured currents flowing through the emissive pixel in a look up table;
selecting desired current flow value through the emissive pixel;
using the look up table to determine the corresponding drive voltage value for the desired current flow value; and
providing the drive transistor with the drive voltage determined by using the look up table to cause the desired current to flow through the pixel. - View Dependent Claims (2, 3, 4, 5, 6, 25)
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7. A method for an emissive display, comprising:
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measuring a plurality of electrical properties for a current driver of an emissive pixel;
associating values with the measured properties; and
using the values associate with the measured properties to mathematically calculate the value of the drive voltage to be provided to a current driver of the emissive pixel for causing a desired current to flow through the emissive pixel. - View Dependent Claims (8, 9, 10)
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11. A method for an emissive display comprising:
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generating a current table associating values of currents flowing through a pixel material and the corresponding voltages applied to the pixel material to cause the currents to flow through the pixel material;
generating a luminance table associating values of the amounts of light emitted by the pixel material and the corresponding voltages applied to the pixel material to cause the pixel material to emit the light;
generating the current and luminance tables at a selected active usage age point of the pixel material;
repeating the generation of the first and second tables at various active usage age points of the pixel material;
storing the tables in memory; and
for an emissive pixel circuitry fabricated from using the same type of pixel material used to generate the tables, using the current and luminance tables generated at the active usage age point that is approximately the same as the active usage age point of the emissive pixel for determining the voltage level to be provided to the drive circuitry of the emissive pixel for obtaining a desired pixel luminosity;
whereinthe active usage age refers to the active application of drive voltage to the pixel material to cause luminance. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. A method for measuring a current flowing through an emissive pixel of a flat panel display comprising:
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measuring a noise current of the display and associating a value with the measured noise current;
providing a drive voltage to the drive circuitry of the pixel to cause the pixel to output a current including a combination of the noise current and a current caused by the drive voltage;
measuring the output current of the pixel including the combined noise current and the current caused by the drive voltage, and associating a value with the output current;
subtracting the value associated with the noise current from the value associated with the combined output current;
storing a result of a subtraction;
whereinthe result of the comparison represents the corresponding pixel current for the drive voltage. - View Dependent Claims (26, 27)
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28. A flat panel display comprising:
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a matrix of pixels;
means for causing a noise current of the display to flow to the ground through a first current path;
means for limiting the current flow capacity of the first current path according to the amount of the noise current;
means for providing a drive voltage to a selected pixel circuitry and causing an output current to flow through the selected pixel, the output current including a combination of the noise current and the current flow caused by the drive voltage; and
means for providing a second path for the output current in excess of the noise current to flow.
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29. A flat panel display comprising:
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A matrix of pixels;
the drain of a field effect transistor (FET) coupled to the cathodes of light emitting elements of a plurality of pixels of the matrix of pixels;
the source of the FET coupled to the ground;
the FET providing a flow through switch for the noise current of the display to flow to the ground;
an equilibrium circuit coupled to the gate of the FET for adjusting the flow through capacity of the FET according to the noise current of the display;
a drive circuit for providing a drive voltage to a selected pixel circuitry and causing an output current to flow through the selected pixel, the output current including the combination of the noise current and the current flow caused by the drive voltage;
the equilibrium circuit for providing a different path from the flow through switch for the output current in excess of the noise current to flow;
a measurement circuit coupled to the different path for measuring the current flowing through the different path and associating a value to the current flowing through the different path; and
a comparison circuit for comparing the value associated with the current flowing through the different path with a stored value to determine the age of the pixel;
wherein;
the FET provides a flow through path only for the flow of the noise current; and
the equilibrium circuit includes a switch for coupling the separate path to the cathode of the light emitting diode of the selected pixel when the output current of the pixel exceeds the noise current. - View Dependent Claims (30, 31)
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Specification