TFT pixel threshold voltage compensation circuit with short one horizontal time

Patent metadata

Field	Value
Publication number	US-10650752-B1
Application number	US-201816171724-A
Country	US
Kind code	B1
Filing date	Oct 26, 2018
Priority date	Oct 26, 2018
Publication date	May 12, 2020
Grant date	May 12, 2020

Abstract

A pixel circuit for a display device is operable in a compensation phase, a data programming phase, and an emission phase, whereby the one horizontal time is minimized while maintaining accurate compensation of the threshold voltage of the drive transistor. The pixel circuit includes: a storage capacitor having a first plate connected to a third terminal of the drive transistor that receives a voltage input, and a second plate connected to the gate of the drive transistor; and a programming capacitor having a first plate connected to second and third transistors, and a second plate of the programming capacitor is electrically connected to a data voltage input during the data programming phase, wherein the first plate of the programming capacitor is electrically connected to the second plate of the storage capacitor when the second transistor is in an on state. The second plate of the programming capacitor further is electrically connected to a reference voltage input to perform the compensation phase, and the programming capacitor further is electrically isolated from the storage capacitor and the drive transistor by the second and third transistors during the emission phase.

First claim

What is claimed is:

1. A pixel circuit for a display device operable in a compensation phase, a data programming phase, and an emission phase, the pixel circuit comprising:
a drive transistor configured to control an amount of current to a light-emitting device during the emission phase depending upon a voltage input applied to a gate of the drive transistor;
a second transistor and a third transistor, wherein the second transistor is directly connected between the gate of the drive transistor and the third transistor, and the third transistor is directly connected between the second transistor and a second terminal of the drive transistor, such that when the second and third transistors are in an on state the drive transistor becomes diode-connected such that the gate and the second terminal of the drive transistor are electrically connected through the second and third transistors, wherein a threshold voltage of the drive transistor is compensated during the compensation phase while the drive transistor is diode connected;
wherein the light-emitting device is electrically connected at a first node to the second terminal of the drive transistor during the emission phase and at a second node to a first voltage input;
a storage capacitor having a first plate connected to a third terminal of the drive transistor that receives a second voltage input, and a second plate connected to the gate of the drive transistor, and
a programming capacitor having a first plate directly connected to the second and third transistors, and a second plate of the programming capacitor is electrically connected to a data voltage input during the data programming phase, wherein the first plate of the programming capacitor is electrically connected to the second plate of the storage capacitor when the second transistor is in an on state;
wherein the second plate of the programming capacitor further is electrically connected to a reference voltage input to perform the compensation phase, and the programming capacitor further is electrically isolated from the storage capacitor and the drive transistor by the second and third transistors during the emission phase.

2. The pixel circuit of claim 1 , further comprising a fourth transistor connected between the first node of the light-emitting device and an initialization voltage input, wherein the pixel circuit further is operable in an initialization phase during which the initialization voltage is applied to the light emitting device and to the gate of the drive transistor while diode connected.

3. The pixel circuit of claim 2 , wherein the reference voltage input is the same as the initialization voltage input.

4. The pixel circuit of claim 1 , wherein the reference voltage input is the same as the second voltage input applied to the third terminal of the drive transistor.

5. The pixel circuit of claim 1 , further comprising a fifth transistor that is connected between the second terminal of the drive transistor and the first node of the light-emitting device, wherein the light-emitting device is electrically connected to the drive transistor through the fifth transistor during the emission phase and electrically isolated from the drive transistor during the compensation and data programming phases.

6. The pixel circuit of claim 1 , further comprising a sixth transistor that is connected between the reference voltage input and the second plate of the programming capacitor.

7. The pixel circuit of claim 1 , further comprising a seventh transistor that connected between the second plate of the programming capacitor and the data voltage input.

8. The pixel circuit of claim 1 , further comprising a seventh transistor and an eighth transistor, wherein the seventh transistor is connected between the second plate of the programming capacitor and the eighth transistor, and the eighth transistor is connected between the seventh transistor and the data voltage input.

9. The pixel circuit of claim 7 , further comprising the light-emitting device, wherein the light-emitting device is electrically connected to the drive transistor during the emission phase and electrically isolated from the drive transistor during the compensation and data programming phases.

10. The pixel circuit 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.

11. The pixel circuit of claim 1 , wherein the transistors are p-type transistors.

12. The pixel circuit of claim 1 , wherein the transistors are n-type transistors.

13. A method of operating a pixel circuit for a display device comprising the steps of:
providing a pixel circuit comprising:
a drive transistor configured to control an amount of current to a light-emitting device during the emission phase depending upon a voltage input applied to a gate of the drive transistor;
a second transistor and a third transistor, wherein the second transistor is connected between the gate of the drive transistor and the third transistor, and the third transistor is connected between the second transistor and a second terminal of the drive transistor, such that when the second and third transistors are in an on state the drive transistor becomes diode-connected such that the gate and the second terminal of the drive transistor are electrically connected through the second and third transistors;
a storage capacitor having a first plate connected to a third terminal of the drive transistor that receives a second voltage input, and a second plate connected to the gate of the drive transistor, and
a programming capacitor having a first plate connected to the second and third transistors, and a second plate of the programming capacitor is electrically connectable to a data voltage input;

performing a compensation phase to compensate a threshold voltage of the drive transistor comprising diode-connecting the drive transistor through the second and third transistors and applying the reference voltage at the second plate of the programming capacitor while the drive transistor is diode connected, wherein the programming capacitor is isolated from the reference voltage at the end of the compensation phase;
performing a data programming phase to program the data voltage to the programming capacitor comprising applying the data voltage at a second plate of the programming capacitor while the second transistor is in an on state; and
performing an emission phase during which light is emitted from the light-emitting device comprising isolating the programming capacitor from the storage capacitor and the drive transistor, and applying the second voltage input through the drive transistor to the light emitting device.

14. The method of operating of claim 13 , wherein the programming phase follows the threshold compensation phase.

15. The method of operating of claim 13 , wherein a duration of the data programming phase is shorter than a duration of the compensation phase.

16. The method of operating of claim 13 , further comprising performing an initialization phase comprising, prior to the compensation and data programming phases, applying an initialization voltage to a first node of the light emitting device and to the gate of the drive transistor via the diode-connection through the second and third transistors.

17. The method of operating of claim 16 , wherein the reference voltage is the initialization voltage.

18. The method operating of claim 13 , wherein the reference voltage is the second voltage input applied to the third terminal of the drive

Assignees

• Sharp Kk

Inventors

• Lu Tong
• Brownlow Michael James

Classifications

• G09G3/3233

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

• G09G3/3258 Primary

  with pixel circuitry controlling the voltage across the light-emitting element · CPC title

• H01L27/1214

  Electricity · mapped topic

• H10D86/60

  wherein the TFTs are in active matrices · CPC title

• H10D86/40

  characterised by multiple TFTs · CPC title