Systems and methods of hybrid calibration of bias current

1. A system for providing biasing currents to pixels of an emissive display system, each pixel having a light-emitting device, the system comprising:

a plurality of current biasing elements external to said pixels;

a plurality of current bias lines coupling said plurality of current biasing elements to said pixels; and

a controller coupled to said current biasing elements for controlling a programming of said current biasing elements over a plurality of signal lines;

wherein each current biasing element comprises:

at least one current driving transistor coupled to a current bias line for providing a biasing current over the current bias line; and

a storage capacitance for being programmed and for setting a magnitude of the biasing current provided by the at least one current driving transistor;

wherein the controller's controlling the programming of each current biasing element comprises:

during a programming cycle charging the storage capacitance to a defined level; and

subsequent to the programming cycle, during a calibration cycle, partially discharging the storage capacitance as a function of characteristics of the at least one driving transistor.

2. The system of claim 1 , wherein the plurality of signal lines comprises a plurality of data lines coupling a source driver of the emissive display system to the pixels and for programming said pixels, the data lines for coupling the controller and the plurality of current biasing elements at times different from when the data lines couple the source driver to the pixels.

3. The system of claim 2 , further comprising a reference monitor line shared by the plurality of current biasing elements and coupling the plurality of current biasing elements to the controller.

4. The system of claim 2 wherein each current biasing element is a current sink, wherein the at least one current driving transistor comprises a single current driving transistor, wherein the storage capacitance is coupled across a gate of said current driving transistor and one of a source and drain of said current driving transistor, the other of said source and drain of said current driving transistor coupled to a voltage supply, wherein during the calibration cycle, the current driving transistor is allowed to partially discharge said storage capacitance through the current driving transistor to said voltage supply.

5. The system of claim 2 wherein each current biasing element is a current source, wherein the at least one current driving transistor comprises a single current driving transistor, wherein the storage capacitance is coupled across a gate of said current driving transistor and one of a source and drain of said current driving transistor, the one of said source and drain of said current driving transistor coupled to a voltage supply, wherein during the calibration cycle, the current driving transistor is allowed to partially discharge said storage capacitance through the current driving transistor to said voltage supply.

6. A system for providing biasing currents to pixels of an emissive display system, each pixel having a light-emitting device, the system comprising:

a plurality of current biasing elements;

a plurality of current bias lines coupling said plurality of current biasing elements to said pixels;

a controller coupled to said current biasing elements for controlling a programming of said current biasing elements over a plurality of signal lines; and

a monitor coupled to the plurality of current biasing elements for monitoring a biasing current produced by each current biasing element and for storing in a memory a measurement representing said biasing current for each current biasing element;

wherein each current biasing element comprises:

at least one current driving transistor coupled to a current bias line for providing a biasing current over the current bias line; and

a storage capacitance for being programmed and for setting a magnitude of the biasing current provided by the at least one current driving transistor;

wherein the controller's controlling the programming of each current biasing element comprises:

retrieving from said memory said measurement representing said biasing current for the current biasing element;

determining a deviation of said biasing current represented by said measurement from an expected biasing current; and

charging the storage capacitance to a defined compensated level which compensates for said deviation so that said current biasing element produces the expected biasing current.

7. The system of claim 6 , wherein the plurality of signal lines comprises a plurality of data lines coupling a source driver of the emissive display system to the pixels and for programming said pixels, the data lines for coupling the controller and the plurality of current biasing elements at times different from when the data lines couple the source driver to the pixels.

8. The system of claim 6 , further comprising a reference monitor line shared by the plurality of current biasing elements and coupling the plurality of current biasing elements to the controller, the controller coupled to the monitor.

9. A method of providing biasing currents to pixels of an emissive display system, each pixel having a light-emitting device, the emissive display system including a plurality of current biasing elements external to said pixels and a plurality of current bias lines coupling said plurality of current biasing elements to said pixels, each current biasing element including at least one current driving transistor coupled to a current bias line for providing a biasing current over the current bias line and a storage capacitance for being programmed and for setting a magnitude of the biasing current provided by the at least one current driving transistor, the method comprising:

programming each current biasing element over a plurality of signal lines comprising:

charging the storage capacitance to a defined level during a programming cycle; and

subsequent to the programming cycle, during a calibration cycle, partially discharging the storage capacitance as a function of characteristics of the at least one driving transistor.

10. The method of claim 9 , wherein the plurality of signal lines comprises a plurality of data lines coupling a source driver of the emissive display system to the pixels and for programming said pixels, the data lines for coupling the controller and the plurality of current biasing elements for performing said programming each current biasing element at times different from when the data lines couple the source driver to the pixels.

11. The method of claim 10 , wherein a reference monitor line is shared by the plurality of current biasing elements and wherein said charging said storage capacitance comprises coupling to the controller over said reference monitor line each current biasing element being charged while de-coupling from the controller current biasing elements not being charged.

12. The method of claim 10 wherein each current biasing element is a current sink, wherein the at least one current driving transistor comprises a single current driving transistor, wherein the storage capacitance is coupled across a gate of said current driving transistor and one of a source and drain of said current driving transistor, the other of said source and drain of said current driving transistor coupled to a voltage supply, wherein during the calibration cycle, partially discharging the storage capacitance comprises allowing the current driving transistor to partially discharge said storage capacitance through the current driving transistor to said voltage supply.

13. The method of claim 10 wherein each current biasing element is a current source, wherein the at least one current driving transistor comprises a single current driving transistor, wherein the storage capacitance is coupled across a gate of said current driving transistor and one of a source and drain of said current driving transistor, the one of said source and drain of said current driving transistor coupled to a voltage supply, wherein during the calibration cycle, partially discharging the storage capacitance comprises allowing the current driving transistor to partially discharge said storage capacitance through the current driving transistor to said voltage supply.

14. A method of providing biasing currents to pixels of an emissive display system, each pixel having a light-emitting device, the emissive display system including a plurality of current biasing elements, a plurality of current bias lines coupling said plurality of current biasing elements to said pixels, each current biasing element including at least one current driving transistor coupled to a current bias line for providing a biasing current over the current bias line and a storage capacitance for being programmed and for setting a magnitude of the biasing current provided by the at least one current driving transistor, the method comprising:

monitoring a biasing current produced by each current biasing element;

storing in a memory a measurement representing said biasing current for each current biasing element; and

programming each current biasing element over a plurality of signal lines comprising:

retrieving from said memory said measurement representing said biasing current for the current biasing element;

determining a deviation of said biasing current represented by said measurement from an expected biasing current; and

charging the storage capacitance to a defined compensated level which compensates for said deviation so that said current biasing element produces the expected biasing current.

15. The method of claim 14 , wherein the plurality of signal lines comprises a plurality of data lines coupling a source driver of the emissive display system to the pixels and for programming said pixels, the data lines for coupling the controller and the plurality of current biasing elements for performing said programming each current biasing element at times different from when the data lines couple the source driver to the pixels.

16. The method of claim 14 , wherein the controller is coupled to the monitor, a reference monitor line is shared by the plurality of current biasing elements and wherein said monitoring each current biasing element comprises coupling to the controller over the reference monitor line each current biasing element being measured while de-coupling from the controller current biasing elements not being measured.