Display device switched to different driving modes according to gray level

1. A display device, comprising:

a plurality of pixels, at least one of the plurality of pixels comprising a light emitting unit and a driving circuit;

wherein to present a first gray level lower than or equal to a predetermined gray level, the driving circuit is configured to drive the light emitting unit in a pulse width modulation (PWM) mode, and to present a second gray level higher than the predetermined gray level, the driving circuit is configured to drive the light emitting unit in a current mode;

wherein the driving circuit comprises:

a driving thin film transistor (TFT) having a first terminal coupled to a first voltage terminal, a second terminal coupled to the light emitting unit, and a control terminal; and

a scanning TFT having a first terminal coupled to a data line, a second terminal coupled to the control terminal of the driving TFT, and a control terminal configured to receive a scan signal;

wherein during a scan operation, the scanning TFT is turned on, and the control terminal of the driving TFT receives a data signal on the data line through the scanning TFT.

2. The display device of claim 1 , wherein a driving current generated by the driving circuit in the PWM mode has a duty ratio less than 100%.

3. The display device of claim 1 , wherein in the current mode, the light emitting unit is driven with a variable driving current.

4. The display device of claim 1 , wherein the driving circuit comprises a second capacitor having a first terminal coupled to the first terminal of the driving TFT, and a second terminal coupled to the control terminal of the driving TFT.

5. The display device of claim 1 , wherein during the scan operation when the driving circuit drives the light emitting unit in the PWM mode to present the first gray level:

a duty ratio of the data signal is determined according to the first gray level.

6. The display device of claim 1 , wherein after the scan operation, during a hold operation when the driving circuit drives the light emitting unit in the current mode to present the second gray level:

the scanning TFT is turned off; and

a voltage of the data signal is determined according to the second gray level.

7. The display device of claim 1 , wherein the driving circuit further comprises:

an emission control TFT coupled between the driving TFT and the light emitting unit, and the emission control TFT having a first terminal coupled to the second terminal of the driving TFT, a second terminal coupled to the light emitting unit, and a control terminal configured to receive an emission control signal; and

a first capacitor coupled between the control terminal of the driving TFT and the second terminal of the scanning TFT, and the first capacitor having a first terminal coupled to the control terminal of the driving TFT, and a second terminal coupled to the second terminal of the scanning TFT.

8. The display device of claim 7 , wherein the driving circuit further comprises:

a reset TFT having a first terminal coupled to the control terminal of the driving TFT, a second terminal coupled to a reset voltage terminal, and a control terminal configured to receive a reset signal.

9. The display device of claim 8 , wherein during a reset operation:

the scanning TFT is turned off; and

the reset TFT is turned on.

10. The display device of claim 8 , wherein the driving circuit further comprises:

a first compensation TFT having a first terminal coupled to the first terminal of the reset TFT, a second terminal coupled to the second terminal of the driving TFT, and a control terminal configure to receive a compensation signal.

11. The display device of claim 10 , wherein during a compensation operation:

the scanning TFT and the first compensation TFT are turned on; and

the data line is coupled to a reference voltage terminal.

12. The display device of claim 10 , wherein the driving circuit further comprises:

a second compensation TFT having a first terminal coupled to the second terminal of the first capacitor, a second terminal coupled to a reference voltage terminal, and a control terminal configure to receive the compensation signal.

13. The display device of claim 12 , wherein during a compensation operation:

the scanning TFT is turned off; and

the first compensation TFT and the second compensation TFT are turned on.

14. The display device of claim 7 , wherein the driving circuit further comprises:

a reset TFT having a first terminal coupled to the second terminal of the first capacitor, a second terminal coupled to the first terminal of the first capacitor, and a control terminal configured to receive a reset signal; and

a compensation TFT having a first terminal coupled to the second terminal of the reset TFT, a second terminal coupled to the second terminal of the driving TFT, and a control terminal configured to receive a compensation signal.

15. The display device of claim 14 , wherein during a reset operation:

the scanning TFT and the reset TFT are turned on;

the compensation TFT is turned off; and

the data line is coupled to a reset voltage terminal.

16. The display device of claim 14 , wherein during a compensation operation:

the scanning TFT and the compensation TFT are turned on; and

the reset TFT is turned off; and

the data line is coupled to a reference voltage terminal.

17. The display device of claim 7 , wherein the driving circuit further comprises:

a third capacitor having a first terminal coupled to the first terminal of the driving TFT, and a second terminal coupled to the second terminal of the first capacitor.

18. The display device of claim 1 , further comprising:

a signal control circuit configured to provide a reference voltage, a reset voltage, or a data signal according to an operation of the pixel.