LCD overdriving using difference between average values of groups of pixels between two frames

• US 9,449,574 B2
• Filed: 10/09/2013
• Issued: 09/20/2016
• Est. Priority Date: 10/12/2012
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Miyake, Hiroyuki, Shishido, Hideaki, Inoue, Seiko
• Primary Examiner(s): Wang, Quan-Zhen
• Assistant Examiner(s): Dicke, Chad
• Application Number:
  US14/049,300
• Publication Number:
  US 20140104262A1
• Time in Patent Office: 1,077 Days
• US Class Current: 1/1
• CPC Class Codes: G02F 1/1368 in which the switching element is a three-electrode device G02F1/136277 takes precedence
• CPC Class Codes: G09G 2320/0219 Reducing feedthrough effects in active matrix panels, i.e. voltage changes on the scan electrode influencing the pixel voltage due to capacitive coupling
• CPC Class Codes: G09G 3/3614 Control of polarity reversal in general
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3688 suitable for active matrices only
• CPC Class Codes: G09G 3/3696 Generation of voltages supplied to electrode drivers

Abstract

In a video voltage comparator circuit, an average of first video voltages applied to pixel electrodes of pixels in the second-half rows in a k-th frame period (k is a natural number) is compared with an average of second video voltages applied to pixel electrodes of pixels in the first-half rows in a (k+1)th frame period for each row. In an overdrive voltage switching circuit, when a difference obtained from the comparison in the video voltage comparator circuit is greater than or equal to a threshold value, the overdrive voltage in the (k+1)th frame period is switched to a first overdrive voltage, and when the difference obtained from the comparison in the video voltage comparator circuit is less than the threshold value, the overdrive voltage in the (k+1)th frame period is switched to a second overdrive voltage lower than the first overdrive voltage.

Claims

1. A liquid crystal display device comprising:

a pixel portion including pixels arranged in m rows and n columns, where m and n are each a natural number greater than or equal to 2; and

an overdrive voltage generation portion in which an overdrive voltage higher than a video voltage is generated, and the overdrive voltage and the video voltage are applied to a pixel electrode of a pixel during a gate selection period,

wherein the overdrive voltage generation portion comprises;

a video voltage comparator circuit in which an average of first video voltages applied to pixel electrodes of pixels in an (x+1)th row to an m-th row in a k-th frame period is, for each row, compared with an average of second video voltages applied to pixel electrodes of pixels in a first row to an x-th row in a (k+1)th frame period, where x is a natural number greater than 1 and less than m, and where k is a natural number; and

an overdrive voltage switching circuit in which when a difference obtained from a comparison in the video voltage comparator circuit is greater than or equal to a threshold value, the overdrive voltage in the (k+1)th frame period is switched to a first overdrive voltage, and when the difference obtained from the comparison in the video voltage comparator circuit is less than the threshold value, the overdrive voltage in the (k+1)th frame period is switched to a second overdrive voltage lower than the first overdrive voltage,

wherein a pixel density in the pixel portion is higher than or equal to 300 ppi,

wherein an aperture ratio in the pixel is higher than or equal to 60%, and

wherein a capacitor in the pixel comprises a static capacitance of 30 fF or lower,

wherein the video voltage comparator circuit comprises;

a first selection circuit configured to sort data signals input to the first selection circuit for each frame period,

a first storage circuit configured to store a first data signal in one frame period,

a second storage circuit configured to store a second data signal in one frame period,

an arithmetic circuit configured to add the first and second data signals in the respective frame periods, which are stored in the first storage circuit and the second storage circuit and calculate an average,

a comparator circuit configured to calculate a difference between the average of the video voltages in the k-th frame period and the average of the video voltages in the (k+1)th frame period, and compare the difference with a reference voltage which is to be the threshold value, and output a comparison data signal, and

a second selection circuit configured to select a data signal in a frame period during which the overdrive voltage is determined between a data signal data_k in the k-th frame period and a data signal data_k+1 in the (k+1)th frame period, and output the data signal in order to the overdrive voltage switching circuit,

wherein the overdrive voltage switching circuit comprises;

a lookup table address generation circuit for generating a lookup table address indicating a lookup table which stores the overdrive voltage obtained based on inputted the data signal,

a third selection circuit configured to sort the lookup table address in accordance with the compared data signal,

a first lookup table configured to sort a first compensation coefficient corresponding to each bit when the difference is higher than the threshold value, which is necessary for calculating the first overdrive voltage with use of the video voltage,

a second lookup table configured to sort a second compensation coefficient corresponding to each bit when the difference is lower than the threshold value, which is necessary for calculating the second overdrive voltage with use of the video voltage, and

an overdrive voltage arithmetic circuit configured to perform interpolation of the video voltage in accordance with the first compensation coefficient or the second compensation coefficient in order to convert the video voltage into the overdrive voltage.

2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a transflective liquid crystal display device.

3. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a transmissive liquid crystal display device.

4. The liquid crystal display device according to claim 1,

wherein the threshold value is a voltage level of half a video voltage with the maximum grayscale level of a video image signal.

5. An electronic device comprising the liquid crystal display device according to claim 1, wherein the electronic device is selected from the group consisting of a portable information terminal, a cellular phone, and an audio reproducing device.

6. A liquid crystal display device comprising:

a pixel portion including pixels arranged in m rows and n columns, where m and n are each a natural number greater than or equal to 2; and

an overdrive voltage generation portion in which an overdrive voltage higher than a video voltage is generated, and the overdrive voltage and the video voltage are applied to a pixel electrode of a pixel during a gate selection period,

wherein the overdrive voltage generation portion comprises;

a video voltage comparator circuit in which an average of first video voltages applied to pixel electrodes of pixels in an (x+1)th row to an m-th row in a k-th frame period is, for each row, compared with an average of second video voltages applied to pixel electrodes of pixels in a first row to an x-th row in a (k+1)th frame period, where x is a natural number greater than 1 and less than m, and where k is a natural number; and

an overdrive voltage switching circuit in which when a difference obtained from a comparison in the video voltage comparator circuit is greater than or equal to a threshold value, the overdrive voltage in the (k+1)th frame period is switched to a first overdrive voltage, and when the difference obtained from the comparison in the video voltage comparator circuit is less than the threshold value, the overdrive voltage in the (k+1)th frame period is switched to a second overdrive voltage lower than the first overdrive voltage,

wherein the video voltage comparator circuit comprises;

a first selection circuit configured to sort data signals input to the first selection circuit for each frame period,

first storage circuit configured to store a first data signal in one frame period,

a second storage circuit configured to store a second data signal in one frame period,

an arithmetic circuit configured to add the first and second data signals in the respective frame periods, which are stored in the first storage circuit and the second storage circuit and calculate an average,

a comparator circuit configured to calculate a difference between the average of the video voltages in the k-th frame period and the average of the video voltages in the (k+1)th frame period, and compare the difference with a reference voltage which is to be the threshold value, and output a comparison data signal, and

a second selection circuit configured to select a data signal in a frame period during which the overdrive voltage is determined between a data signal data_k in the k-th frame period and a data signal data_k+1 in the (k+1)th frame period, and output the data signal in order to the overdrive voltage switching circuit,

wherein the overdrive voltage switching circuit comprises;

a lookup table address generation circuit for generating a lookup table address indicating a lookup table which stores the overdrive voltage obtained based on inputted the data signal,

a third selection circuit configured to sort the lookup table address in accordance with the compared data signal,

a first lookup table configured to sort a first compensation coefficient corresponding to each bit when the difference is higher than the threshold value, which is necessary for calculating the first overdrive voltage with use of the video voltage,

a second lookup table configured to sort a second compensation coefficient corresponding to each bit when the difference is lower than the threshold value, which is necessary for calculating the second overdrive voltage with use of the video voltage, and

an overdrive voltage arithmetic circuit configured to perform interpolation of the video voltage in accordance with the first compensation coefficient or the second compensation coefficient in order to convert the video voltage into the overdrive voltage, and

wherein a semiconductor layer included in a transistor in the pixel portion comprises an oxide semiconductor layer.

7. The liquid crystal display device according to claim 6,

wherein a pixel density in the pixel portion is higher than or equal to 300 ppi,

wherein an aperture ratio in the pixel is higher than or equal to 60%, and

wherein a capacitor in the pixel portion comprises a static capacitance of 30 fF or lower.

8. The liquid crystal display device according to claim 6, wherein the semiconductor layer comprises a substantially intrinsic semiconductor.

9. The liquid crystal display device according to claim 6, wherein a carrier density of the semiconductor layer is equal to or lower than 1×

10¹⁷/cm³.

10. The liquid crystal display device according to claim 6, wherein the liquid crystal display device is a transflective liquid crystal display device.

11. The liquid crystal display device according to claim 6, wherein the liquid crystal display device is a transmissive liquid crystal display device.

12. The liquid crystal display device according to claim 6, wherein the threshold value is a voltage level of half a video voltage with the maximum grayscale level of a video image signal.

13. An electronic device comprising the liquid crystal display device according to claim 6, wherein the electronic device is selected from the group consisting of a portable information terminal, a cellular phone, and an audio reproducing device.

14. A method for driving a liquid crystal display device comprising pixels arranged in m rows and n columns, where m and n are each a natural number greater than or equal to 2, and performing overdriving in which an overdrive voltage higher than a video voltage is applied to a pixel electrode of a pixel during a gate selection period, and then the video voltage is applied to the pixel electrode,

the method for driving the liquid crystal display device comprising the steps of:

comparing an average of first video voltages applied to pixel electrodes of pixels in an (x+1)th row to an m-th row in a k-th frame period with an average of second video voltages applied to pixel electrodes of pixels in a first row to an x-th row in a (k+1)th frame period for each row, where x is a natural number greater than 1 and less than m, and where k is a natural number in a video voltage comparator circuit comprising a first selection circuit, a first storage, a second storage, an arithmetic circuit, a comparator circuit, and a second selection circuit; and

performing overdriving in the (k+1)th frame period, with use of a first overdrive voltage when a difference obtained from a comparison is greater than or equal to a threshold value, and with use of a second overdrive voltage when the difference obtained from the comparison is less than the threshold value in an overdrive voltage switching circuit comprising a lookup table address generation circuit, a third selection circuit, a first lookup table, a second lookup table, and an overdrive voltage arithmetic circuit,

wherein data signals data input to the first selection circuit are sorted in the first selection circuit for each frame period,

wherein a first data signal is stored in the first storage circuit in one frame period,

wherein a second data signal is stored in the second storage circuit in one frame period,

wherein the first and second data signals in the respective frame periods are added, which are stored in the first storage circuit and the second storage circuit, and an average is calculated in the arithmetic circuit,

wherein a difference between the average of the video voltages in the k-th frame period and the average of the video voltages in the (k+1)th frame period is calculated, and the difference with a reference voltage which is to be the threshold value is compared in the comparator circuit, and output a comparison data signal,

wherein a data signal in a frame period during which the overdrive voltage is determined between the data signal data_k in the k-th frame period and the data signal data_k+1 in the (k+1)th frame period is selected, and the data signal to the overdrive voltage switching circuit is output in the second selection circuit,

wherein a lookup table address indicating the lookup tables which store the overdrive voltage obtained based on the data signal is generated in the lookup table address generation circuit,

wherein the lookup table address in accordance with the comparison data signal is sorted in the third selection circuit,

wherein a first compensation coefficient corresponding to each bit, which is necessary for calculating a first overdrive voltage with use of an video voltage is stored in the first lookup table,

wherein a second compensation coefficient corresponding to each bit, which is necessary for calculating a second overdrive voltage with use of the original video voltage is stored in the second lookup table, and

wherein interpolation of the video voltage in accordance with the first compensation coefficient or the second compensation coefficient is performed in the overdrive voltage arithmetic circuit in order to convert the video voltage into the overdrive voltage.

15. The method for driving a liquid crystal display device, according to claim 14, wherein frame inversion driving is performed in the k-th frame period and the (k+1)th frame period.

16. The method for driving a liquid crystal display device, according to claim 14, wherein source line inversion driving is performed in the k-th frame period and the (k+1)th frame period.

17. The method for driving a liquid crystal display device, according to claim 14, wherein a semiconductor layer included in a transistor in a pixel portion including the pixels comprises an oxide semiconductor layer.

18. The method for driving a liquid crystal display device, according to claim 14,

wherein the threshold value is a voltage level of half a video voltage with the maximum grayscale level of a video image signal.

19. The method for driving a liquid crystal display device, according to claim 14,

wherein a pixel density in the pixel portion is higher than or equal to 300 ppi,

wherein an aperture ratio in the pixel is higher than or equal to 60%, and

wherein a capacitor in the pixel comprises a static capacitance of 30 fF or lower.