Active matrix organic electroluminescent display device
First Claim
1. An active matrix electroluminescent display device comprising an array of display pixels, each pixel comprising:
- an electroluminescent display element;
a drive transistor for driving a current through the display element, a drive voltage being provided to the gate of the drive transistor;
and a storage capacitor for storing a pixel voltage, said storage capacitor being connected between an input to the pixel and the gate of the drive transistor,wherein a driver circuitry provides a stepped voltage waveform to the input of the pixel, the stepped voltage waveform being voltage-shifted by the storage capacitor before application to the gate of the drive transistor, and wherein a height of steps in the stepped voltage waveform is greater than a voltage width of a linear operating region of the drive transistor so that the linear operating region of the drive transistor is avoided, the pixel voltage being selected so that a voltage range of the linear operating region corresponds to voltage levels between a transition of two steps of the stepped voltage waveform.
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Accused Products
Abstract
An active matrix electroluminescent display device uses a stepped voltage waveform to the input of the pixel, the stepped voltage waveform being voltage-shifted by a previously stored pixel drive voltage before application to the gate of a drive transistor. The level of the voltage shift determines the duty cycle with which the display element is driven, and thereby controls the grey level output. The height of the steps in the stepped voltage waveform is greater than the voltage width of linear operating region of the drive transistor, so that a selected step of the stepped waveform defines a transition from the drive transistor between fully on and fully off. In this way, the drive transistor is never driven in the linear region.
17 Citations
18 Claims
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1. An active matrix electroluminescent display device comprising an array of display pixels, each pixel comprising:
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an electroluminescent display element; a drive transistor for driving a current through the display element, a drive voltage being provided to the gate of the drive transistor; and a storage capacitor for storing a pixel voltage, said storage capacitor being connected between an input to the pixel and the gate of the drive transistor, wherein a driver circuitry provides a stepped voltage waveform to the input of the pixel, the stepped voltage waveform being voltage-shifted by the storage capacitor before application to the gate of the drive transistor, and wherein a height of steps in the stepped voltage waveform is greater than a voltage width of a linear operating region of the drive transistor so that the linear operating region of the drive transistor is avoided, the pixel voltage being selected so that a voltage range of the linear operating region corresponds to voltage levels between a transition of two steps of the stepped voltage waveform. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An active matrix electroluminescent display device comprising an array of display pixels, each pixel comprising:
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an electroluminescent display element; a drive transistor for driving a current through the display element, a drive voltage waveform being provided to the gate of the drive transistor; an address transistor, connected between a power supply line and the gate of the drive transistor; means for disabling the driving of the current by the drive transistor through the display element; and a storage capacitor for storing a pixel voltage, said storage capacitor being connected between an input to the pixel and the gate of the drive transistor, wherein a driver circuitry provides a stepped voltage waveform to the input of the pixel, the stepped voltage waveform being voltage-shifted by the storage capacitor before application to the gate of the drive transistor to form the drive voltage waveform, and wherein a height of steps in the stepped voltage waveform is greater than a voltage width of a linear operating region of the drive transistor, the pixel voltage being selected so that a voltage range of the linear operating region corresponds to voltage levels between a transition of two steps of the stepped voltage waveform, and wherein the device is operable in two modes; a first mode in which the pixel voltage is applied to the input of the pixel, the address transistor is turned on, the disabling means is turned on to turn off the display element and the storage capacitor is charged to the pixel voltage; and a second mode in which the address transistor is turned off, the disabling means is turned off and the stepped voltage waveform is applied to the input of the pixel. - View Dependent Claims (10)
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11. A method of addressing an active matrix electroluminescent display device comprising an array of display pixels, each pixel comprising an electroluminescent display element, a drive transistor for driving a current through the display element, and a storage capacitor connected between an input to the pixel and a gate of the drive transistor, the method comprising the acts of:
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storing a pixel voltage on the storage capacitor; providing a stepped voltage waveform to the input of the pixel, the stepped voltage waveform being voltage-shifted by the pixel voltage stored on the storage capacitor before application to the gate of the drive transistor, such that for a first set of voltage steps of the stepped voltage waveform applied to the gate of the drive transistor, the drive transistor is turned on, and for a second set of the voltage steps applied to the gate of the drive transistor, the drive transistor is turned off, the first and second sets being determined by the stored pixel voltage; and avoiding a linear operating region of the drive transistor by having a height of the voltage steps of the first set and the second set being greater than a voltage width of a linear operating region of the drive transistor, the pixel voltage being selected so that a voltage range of the linear operating region corresponds to voltage levels between a transition of two steps of the stepped voltage waveform. - View Dependent Claims (12, 13, 14, 15, 16)
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17. A method of addressing an active matrix electroluminescent display device comprising an array of display pixels, each pixel comprising an electroluminescent display element, a drive transistor for driving a current through the display element, and a storage capacitor connected between an input to the pixel and the gate of the drive transistor, the method comprising the acts of:
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storing a pixel voltage on the storage capacitor; providing a stepped voltage waveform to the input of the pixel, the stepped voltage waveform being voltage-shifted by the pixel voltage stored on the storage capacitor before application to a gate of the drive transistor, such that for a first set of the voltage steps applied to the gate of the drive transistor, the drive transistor is turned on, and for a second set of the voltage steps applied to the gate of the drive transistor, the drive transistor is turned off, the first and second sets being determined by the stored pixel voltage; disabling the driving of the current by the drive transistor through the display element during the storing of the pixel voltage on the storage capacitor; in a first mode in which the pixel voltage is applied to the input to the pixel, turning on the address transistor, turning off the display element, and charging the storage capacitor to a level derived from the drive voltage; and in a second mode in which the address transistor is turned off, applying the stepped voltage waveform to the input of the pixel; wherein a height of steps in the stepped voltage waveform is greater than a voltage width of a linear operating region of the drive transistor so that the linear operating region of the drive transistor is avoided, and wherein the pixel voltage is selected so that a voltage range of the linear operating region corresponds to voltage levels between a transition of two steps of the stepped voltage waveform. - View Dependent Claims (18)
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Specification