Pixel circuits for AMOLED displays
A system for controlling a display in which each pixel circuit comprises a light-emitting device, a drive transistor, a storage capacitor, a reference voltage source, and a programming voltage source. The storage capacitor stores a voltage equal to the difference between the reference voltage and the programming voltage, and a controller supplies a programming voltage that is a calibrated voltage for a known target current, reads the actual current passing through the drive transistor to a monitor line, turns off the light emitting device while modifying the calibrated voltage to make the current supplied through the drive transistor substantially the same as the target current, modifies the calibrated voltage to make the current supplied through the drive transistor substantially the same as the target current, and determines a current corresponding to the modified calibrated voltage based on predetermined current-voltage characteristics of the drive transistor.
1. A system comprising:
a pixel circuit of a display including
a light-emitting device,
a drive transistor for driving current through the light-emitting device according to a driving voltage across the drive transistor during an emission cycle,
a storage capacitor coupled to a gate of said drive transistor for storing said driving voltage,
a first switching transistor that controls a coupling of a reference voltage source to said storage capacitor, and
a controller configured to:
enable the first switch transistor for resetting a node between the drive transistor and the light-emitting device; and
disable the first switch transistor for allowing the node between the drive transistor and the light-emitting device to charge to a voltage that is a function of the characteristics of the drive transistor.
2. The system of claim 1 further comprising a monitor line coupled to the node through a read transistor.
3. The system of claim 2 wherein the controller is further configured to read from the monitor line a voltage of said light-emitting device.
4. The system of claim 2 wherein the controller is further configured to, during an operation cycle prior to a compensation interval,
enable the read transistor before enabling the first switching transistor for resetting the node between the drive transistor and the light-emitting device.
5. The system of claim 4 wherein the controller is further configured to, during the operation cycle prior to the compensation interval, disable the first switching transistor and disable the read transistor at different times.
6. The system of claim 4 wherein the controller is further configured to, during the operation cycle prior to the compensation interval, enable the first switching transistor before disabling the read transistor.
7. The system of claim 2 wherein the controller is further configured to control the first switching transistor and the read transistor with a common signal.
8. The system of claim 2 wherein the controller is further configured to disable the read transistor while disabling the first switch transistor for said allowing said node to charge to a voltage that is a function of the characteristics of the drive transistor.
9. The system of claim 1 wherein the pixel circuit further includes
a second switching transistor that controls a coupling of a programming voltage source to the gate of said drive transistor, the second switching transistor controlled by a signal used to control the first switching transistor of the pixel circuit in an adjacent row of the display, and
wherein the controller is further configured to
charge the node between said storage capacitor and the gate of said drive transistor to said programming voltage.
10. The system of claim 9 further comprising a monitor line coupled through a read transistor to the node between the drive transistor and the light-emitting device, wherein the controller is further configured to charge the node between said storage capacitor and the gate of said drive transistor with said programming voltage including enabling the second switch transistor after disabling the read transistor and the first switch transistor.
11. A method of controlling a display including a pixel circuit including a light-emitting device, a drive transistor for driving current through the light-emitting device according to a driving voltage across the drive transistor during an emission cycle, a storage capacitor coupled to a gate of said drive transistor for storing said driving voltage, and a first switching transistor that controls a coupling of a reference voltage source to said storage capacitor, the method comprising:
enabling the first switch transistor for resetting a node between the drive transistor and the light-emitting device; and
disabling the first switch transistor for allowing the node between the drive transistor and the light-emitting device to charge to a voltage that is a function of the characteristics of the drive transistor.
12. The method of claim 11 wherein the display includes a monitor line coupled through a read transistor to the node between the drive transistor and the light-emitting device, the method further comprising:
reading from the monitor line a voltage of said light-emitting device.
13. The method of claim 11 wherein the display includes a monitor line coupled through a read transistor to the node between the drive transistor and the light-emitting device, the method further comprising, during an operation cycle prior to a compensation interval:
enabling the read transistor before enabling the first switching transistor for resetting the node between the drive transistor and the light-emitting device.
14. The method of claim 13 further comprising, during the operation cycle prior to the compensation interval:
disabling the first switching transistor and disabling the read transistor at different times.
15. The method of claim 13 further comprising, during the operation cycle prior to the compensation interval:
enabling the first switching transistor before disabling the read transistor.
16. The method of claim 11 wherein the display includes a monitor line coupled through a read transistor to the node between the drive transistor and the light-emitting device, the method further comprising:
controlling the first switching transistor and the read transistor with a common signal.
17. The method of claim 11 wherein the display includes a monitor line coupled through a read transistor to the node between the drive transistor and the light-emitting device, the method further comprising:
disabling the read transistor while disabling the first switch transistor for said allowing said node between the drive transistor and the light-emitting device to charge to a voltage that is a function of the characteristics of the drive transistor.
18. The method of claim 11 wherein the pixel circuit includes a second switching transistor that controls a coupling of a programming voltage source to the gate of said drive transistor, the second switching transistor controlled by a signal used to control the first switching transistor of the pixel circuit in an adjacent row of the display, the method further comprising:
charging the node between said storage capacitor and the gate of said drive transistor to said programming voltage.
19. The method of claim 18 wherein the display includes a monitor line coupled through a read transistor to the node between the drive transistor and the light-emitting device, the method further comprising:
charging the node between said storage capacitor and the gate of said drive transistor with said programming voltage including enabling the second switch transistor after disabling the read transistor and the first switch transistor.