Pixel circuits for amoled displays
A system for driving a display that includes a plurality of pixel circuits arranged in an array, each of the pixel circuits including a light emitting device and a driving transistor for conveying a driving current through the light emitting device. Methods of measuring characteristics of circuit elements of pixels sharing a monitor line include the control of biasing to selectively turn off circuit elements or render their response known while measuring other circuit elements of interest.
1. A method of determining a characteristic of a circuit element of a first pixel of a display device, the first pixel sharing a monitor line with a second pixel of the display device, the method comprising:
biasing the first pixel;
biasing the second pixel to fix a current passing through the second pixel over the monitor line to a known current; and
measuring the characteristic of the circuit element of the first pixel with use of said monitor line.
2. The method of claim 1 , wherein measuring the characteristic of the circuit element of the first pixel with use of said monitor line comprises measuring a current over the monitor line.
3. The method of claim 2 , wherein measuring the characteristic of the circuit element of the first pixel with use of said monitor line further comprises subtracting from a current value of the measured current a current value of the known current.
4. The method of claim 1 , wherein the known current is zero.
5. The method of claim 1 , wherein biasing the second pixel comprises biasing an optoelectronic device of the second pixel to turn off the optoelectronic device.
6. The method of claim 5 , wherein the second pixel includes a drive transistor for supplying current to the optoelectronic device and coupled between a supply voltage and the optoelectronic device, and wherein biasing the optoelectronic device comprises biasing the drive transistor to set a voltage at a node between the drive transistor and the optoelectronic device, to bias the optoelectronic device and turn the optoelectronic device off.
7. The method of claim 1 , wherein the second pixel includes a source switch coupled between the monitor line and remaining elements of the second pixel, and wherein biasing the second pixel comprises biasing the source switch.
8. The method of claim 7 , wherein biasing the source switch comprises biasing with a known voltage difference across a source and a drain of the source switch resulting in the known current passing through the source switch.
9. The method of claim 8 , wherein the known voltage difference is zero.
10. The method of claim 8 , further comprising prior to biasing with the known voltage difference across the source and the drain of the source switch, determining the known voltage difference across the source and the drain of the source switch which results in the known current passing through the source switch including:
biasing the first pixel to turn off an optoelectronic device of the first pixel and then biasing the first pixel to turn off a drive transistor of the first pixel;
biasing the monitor line to a first voltage and biasing the second pixel so that the known current passes through the source switch as a result of a particular voltage difference across the source and the drain of the source switch; and
determining the known voltage difference from the particular voltage difference.
11. The method of claim 8 , wherein the first pixel includes a drive transistor for supplying current to an optoelectronic device of the first pixel and coupled between a supply voltage and the optoelectronic device, and wherein biasing the first pixel comprises biasing the drive transistor to turn the drive transistor off and biasing over the monitor line the optoelectronic device to turn the optoelectronic device on.
12. The method of claim 11 , further comprising prior to the biasing with the known voltage difference across the source and the drain of the source switch, determining the known voltage difference across the source and the drain of the source switch which results in the known current passing through the source switch including:
biasing the first pixel to turn off the optoelectronic device and then biasing the first pixel to turn off the drive transistor;
biasing the monitor line to a first voltage and biasing the second pixel so that the known current passes through the source switch as a result of a particular voltage difference across the source and the drain of the source switch; and
determining the known voltage difference from the particular voltage difference.
13. The method of claim 1 , further comprising prior to biasing the second pixel to fix the current passing through the second pixel over the monitor line to the known current, determining the known current which results from said biasing of the second pixel by:
varying a biasing of the second pixel so that the known current passes through the source switch as a result of a particular biasing of the second pixel; and
determining the biasing of the second pixel from the particular biasing of the second pixel.
14. The method of claim 1 , wherein the first pixel includes a drive transistor for supplying current to an optoelectronic device of the first pixel and coupled between a supply voltage and the optoelectronic device, and wherein the first pixel includes a source switch coupled between the monitor line and remaining elements of the first pixel, and wherein biasing the first pixel comprises:
at a first time, biasing the drive transistor to cause a first current to pass through the source switch; and
at a second time after the first time, adjusting a biasing of the drive transistor to maintain the same first current passing through the source switch;
determining a change in a current characteristic of the optoelectronic device from the change in the biasing of the drive transistor which maintains the same first current passing through the source switch.