Organic light emitting diode display device performing low frequency driving

Patent metadata

Field	Value
Publication number	US-10971077-B2
Application number	US-202016923008-A
Country	US
Kind code	B2
Filing date	Jul 7, 2020
Priority date	Jul 31, 2019
Publication date	Apr 6, 2021
Grant date	Apr 6, 2021

Abstract

An OLED display device includes display panel and a panel driver. The panel driver receives input image data at an input frame frequency and determines whether the input image data represent a still image. When the input image data do not represent the still image, the panel driver drives the display panel at a first output frame frequency substantially equal to the input frame frequency. When the input image data represent the still image, the panel driver drives the display panel at a second output frame frequency lower than the input frame frequency for a low frequency driving time and drives the display panel at a third output frame frequency higher than the second output frame frequency for a high frequency insertion time determined by one of a panel characteristic of the display panel and a representative gray level of the input image data, after the low frequency driving time.

First claim

What is claimed is:

1. An organic light emitting diode (OLED) display device comprising:
a display panel including a plurality of pixels each having an OLED; and
a panel driver configured to drive the display panel,
wherein the panel driver receives input image data at an input frame frequency and determines whether the input image data represent a still image,
wherein, when the input image data do not represent the still image, the panel driver drives the display panel at a first output frame frequency substantially equal to the input frame frequency,
wherein, when the input image data represent the still image, the panel driver drives the display panel at a second output frame frequency lower than the input frame frequency for a low frequency driving time, and drives the display panel at a third output frame frequency higher than the second output frame frequency for a high frequency insertion time after the low frequency driving time, and
wherein the high frequency insertion time is determined based on at least one of a panel characteristic of the display panel and a representative gray level of the input image data.

2. The OLED display device of claim 1 , wherein a threshold voltage shift of a plurality of driving transistors included in the plurality of pixels which occurs during the low frequency driving time is compensated during the high frequency insertion time.

3. The OLED display device of claim 1 , wherein the third output frame frequency is lower than or equal to the first output frame frequency.

4. The OLED display device of claim 1 , wherein the high frequency insertion time is periodically inserted while the still image represented by the input image data is not changed.

5. The OLED display device of claim 1 , wherein each of the plurality of pixels includes:
a driving transistor configured to generate a driving current;
a switching transistor configured to transfer a data signal to a source of the driving transistor;
a compensating transistor configured to diode-connect the driving transistor;
a storage capacitor configured to store the data signal transferred through the switching transistor and the diode-connected driving transistor;
a first initializing transistor configured to provide an initialization voltage to the storage capacitor and a gate of the driving transistor in response to an initialization signal;
a first emission controlling transistor configured to connect a line of a power supply voltage to the source of the driving transistor in response to an emission control signal;
a second emission controlling transistor configured to connect a drain of the driving transistor to the OLED in response to the emission control signal; and
a second initializing transistor configured to provide the initialization voltage to the OLED in response to the first scan signal,
wherein the OLED is configured to emit light based on the driving current, and
wherein at least one of the driving transistor, the switching transistor, the compensating transistor, the first initializing transistor, the first emission controlling transistor, the second emission controlling transistor and the second initializing transistor is implemented with a P-type Metal Oxide Semiconductor (PMOS) transistor, and at least one of the driving transistor, the switching transistor, the compensating transistor, the first initializing transistor, the first emission controlling transistor, the second emission controlling transistor and the second initializing transistor is implemented with an N-type Metal Oxide Semiconductor (NMOS) transistor.

6. The OLED display device of claim 1 , wherein each of the plurality of pixels includes:
a driving transistor configured to generate a driving current;
a first switching transistor configured to transfer a data signal;
a storage capacitor configured to store the data signal transferred through the first switching transistor;
a second switching transistor configured to connect the storage capacitor and the driving transistor to an initialization line; and
an emission controlling transistor configured to connect a line of a power supply voltage to the driving transistor,
wherein the OLED is configured to emit light based on the driving current, and
wherein at least one of the driving transistor, the first switching transistor, the second switching transistor and the emission controlling transistor is implemented with a P-type Metal Oxide Semiconductor (PMOS) transistor, and at least one of the driving transistor, the first switching transistor, the second switching transistor and the emission controlling transistor is implemented with an N-type Metal Oxide Semiconductor (NMOS) transistor.

7. The OLED display device of claim 1 , wherein the panel driver includes:
a still image detector configured to determine whether the input image data represent the still image by comparing the input image data in a previous frame and the input image data in a current frame.

8. The OLED display device of claim 1 , wherein the high frequency insertion time is determined according to, as the panel characteristic of the display panel, a luminance decrease rate of the display panel during the low frequency driving time.

9. The OLED display device of claim 1 , wherein the panel driver includes:
a driving frequency changer comprising:
a high frequency insertion time storage configured to store the high frequency insertion time that is determined according to a luminance decrease rate of the display panel during the low frequency driving time; and
a driving frequency changing unit configured to output output image data at the first output frame frequency when the input image data do not represent the still image, to output the output image data at the second output frame frequency for the low frequency driving time when the input image data represent the still image, and to output the output image data at the third output frame frequency for the high frequency insertion time stored in the high frequency insertion time storage after the low frequency driving time, and
a data driver configured to provide data signals to the plurality of pixels based on the output image data.

10. The OLED display device of claim 1 , wherein the high frequency insertion time is determined according to, as the representative gray level of the input image data, an average value, a maximum value, or a minimum value of gray levels of the input image data.

11. The OLED display device of claim 1 , wherein the panel driver includes:
a representative gray level calculating unit configured to calculate the representative gray level of the input image data;
a driving frequency changing unit configured to output output image data at the first output frame frequency when the input image data do not represent the still image, to output the output image data at the second output frame frequency for the low frequency driving time when the input image data represent the still image, and to output the output image data at the third output frame frequency for the high frequency insertion time corresponding to the representative gray level calculated by the representative gray level calculating unit after the low frequency driving time; and
a data driver configured to provide data signals to the plurality of pixels based on the output image data.

12. The OLED display device of claim 11 , wherein the driving frequency changing unit determines the high frequency insertion time as a first time when the representative gray level is within a high gray range,
wherein the driving frequency changing unit determines the high frequency insertion time as a second time shorter than the first ti

Assignees

• Samsung Display Co Ltd

Inventors

• Kwon Sangan
• Lee Hyojin
• Roh Jinyoung
• Park Sehyuk

Classifications

• G09G2360/12

  Frame memory handling · CPC title

• G09G2320/0247

  Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes · CPC title

• G09G3/3225 Primary

  using an active matrix · CPC title

• G09G3/2007 Primary

  Display of intermediate tones · CPC title

• G09G3/3233

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