Method and system for driving an active matrix display circuit

1. A display system, the system comprising: a pixel circuit for being programmed according to programming information during a programming cycle, and driven to emit light according to the programming information during an emission cycle, the pixel circuit comprising: a light emitting device for emitting light during the emission cycle, a drive transistor for conveying a drive current through the light emitting device during the emission cycle, said drive transistor having gate, source and drain terminals, a storage capacitor for being charged with a voltage based at least in part on the programming information during the programming cycle, said storage capacitor having first and second terminals, said first terminal being coupled to the gate of said drive transistor, a first switch transistor, operated according to a first select line, for conveying the voltage to the storage capacitor during the programming cycle, and a regulating transistor for conveying a leakage current to a gate terminal of the drive transistor, thereby adjusting a gate voltage of the drive transistor, said regulating transistor having gate, source and drain terminals, said gate terminal of the regulating transistor being coupled to one of said terminals of said storage capacitor, one of the source and drain terminals of said regulating transistor being coupled to said gate terminal of said drive transistor, and the other of said source and drain terminals of said regulating transistor being coupled via a conductive path to a node between said light emitting device and said drive transistor, the conductive path does not include the drive transistor and does not include the light emitting device, wherein the pixel circuit provides constant averaged current over a frame time.

2. The system according to claim 1 , further comprising:

a display array including a plurality of pixel circuits arranged in rows and columns, and

a driver for driving the display array.

3. The system according to claim 2 , further comprising:

a display array including a plurality of pixel circuits arranged in rows and columns; and

a driver for driving the display array,

wherein the bias line is shared by more than one pixel circuit of the plurality of pixel circuits.

4. The system according to claim 1 , further comprising:

a data driver for programming the pixel circuit via a data line by charging the storage capacitor according to the programming information;

a gate driver to drive the first select line; and

a controller for operating the data driver and the gate driver.

5. The system according to claim 1 , wherein the regulating transistor is biased in sub-threshold regime.

6. A display system, the system comprising:

a pixel circuit for being programmed according to programming information during a programming cycle, and driven to emit light according to the programming information during an emission cycle, the pixel circuit comprising:

a light emitting device for emitting light during the emission cycle,

a drive transistor for conveying a drive current through the light emitting device during the emission cycle, said drive transistor having gate, source and drain terminals,

a storage capacitor for being charged with a voltage based at least in part on the programming information during the programming cycle, said storage capacitor having first and second terminals, said first terminal being coupled to the gate of said drive transistor,

a first switch transistor, operated according to a first select line, for conveying the voltage to the storage capacitor during the programming cycle, and

a regulating transistor for conveying a leakage current to a gate terminal of the drive transistor, thereby adjusting a gate voltage of the drive transistor, said regulating transistor having gate, source and drain terminals,

said gate terminal of the regulating transistor being coupled to one of said terminals of said storage capacitor,

one of the source and drain terminals of said regulating transistor being coupled to said gate terminal of said drive transistor, and

the other of said source and drain terminals of said regulating transistor being coupled to a node between said light emitting device and said drive transistor,

at least one switch, said other of said source and drain terminals of said regulating transistor being coupled via said at least one switch to said node between said light emitting device and said drive transistor,

wherein the pixel circuit provides constant averaged current over a frame time.

7. A method of operating a display having a pixel circuit for driving a light emitting device, the method comprising: charging the pixel circuit, during a programming cycle, by turning on a first switch transistor such that a voltage is charged on a storage capacitor having first and second terminals with the first terminal coupled to a gate terminal of a drive transistor that also has source and drain terminals; and conveying a leakage current by a regulating transistor having gate, source and drain terminals, said gate terminal of said regulating transistor being coupled to the second terminal of said storage capacitor, one of the source and drain terminals of said regulating transistor being coupled to the gate terminal of the drive transistor, and the other of said source and drain terminals of said regulating transistor being coupled via a conductive path to a node between said light emitting device and said drive transistor, the conductive path does not include the drive transistor and does not include the light emitting device, thereby adjusting the voltage at said node.

8. The method according to claim 7 , wherein the pixel circuit provides constant averaged current over a frame time.

9. The method according to claim 7 , wherein the first switch transistor is turned on by a select line.

10. The method according to claim 7 , wherein the drive transistor and the regulating transistor have the same bias condition.

11. The method according to claim 7 , wherein the regulating transistor is biased in sub-threshold regime.

12. The method according to claim 7 , further comprising:

forcing the regulating transistor into a linear regime of operation, by turning on a second switch transistor.

13. The method according to claim 7 , further comprising:

detecting energy transfer from the pixel circuit by a sensor.

14. The method according to claim 13 , wherein the regulating transistor discharges the voltage at the node according to a conductance of the sensor.

15. A method of operating a display having a pixel circuit for driving a light emitting device, the method comprising:

charging the pixel circuit, during a programming cycle, by turning on a first switch transistor such that a voltage is charged on a storage capacitor having first and second terminals with the first terminal coupled to a gate terminal of a drive transistor that also has source and drain terminals;

conveying a leakage current by a regulating transistor having gate, source and drain terminals, said gate terminal of said regulating transistor being coupled to the second terminal of said storage capacitor, one of the source and drain terminals of said regulating transistor being coupled to the gate terminal of the drive transistor, and the other of said source and drain terminals of said regulating transistor being coupled to a node between said light emitting device and said drive transistor, thereby adjusting the voltage at said node, wherein said other of said source and drain terminals of said regulating transistor is coupled via at least one switch to said node between said light emitting device and said drive transistor; and

controlling by the at least one switch, at least one of a time said regulating transistor is active and a current of said regulating transistor.