WO2006090315A2

WO2006090315A2 - Electrophoretic display panel showing reset image

Info

Publication number: WO2006090315A2
Application number: PCT/IB2006/050523
Authority: WO
Inventors: Mark T. Johnson
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2005-02-22
Filing date: 2006-02-17
Publication date: 2006-08-31
Also published as: WO2006090315A3; KR20070106006A; CN101128862A; JP2008537159A; TW200634689A

Abstract

The display panel (1) for displaying an image has a plurality of pixels (2) having optical states, and a controller (10,11,100) for controlling an image update to the image. For the display panel (1) to be able to display an increased information content, the controller (10,11,100) is arranged to provide the pixels (2) with reset optical states for resetting the pixels (2) during at least part of the image update, thereby displaying a reset image representing reset image information, and subsequently to provide the pixels (2) with optical states for displaying the image representing image information, the reset image being unrelated to the image.

Description

Display panel

The invention relates to a display panel for displaying an image. The invention also relates to a display device comprising such a display panel. The invention further relates to a controller for such a display panel, a method for driving such a display panel, and a method of selling information and/or display time of the information for such a display panel.

A display panel of the type mentioned in the opening paragraph is an electrophoretic display panel. Electrophoretic display panels in general are based on the motion of charged, usually colored particles in a fluid under the influence of an electric field between electrodes. With these display panels, dark or colored characters can be imaged on a light or colored background, and vice versa. Electrophoretic display panels are therefore notably used in display devices taking over the function of paper, referred to as "paper white" applications, e.g. electronic newspapers and electronic diaries.

An electrophoretic display panel is disclosed in US 6,704,113. The disclosed electrophoretic display panel has a plurality of pixels. Each pixel has particles, which are able to occupy extreme positions near the electrodes of the respective pixel and intermediate positions in between the electrodes of the respective pixel. Each pixel has an optical state depending on the position of the particles. The optical state depends on the potential difference received by the electrodes and on the history of the respective potential difference. The controller is arranged to control the potential differences to reset the pixels, which reduces the dependency on the history. As a result the particles are brought in extreme positions and the pixels have mutually equal reset optical states. Then the display panel shows, e.g. for black particles in a white fluid, a black or white image. Subsequently, the controller is arranged to control the potential differences to provide the pixels with optical states for displaying the image representing image information. However, the information content displayed in this way is relatively low. It is an object of the invention to provide a display panel of the kind mentioned in the opening paragraph, which is able to display an increased information content.

To achieve this object, the invention provides a display panel for displaying an image comprising - a plurality of pixels having optical states, and

- a controller for controlling an image update to the image, the controller being arranged

- to provide the pixels with reset optical states for resetting the pixels during at least part of the image update, thereby displaying a reset image representing reset image information, and subsequently

- to provide the pixels with optical states for displaying the image representing image information, the reset image being unrelated to the image.

The invention is based on the insight that the reset image can represent information content while being unrelated to the image. The information content may e.g. relate to advertisement information. This is in contrast to the electrophoretic display panel disclosed in US 6,704,113, where the reset image is black or white, not representing information content.

This is also in contrast to the electrophoretic display panel disclosed in WO2004/034366-A1, where the display panel displays an estimate of the image as the reset image. Then the observer perceives a relatively smooth transition via the estimate of the image to the image. However, the reset image, although representing information content, is not unrelated to the image.

Resetting a pixel can e.g. be considered as bringing the pixel in a state, e.g. an extreme optical state, from which a next state can accurately be obtained. Therefore, resetting is part of the image update.

In an embodiment the controller is arranged to provide the pixels with optical states for displaying a previous image representing previous image information prior to providing the pixels with reset optical states for resetting the pixels, the reset image being unrelated to the previous image. Then the reset image is displayed between the previous image and the image, i.e. during part of an image update.

The reset image information may comprise any informative image information or decorative image information. In an embodiment the reset image information comprises advertisement image information. Then the reset image can be exploited to insert an un- requested, e.g. by the viewer, advertisement image as the reset image between the previous image and the image. In this manner, the reset image forms the basis of a business model for selling information for e.g. e-books, e-newspapers, e-magazines, with guaranteed advertising exposure, as the advertisement image will appear every time a page is changed or after a predefined number of page changes. As an example, the duration of displaying the reset image may be predefined. In a variation on the embodiment a duration of displaying the reset image is adjustable.

In another embodiment the display panel is an electrophoretic display panel wherein each pixel comprises an electrophoretic medium comprising charged particles in a fluid, the optical state of each pixel depends on a position of the particles in the pixel, and the controller comprises drive means and, for each pixel, electrodes for receiving a potential difference, the drive means being arranged

- to provide reset potential differences for providing the pixels with reset optical states and subsequently,

- to provide image potential differences for providing the pixels with optical states for displaying the image. In this kind of display panel updating an image is relatively simply achieved by applying potential differences to the electrodes. In a variation on the embodiment the reset potential differences have adjustable durations, which is a relatively simple way of incorporating the business model. The particles may move in a plane substantially parallel of the viewer, so-called in plane motion, or in a plane substantially perpendicular to the viewer, so-called vertical motion. In an example of both embodiments for each pixel the charged particles are able to occupy a position being one of extreme positions near the electrodes and intermediate positions in between the electrodes. If, furthermore, for each pixel the reset potential difference has a reset value and a reset duration for enabling the particles to substantially occupy one of the extreme positions, the dependency of the optical states of the pixels on the history of the potential differences is reduced. The particles substantially occupy an extreme position e.g. if the particles are present at the surface of the electrode. However, then it may still occur that some particles, having a negligible contribution to the optical state, are not present at the surface of the electrode. Furthermore, it will be clear that, if the number of particles is so large that not all particles can be present at the surface of the electrode, a portion of the particles can in its extreme only occupy a position near the particles at the surface of the electrode.

In a variation on the embodiment for at least a number of the pixels the reset potential differences have additional reset durations. The number of the pixels is denoted by subset. For each pixel of the subset the driving force driving particles towards one of the extreme positions is present for a relatively long time interval, resulting in a reduced dependency of the optical state of the pixel on the history.

Furthermore, it has been observed that particularly additional reset durations larger than one tenth of a reference duration largely reduce the dependency of the optical states of the pixels on the history. The reference duration of a pixel is equal to a duration to change the position of the particles of the pixel from one of the extreme positions to the other one of the extreme positions. Therefore, it is favorable, if each additional reset duration is larger than one tenth of a reference duration, the reference duration being equal to a duration to change the position of the particles of the respective pixel from one of the extreme positions to the other one of the extreme positions.

It is also favorable, if, for each pixel of the number of pixels the respective reset duration and the respective additional reset duration have a respective sum being substantially equal to a constant. Then the reset potential differences can be controlled relatively simply by the drive means. It is furthermore favorable, if for each pixel of the number of pixels the respective potential difference is a sequence of preset potential differences prior to being the reset potential difference, the sequence of preset potential differences having preset values and associated preset durations, the preset values in the sequence alternating in sign, each preset potential difference representing a preset energy sufficient to release particles present in one of the extreme positions from their position but insufficient to enable said particles to reach the other one of the extreme positions. As an advantage, the sequences of preset potential differences reduce the dependency of the optical states of the pixels on the history of the potential differences.

Electrophoretic display panels can form the basis of a variety of applications where information may be displayed, for example in the form of information signs, public transport signs, advertising posters, pricing labels, billboards etc.

Another aspect of the invention provides a display device comprising the display panel as claimed in claim 1 and a circuitry to provide image information to the display panel.

Another aspect of the invention provides a controller for a display panel, the display panel for displaying an image comprising a plurality of pixels having optical states, the controller for controlling an image update to the image being arranged - to provide the pixels with reset optical states for resetting the pixels during at least part of the image update, thereby displaying a reset image representing reset image information, and subsequently

- to provide the pixels with optical states for displaying the image representing image information, the reset image being unrelated to the image. Another aspect of the invention provides a method for driving a display panel, the display panel for displaying an image comprising a plurality of pixels having optical states, the method comprising the steps of

- providing the pixels with reset optical states for resetting the pixels during at least part of the image update, thereby displaying a reset image representing reset image information, and subsequently

- providing the pixels with optical states for displaying the image representing image information, the reset image being unrelated to the image.

In an embodiment the reset image information comprises advertisement image information and a duration of displaying the reset image is adjustable. In a variation on the embodiment the duration of displaying the reset image is provided by a server associated with a service provider. In a variation on the embodiment the server selects the duration of displaying the reset image based on an amount of money paid to the service provider.

Another aspect of the invention provides a method of selling information and/or display time of the information for a display panel, the information comprising reset image information, the display panel for displaying an image comprising

- a plurality of pixels having optical states, and

- a controller, the controller being arranged - to provide the pixels with reset optical states for resetting the pixels, thereby displaying a reset image representing the reset image information, and subsequently

The mere fact that certain measures are mentioned in different claims does not indicate that a combination of these measures cannot be used to advantage.

These and other aspects of the display panel of the invention will be further elucidated and described with reference to the drawings, in which: Figure 1 shows diagrammatically a front view of an embodiment of the display panel;

Figure 2 shows diagrammatically a cross-sectional view along II-II in Figure 1, the cross-sectional view representing a layout of the pixel; Figure 3 shows diagrammatically a cross-sectional view along III-III in Figure

2;

Figure 4 shows diagrammatically an other layout of the pixel;

Figures 5A-5C shows elements of an image update: Figure 5A shows a previous image; Figure 5B shows a reset image; Figure 5C shows an image; and Figure 6 shows schematic drive waveforms illustrating two methods to increase the duration of the reset image.

In all the Figures corresponding parts are referenced to by the same reference numerals.

Figures 1-3 show an example of the display panel 1 having a first substrate 8, a second transparent opposed substrate 9 and a plurality of light modulating elements 2, being pixels 2. Preferably, the pixels 2 are arranged along substantially straight lines in a two-dimensional structure. Other arrangements of the pixels 2 are possible, e.g. a honeycomb arrangement. In an active matrix embodiment, the pixels 2 may further comprise switching electronics, for example, thin film transistors (TFTs), diodes, MIM devices or the like.

The pixel 2 has an electrophoretic medium 5. The electrophoretic medium 5, having charged particles 6 in a fluid, is present between the substrates 8,9. Electrophoretic media 5 are known per se from e.g. US 2002/0180688. The particles 6 and the fluid have dissimilar optical properties. The particles 6 may have any color, whereas the fluid may have any color different from the color of the particles 6 or may be transparent. Examples of the color of the particles 6 are for instance red, green, blue, yellow, cyan, magenta, white or black. The particles 6 may be large enough to scatter light, or small enough to substantially not scatter light. The fluid may for example be a liquid or a gas. The pixel 2 has a viewing surface 91 for being viewed by a viewer.

Furthermore, the barriers 514 forming pixel walls separate the pixel 2 from its environment. The optical state of the pixel 2 depends on the position of the particles 6.

In transmissive mode, the optical state of the pixel 2 is determined by the portion of the visible spectrum incident on the pixel 2 at the side 92 of the first substrate 8 that survives the cumulative effect of traversing through the first substrate 8, medium 5 and the second substrate 9. In reflective mode, the optical state of the pixel 2 is determined by the portion of the visible spectrum incident on the pixel 2 at the side of the second substrate 9 that survives the cumulative effect of traversing through the second substrate 9, medium 5, subsequently interacting with surface 15 of the first substrate 8 which may be reflective or have any color and subsequently traversing back through medium 5 and the second substrate 9.

If the fluid is substantially non-contributing to the optical state of the pixel 2, the amount and color of the light transmitted by medium 5 is controlled by the position and color of the particles 6. When the particles 6 are positioned in the path of the light that enters the pixel 2, the particles 6 absorb or scatter a selected portion of the light and the remaining light is transmitted. When the particles 6 are substantially removed from the path of the light entering the pixel 2, the light can pass through the pixel 2 and emerge without significant visible change. The light seen by the viewer, therefore, depends on the distribution of particles 6 in the pixel 2.

The controller is arranged to provide the pixels 2 with reset optical states for resetting the pixels 2, thereby displaying a reset image representing reset image information, and subsequently to provide the pixels 2 with optical states for displaying the image representing image information, the reset image being unrelated to the image. The controller has for each pixel 2 electrodes 10,11 for receiving a potential difference. Furthermore, the controller has drive means 100 being arranged to control the potential differences. In this case, each one of the electrodes 10,11 has a substantially flat surface 110,111 facing the medium 5. Furthermore, in this layout the electrodes 10,11 are arranged to enable the particles 6 to move in a plane parallel to the viewing surface 91. Another example of a pixel layout is shown in Figure 4. In Figure 4 the first substrate 8 has for each pixel 2 a first electrode 10, and the second substrate 9 has for each pixel 2 a second electrode 11. In this case, each one of the electrodes 10,11 has a substantially flat surface 110,111 facing the medium 5. Furthermore, in this layout the electrodes 10,11 are arranged to enable the particles 6 to move in a plane perpendicular to the viewing surface 91. Each pixel 2 has an optical state, being one of a first and a second extreme optical state and intermediate optical states between the first and the second extreme optical states. As an example, the electrophoretic medium 5 comprises negatively charged black particles 6 in a white fluid. When the charged particles 6 are positioned near the first electrode 10 due to a potential difference of 15 Volts, the pixel 2 has a first extreme optical state, i.e. white. When the charged particles 6 are positioned near the second electrode 11, due to a potential difference of opposite polarity, i.e. -15 Volts, the pixel 2 has a second extreme optical state, i.e. black. The intermediate optical states, e.g. light gray and dark gray, are gray levels between white and black, and may be obtained by providing the particles 6 with a different energy (energy is defined as the product of potential difference and time duration of the potential difference).

Furthermore, the controller is arranged to provide the pixels 2 with optical states for displaying a previous image representing previous image information prior to providing the pixels 2 with reset optical states for resetting the pixels, the reset image being unrelated to the previous image. Figures 5A-5C show an example. In Figure 5 A, showing inter alia a drawing of a man and some text, the pixels 2 have optical states for displaying a previous image representing previous image information. Subsequently, the drive means 100 apply reset potential differences to the pixels 2 for providing the pixels 2 with reset optical states, thereby displaying a reset image representing reset image information. The reset image is shown in Figure 5B and represents advertisement information: in this case the Philips logo. Subsequently, the drive means 100 apply image potential differences for providing the pixels 2 with optical states for displaying the image. The image, a bottle and two glasses, is shown in Figure 5C. The reset image is unrelated to both the previous image and the image. In this example the resetting of the pixels is made highly visible. In this case, the reset has the function of introducing extra displayed information between the erasing of the previous image and the writing of the image. The image update sequence is therefore (see Figures 5A- 5C): previous image -> reset image -> image. The reset image may be a purely 1-bit image (could also be 1 bit per color in a display panel with a color filter arrangement or a stacked display panel with one colored particle type in each layer), whilst the previous image and the image will in general contain more bits of information. The reset image may be exploited to insert an un-requested (advertising) image between 2 desired images. In this manner, the reset image could form the basis of a business model for selling e-books/e-newspapers/e- magazines with guaranteed advertising exposure (as the advertising image will appear every time a page is changed). In an electrophoretic display panel according to the prior art, an image is generally updated by comparing the content of the image with the (stored) previous image on a pixel-by-pixel basis, and defining a driving waveform for all possible optical transitions. For example, in a 2-bit display panel, there are 16 waveforms to account for all possible transitions from any of the 4 brightness levels in the previous image to any of the 4 brightness levels in the image. No further image waveforms are required, since the reset state is always uniquely defined - by either the image (in the electrophoretic display panel disclosed in WO2004/034366-A1), or by the fact that every reset image is the same (in the electrophoretic display panel disclosed in US 6,704,113). In the electrophoretic display panel according to the invention, extra driving waveforms and image memory are required. A possible approach to image update is:

• Compare the content of the previous image, the (1 bit) reset image and the image. This requires an additional image memory - the memory will however be small (as the image is only 1 bit). • Define for each pixel 2 a driving waveform depending upon this comparison.

As each reset optical state can be randomly either black or white, this means that additional driving waveforms are required. In the most simple situation, the number of driving waveforms is doubled - one set for each possible reset optical state (from 16 to 32 in the example of a 2-bit display panel described above). • Apply the drive waveform to each pixel 2 whereby the reset image will appear as required between the previous image and the image.

In another embodiment, the reset potential differences will be situated as close to the start of the driving waveform as is possible, to ensure that the reset image appears as quickly as possible and to maximize its visibility. In prior art waveforms, reset potential differences are often delayed to either smooth the image transition or for other reasons (i.e. to reduce cross-talk).

It may be desired to vary the duration of the reset image, depending upon e.g. the amount of money paid by the individual advertiser. This feature may be part of a business model. Increasing the reset time can be realized by either introducing a non-driven period to the waveform after the reset image is created, or alternatively by increasing the duration of the reset potential difference in the waveform (for example by increasing the frame period during this part of the waveform) - see Figure 6. It has been observed that an increased reset duration is beneficial to the image quality (as it reduces image retention and ghosting) and as such this approach may be preferred.

In general, the quality of the image in an electrophoretic display panel 1 decreases slightly after the image has been written and the power turned off (i.e. when the display panel 1 is in its bistable state) - for example the black and white pixels 2 become slightly grayer. In order to restore the image quality to its desired level, use is made of a so- called image refresh, where the same image is re-written to the display panel 1. This may occur after a given period of time. In an embodiment a reset (advertising) image is inserted into the image refresh sequence. Again, the frequency of the image update can be related to the amount of money paid by the individual advertiser, a higher cost resulting in a shorter time period between refreshes, e.g. as part of a business model.

Whilst the above embodiments have been described in relation to an electrophoretic display panel 1 based on e.g. E-newspapers, they are be also applicable to other display panels which may make use of resetting the pixels during image update, for example ferro-electric liquid crystal displays, MEMs based displays (such as moving foil displays or rolling foil displays), electrochromic displays or electro-wetting displays.

Claims

CLAIMS:

1. A display panel (1) for displaying an image comprising

- a plurality of pixels (2) having optical states, and

- a controller (10,11,100) for controlling an image update to the image, the controller (10,11,100) being arranged - to provide the pixels (2) with reset optical states for resetting the pixels (2) during at least part of the image update, thereby displaying a reset image representing reset image information, and subsequently

- to provide the pixels (2) with optical states for displaying the image representing image information, the reset image being unrelated to the image.

2. A display panel (1) as claimed in claim 1 characterized in that the controller (10,11,100) is arranged to provide the pixels (2) with optical states for displaying a previous image representing previous image information prior to providing the pixels (2) with reset optical states for resetting the pixels (2), the reset image being unrelated to the previous image.

3. A display panel (1) as claimed in claim 1 characterized in that the reset image information comprises advertisement image information.

4. A display panel (1) as claimed in claim 1 characterized in that a duration of displaying the reset image is adjustable.

5. A display panel (1) as claimed in claim 1 characterized in that each pixel (2) comprises an electrophoretic medium (5) comprising charged particles (6) in a fluid, the optical state of each pixel (2) depends on a position of the particles (6) in the pixel (2), and the controller (10,11,100) comprises drive means (100) and, for each pixel (2), electrodes (10,11) for receiving a potential difference, the drive means (100) being arranged

- to provide reset potential differences for providing the pixels (2) with reset optical states and subsequently, - to provide image potential differences for providing the pixels (2) with optical states for displaying the image.

6. A display panel (1) as claimed in claim 5 characterized in that the reset potential differences have adjustable durations.

7. A display panel (1) as claimed in claim 5 characterized in that for each pixel (2) the charged particles (6) are able to occupy a position being one of extreme positions near the electrodes (10,11) and intermediate positions in between the electrodes (10,11).

8. A display panel (1) as claimed in claim 7 characterized in that for each pixel (2) the reset potential difference has a reset value and a reset duration for enabling the particles (6) to substantially occupy one of the extreme positions.

9. A display panel (1) as claimed in claim 8 characterized in that for at least a number of the pixels (2) the reset potential differences have additional reset durations.

10. A display panel (1) as claimed in claim 9 characterized in that each additional reset duration is larger than one tenth of a reference duration, the reference duration being equal to a duration to change the position of the particles (6) of the respective pixel (2) from one of the extreme positions to the other one of the extreme positions.

11. A display panel (1) as claimed in claim 9 characterized in that for each pixel (2) of the number of pixels (2) the respective reset duration and the respective additional reset duration have a respective sum being substantially equal to a constant.

12. A display panel (1) as claimed in claim 8 characterized in that for each pixel (2) of the number of pixels (2) the respective potential difference is a sequence of preset potential differences prior to being the reset potential difference, the sequence of preset potential differences having preset values and associated preset durations, the preset values in the sequence alternating in sign, each preset potential difference representing a preset energy sufficient to release particles (6) present in one of the extreme positions from their position but insufficient to enable said particles (6) to reach the other one of the extreme positions.

13. A display device comprising the display panel (1) as claimed in claim 1 and a circuitry to provide image information to the display panel (1).

14. A controller for a display panel (1), the display panel (1) for displaying an image comprising a plurality of pixels (2) having optical states, the controller for controlling an image update to the image being arranged

- to provide the pixels (2) with reset optical states for resetting the pixels (2) during at least part of the image update, thereby displaying a reset image representing reset image information, and subsequently - to provide the pixels (2) with optical states for displaying the image representing image information, the reset image being unrelated to the image.

15. A method for driving a display panel (1), the display panel for displaying an image comprising a plurality of pixels (2) having optical states, the method comprising the steps of

- providing the pixels (2) with reset optical states for resetting the pixels (2) during at least part of the image update, thereby displaying a reset image representing reset image information, and subsequently

- providing the pixels (2) with optical states for displaying the image representing image information, the reset image being unrelated to the image.

16. A method as claimed in claim 15 characterized in that the reset image information comprises advertisement image information and a duration of displaying the reset image is adjustable.

17. A method as claimed in claim 16 characterized in that the duration of displaying the reset image is provided by a server associated with a service provider.

18. A method as claimed in claim 17 characterized in that the server selects the duration of displaying the reset image based on an amount of money paid to the service provider.

19. A method of selling information and/or display time of the information for a display panel (1), the information comprising reset image information, the display panel (1) for displaying an image comprising

- a plurality of pixels (2) having optical states, and - a controller (10,11,100), the controller (10,11,100) being arranged

- to provide the pixels (2) with reset optical states for resetting the pixels (2), thereby displaying a reset image representing the reset image information, and subsequently