Tft pixel circuit for oled external compensation

Patent metadata

Field	Value
Publication number	US-2020184888-A1
Application number	US-201816214437-A
Country	US
Kind code	A1
Filing date	Dec 10, 2018
Priority date	Dec 10, 2018
Publication date	Jun 11, 2020
Grant date	—

Abstract

A display system includes a pixel circuit and an external compensation system that is operable with the pixel circuit to compensate for differences in a property of the drive transistor and/or light-emitting device. The pixel circuit includes a drive transistor configured to control an amount of current to a light-emitting device; a second transistor having a first terminal connected to the gate of the drive transistor and a second terminal connected to a data voltage input that is supplied by the external compensation system, and a gate of the second transistor is connected to a first control signal; a third transistor having a first terminal connected to a second terminal of the drive transistor and a second terminal connected to a second voltage supply input that is supplied from the external compensation system, wherein a current flow from the second voltage supply input is measured by the external compensation system, and wherein a gate of the third transistor is connected to a second control signal; and a fourth transistor having a first terminal connected to the second terminal of the drive transistor and a second terminal connected to a third voltage supply input, wherein a gate of the fourth transistor is connected to a third control signal. The external voltage compensation system is configured to adjust the data voltage input based on the measured current flow to compensate for a variation in a property of the drive transistor and/or the light-emitting device.

First claim

1 . A display system comprising a pixel circuit and an external compensation system that is operable with the pixel circuit;
the pixel circuit comprising: a drive transistor configured to control an amount of current to a light-emitting device depending upon a voltage applied to a gate of the drive transistor, wherein the light-emitting device is connected at a first node to a first terminal of the drive transistor and at a second node to a first voltage supply input; a second transistor having a first terminal connected to the gate of the drive transistor and a second terminal connected to a data voltage input that is supplied by the external compensation system, and a gate of the second transistor is connected to a first control signal; a third transistor having a first terminal connected to a second terminal of the drive transistor and a second terminal connected to a second voltage supply input that is supplied from the external compensation system, wherein a current flow from the second voltage supply input is measured by the external compensation system, and wherein a gate of the third transistor is connected to a second control signal; and a fourth transistor having a first terminal connected to the second terminal of the drive transistor and a second terminal connected to a third voltage supply input, wherein a gate of the fourth transistor is connected to a third control signal; wherein the external voltage compensation system is configured to adjust the data voltage input based on the measured current flow to compensate for a variation in a property of the drive transistor and/or the light-emitting device.

2 . The display system of claim 1 , wherein the external compensation system is an analogue external compensation system.

3 . The display system of claim 2 , wherein the first control signal is the same as the second control signal.

4 . The display system of claim 2 , wherein the analogue external compensation system comprises:
a current mirror that mirrors the current flow from the second voltage supply input and outputs the mirrored current; and an integrator that receives the output of the mirrored current and receives a programming reference current, wherein the integrator outputs the adjusted data voltage based on a comparison between the mirrored current and the programming reference current.

5 . The display system of claim 1 , wherein the external compensation system is a digital external compensation system.

6 . The display system of claim 5 , wherein the first control signal is different from the second control signal.

7 . The display system of claim 5 , wherein the digital external compensation system comprises:
a current measurement device that measures the current flow from the second voltage supply input; a memory device that stores said measured current flow; a compensation calculator that obtains the measured current flow from the memory device and receives an image data input, wherein the compensation calculator determines a compensated data voltage based on a comparison between the measured current flow and a reference current corresponding to the image data; and a data voltage generation unit that generates the compensated data voltage and outputs the compensated data voltage to the pixel circuit.

8 . The display system of any of claim 1 , wherein the second voltage supply input and the third voltage supply input have the same voltage level.

9 . The display system of claim 1 , wherein the second voltage supply input and the third voltage supply input have a voltage difference, and current flow to the light-emitting device is compensated to be the same when the pixel circuit is connected to the second voltage supply input or the third voltage supply input.

10 . The display system of claim 1 , wherein the transistors are n-type transistors.

11 . The display system of claim 1 , wherein the transistors are p-type transistors.

12 . The display system of claim 1 , wherein the pixel circuit further comprises a storage capacitor connected to the gate of the drive transistor that stores the data voltage.

13 . The display system of claim 1 , wherein the light-emitting device is one of an organic light-emitting diode, a micro light-emitting diode (LED), or a quantum dot LED.

14 . A method of operating a display system comprising a pixel circuit and an analogue external compensation system that is operable with the pixel circuit;
wherein the pixel circuit comprises: a drive transistor configured to control an amount of current to a light-emitting device depending upon a voltage applied to a gate of the drive transistor; wherein the light-emitting device is connected at a first node to a first terminal of the drive transistor and at a second node to a first voltage supply input; a second transistor having a first terminal connected to the gate of the drive transistor and a second terminal connected to a data voltage input that is supplied by the analogue external compensation system, and a gate of the second transistor is connected to a first control signal; a third transistor having a first terminal connected to a second terminal of the drive transistor and a second terminal connected to a second voltage supply input that is supplied from the analogue external compensation system, wherein a current flow from the second voltage supply input is measured by the analogue external compensation system, and wherein a gate of the third transistor connected to the first control signal; and a fourth transistor having a first terminal connected to the second terminal of the drive transistor and a second terminal connected to a third voltage supply input, wherein a gate of the fourth transistor is connected to a second control signal; the method of operating comprising the steps of: during a current sensing and data programming phase: disconnecting the drive transistor from the third voltage supply input and connecting the drive transistor to the second voltage supply input; measuring a current through the third transistor using the analogue external compensation system; comparing the measured current with a programming reference current, wherein a difference between the measured current and reference current is converted to an adjusted data voltage; and outputting the adjusted data voltage to the pixel circuit; and during an emission phase: disconnecting the drive transistor from the second voltage supply input and connecting the drive transistor to the third voltage supply input, wherein the adjusted data voltage is applied to the gate of the drive transistor to control the current through the light emitting device.

15 . The method of operating of claim 14 , wherein the adjusted data voltage becomes stable when the measured current approaches the programming reference current.

16 . The method of operating of claim 14 , further comprising storing the adjusted data voltage on a storage capacitor that is connected to the gate of the drive transistor.

17 . A method of operating a display system comprising a pixel circuit and a digital external compensation system that is operable with the pixel circuit;
wherein the pixel circuit comprises: a drive transistor configured to control an amount of current to a light-emitting device depending upon a voltage applied to a gate of the drive transistor; wherein the light-emitting device is connected at a first node to a first terminal of the drive transistor and at a second node to a first voltage supply input; a second transistor having a first terminal connected to the gate of the drive transist

Assignees

• Sharp Kk

Inventors

• Brownlow Michael James
• Lu Tong

Classifications

• G09G2310/08

  Details of timing specific for flat panels, other than clock recovery · CPC title

• G09G3/3275 Primary

  Details of drivers for data electrodes · CPC title

• G09G2320/029

  by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel · CPC title

• G09G2320/0295

  by monitoring each display pixel · CPC title

• G09G3/325

  the data current flowing through the driving transistor during a setting phase, e.g. by using a switch for connecting the driving transistor to the data driver · CPC title