Fast data programming TFT pixel threshold voltage compensation circuit with improved compensation accuracy

Patent metadata

Field	Value
Publication number	US-11114030-B1
Application number	US-202016925396-A
Country	US
Kind code	B1
Filing date	Jul 10, 2020
Priority date	Jul 10, 2020
Publication date	Sep 7, 2021
Grant date	Sep 7, 2021

Abstract

A pixel circuit for a display device provides enhanced performance by performing a partial threshold compensation during programming and performing further compensation independent of programming to achieve a short programming time while ensuring threshold compensation accuracy. The pixel circuit is operated in a relatively shortened duration first combined data programming and threshold compensation phase, and in a relatively prolonged duration second threshold compensation phase for improved compensation accuracy. During the combined programming and threshold compensation phase, a drive transistor is diode connected, and a data voltage is applied to a programming a capacitor that also stores a portion of a threshold voltage of the drive transistor. This permits a short programming time. During the prolonged threshold compensation phase, to further compensate the threshold voltage of the drive transistor for compensation accuracy, the drive transistor remains diode connected and a storage capacitor stores the threshold voltage of the drive transistor.

First claim

What is claimed is:

1. A pixel circuit for a display device operable in an initialization phase, a combined data programming and threshold compensation phase, a prolonged threshold compensation 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 applied to a gate of the drive transistor, the drive transistor having a first terminal and a second terminal with the second terminal being connected to a first voltage supply line;
a programming capacitor having a first plate connected to the first terminal of the drive transistor, and a second plate that is electrically connected to the gate of the drive transistor during the initialization phase and the emission phase, wherein the programming capacitor stores a data voltage and a portion of a threshold voltage of the drive transistor during the combined data programming and threshold compensation phase;
a storage capacitor having a first plate connected to the first terminal of the drive transistor and a second plate connected to the gate of the drive transistor, wherein the storage capacitor stores the threshold voltage of the drive transistor during the prolonged threshold compensation phase;
the light-emitting device having a first terminal that is electrically connected to the first terminal of the drive transistor during the emission phase, and a second terminal connected to a second voltage supply line; and
a first switch transistor connected between the gate of the drive transistor and the first voltage supply line, wherein the first transistor is placed in an on state during the initialization phase, the combined data programming and threshold compensation phase, and the prolonged threshold compensation phase to electrically connect the gate and the second terminal of the drive transistor for threshold compensation of the threshold voltage of the drive transistor.

2. The pixel circuit of claim 1 , further comprising a second switch transistor connected between the gate of the drive transistor and the second plate of the programming capacitor, wherein the second switch transistor is placed in an on state to electrically connect the second plate of the programming capacitor to the gate of the drive transistor.

3. The pixel circuit of claim 2 , further comprising a third switch transistor connected between the second plate of the programming capacitor and a data voltage supply line that supplies the data voltage, wherein the third switch transistor is placed in an on state during the combined data programming and threshold compensation phase to apply the date voltage to the second plate of the programming capacitor.

4. The pixel circuit of claim 3 , further comprising a fourth switch transistor connected between an initialization voltage supply line that supplies an initialization voltage and the first terminal of the light-emitting device, wherein the fourth switch transistor is placed in an on state to apply the initialization voltage to the first terminal of the light-emitting device and to a node N 1 corresponding to a connection of the first terminal of the drive transistor, the first plate of the programming capacitor, and the first plate of the storage capacitor.

5. The pixel circuit of claim 4 , further comprising a fifth switch transistor that is connected between the node N 1 and the first terminal of the light-emitting device, wherein the fifth transistor is placed in an on state to electrically connect the first terminal of the light-emitting device to the node N 1 .

6. The pixel circuit of claim 1 , wherein at least one of the transistors is an indium gallium zinc oxide (IGZO) transistor.

7. 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.

8. A method of operating a pixel circuit for a display device comprising the steps of:
providing the pixel circuit comprising:
a drive transistor configured to control an amount of current to a light-emitting device during an emission phase depending upon a voltage applied to a gate of the drive transistor, the drive transistor having a first terminal and a second terminal with the second terminal being connected to a first voltage supply line;
a programming capacitor having a first plate connected to the first terminal of the drive transistor, and a second plate that is electrically connectable to the gate of the drive transistor;
a storage capacitor having a first plate connected to the first terminal of the drive transistor and a second plate connected to the gate of the drive transistor;
the light-emitting device having a first terminal that is electrically connectable to the first terminal of the drive transistor, and a second terminal connected to a second voltage supply line; and
a first switch transistor connected between the gate of the drive transistor and the first voltage supply line;

performing a combined data programming and threshold compensation phase to program data and to compensate a portion of a threshold voltage of the drive transistor comprising steps of:
placing the first switch transistor in an on state, thereby diode connecting the drive transistor by electrically connecting the gate and the second terminal of the drive transistor through the first switch transistor;
electrically disconnecting the first terminal of the drive transistor from the first terminal of the light-emitting device; and
electrically connecting the second plate of the programming capacitor to a data voltage supply line that supplies a data voltage, wherein the programming capacitor stores the data voltage and the portion of the threshold voltage of the drive transistor;

performing a prolonged threshold compensation phase to further compensate the threshold voltage of the drive transistor comprising maintaining the first switch transistor in the on state such that the drive transistor remains diode connected, wherein the storage capacitor stores the threshold voltage of the drive transistor; and
performing an emission phase during which light is emitted from the light-emitting device comprising electrically connecting the first terminal of the light-emitting device to the first terminal of the drive transistor and applying a driving voltage from the first voltage supply line to the light-emitting device through the drive transistor.

9. The method of operating of claim 8 , wherein the pixel circuit further comprises a second switch transistor connected between the gate of the drive transistor and the second plate of the programming capacitor; and
wherein the emission phase further comprises placing the second switch transistor in an on state to electrically connect the second plate of the programming capacitor to the gate of the drive transistor through the second switch transistor.

10. The method of operating of claim 9 , wherein the pixel circuit further comprises a third switch transistor connected between the second plate of the programming capacitor and a data voltage supply line that supplies the data voltage; and
wherein the combined data programming and threshold compensation phase further comprises placing the third switch transistor in an on state to apply the date voltage to the second plate of the programming capacitor through the third switch transistor.

11. The method of operating of claim 9 , further comprising performing an initialization phase to initialize voltages within the pixel circuit comprising the steps of:
electrically connecting the first terminal of the light-emitting device to an initialization voltage

Assignees

• Sharp Kk

Inventors

• Lu Tong

Classifications

• G09G3/3233 Primary

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

• G09G2300/0842

  forming a memory circuit, e.g. a dynamic memory with one capacitor · CPC title

• G09G2320/0233

  Improving the luminance or brightness uniformity across the screen · CPC title