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 method of determining characteristics of at least one circuit element of at least one selected pixel in an array of pixels in a display in which each pixel includes a drive transistor for supplying current to an optoelectronic device of the pixel, the method comprising:
controlling a biasing of a selected pixel of the at least one selected pixel including a biasing over a monitor line coupled to the selected pixel;
controlling a biasing of a first drive transistor; of a first pixel such that a first optoelectronic device of said first pixel is biased so that the first optoelectronic device is turned off, the first pixel sharing the monitor line with the selected pixel; and
measuring at least one characteristic of the at least one circuit element of said selected pixel with use of said monitor line.
2. The method of claim 1 wherein one of a source and a drain terminal of the first drive transistor is coupled to the first optoelectronic device and the other of the source and drain terminal of the first drive transistor is coupled to a first supply voltage, and wherein the monitor line is coupled via a first source switch to a first node of the first pixel, the first node between the optoelectronic device and the one of a source and a drain terminal of the first drive transistor, wherein controlling a biasing of the first drive transistor of the first pixel comprises adjusting at least a voltage of the first supply voltage and a gate terminal of the first drive transistor to ensure the first optoelectronic device is off.
3. A method of determining the characteristics of circuit elements of at least one selected pixel in an array of pixels in a display in which each pixel includes a drive transistor for supplying current to an optoelectronic device of the pixel, the method comprising:
controlling a biasing of a selected pixel of the at least one selected pixel, said biasing including a biasing over a monitor line coupled to the selected pixel;
controlling a biasing of a first pixel coupled to the monitor line via source and drain terminals of a first source switch such that the first source switch is biased with at least one of a zero voltage and a fixed known voltage across the source and the drain terminal of the first source switch resulting in a corresponding one of a zero current and a fixed known current passing through the first source switch, the monitor line shared with the selected pixel; and
measuring at least one characteristic of at least one circuit element of said selected pixel with use of said monitor line.
4. The method according to claim 3 , wherein measuring at least one characteristic of at least one circuit element of said selected pixel comprises measuring the current of the selected optoelectronic device by measuring a current over the monitor line.
5. The method according to claim 4 , wherein one of a source and a drain terminal of the first drive transistor is coupled to the first optoelectronic device and the other of the source and drain terminal of the first drive transistor is coupled to a first supply voltage, and wherein one of the source and the drain terminal of the first source switch is coupled to a first node of the first pixel between the optoelectronic device and the one of a source and a drain terminal of the first drive transistor, and the other of the source and the drain terminal of the first source switch is coupled to the monitor line, wherein controlling a biasing of the first pixel comprises biasing a gate of the first drive transistor to turn the first drive transistor on and adjusting a biasing over the monitor line to one of a voltage equal the voltage of the supply voltage and a voltage different from the voltage of the supply voltage by the fixed known voltage, and wherein biasing of the selected pixel comprises biasing a gate of the selected drive transistor to turn the selected drive transistor off.
6. The method according to claim 4 , wherein measuring at least one characteristic of at least one circuit element of said selected pixel further comprises subtracting a value of the fixed known current from the current measured over the monitor line.