Method of Driving Pixel Element in Active Matrix Display

Abstract

A method of driving a pixel element in a matrix of pixel elements includes (1) setting the bias voltage of a first transistor to a value that is substantially close to a threshold voltage of the first transistor by changing a voltage across a first capacitive element with a current passing through the first transistor; (2) setting the bias voltage of the first transistor to a value that is different from the threshold voltage of the first transistor; and (3) causing a change of the bias voltage of the first transistor.

What is claimed is: 
     
         1 . A method of driving a pixel element in a matrix of pixel elements, the pixel element comprising (1) a first capacitive element, (2) a first transistor having a semiconductor channel, a first terminal of the semiconductor channel of the first transistor being electrically connected to a first terminal of the first capacitive element, and (3) a light-emitting element operationally coupled to the first transistor such that light emitted from the light-emitting element depends upon a bias voltage of the first transistor, wherein the bias voltage is a voltage difference between the gate of the first transistor and a first terminal of the semiconductor channel of the first transistor, the method comprising:
 setting the bias voltage of the first transistor to a value that is substantially close to a threshold voltage of the first transistor by changing a voltage across the first capacitive element with a current passing through the first transistor;   setting the bias voltage of the first transistor to a value that is different from the threshold voltage of the first transistor while substantially maintaining the voltage across the first capacitive element; and   detecting a portion of light emitted from the light-emitting element to cause a change of the bias voltage of the first transistor.   
     
     
         2 . The method of  claim 1 , wherein the pixel element further comprises a second transistor having a semiconductor channel operationally coupled to a second terminal of the semiconductor channel of the first transistor. 
     
     
         3 . The method of  claim 1 , wherein the setting the bias voltage of the first transistor to a value that is substantially close to a threshold voltage of the first transistor by changing a voltage across the first capacitive element with a current passing through the first transistor comprises:
 (1) setting a voltage on the gate of the first transistor at a first gate-voltage value and (2) setting a voltage at a second terminal of the first capacitive element at a first reference-voltage value.   
     
     
         4 . The method of  claim 3 , wherein the setting the bias voltage of the first transistor to a value that is different from the threshold voltage of the first transistor comprises:
 (1) setting the voltage on the gate of the first transistor at a second gate-voltage value and (2) setting the voltage at the second terminal of the first capacitive element at a second reference-voltage value.   
     
     
         5 . The method of  claim 4 , wherein the first reference-voltage value is equal to the second reference-voltage value. 
     
     
         6 . The method of  claim 4 , wherein the first gate-voltage value is equal to the second gate-voltage value. 
     
     
         7 . The method of  claim 1 , wherein the changing a voltage across the first capacitive element with a current passing through the first transistor comprises:
 (1) driving the semiconductor channel of the first transistor to a low-impedance state and (2) enabling current flow into or flow from the second terminal of the semiconductor channel of the first transistor.   
     
     
         8 . The method of  claim 2 , wherein the changing a voltage across the first capacitive element with a current passing through the first transistor comprises:
 (1) driving the semiconductor channel of the first transistor to a low-impedance state and (2) driving the semiconductor channel of the second transistor to a low-impedance state.   
     
     
         9 . The method of  claim 1 , wherein the substantially maintaining the voltage across the first capacitive element comprises:
 driving the semiconductor channel of the first transistor to a high-impedance state.   
     
     
         10 . The method of  claim 1 , wherein the substantially maintaining the voltage across the first capacitive element comprises:
 substantially preventing current flow into or flow from the second terminal of the semiconductor channel of the first transistor.   
     
     
         11 . The method of  claim 2 , wherein the substantially maintaining the voltage across the first capacitive element comprises:
 driving the semiconductor channel of the second transistor to a high-impedance state.   
     
     
         12 . The method of  claim 1 , wherein the detecting a portion of light emitted from the light-emitting element to cause a change of the bias voltage of the first transistor comprises:
 detecting a portion of light emitted from the light-emitting element to cause a change of the voltage across the first capacitive element.   
     
     
         13 . The method of  claim 1 , wherein the pixel element comprises a second capacitive element operationally coupled to a gate of the first transistor such that a voltage on the gate of the first transistor depends upon a voltage across the second capacitive element, and wherein the detecting a portion of light emitted from the light-emitting element to cause a change of the bias voltage of the first transistor comprises:
 detecting a portion of light emitted from the light-emitting element to cause a change of the voltage across the second capacitive element.   
     
     
         14 . A method of driving a pixel element in a matrix of pixel elements, the pixel element comprising (1) a first capacitive element, (2) a first transistor having a semiconductor channel, a first terminal of the semiconductor channel of the first transistor being electrically connected to a first terminal of the first capacitive element, and (3) a light-emitting element operationally coupled to the first transistor such that light emitted from the light-emitting element depends upon a bias voltage of the first transistor, wherein the bias voltage is a voltage difference between the gate of the first transistor and a first terminal of the semiconductor channel of the first transistor, the method comprising:
 setting the bias voltage of the first transistor to a value that is substantially close to a threshold voltage of the first transistor by changing a voltage across the first capacitive element with a current passing through the first transistor;   setting the bias voltage of the first transistor to a value that is different from the threshold voltage of the first transistor; and   causing a change of the bias voltage of the first transistor.   
     
     
         15 . The method of  claim 14 , wherein the pixel element further comprises a second transistor having a semiconductor channel operationally coupled to a second terminal of the semiconductor channel of the first transistor. 
     
     
         16 . The method of  claim 14 , wherein the causing a change of the bias voltage of the first transistor comprises:
 causing a change of the bias voltage of the first transistor with a current generated by a photo-detecting element.   
     
     
         17 . The method of  claim 14 , wherein the causing a change of the bias voltage of the first transistor comprises:
 causing a change of the bias voltage of the first transistor with a current passing through a resistive element.   
     
     
         18 . The method of  claim 14 , wherein the causing a change of the bias voltage of the first transistor comprises:
 monitoring a current flowing through the light-emitting element; and   
       causing a change of the bias voltage of the first transistor with a current that is proportional to the current flowing through the light-emitting element.