Organic light-emitting diode display with compensation for transistor variations

Patent metadata

Field	Value
Publication number	US-9721502-B2
Application number	US-201414500738-A
Country	US
Kind code	B2
Filing date	Sep 29, 2014
Priority date	Apr 14, 2014
Publication date	Aug 1, 2017
Grant date	Aug 1, 2017

Abstract

A display may include an array of organic light-emitting diode display pixels having transistors characterized by threshold voltages subject to transistor variations. Compensation circuitry may be used to measure at transistor threshold voltage for a pixel. The threshold voltage may be sampled by controlling the pixel to sample the threshold voltage onto a capacitor at the pixel. The compensation circuitry may include sense circuitry that may be operated in combination with the pixel to transfer charge from the capacitor to the sense circuitry such that the threshold voltage is produced at an output of the sense circuitry. The compensation circuitry may generate compensation data based on the measured threshold voltage. During display operations, data circuitry may receive digital image data and process the digital image data along with the compensation data to generate analog data signals for the pixel.

First claim

What is claimed is:

1. A method of operating light-emitting diode display having pixels, the method comprising:
with compensation circuitry, measuring a transistor threshold voltage of at least one pixel of the display;
with the compensation circuitry, generating compensation data based on the measured transistor threshold voltage;
with circuitry, receiving image data; and
with the circuitry, processing the received image data along with the compensation data to generate analog data signals for the at least one pixel of the display, wherein the at least one pixel of the display comprises a current source transistor coupled to a light-emitting diode and wherein measuring the transistor threshold voltage comprises:
sampling the transistor threshold voltage onto a capacitor coupled between gate and source terminals of the current source transistor, wherein the compensation circuitry comprises sense circuitry having an amplifier and a feedback capacitor coupled in a feedback loop between a first input and an output of the amplifier.

2. The method defined in claim 1 , wherein a second input of the amplifier receives a bias voltage, and wherein measuring the transistor threshold voltage further comprises:
precharging the input and the output of the amplifier and the gate and source terminals of the current source transistor.

3. The method defined in claim 2 wherein a feedback switch is coupled between the input and the output of the amplifier and wherein measuring the transistor threshold voltage further comprises:
opening the feedback switch to transfer charge between the capacitor and the feedback capacitor, wherein the output of the amplifier has a voltage equal in magnitude to the transistor threshold voltage.

4. The method defined in claim 3 wherein generating the compensation data comprises generating the compensation data based on the voltage at the output of the amplifier.

5. The method defined in claim 4 wherein the compensation circuitry further comprises control circuitry and a comparator, the method further comprising:
with the comparator, comparing a plurality of analog gray level voltages to the voltage at the output of the amplifier, wherein each analog gray level voltage of the plurality of analog gray level voltages has a corresponding digital data value; and
with the control circuitry, determining which analog gray level voltage and corresponding digital data value matches the voltage at the output of the amplifier.

6. The method defined in claim 5 wherein generating the compensation data based on the measured transistor threshold voltage comprises:
with the control circuitry, storing the digital data value that matches the voltage at the output of the amplifier as the compensation data.

7. The method defined in claim 5 wherein generating the compensation data based on the measured transistor threshold voltage comprises:
with the control circuitry, normalizing the digital data value that matches the voltage at the output of the amplifier across multiple pixels of the display; and
with the control circuitry, storing the normalized digital data value as the compensation data.

8. The method defined in claim 4 wherein the compensation data comprises offset data and wherein processing the received image data along with the compensation data to generate the analog data signals for the at least one pixel of the display comprises:
summing the offset data and the received image data to produce a summed digital value.

9. A method of operating a light-emitting diode display having a plurality of pixels, wherein each pixel includes a current source transistor, a light-emitting diode, and a capacitor coupled between source and gate terminals of the current source transistor, the method comprising:
selecting a pixel;
with demultiplexing circuitry, electrically coupling the selected pixel to sense circuitry;
for the selected pixel, storing a transistor threshold voltage of the current source transistor across the capacitor using the current source transistor;
with the sense circuitry, measuring the transistor threshold voltage that is stored across the capacitor, wherein the sense circuitry comprises an amplifier having an input coupled to the demultiplexing circuitry and an output coupled to the input through a feedback switch; and
after electrically coupling the selected pixel to the sense circuitry, disabling the feedback switch.

10. The method defined in claim 9 further comprising:
with analog-to-digital converter circuitry, converting the measured transistor threshold voltage to a digital value;
with data circuitry, receiving digital image data; and
with the data circuitry, generating an analog data signal for the selected pixel based on the received digital image data and the digital value.

11. The method defined in claim 10 , further comprising:
with storage circuitry, storing the digital value.

12. The method defined in claim 10 , wherein generating the analog data signal comprises adding offset data to the digital image data.

13. The method defined in claim 9 , wherein each pixel further includes a switch coupled between the capacitor and a data line, the method further comprising:
after electrically coupling the selected pixel to the sense circuitry, enabling the switch in the selected pixel to pass a ground voltage to the capacitor in the selected pixel.

14. The method defined in claim 13 , wherein each pixel further includes an additional switch coupled between the current source transistor and a power supply terminal, the method further comprising:
disabling the additional switch in the selected pixel while the switch is enabled to pass the ground voltage to the capacitor in the selected pixel.

15. The method defined in claim 14 , wherein each pixel further includes a third switch coupled between the light-emitting diode and the sense circuitry, the method further comprising:
enabling the third switch in the selected pixel while the additional switch is disabled and while the switch is enabled in the selected pixel.

16. The method defined in claim 9 , wherein each pixel further includes a switch coupled between the capacitor and a data line, the method further comprising:
after electrically coupling the selected pixel to the sense circuitry, enabling the switch in the selected pixel to pass a ground voltage to the capacitor in the selected pixel while the feedback switch is disabled.

17. The method defined in claim 16 further comprising:
with converter circuitry, converting the measured transistor threshold voltage to a digital value;
with data circuitry, receiving digital image data; and
with the data circuitry, generating an analog data signal for the selected pixel based on the received digital image data and the digital value.

18. The method defined in claim 17 , further comprising:
driving the selected pixel based on the generated analog data signal.

Assignees

• Apple Inc

Inventors

• Bi Yafei
• Yao Wei H

Classifications

• G09G2320/0295

  by monitoring each display pixel · CPC title

• G09G2320/0285

  using tables for spatial correction of display data · CPC title

• G09G2320/043

  Preventing or counteracting the effects of ageing · CPC title

• G09G3/3233 Primary

  with pixel circuitry controlling the current through the light-emitting element · CPC title