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 for controlling an array of pixels in a display in which each pixel includes a light-emitting device, the system comprising
a pixel circuit in each of said pixels, said circuit including said 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, said drive transistor having a gate, a source and a drain,
a storage capacitor coupled to the gate of said drive transistor for controlling said driving voltage,
a reference voltage source coupled to a first switching transistor that controls the coupling of said reference voltage source to said storage capacitor, and
a programming voltage source coupled to a second switching transistor that controls the coupling of said programming voltage to the gate of said drive transistor, so that said storage capacitor stores a voltage equal to the difference between said reference voltage and said programming voltage,
a monitor line coupled to a node between the drive transistor and the light-emitting device through a read transistor, and
a controller configured to
allow said node to charge to a voltage that is a function of the characteristics of the drive transistor, and
charge a node between said storage capacitor and the gate of said drive transistor to said programming voltage.
2. The system according to claim 1 wherein the controller's being configured to allow said node to charge to a voltage that is a function of the characteristics of the drive transistor comprises the controller being configured to
disable the read transistor and disable the first switch transistor.
3. The system according to claim 1 wherein the controller is further configured to
read from the monitor line a voltage of said light-emitting device.
4. The system according to claim 1 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 according to 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 according to 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 according to claim 1 wherein the controller is further configured to
control the first switching transistor and the read transistor with a common signal.
8. The system according to claim 2 wherein the controller's being configured to charge a node between said storage capacitor and the gate of said drive transistor to said programming voltage comprises the controller being configured to
enable the second switch transistor after disabling the read transistor and the first switch transistor.