Pixel circuits for AMOLED displays
A method and system determine the characteristics of drive devices and load devices in selected pixels in an array of pixels in a display in which each pixel includes a drive device for supplying current to a load device. The method and system supply current to the load device via the drive device in a selected pixel, the current being a function of a current effective characteristic of at least one of the drive device and the load device; measure the current via a measurement line that is shared by adjacent pixels, and extract the value of a selected effective characteristic of one of the drive and load devices from the effect of the current on another of the drive and load devices. Current may be measured via a read transistor in each pixel.
1. A method of determining at least one characteristic of an organic light emitting device (OLED) in a first pixel in an array of pixels in a display in which each pixel includes a supply voltage source, a drive transistor coupling said supply voltage source to an OLED for controlling the supply of current to the OLED from said supply voltage source, said first pixel being one of a pair of pixels, said display including a monitor line controllably coupled to said pair of pixels at a node between said drive transistor and said OLED in each pixel of the pair of pixels, said method comprising:
measuring the at least one characteristic over the monitor line generating one or more measurements; and
determining the at least one characteristic of the OLED of the first pixel with use of a measurement including an effect of an OLED voltage or current of a second pixel of the pair of pixels on the one or more measurements and a measurement including an effect of the at least one characteristic of the OLED of the first pixel on the one or more measurements.
2. The method of claim 1 wherein determining the at least one characteristic of the OLED of the first pixel comprises extracting from a measurement of the one or more measurements, the effect of the OLED voltage or current of the second pixel on the one or more measurements.
3. The method of claim 1 further comprising:
during the measuring the at least one characteristic, forcing the first pixel into one or more states,
wherein measuring the at least one characteristic over the monitor line comprises:
for each of the one or more states, generating at least one measurement including the effect of the at least one characteristic of the OLED of the first pixel, and
wherein determining the at least one characteristic of the OLED of the first pixel comprises extracting from the the at least one measurement, the effect of the OLED voltage or current of the second pixel on the one or more measurements.
4. The method of claim 3 wherein forcing the first pixel into the one or more states comprises controlling a state of the OLED of the first pixel with use of the monitor line.
5. The method of claim 1 further comprising prior to measuring the at least one characteristic, forcing the second pixel of the pair of pixels into a known state.
6. The method of claim 5 wherein forcing the second pixel of the pair of pixels into the known state comprises programming the drive transistor of the second pixel to a full ON state.
7. The method of claim 6 wherein forcing the second pixel of the pair of pixels into the known state comprises adjusting the voltage of the supply voltage source of the second pixel.
8. The method of claim 1 further comprising:
prior to measuring the at least one characteristic, forcing the first pixel and the second pixel into a known state;
wherein measuring the at least one characteristic over the monitor line comprises:
measuring the at least one characteristic while the first and second pixels are in the known state, generating a first measurement of the one or more measurements, and
measuring the at least one characteristic after the OLED of the first pixel has been controlled by the monitor line into a different state, generating a second measurement of the one or more measurements;
wherein determining the at least one characteristic of the OLED of the first pixel comprises extracting the at least one characteristic of the OLED of the first pixel from the second measurement by subtracting out the effect of the OLED voltage or current of the second pixel on the second measurement with use of the first measurement.
9. A system for determining at least one characteristic of an organic light emitting device (OLED) in a first pixel in an array of pixels in a display in which each pixel includes a supply voltage source, a drive transistor coupling said supply voltage source to an OLED for controlling the supply of current to the OLED from said supply voltage source, said first pixel being one of a pair of pixels, said system including a monitor line controllably coupled to said pair of pixels at a node between said drive transistor and said OLED in each pixel of the pair of pixels, said system comprising a controller adapted to:
measure the at least one characteristic over the monitor line generating one or more measurements; and
determine the at least one characteristic of the OLED of the first pixel with use of a measurement including an effect of an OLED voltage or current of a second pixel of the pair of pixels on the one or more measurements and a measurement including an effect of the at least one characteristic of the OLED of the first pixel on the one or more measurements.
10. The system of claim 9 in which said controller is adapted to determine the at least one characteristic of the OLED of the first pixel by extracting from a measurement of the one or more measurements, the effect of the OLED voltage or current of the second pixel on the one or more measurements.
11. The system of claim 9 wherein the controller is further adapted to:
during measuring the at least one characteristic, force the first pixel into one or more states,
wherein the controller is adapted to measure the at least one characteristic over the monitor line by:
for each of the one or more states, generating at least one measurement including the effect of the at least one characteristic of the OLED of the first pixel, and
wherein the controller is adapted to determine the at least one characteristic of the OLED of the first pixel by extracting from the at least one measurement, the effect of the OLED voltage or current of the second pixel on the one or more measurements.
12. The system of claim 11 wherein the controller is adapted to force the first pixel into the one or more states by controlling a state of the OLED of the first pixel with use of the monitor line.
13. The system of claim 9 wherein the controller is adapted to, prior to measuring the at least one characteristic, force the second pixel into a known state.
14. The system of claim 13 wherein the controller is adapted to force the second pixel of the pair of pixels into the known state by programming the drive transistor of the second pixel to a full ON state.
15. The system of claim 14 wherein the controller is adapted to force the second pixel of the pair of pixels into the known state by adjusting the voltage of the supply voltage source of the second pixel.
16. The system of claim 9 wherein the controller is further adapted to:
prior to measuring the at least one characteristic, force the first pixel and the second pixel into a known state;
wherein the controller is adapted to measure the at least one characteristic over the monitor line by:
measuring the at least one characteristic while the first and second pixels are in the known state, generating a first measurement of the one or more measurements, and
measuring the at least one characteristic after the OLED of the first pixel has been controlled by the monitor line into a different state, generating a second measurement of the one or more measurements;
wherein the controller is adapted to determine the at least one characteristic of the OLED of the first pixel by extracting the at least one characteristic of the OLED of the first pixel from the second measurement by subtracting out the effect of the OLED voltage or current of the second pixel on the second measurement with use of the first measurement.