Pixel circuits for AMOLED displays
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 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 light-emitting device and a drive transistor for supplying current to said light-emitting device, said method comprising
storing a programming voltage in the selected pixel using the light-emitting device of the selected pixel, the stored programming voltage being a function of the current effective voltage V OLED of said light-emitting device,
supplying current to said light-emitting device via said drive transistor in said selected pixel according to said stored programming voltage, 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.
2. The method of claim 1 in which said light-emitting devices are OLEDs.
3. The method of claim 1 in which said current is supplied to said light-emitting device via a drive transistor in each pixel.
4. The method of claim 1 in which said current is measured via a read transistor in each pixel.
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 light-emitting device and a drive transistor for supplying current to said light-emitting device, said method comprising
supplying a first predetermined programming voltage to said selected pixel to store a first programming voltage in the selected pixel, the stored first programming voltage being independent of the current effective voltage V OLED of said light-emitting device,
supplying a first current to said light-emitting device in said selected pixel according to said stored first programming voltage, said first current being independent of the effective voltage V OLED of said light-emitting device,
measuring said first current,
supplying a second predetermined programming voltage to said selected pixel to store a second programming voltage in the selected pixel using the light-emitting device of the selected pixel, the stored second programming voltage being a function of the current effective voltage V OLED of said light-emitting device,
supplying a second current to said light-emitting device in said selected pixel according to said stored second programming voltage, said second current being a function of the current effective voltage V OLED of said light-emitting device,
measuring said second current, and
extracting the value of the current effective voltage V OLED of said light-emitting device from the difference between said first and second currents and current-voltage characteristics of said selected pixel.
6. A system for determining the current effective voltage V OLED of a light-emitting device of a selected pixel in an array of pixels in a display in which each pixel includes a light-emitting device and a drive transistor for supplying current to the light-emitting device, the system comprising a controller adapted to
store a programming voltage in the selected pixel using the light-emitting device of the selected pixel, the stored programming voltage being a function of the current effective voltage V OLED of said light-emitting device,
supply current to said light-emitting device via said drive transistor in said selected pixel according to said stored programming voltage, 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.