Pixels and reference circuits and timing techniques
What is disclosed are systems and methods of compensation of images produced by active matrix light emitting diode device (AMOLED) and other emissive displays. Anomalies in luminance produced by pixel circuits and bias currents produced by current biasing circuits for driving current biased voltage programmed pixels are corrected through calibration and compensation while re-using existing data or other lines that can be controlled individually to perform said calibration and compensation.
1. A system for generating currents for pixels of an emissive display system, each pixel having a light-emitting device, the system comprising:
a plurality of pixels;
a plurality of current generating circuits for providing a current for at least one respective pixel; and
a controller coupled to said current generating circuits for controlling said current generating circuits over a plurality of signal lines;
wherein each current generating circuit comprises:
at least one driving transistor for providing the current for the pixel; and
a storage capacitance for being programmed and for setting a magnitude of the current provided by the at least one driving transistor;
wherein the controller's controlling each current generating circuit 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 at least one driving transistor comprises a driving transistor and the controller's controlling each current generating circuit further comprises:
during the programming cycle charging the storage capacitance connected to a gate terminal of the driving transistor to include at least a threshold voltage of the driving transistor, such that during an emission cycle, a voltage across the source terminal and the drain terminal during the emission cycle is a function of the threshold voltage of the driving transistor.
3. The system of claim 1 , wherein the at least one driving transistor comprises a driving transistor and the controller's controlling each current generating circuit further comprises:
during the programming cycle charging the storage capacitance connected to a gate terminal of the driving transistor to include at least a first voltage applied to a source terminal of the driving transistor, such that during an emission cycle, during which a first voltage is maintained at the source terminal of the driving transistor, a voltage across the source terminal and the drain terminal is independent of the first voltage.
4. The system of claim 3 , wherein the first voltage is one of V DD and V MON .
5. The system of claim 1 , wherein each current generating circuit comprises one of a reference current sink and a reference current source for providing the current for the at least one respective pixels, the current provided to provide reference current biasing for the at least one respective pixels.
6. The system of claim 1 , wherein each pixel comprises the current generating circuit for providing the current for said pixel, the current provided to drive the light-emitting device of said pixel.
7. The system of claim 6 , wherein the light emitting device is an Organic Light Emitting Diode (OLED).
8. The system of claim 7 , wherein the controller's controlling each current generating circuit further comprises:
during a reset cycle commencing substantially simultaneously with an emission cycle, resetting to a low reference voltage at least one of an anode of the OLED and a terminal of the at least one driving transistor.
9. A method for generating currents for pixels of an emissive display system, each pixel having a light-emitting device, the system comprising a plurality of pixels, a plurality of current generating circuits for providing a current for at least one respective pixel, each current generating circuit comprising at least one driving transistor for providing the current for the pixel, and a storage capacitance for being programmed and for setting a magnitude of the current provided by the at least one driving transistor, the method comprising:
controlling each current generating circuit over a plurality of 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 at least one driving transistor comprises a driving transistor and controlling each current generating circuit further comprises:
during the programming cycle, charging the storage capacitance connected to a gate terminal of the driving transistor to include at least a threshold voltage of the driving transistor, such that during an emission cycle a voltage across the source terminal and the drain terminal is a function of the threshold voltage of the driving transistor.
11. The method of claim 9 wherein the at least one driving transistor comprises a driving transistor and controlling each current generating circuit further comprises:
during the programming cycle charging the storage capacitance connected to a gate terminal of the driving transistor to include at least a first voltage applied to a source terminal of the driving transistor, such that during an emission cycle, during which a first voltage is maintained at the source terminal of the driving transistor, a voltage across the source terminal and the drain terminal is independent of the first voltage.
12. The method of claim 11 , wherein the first voltage is one of V DD and V MON .
13. The method of claim 9 , wherein each current generating circuit comprises one of a reference current sink and a reference current source for providing the current for the at least one respective pixels, the current provided to provide reference current biasing for the at least one respective pixels.
14. The method of claim 9 , wherein each pixel comprises the current generating circuit for providing the current for said pixel, the current provided to drive the light-emitting device of said pixel.
15. The method of claim 14 , wherein the light emitting device is an Organic Light Emitting Diode (OLED).
16. The method of claim 15 , wherein the controlling each current generating circuit further comprises:
during a reset cycle commencing substantially simultaneously with an emission cycle, resetting to a low reference voltage at least one of an anode of the OLED and a terminal of the at least one driving transistor.