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 operational voltage V OLED of a light-emitting device in a pixel in an array of pixels in a display, the pixel including a storage capacitor coupled to a drive transistor for supplying current to said light-emitting device as a function of a programming of the storage capacitor, the system comprising:
a controller adapted to:
vary a first programming of the storage capacitor and measure a first current supplied to said light-emitting device via said drive transistor, until reaching a final first programming of the storage capacitor when the first current equals a predetermined current, wherein one of the first current and the predetermined current is a function of the operational voltage V OLED of said light-emitting device; and
extract the value of the operational voltage V OLED of said light-emitting device with use of the final first programming of the storage capacitor.
2. The system of claim 1 wherein the predetermined current is a known reference current and the first current is a function of the operational voltage V OLED of said light-emitting device.
3. The system of claim 1 wherein the predetermined current is a previously measured second current, the second current previously supplied to said light-emitting device via said drive transistor according to a second programming of the storage capacitor.
4. The system of claim 3 wherein the controller is adapted to extract the operational voltage V OLED of the light-emitting device with use of the second programming of the storage capacitor.
5. The system of claim 4 wherein the controller is adapted to extract the operational voltage V OLED of the light-emitting device from a difference between the final first programming of the storage capacitor and the second programming of the storage capacitor.
6. The system of claim 3 wherein the controller is further adapted to, prior to said varying the first programming of the storage capacitor, setting the second programming of the storage capacitor to supply the second current to said light-emitting device via said drive transistor, wherein only one of the first current and the predetermined current is a function of the operational voltage V OLED of said light-emitting device.
7. The system of claim 1 wherein the one of the first current and the predetermined current which is a function of the operational voltage V OLED of said light-emitting device, is a function of the programming of the storage capacitor which is a function of the operational voltage V OLED of said light-emitting device.
8. The system of claim 1 wherein the first current is a function of the operational voltage V OLED of said light-emitting device, and wherein the controller is further adapted to:
at an earlier time previous to said extracting of the operational voltage V OLED , vary a third programming of the storage capacitor and measure a third current supplied to said light-emitting device via said drive transistor, until reaching a final third programming of the storage capacitor when the third current equals the predetermined current, wherein one of the predetermined current and the third current is a function of the operational voltage V OLED of said light-emitting device at the earlier time, and extract the value of the operational voltage V OLED of said light-emitting device at the earlier time with use of the final third programming of the storage capacitor; and
extract the value of the operational voltage V OLED of said light-emitting device with use of the final third programming of the storage capacitor and the final first programming of the storage capacitor and the value of the operational voltage V OLED of said light-emitting device at the earlier time.
9. The system of claim 8 wherein only one of the predetermined current and the third current is a function of the operational voltage V OLED of said light-emitting device at the earlier time.
10. A method of determining the operational voltage V OLED of a light-emitting device in a pixel in an array of pixels in a display, the pixel including a storage capacitor coupled to a drive transistor for supplying current to said light-emitting device as a function of a programming of the storage capacitor, the method comprising:
varying a first programming of the storage capacitor and measuring a first current supplied to said light-emitting device via said drive transistor, until reaching a final first programming of the storage capacitor when the first current equals a predetermined current, wherein one of the first current and the predetermined current is a function of the operational voltage V OLED of said light-emitting device; and
extracting the value of the operational voltage V OLED of said light-emitting device with use of the final first programming of the storage capacitor.
11. The method of claim 10 wherein the predetermined current is a known reference current and the first current is a function of the operational voltage V OLED of said light-emitting device.
12. The method of claim 10 wherein the predetermined current is a previously measured second current, the second current previously supplied to said light-emitting device via said drive transistor according to a second programming of the storage capacitor.
13. The method of claim 12 wherein said extracting comprises extracting the operational voltage V OLED of the light-emitting device with use of the second programming of the storage capacitor.
14. The method of claim 13 wherein said extracting comprises extracting the operational voltage V OLED of the light-emitting device from a difference between the final first programming of the storage capacitor and the second programming of the storage capacitor.
15. The method of claim 12 further comprising:
prior to said varying the first programming of the storage capacitor, setting the second programming of the storage capacitor to supply the second current to said light-emitting device via said drive transistor, wherein only one of the first current and the predetermined current is a function of the operational voltage V OLED of said light-emitting device.
16. The method of claim 10 wherein the one of the first current and the predetermined current which is a function of the operational voltage V OLED of said light-emitting device, is a function of the programming of the storage capacitor which is a function of the operational voltage V OLED of said light-emitting device.
17. The method of claim 10 wherein the first current is a function of the operational voltage V OLED of said light-emitting device, the method further comprising:
at an earlier time previous to said extracting of the operational voltage V OLED , varying a third programming of the storage capacitor and measuring a third current supplied to said light-emitting device via said drive transistor, until reaching a final third programming of the storage capacitor when the third current equals the predetermined current, wherein one of the predetermined current and the third current is a function of the operational voltage V OLED of said light-emitting device at the earlier time, and extracting the value of the operational voltage V OLED of said light-emitting device at the earlier time with use of the final third programming of the storage capacitor; and
extracting the value of the operational voltage V OLED of said light-emitting device with use of the final third programming of the storage capacitor and the final first programming of the storage capacitor and the value of the operational voltage V OLED of said light-emitting device at the earlier time.
18. The method of claim 17 wherein only one of the predetermined current and the third current is a function of the operational voltage V OLED of said light-emitting device at the earlier time.