Fast data programming TFT pixel threshold voltage compensation circuit with two phase threshold compensation

Patent metadata

Field	Value
Publication number	US-11087685-B1
Application number	US-202016925402-A
Country	US
Kind code	B1
Filing date	Jul 10, 2020
Priority date	Jul 10, 2020
Publication date	Aug 10, 2021
Grant date	Aug 10, 2021

Abstract

A pixel circuit for a display device provides enhanced performance by performing a first threshold compensation phase that also operates to pre-charge a compensating storage capacitor, and then performing a further second threshold compensation combined with data programming during a shortened programming time. During the first threshold compensation phase, the threshold voltage of the drive transistor is stored in the compensating storage capacitor. During the combined data programming and second threshold compensation phase, the data voltage is stored in a programming capacitor, and the drive transistor threshold voltage is also stored in the programming capacitor. As the threshold voltage already is stored at the storage capacitor, and thus the node where the storage capacitor and the programming capacitor connect has been pre-charged with the threshold voltage, the pre-charging effect shortens the time needed for the programming capacitor to store the threshold voltage, which results in a short programming time while achieving high compensation accuracy.

First claim

What is claimed is:

1. A pixel circuit for a display device operable in an initialization phase, a first threshold compensation phase, a combined data programming and second 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 first terminal being connected to a first voltage supply line;
a programming capacitor having a first plate connected to the second 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 threshold voltage of the drive transistor during the combined data programming and second threshold compensation phase;
a storage capacitor having a first plate connected to the second 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 first threshold compensation phase and the stored threshold voltage pre-charges the storage capacitor for the second threshold compensation phase;
a light-emitting device having a first terminal that is electrically connected the second 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 switch transistor is placed in an on state during the initialization phase, the first threshold compensation phase, and the combined data programming and second threshold compensation phase to electrically connect the gate and the first 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 connected 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 second 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 second 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 a 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 first 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 second terminal of the drive transistor and a second plate connected to the gate of the drive transistor;
a light-emitting device having a first terminal that is electrically connectable to the second 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 first threshold compensation phase to compensate a threshold voltage of the drive transistor comprising:
placing the first switch transistor in an on state, thereby diode connecting the drive transistor by electrically connecting the gate and the first terminal of the drive transistor through the first switch transistor; and
electrically disconnecting the second terminal of the drive transistor from the first terminal of the light-emitting device;
wherein the threshold voltage of the drive transistor is stored at the storage capacitor and pre-charges the storage capacitor;

performing a combined data programming and second threshold compensation phase to program data and further compensate the threshold voltage of the drive transistor comprising:
electrically connecting the second plate of the programming capacitor to a data voltage supply line that supplies a data voltage, wherein the date voltage is applied to the second plate of the programming capacitor to store the data voltage; and
storing the threshold voltage at the first plate of the programming capacitor while maintaining the first switch transistor in the on state to further perform threshold compensation of 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 second 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 second 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.

Assignees

• Sharp Kk

Inventors

• Lu Tong

Classifications

• G09G2300/0852

  being a dynamic memory with more than one capacitor · CPC title

• G09G2300/0819

  used for counteracting undesired variations, e.g. feedback or autozeroing · CPC title

• G09G2320/045

  Compensation of drifts in the characteristics of light emitting or modulating elements · CPC title

• 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