AMOLED displays with multiple readout circuits
The OLED voltage of a selected pixel is extracted from the pixel produced when the pixel is programmed so that the pixel current is a function of the OLED voltage. One method for extracting the OLED voltage is to first program the pixel in a way that the current is not a function of OLED voltage, and then in a way that the current is a function of OLED voltage. During the latter stage, the programming voltage is changed so that the pixel current is the same as the pixel current when the pixel was programmed in a way that the current was not a function of OLED voltage. The difference in the two programming voltages is then used to extract the OLED voltage.
1. A system for determining the current effective voltage V OLED of a light-emitting device in a selected pixel in an array of pixels in a display in which each pixel includes a drive transistor for supplying current to said light-emitting device, said light-emitting device emitting light when supplied with the voltage V OLED , the system comprising:
a controller adapted to:
supply a terminal of the light-emitting device in the selected pixel with a voltage that is sufficient to turn on said light-emitting device;
supply current to said light-emitting device via said drive transistor in said selected pixel, said current being a function of the current effective voltage V OLED of said light-emitting device;
measure said current, and
extract the value of the current effective voltage V OLED of said light-emitting device from said current measurement.
2. A system for determining the current effective voltage V OLED of a pixel in an array of pixels in a display in which each pixel includes a light-emitting device that emits light when supplied with a voltage V OLED , the system comprising:
a pixel circuit in each of said pixels, said circuit including:
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 across the source and gate of said drive transistor for providing said driving voltage to said drive transistor;
a monitor line coupled to a read transistor that controls the coupling of said monitor line to a node that is common to the source of said drive transistor and said light-emitting device;
a data line coupled to a switching transistor that controls the coupling of said data line to the gate of said drive transistor; and
a controller coupled to said data and monitor lines and to said switching and read transistors, and adapted to:
turn on said switching and read transistors of a selected pixel while supplying said first node of said selected pixel with a voltage that is sufficient to turn on said light-emitting device of said selected pixel, the current supplied to said light-emitting device being a function of the voltage V OLED of said device;
measure the current flowing through said drive transistor and said light-emitting device of the selected pixel; and
extract from said current measurement the effective voltage V OLED .
3. The system of claim 2 in which said first node of said selected pixel is supplied with a first voltage that is not sufficient to turn on said light-emitting device of said selected pixel so that the current supplied to said light-emitting device is not a function of the voltage V OLED of said device, prior to supplying said first node of said selected pixel with a second voltage that is sufficient to turn on said light-emitting device of the selected pixel so that the current supplied to said light-emitting device is a function of the voltage V OLED of said device.
4. The system of claim 3 in which said voltage V OLED is determined from the difference between said first and second voltages.
5. A method of determining the current effective voltage V OLED of a light-emitting device in a selected pixel in an array of pixels in a display in which each pixel includes a drive transistor for supplying current to said light-emitting device, the light-emitting device emitting light when supplied with the voltage V OLED , the method comprising:
supplying a terminal of the light-emitting device in the selected pixel with a voltage that is sufficient to turn on said light-emitting device;
supplying current to said light-emitting device via said drive transistor in said selected pixel, said current being a function of the current effective voltage V OLED of said light-emitting device;
measuring said current; and
extracting the value of the current effective voltage V OLED of said light-emitting device from said current measurement.
6. The method of claim 5 further comprising, prior to supplying the terminal of the light-emitting device with the voltage, supplying the terminal of the light-emitting device with a first voltage that is not sufficient to turn on said light-emitting device of said selected pixel such that the current supplied to said light-emitting device is not a function of the voltage V OLED of said light-emitting device, wherein supplying said terminal of the light-emitting device in the selected pixel with the voltage that is sufficient to turn on said light-emitting device in the selected pixel is such that the current supplied to said light-emitting device is a function of the voltage V OLED of said light-emitting device.
7. The method of claim 6 in which said voltage V OLED is determined from the difference between said voltage and said first voltage.