Circuit for voltage compensation in an electroluminescent display

Abstract

A circuit for voltage compensation in an electroluminescent (EL) display is disclosed. The circuit includes a pixel unit of the EL display, an impedance load associated with the pixel unit and a switch. The pixel unit includes an electroluminescent (EL) device, a first capacitor configured to store a data associated with the EL device, and a transistor including a gate coupled to a first end of the first capacitor, and a first terminal coupled to a second end of the capacitor. The impedance load includes a second capacitor having a capacitance remarkably larger than that of the first capacitor. The switch selectively connects the pixel unit to a current sink via the impedance load.

What is claimed is: 
     
         1 . A circuit for voltage compensation in an electroluminescent (EL) display, the circuit comprising:
 a pixel unit of the EL display, the pixel unit including:
 an electroluminescent (EL) device; 
 a first capacitor configured to store a data associated with the EL device; and 
 a transistor including a gate coupled to a first end of the first capacitor, and a first terminal coupled to a second end of the capacitor; 
   an impedance load associated with the pixel unit, the impedance load including a second capacitor having a capacitance remarkably larger than that of the first capacitor; and   a switch to selectively connect the pixel unit to a current sink via the impedance load.   
     
     
         2 . The circuit according to  claim 1 , wherein the pixel unit further includes a transistor configured to reset a voltage level at the gate of the transistor during a first phase. 
     
     
         3 . The circuit according to  claim 2 , wherein the transistor is configured to receive a data associated with the EL device during a second phase. 
     
     
         4 . The circuit according to  claim 3 , wherein the second capacitor is configured to maintain a voltage level at the first terminal of the transistor in the second phase substantially identical to that in the first phase. 
     
     
         5 . The circuit according to  claim 3 , wherein the pixel unit further includes another transistor configured to pass a current through the EL device during a third phase. 
     
     
         6 . The circuit according to  claim 5 , wherein the second capacitor is configured to maintain a voltage difference between the gate and the first terminal of the transistor in the third phase substantially identical to that in the second phase. 
     
     
         7 . The circuit according to  claim 5 , wherein the current has a magnitude independent of the threshold voltage of the transistor. 
     
     
         8 . The circuit according to  claim 2 , wherein the pixel unit further includes another transistor configured to establish at the first terminal of the transistor a compensation voltage associated with a threshold voltage of the transistor during the first phase. 
     
     
         9 . The circuit according to  claim 8 , wherein the another transistor includes a terminal, and the switch is configured to selectively connect the terminal to the current sink via the impedance load. 
     
     
         10 . An electroluminescent (EL) display, comprising:
 an array of pixel units, and   a circuit for voltage compensation for the pixel units, the circuit comprising:
 a pixel unit of the EL display, the pixel unit including:
 an electroluminescent (EL) device; 
 a first capacitor configured to store a data associated with the EL device; and 
 a transistor including a gate coupled to a first end of the first capacitor, and a first terminal coupled to a second end of the capacitor; 
 
 an impedance load associated with the pixel unit, the impedance load including a second capacitor having a capacitance remarkably larger than that of the first capacitor; and 
 a switch to selectively connect the pixel unit to a current sink via the impedance load. 
   
     
     
         11 . The EL display according to  claim 10 , wherein the pixel unit further includes a transistor configured to reset a voltage level at the gate of the transistor during a first phase. 
     
     
         12 . The EL display according to  claim 11 , wherein the transistor is configured to receive a data associated with the EL device during a second phase. 
     
     
         13 . The EL display according to  claim 12 , wherein the second capacitor is configured to maintain a voltage level at the first terminal of the transistor in the second phase substantially identical to that in the first phase. 
     
     
         14 . The EL display according to  claim 12 , wherein the pixel unit further includes another transistor configured to pass a current through the EL device during a third phase. 
     
     
         15 . The EL display according to  claim 14 , wherein the second capacitor is configured to maintain a voltage difference between the gate and the first terminal of the transistor in the third phase substantially identical to that in the second phase. 
     
     
         16 . The EL display according to  claim 14 , wherein the current has a magnitude independent of the threshold voltage of the transistor. 
     
     
         17 . The EL display according to  claim 11 , wherein the pixel unit further includes another transistor configured to establish at the first terminal of the transistor a compensation voltage associated with a threshold voltage of the transistor during the first phase. 
     
     
         18 . The EL display according to  claim 17 , wherein the another transistor includes a terminal, and the switch is configured to selectively connect the terminal to the current sink via the impedance load. 
     
     
         19 . The EL display according to  claim 18  further comprising a transistor configured to reset a voltage level at the gate of the transistor in response to the first control signal. 
     
     
         20 . A method of voltage compensation in an electroluminescent (EL) display that comprises an array of pixel units each including an EL device, a transistor and a first capacitor, the method comprising:
 providing a switch to selectively connect one of the pixel units to a current sink via an impedance load associated with the one pixel unit;   resetting a voltage level at a gate of the transistor to a reference voltage;   establishing a compensation voltage associated with a threshold voltage of the transistor at a first terminal of the transistor;   storing data associated with the EL device in the first capacitor and maintaining a voltage level at the first terminal by a second capacitor in the impedance load; and   passing a current through the EL device via the transistor, the current having a magnitude independent of the threshold voltage of the transistor.