Cholesteric liquid crystal display and driving method thereof

Abstract

A cholesteric liquid crystal display and a driving method thereof. The driving method of the cholesteric liquid crystal display includes the following steps. First, a cholesteric liquid crystal display panel is provided, which has a pixel matrix including a plurality of pixel strings. Next, an update operation is performed on at least one of the plurality of pixel strings, and a sustain voltage is applied to the pixel string. Then, the sustain voltage is switched to 0 V in a gradual manner.

Description

TECHNICAL FIELD

[0001] The present application relates to a liquid crystal display and a driving method thereof, and more particularly, to a driving method of a cholesteric liquid crystal display and a cholesteric liquid crystal display using the same. BACKGROUND

[0002] A cholesteric liquid crystal display is a display device using cholesteric liquid crystals. The cholesteric liquid crystals have bistable characteristics, and have two stable states in a natural state. Therefore, the cholesteric liquid crystal display can maintain a displayed content without power consumption, thereby saving energy. In addition, the cholesteric liquid crystal display has high brightness, high contrast, power saving, storage, wide viewing angle, and no flicker, and is successfully applied to various electronic products (e.g., an electronic book).

[0003] Conventionally, the cholesteric liquid crystal display is updated in a full screen using pulse width modulation (PWM), a dynamic driving scheme (DDS), or another suitable method. When a frame is updated, a scan line is updated column by column. For example, in the dynamic driving scheme (DDS), updating one scan line includes three phases of reset / preparation, selection / evolution, and non-selection. In the preparation phase, a pixel is reset to clear a previous state of the liquid crystal. In the selection phase, the pixel liquid crystal is selected by a data line. In the evolution phase, an electric field is applied to the pixel liquid crystal to change a mixture ratio of a transmissive state and a reflective state, thereby displaying a gray scale with different reflectance. In the non-selection phase, a fixed level of a sustain (anchor) voltage is applied to the pixel liquid crystal to maintain a stable state of the liquid crystal.

[0004] However, since the sustain (anchor) voltage applied to each scan line is reduced to 0 V after the full screen is updated, the cholesteric liquid crystal molecules are often changed due to a pressure drop, and thus a white flicker occurs at a switching instant after each frame is updated, thereby affecting an overall visual effect of the frame.

[0005] Therefore, there is a need to provide an advanced driving method of a cholesteric liquid crystal display and a cholesteric liquid crystal display using the same, to solve the problems of the related art. SUMMARY

[0006] An embodiment of the present disclosure is to provide a driving method of a cholesteric liquid crystal display. The driving method of the cholesteric liquid crystal display includes the following steps. First, a cholesteric liquid crystal display is provided, which has a pixel matrix including a plurality of pixel strings. Then, at least one of the plurality of pixel strings is subjected to an update operation, and a sustain voltage is applied to the pixel string. Then, the sustain voltage is switched to 0 V in a gradual manner.

[0007] Another embodiment of the present disclosure is to provide a cholesteric liquid crystal display, which includes a pixel matrix and a driving circuit. The pixel matrix includes a plurality of pixel strings. The driving circuit is configured to: subject at least one of the plurality of pixel strings to an update operation, and apply a sustain voltage to the pixel string; and switch the sustain voltage to 0 V in a gradual manner.

[0008] According to the above-mentioned embodiments, the present disclosure provides a driving method of a cholesteric liquid crystal display and a cholesteric liquid crystal display using the driving method. After the plurality of pixel strings in the pixel matrix are subjected to the update operation, the stable sustain (anchor) voltage used to maintain the liquid crystal state is switched to 0 V in a gradual manner. Thus, the switching moment after each frame of picture is updated is improved, the white flash phenomenon caused by the strong change of the sustain (anchor) voltage is reduced, and the overall visual effect of the picture on the screen of the cholesteric liquid crystal display is improved. BRIEF DESCRIPTION OF DRAWINGS

[0009] In order to better understand the above and other aspects of the present disclosure, the following embodiments are described in detail below with reference to the accompanying drawings:

[0010] Figure 1 FIG. 1 is a schematic diagram of a cholesteric liquid crystal display according to an embodiment of the present disclosure;

[0011] Figure 2 FIG. 2 is a flowchart of a driving method of a cholesteric liquid crystal display according to an embodiment of the present disclosure;

[0012] Figure 3A FIG. 3 is a timing diagram of a voltage applied to a common electrode when a pixel string of a pixel matrix is subjected to an update operation according to an embodiment of the present disclosure;

[0013] Figure 3B FIG. 4 is a timing diagram of a voltage applied to a pixel string when a single pixel string is subjected to an update operation according to an embodiment of the present disclosure; Figure 3A

[0014] Figure 4 ​is a timing chart showing a pulse voltage applied to the common electrode and the plurality of segment electrodes and a cross voltage therebetween when a sustain (anchor) voltage applied to the pixel string is switched to 0 V according to an embodiment of the present specification; and

[0015] Figure 5 is a timing chart showing a pulse voltage applied to the common electrode and the plurality of segment electrodes and a cross voltage therebetween when a sustain (anchor) voltage applied to the pixel string is switched to 0 V according to another embodiment of the present specification.

[0016] BRIEF DESCRIPTION OF DRAWINGS

[0017] 100: cholesteric liquid crystal display device

[0018] 101: display panel

[0019] 101M: pixel matrix

[0020] 101S1, 101S2,... 101Sm: pixel string

[0021] 102: drive circuit

[0022] 102A: controller

[0023] 102B: power supply

[0024] 102C: common driver

[0025] 102S: segment driver

[0026] 301: reset period

[0027] 301a: wait period

[0028] 302: selection period

[0029] 302a: address selection period

[0030] 302b: hold period

[0031] 303: non-selection period

[0032] 304: time interval

[0033] COM1, COM2,... COMm: common electrode

[0034] SEG1, SEG2,... SEGn: segment electrode

[0035] P11, P12,... Pmn: pixel

[0036] S202: providing a cholesteric liquid crystal display

[0037] S204: performing an update operation on at least one of the pixel string lines, and applying a sustain voltage to the pixel string line.

[0038] S206: switching the sustain voltage to 0V in a gradual manner.

[0039] S208: turning off the power supply, and completing the update of one frame of picture. DETAILED DESCRIPTION

[0040] The present specification provides a cholesteric liquid crystal display driving method and a cholesteric liquid crystal display using the same, which can improve the white flash phenomenon at the switching moment of each frame of picture and the overall visual effect of the screen picture. In order to make the above-mentioned embodiments and other purposes, features and advantages of the present specification more obvious and easy to understand, the following preferred embodiments are described in detail with reference to the accompanying drawings.

[0041] However, it should be noted that these specific embodiments and methods are not intended to limit the present application. The present application can also be implemented using other features, elements, methods and parameters. The preferred embodiments are only used to illustrate the technical features of the present application and are not intended to limit the claims of the present application. Those skilled in the art will make equivalent modifications and changes without departing from the scope of the present application based on the description in the following specification. In different embodiments and drawings, the same elements will be represented by the same element symbols.

[0042] Please refer to Figure 1 , Figure 1 is a device schematic diagram of a cholesteric liquid crystal display 100 according to an embodiment of the present specification. In some embodiments of the present specification, the cholesteric liquid crystal display device 100 includes a display panel 101 and a driving circuit 102, which includes a controller 102A, a power supply 102B, a common driver 102C and a segment driver 102S.

[0043] The display panel 101 has a plurality of common electrodes (row electrodes) COM1, COM2... COMm and a plurality of segment electrodes (column electrodes) SEG1, SEG2... SEGn. The common electrodes COM1, COM2... COMm and the segment electrodes SEG1, SEG2... SEGn are arranged alternately with each other, and a cholesteric liquid crystal layer (not shown) is arranged between the common electrodes COM1, COM2... COMm and the segment electrodes SEG1, SEG2... SEGn.

[0044] Thus, a plurality of pixels P11, P12...Pmn can be defined at the intersections of the common electrodes COM1, COM2...COMm and the segment electrodes SEG1, SEG2...SEGn. A plurality of pixels (e.g., pixels P11, P12...P1n) defined by the same common electrode (e.g., common electrode COM1) form a pixel string (e.g., pixel string 101S1). A plurality of pixel strings (e.g., m pixel strings 101S1, 101S2...101Sm) form the pixel matrix 101M of the display panel 101.

[0045] The display panel 101 displays an image according to the potential difference between the common electrodes COM1, COM2...COMm and the segment electrodes SEG1, SEG2...SEGn. In one embodiment, for example, the common drivers COM1, COM2...COMm are coupled to the common electrodes COM1, COM2...COMm of the display panel 101 via a plurality of scan lines 103, respectively, to transmit a select signal SS or a non-select signal NSS to the common electrodes COM1, COM2...COMm. The segment drivers 102S are coupled to the segment electrodes SEG1, SEG2...SEGn of the display panel 101 via a plurality of data lines 104, respectively, to transmit a display signal DS to the segment electrodes SEG1, SEG2...SEGn in response to the select signal SS or the non-select signal NSS output by the common drivers 102C. The rotation direction of the liquid crystal of the selected pixel is determined according to the potential difference between the common electrodes COM1, COM2...COMm and the segment electrodes SEG1, SEG2...SEGn of each group of the intersecting arrangement (i.e., the potential difference between the select signal SS or the non-select signal NSS and the display signal DS). Thus, the image data is written into the pixel matrix 101M of the display panel 101 to form a frame of image for the display panel 101 to display as an image.

[0046] Subsequently, the display panel is updated by the driving circuit 102 (e.g., in a dynamic driving scheme (DDS)) to switch more frames of image and display a dynamic image on the display panel 101. Please refer to Figure 2 , Figure 2 is a flow chart of a driving method of a cholesteric liquid crystal display 100 according to one embodiment of the present specification.

[0047] In some embodiments of the present disclosure, the cholesteric liquid crystal display driving method comprises the following steps: first, as shown in step S202, providing a cholesteric liquid crystal display panel. For example, the display panel 101 of the cholesteric liquid crystal display 100 shown in FIG. 1 is provided, which has a pixel matrix 101M comprising a plurality of pixel strings (for example, m pixel strings 101S1, 101S2...101Sm).

[0048] Next, as shown in step S204, at least one pixel string (for example, m pixel string 101S1) of the plurality of pixel strings (for example, m pixel strings 101S1, 101S2...101Sm) is subjected to an update operation, and a holding voltage is applied to the pixel string 101S1. In some examples of the present disclosure, only a part (or parts) of the pixel strings in the pixel matrix 101M can be subjected to the update operation, and the holding voltage is substantially between 2V and 10V. In the present embodiment, all the pixel strings (for example, m pixel strings (for example, m pixel strings 101S1, 101S2...101Sm)) in the pixel matrix 101M are subjected to the update operation one by one.

[0049] And after the selection stage of the update operation of each pixel string (for example, pixel string 101S1), a fixed level (for example, 5V) holding (anchoring) voltage is applied to the pixels (for example, pixels P11, P12...P1n) of the same pixel string (for example, pixel string 101S1) through the corresponding common electrode (for example, common electrode COM1) and the corresponding segment electrode (for example, segment electrodes SEG1, SEG2...SEGn), so as to keep the liquid crystal state of the pixels (for example, pixels P11, P12...P1n) stable. In other embodiments, the holding (anchoring) voltage can be substantially between 2V and 10V.

[0050] For example, please refer to Figure 3A and Figure 3B , Figure 3A is a timing diagram showing the application of the common electrodes COM1, COM2...COMm when the m pixel strings 101S1, 101S2...101Sm of the pixel matrix 101M are subjected to the update operation according to an embodiment of the present disclosure. As shown in FIG. 2, the common electrodes COM1, COM2...COMm are applied with a voltage of 0V during the selection stage of the update operation of each pixel string (for example, pixel string 101S1), and a fixed level (for example, 5V) holding (anchoring) voltage is applied to the pixels (for example, pixels P11, P12...P1n) of the same pixel string (for example, pixel string 101S1) through the corresponding common electrode (for example, common electrode COM1) and the corresponding segment electrode (for example, segment electrodes SEG1, SEG2...SEGn), so as to keep the liquid crystal state of the pixels (for example, pixels P11, P12...P1n) stable. Figure 3AAs shown, the update operation of each pixel string 101S1, 101S2...101Sm includes (but is not limited to) a reset period 301 (including a wait period 301a), a selection period 302 (including an address selection (dressing) period 302a and a hold period 302b), and a non-selection period 303. The drive circuit 102 applies the update voltage to the common electrode COM1 one by one in a staggered order according to the length of the selection period 302 of each pixel string 101S1, 101S2...101Sm.

[0051] Taking the update operation of pixel string 101S1 as an example, please refer to... Figure 3B , Figure 3B It is based on Figure 3A The diagram illustrates the voltage timing applied to pixel string 101S1 during a single pixel string (e.g., pixel string 101S1) update operation. In this embodiment, the voltage applied to pixel string 101S1 during reset period 301 is ±40V for 120 milliseconds (ms), and a wait period 301a with a voltage of 0V for 120 milliseconds is included before selection period 302. During address selection period 302a (6.2 ms) of selection period 302, the voltage applied to pixel string 101S1 is ±20V. During hold period 302b of selection period 302 and the subsequent non-selection period 303 (250 ms), the voltage applied to pixel string 101S1 is ±5V. The ±5V voltage is used as a stable maintenance (anchoring) voltage to maintain the liquid crystal state of pixels (e.g., pixels P11, P12...P1n).

[0052] After the update operation, as described in step S206, the sustaining (anchoring) voltage is gradually switched to 0V. For example, in this embodiment, after each pixel string 101S1, 101S2...101Sm completes the update operation, the multiple sustaining (anchoring) voltages applied to each pixel string 101S1, 101S2...101Sm can be gradually switched from ±5V to 0V in a proportionally decreasing manner during a time interval 304 between 0.2 seconds and 60 seconds. Figure 3B (As shown).

[0053] The switching of the sustain (anchor) voltages is not limited to this. For example, in some embodiments of the present disclosure, the sustain (anchor) voltages applied to each of the pixel string lines 101S1, 101S2,... 101Sm can be sequentially switched from ±5V to 0V one by one after the update operation is performed on each of the pixel string lines 101S1, 101S2,... 101Sm. In other embodiments of the present disclosure, the sustain (anchor) voltages applied to the plurality of pixel string lines 101S1, 101S2,... 101Sm can be divided into groups of pixel string lines. For example, every ten pixel string lines (e.g., pixel string lines 101S1-101S10, 101S11-101S20,... 101Sm-9-101Sm) can be divided into a group, and all of the pixel string lines 101S1, 101S2,... 101Sm participating in the update operation can be divided into m / 10 groups of pixel string lines.

[0054] Thereafter, one of the m / 10 groups of pixel string lines is selected, and the sustain (anchor) voltages applied to the ten pixel string lines (e.g., pixel string lines 101S1-101S10) in the selected first group of pixel string lines are synchronously switched from ±5V to 0V. Subsequently, another group is sequentially selected, and the sustain (anchor) voltages applied to the ten pixel string lines (e.g., pixel string lines 101S11-101S20) in the selected second group of pixel string lines are synchronously switched from ±5V to 0V. This process is repeated until all of the sustain (anchor) voltages applied to the pixel string lines 101S1, 101S2,... 101Sm are switched from ±5V to 0V.

[0055] Please refer to Figure 4 , Figure 4 FIG. 13 is a timing diagram showing the pulse voltages applied to the common electrode COM1 and the plurality of segment electrodes SEG1, SEG2,... SEGn (e.g., segment electrode SEG1) and the cross-voltage therebetween when the sustain (anchor) voltage applied to the pixel string line (e.g., pixel string line 101S1) is switched to 0V, according to an embodiment of the present disclosure. In this embodiment, during the non-selection period 303 after the update operation is completed, the pulse voltage applied to the segment electrode SEG1 is ±10V, the pulse voltage applied to the common electrode COM1 is ±5V, and the cross-voltage difference therebetween is ±5V, which can serve as the sustain (anchor) voltage for the update operation.

[0056] As Figure 4As shown, after the update operation is completed, the step of switching the sustain (anchor) voltage applied to the pixel array 101S1 to 0V during the time interval 304 includes maintaining the pulse voltage applied to the multiple signal lines 104 (segment electrodes SEG1, SEG2...SEGn) at ±10V during the time interval 304; and gradually increasing the pulse voltage applied to the scan line 103 (common electrode COM1) (in a proportional or non-proportional manner) until the voltage across the multiple signal lines 104 (segment electrodes SEG1, SEG2...SEGn) and the scan line 103 (common electrode COM1) is gradually switched to 0V.

[0057] Please refer to Figure 5 , Figure 5 According to another embodiment of this specification, a timing diagram is shown of the pulse voltages applied to the common electrode COM1 and multiple segment electrodes SEG1, SEG2...SEGn (taking segment electrode SEG1 as an example), and the voltage difference between them, when the sustain (anchoring) voltage applied to the pixel string (e.g., pixel string 101S1) is switched to 0V. In this embodiment, during the non-selection period 303 after the update operation is completed, the pulse voltage applied to the segment electrode SEG1 is ±10V, the pulse voltage applied to the common electrode COM1 is ±5V, and the voltage difference between them is ±5V, which can be used as the sustain (anchoring) voltage for the update operation.

[0058] like Figure 5 As shown, after the update operation is completed, the step of switching the sustain (anchor) voltage applied to the pixel array 101S1 to 0V in time interval 304 includes reducing the pulse voltage applied to the multiple signal lines 104 (segment electrodes SEG1, SEG2...SEGn) to 0V in time interval 304; and gradually reducing the pulse voltage applied to the scan line 103 (common electrode COM1) (in a proportional or non-proportional manner) until the voltage across the multiple signal lines 104 (segment electrodes SEG1, SEG2...SEGn) and the scan line 103 (common electrode COM1) is gradually switched to 0V.

[0059] Subsequently, as described in step S208: power supply 102B is turned off to complete the update of one frame.

[0060] According to the above-mentioned embodiments, the present specification provides a cholesteric liquid crystal display driving method and a cholesteric liquid crystal display 100 using the driving method. After updating a plurality of pixel strings 101S1, 101S2...101Sm in a pixel matrix 101M of a display panel 101, the stable maintaining (anchoring) voltage used to maintain the liquid crystal state of pixels P11, P12...Pmn is switched to 0V in a gradual manner, thereby improving the overall visual effect of the screen picture of the display panel 101 of the cholesteric liquid crystal display 100 after the switching moment of each frame picture after updating, and improving the white flash phenomenon caused by the strong change of the maintaining (anchoring) voltage.

[0061] Although the present application has been disclosed in preferred embodiments as above, it is not intended to limit the present application, and any person skilled in the art can make some changes and modifications without departing from the concept and scope of the present application, and therefore the protection scope of the present application shall be subject to the claims.

Claims

1. A method for driving a cholesteric liquid crystal display, comprising: providing a cholesteric liquid crystal display panel having a pixel matrix comprising a plurality of pixel strings; performing an update operation on at least one of the plurality of pixel strings and applying a sustain voltage to the at least one of the plurality of pixel strings; and switching the sustain voltage to 0 V in a gradual manner.

2. The driving method of a cholesterol liquid crystal display device as claimed in claim 1, wherein the step of switching the sustain voltage to 0 V in the gradual change manner comprises: synchronously switching a plurality of the sustain voltages applied to the plurality of pixel strings to 0 V in the gradual manner.

3. The driving method of a cholesterol liquid crystal display device as claimed in claim 1, wherein the step of switching the sustain voltage to 0 V in the ramping manner comprises: switching the sustain voltage applied to each of the plurality of pixel strings to 0 V in the gradual manner one by one.

4. The method for driving a cholesteric liquid crystal display of claim 1, wherein the step of switching the sustain voltage to 0 V in the gradual manner comprises: classifying the plurality of pixel strings after the update operation into a plurality of groups of pixel strings; and synchronously switching a plurality of the sustain voltages applied to one of the plurality of groups of pixel strings to 0 V in the gradual manner; and then synchronously switching a plurality of the sustain voltages applied to another of the plurality of groups of pixel strings to 0 V in the gradual manner.

5. The method for driving a cholesteric liquid crystal display of claim 1, wherein the pixel matrix further comprises a plurality of signal lines and at least one scan line, respectively electrically connected to the at least one of the plurality of pixel strings; and the step of switching the sustain voltage to 0 V in the gradual manner comprises: wherein maintaining a plurality of pulse voltages applied to the plurality of signal lines; and gradually increasing a pulse voltage applied to the at least one scan line until a cross voltage between each of the plurality of signal lines and the at least one scan line is 0 V.

6. The method for driving a cholesteric liquid crystal display of claim 1, wherein the pixel matrix further comprises a plurality of signal lines and at least one scan line, respectively electrically connected to the at least one of the plurality of pixel strings; and the step of switching the sustain voltage to 0 V in the gradual manner comprises: wherein decreasing a plurality of pulse voltages applied to the plurality of signal lines to 0 V; and gradually decreasing a pulse voltage applied to the at least one scan line until a cross voltage between each of the plurality of signal lines and the at least one scan line is 0 V. switching the sustain voltage from ±5 V to 0 V in a time interval between 0.2 seconds and 60 seconds.

7. The driving method of a cholesterol liquid crystal display device as claimed in claim 1, wherein the step of switching the sustain voltage to 0 V in the ramping manner comprises: switching the sustain voltage from ±5 V to 0 V in a proportional gradual manner.

8. The driving method of a cholesterol liquid crystal display device as claimed in claim 1, wherein the step of switching the sustain voltage to 0 V in the ramping manner comprises: switching the sustain voltage from ±5 V to 0 V in a non-proportional gradual manner.

9. The driving method of a cholesterol liquid crystal display device as claimed in claim 1, wherein the step of switching the sustain voltage to 0 V in the gradual change manner comprises:

10. A cholesteric liquid crystal display, comprising: a cholesteric liquid crystal display panel having a pixel matrix comprising a plurality of pixel strings; and a driving circuit configured to: perform an update operation on at least one of the plurality of pixel strings and apply a sustain voltage to the at least one of the plurality of pixel strings; and switch the sustain voltage to 0 V in a gradual manner.

11. The cholesteric liquid crystal display of claim 10, further comprising: a plurality of signal lines, respectively electrically connected to the at least one of the plurality of pixel strings; and at least one scan line electrically connected to the at least one of the plurality of pixel strings; and wherein the step of switching the sustain voltage to 0 V in the gradual manner comprises: ​ ​ ​ maintaining a plurality of biases applied to the plurality of signal lines; and gradually lowering a bias applied to the at least one scan line until a cross voltage between each of the plurality of signal lines and the at least one scan line is 0 V.

12. The cholesterol liquid crystal display of claim 10, further comprising: a plurality of signal lines electrically connected to the at least one pixel string, respectively; and at least one scan line electrically connected to the at least one pixel string; wherein the step of switching the sustain voltage to 0 V in the gradual manner comprises: lowering the plurality of biases applied to the plurality of signal lines to 0 V; and gradually lowering a bias applied to the at least one scan line until a cross voltage between each of the plurality of signal lines and the at least one scan line is 0 V.

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