DRIVING METHODS FOR ELECTRO-OPTIC DISPLAYS

Abstract

A driving method an electro-optic display having a plurality of display pixels, the method include applying a first set of waveform to a first display pixel, the first set of waveform having at least one active portion configured to affect the optical state of the first display pixel and at least one non-active portion configured not to substantially affect the optical state of the first display pixel. The method also include applying a second set of waveform to a second display pixel, the second set of waveform having at least one active portion configured to affect the optical state of the second display pixel and at least one non-active portion configured not to substantially affect the optical state of the second display pixel, where the at least one active portions of the first and second set of waveforms do not overlap in time.

Claims

1. A method for driving an electro-optic display having a plurality of display pixels, the method comprising: applying a first set of waveform to a first display pixel, the first set of waveform having at least one active portion configured to affect the optical state of the first display pixel and at least one non-active portion configured not to substantially affect the optical state of the first display pixel; and applying a second set of waveform to a second display pixel, the second set of waveform having at least one active portion configured to affect the optical state of the second display pixel and at least one non-active portion configured not to substantially affect the optical state of the second display pixel; wherein the at least one active portions of the first and second set of waveforms do not overlap in time.

2. The method of claim 1, wherein the first and second display pixels are positioned adjacent to one another.

3. The method of claim 1, wherein the at least one active portions of the first and second set of waveform have opposite voltage values.

4. The method of claim 1, wherein the at least one non-active portion of the first set of waveform is a zero volt segment.

5. The method of claim 1, wherein the at least one non-active portion of the second set of waveform is a zero volt segment.

6. The method of claim 1 further comprising applying a third set of waveform to the first and second display pixels, wherein the third set of wave form having at least one active portion configured to affect the optical state of the first and second display pixels and at least one non-active portion configured not to substantially affect the optical state of the first and second display pixels.

7. The method of claim 6 wherein the at least one active portions of the first, second and third set of waveforms do not overlap in time.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0033] FIG. 1 illustrates a top view of a display pixel in accordance with the subject matter disclosed herein;

[0034] FIG. 2 illustrates exemplary driving Voltage Lists in accordance with the subject matter disclosed herein;

[0035] FIG. 3 illustrates alternative embodiments of the Voltage Lists illustrated in FIG. 2 for reducing pixel voltage shifts in accordance with the subject matter presented herein;

[0036] FIG. 4 illustrates a top view of a display pixel with a T-wire line in accordance with the subject matter presented herein;

[0037] FIG. 5 illustrates an exemplary driving Voltage List for the T-wire Line in accordance with the subject matter presented herein; and

[0038] FIG. 6 illustrates further embodiments of Voltage Lists in accordance with the subject matter presented herein.

DETAILED DESCRIPTION

[0039] As indicated above, the present invention provides driving methods for electro-optic displays where crosstalk can be reduced. Such driving methods may include portions or segments where zero volt potential or bias is applied to a pixel electrode, in another word, during such portion or segment, the pixel electrode does not experience an optical shift or change.

[0040] It should be firstly appreciated that the methods described herein may be applied to an electro-optic display comprising a layer of electro-optic medium disposed on the backplane and covering the pixel electrode. Such an electro-optic display may use any of the types of electro-optic medium previously discussed or commonly adopted in the industry, for example, the electro-optic medium may be a liquid crystal, a rotating bichromal member or electrochromic medium, or an electrophoretic medium, preferably an encapsulated electrophoretic medium. In some embodiments, when an electrophoretic medium is utilized, a plurality of charged particles can move through a suspending fluid under the influence of an electric field. Such electrophoretic displays can have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption when compared with liquid crystal displays.

[0041] FIG. 1 illustrates a top view of an exemplary display pixel 100 using a TFT as means for switching. The pixel 100 can include a gate line 102 functioning as a source line to the display pixel and configured to supply switching signals to a pixel electrode 104. A data line 106 may be electrically coupled to the pixel electrode 104 and the gate line 102 for supplying driving signals (e.g., waveforms) or a voltage list to the pixel electrode 104. Voltage list are referred to herein as a set of waveforms or voltage values applied to the pixel over a period of time to effect the optical transition of the pixel from one gray level to a desired final gray level. Similarly, another data line 108 may be positioned adjacent to the pixel electrode 104 on an opposite side from the data line 104 for providing driving waveforms to a neighboring pixel electrode (not shown). From the top view illustrated in FIG. 1A, the data lines 106 and 108 are separated from the pixel electrode 104 by gap spaces 116 and 118 respectfully.

[0042] In operation, when the display pixel 100 is being addressed (i.e., pixel TFT in conduction), driving voltage signals (i.e., waveforms) or voltage lists are transferred from the data line 106 to the pixel electrode 104. However, problems can arise when while the display pixel 100 is being driven with one set of voltage list (e.g., Voltage list A or waveform A 200 illustrated in FIG. 2) and the adjacent pixel (not shown) is driven by another set of voltage list or waveform (e.g., Voltage list B or waveform B 202). This driving configuration, because of the overlapping of different waveform or voltage values present in the two data liens 106 and 108, will cause differentiating and disruptive capacitive couplings and/or cross-talks between the data lines 106, 108 and the pixel electrode 104, which in term resulting in the voltage values of the pixel electrode 104 to shift in an undesired fashion, causing image artifacts such as streaking.

[0043] As described above, the capacitive coupling between the data lines 106, 108 and the pixel electrode 104 creates undesirable cross-talks and such cross-talks can lead to unwanted voltage shifts that in turn will lead to unwanted optical transitions. One way to reduce such crosstalk and/or voltage shift is by time shift the voltage lists supplied through one of the data lines (e.g., date line 106) (e.g., to avoid the overlapping of the different voltage values in adjacent data lines), which is described in more details below.

[0044] FIG. 2 illustrates two exemplary voltage lists A and B discussed above that may be transmitted or supplied to display pixels using the data lines presented in FIG. 1. In use, an electro-optic display such as an electrophoretic display will typically have multiple rows and columns of display pixels, where each row or column of display pixels may share a gate line (e.g., gate line 102 illustrated in FIG. 1) and may be activated by this gate line. For the purpose of explaining the concepts illustrated herein, Voltage List A 200 may be a set of waveforms applied to a first column of display pixels to bring the pixels to a desired grayscale level, and Voltage list B 202 may be a set of voltages applied to a second column of display pixels. As shown in FIG. 2, Voltage lists A 200 and B 202 are to be transmitted with a time frame T1 to the pixel rows A and B. In operation, pixel rows A or B will be selectively turned on and off during this time frame T1 while data line 106 transmits the corresponding voltage list to the selected pixel row. However, cross talk and voltage shifts will occur under such bias scheme even when both columns are selected and driven, the waveforms being transmitted through the data line 106 and 108 will have different values and overlap in time and resulting in unwanted crosstalk.

[0045] To remedy such deficiency in the display driving scheme, FIG. 3 illustrates a shifting of the voltage lists shown in FIG. 2 in accordance with the subject matter disclosed herein for the purpose of reducing the crosstalk. In practice, each set of waveform or voltage list can include at least one active portion configured to change or affect the optical state of the display pixel, and at least one non-active portion configured not to substantially affect or change the optical of the display pixel. In some embodiments, the non-active portions may be a zero volt segment where no waveform or voltage bias is applied to the pixel. In an exemplary configuration shown in FIG. 3, a segment of the zero volts are added to segment 2, or the active portion, of voltage list A, effectively creating a new voltage list A2. Similarly, a segment of zero volts are added to segment 1, also the active portion, of voltage list B, effectively creating the new voltage list B2, where such zero volt segment causes almost no optical transition or grayscale shift in the pixel. It should be appreciated that this is possible to do with electrophoretic displays (EPD) because the physical nature of the EPDs dictates that even under a zero bias potential across the EPD's display medium, its display pixels are capable of maintaining their prior optical states. In this fashion, bias voltages from the original voltage lists A and B may be separated in time, and as such, cross-talks and voltage shifts in pixel electrodes may be greatly reduced. In practice, the voltage lists in each segments may be determined through a selection process tailored to each electro-optic displays.

[0046] In some other embodiments, a TFT backplane for driving an electrophoretic display may comprise an additional bias line (e.g., T-wire line) as illustrated in FIG. 4. The T-wire line may be configured to connect the source driver outputs to data lines. FIG. 5 illustrates an exemplary Voltage List C that may be applied through the T-wire line to selectively switch the rows of display pixels. This Voltage List C, when applied during the same time frame as the Voltage List A and B, will introduce additional voltage shifts to the display pixels. Similar to the configuration illustrated in FIG. 3, the Voltage List C may be time shifted such that its active biasing portion is at a different time segment from Voltage List A and B. Accordingly, capacitive coupling due to Voltage List C may be minimized.

[0047] In practice, the voltage list applied to the t-wire will be applied to both the display pixel 104 and its adjacent display pixel (not shown). In this case, all three voltage lists discussed above (i.e., voltage lists A, B, and C) may be time shifted such that their active portions do not overlap each other in the time domain. FIG. 6 illustrate a such driving scheme where three voltage lists are time shifted, such that the non-zero driving or active portions of the driving lists are separated in the time domain (e.g., Voltage list A3 in segment 2, Voltage list B3 in segment 1, and Voltage list C3 in segment 3) to reduce crosstalk. It should be appreciated that the concept illustrated herein may be conveniently adopted to driving schemes with a large number of voltage lists (e.g., 256), where each voltage list may be time shifted to reduce crosstalk.

[0048] It will be apparent to those skilled in the art that numerous changes and modifications can be made in the specific embodiments of the invention described above without departing from the scope of the invention. Accordingly, the whole of the foregoing description is to be interpreted in an illustrative and not in a limitative sense.