WO2006079957A1

WO2006079957A1 - Display driver

Info

Publication number: WO2006079957A1
Application number: PCT/IB2006/050221
Authority: WO
Inventors: Guofu Zhou; Harrie Brunklaus; Jan Van De Kamer; Mark T. Johnson
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2005-01-25
Filing date: 2006-01-20
Publication date: 2006-08-03
Also published as: CN101107648A; JP2008529052A; EP1844463A1

Abstract

The method of driving a display of the invention comprises the step of supplying a plurality of driving waveforms for updating an image. The supply of respective ones of the plurality of driving waveforms is started in respective ones of successive periods of time. At least a subsequent subset of the plurality of driving waveforms is supplied for one or more subsequent pixels and each of the one or more subsequent pixels is closer to an opposite side of the image than one or more previous pixels for which a previous one of the subsequent subset of driving waveforms was supplied. The display driver of the invention performs the method of the invention. The control software of the invention is operative to enable a display driver to perform the method of the invention. The display panel of the invention comprises the display driver of the invention. The electronic device of the invention comprises the display panel of the invention.

Description

Display driver

The invention relates to a display driver, a display panel comprising such a driver, an electronic device comprising such a display panel, a method of driving a display, and control software operative to enable a display driver to perform a method of driving a display. The display may be, for example, a bistable display.

A display device of the type mentioned in the opening paragraph is known from international patent application WO 99/53373. This patent application discloses an electronic ink display (further also referred to as E- ink display) which comprises two substrates. One substrate is transparent, the other substrate is provided with electrodes arranged in rows and columns. Display elements or pixels are associated with intersections of the row and column electrodes. Each display element is coupled to the column electrode via a main electrode of a thin- film transistor (further also referred to as TFT). A gate of the TFT is coupled to the row electrode. This arrangement of display elements, TFTs and row and column electrodes jointly forms an active matrix display device.

Each pixel comprises a pixel electrode which is the electrode of the pixel connected to the column electrodes via the TFT. During an image update or image refresh period, a row driver is controlled to select all the rows of display elements one by one, and the column driver is controlled to supply data signals in parallel with the selected row of display elements via the column electrodes and the TFTs. The data signals correspond to image data to be displayed on the matrix display device.

Furthermore, an electronic ink is provided between the pixel electrode and a common electrode provided on the transparent substrate. The electronic ink is thus sandwiched between the common electrode and the pixel electrodes. The electronic ink comprises multiple microcapsules of about 10 to 50 microns. Each microcapsule comprises positively charged white particles and negatively charged black particles suspended in a fluid. When a positive voltage is applied to the pixel electrode, the white particles move to the side of the microcapsule directed to the transparent substrate, and the display element appears white to a viewer. Simultaneously, the black particles move to the pixel electrode at the opposite side of the microcapsule where they are hidden from the viewer. By applying a negative voltage to the pixel electrode, the black particles move to the common electrode at the side of the microcapsule directed to the transparent substrate, and the display element appears dark to a viewer. When the electric field is removed, the display device remains in the acquired state and exhibits a bistable character. This electronic ink display with its black and white particles is particularly useful as an electronic book.

Grey scales can be created in the display device by controlling the amount of particles that move to the common electrode at the top of the microcapsules. For example, the energy of the positive or negative electric field, defined as the product of field strength and time of application, controls the amount of particles moving to the top of the microcapsules.

A drawback of the known display device is the frequent occurrence of flashing and/or optical flicker.

It is an object of the invention to reduce the visibility of flashing and/or optical flicker.

A first aspect of the invention provides a display driver comprising a processor operative to supply a plurality of driving waveforms for updating an image, wherein the supply of respective ones of the plurality of driving waveforms is started in respective ones of successive periods of time, at least a subsequent subset of the plurality of driving waveforms being supplied for one or more subsequent pixels, each of the one or more subsequent pixels being closer to an opposite side of the image than one or more previous pixels for which a previous one of the subsequent subset of driving waveforms was supplied. The inventors have recognized that optical flicker or flashing appears as shaking effects during page transition because complicated driving waveforms are usually needed for various optical transitions to reduce image artefacts or ghosting. The image update time, i.e. the time to turn a page, is typically 1 to 2 seconds. The invention reduces these shaking effects by creating an intentional video effect, hereinafter called 'wave moving' effect. This effect can be achieved in a matrix display by intentionally introducing a delay pixel by pixel or line by line in an image update, which is visibly longer than a natural line time available in the matrix display.

This 'wave moving' effect preferably provides the same feeling as turning a page in a conventional paper book or newspaper. A page can be turned, for example, from left to right, from right to left, from the top-right corner to the bottom- left corner, or from the bottom-right corner to the top-left corner. For example, the waves can start from the first line on the right and move gradually to the left across the page when a line-by-line delay time is sequentially introduced, and can start from the first pixel in the top-right corner and gradually move in the diagonal direction to the bottom- left corner when a sequential pixel-by-pixel delay time is used. Supply of each driving waveform or supply of each group of driving waveforms (e.g. one group per line of pixels) may start at a different time. 'Wave moving' effects other than a conventional page turning effect may be provided. For example, the image update may start at all edges of the image and proceed to the centre of the image, or it may start at the centre of the image and proceed to all edges of the image. The subset of the plurality of driving waveforms may comprise all driving waveforms of the plurality of driving waveforms, but this is not necessary. The subset only needs to be large enough to create the 'wave moving' effect.

In an embodiment of the display driver of the invention, specific ones of the plurality of driving waveforms are supplied in one or more first ones of the successive periods of time, the specific ones being driving waveforms for image transitions towards a grey scale. Driving waveforms for image transitions towards a grey scale are generally the longest waveforms. By supplying these in one or more first ones of the successive periods of time, e.g. at the beginning of the image update, the increase in total image update time can be limited. Additionally or alternatively, the specific ones may be driving waveforms for image transitions occurring relatively infrequently. Delay of frequently occurring image transitions has been determined to be sufficient to create a 'wave moving' effect.

The specific ones of the plurality of driving waveforms may comprise driving waveforms for all image transitions except white-to-white image transitions. White-to-white image transitions occur frequently in electronic books and newspapers.

The display driver may limit a duration of the successive periods of time based on a user-specified period of time. The 'wave moving' effect is intensified with an increased delay time, but also results in a longer refresh time for updating the entire page. It is therefore further beneficial that selection of a personalized total delay time is enabled, with, for example, a default value of about 1 second, similar to reading a conventional paper book.

The order in which the driving waveforms are supplied may be user- programmable. The user may be able to select a certain 'wave moving' effect that he prefers, thereby possibly reducing a perceived delay in the image update. The display driver may determine a period of time for starting supply of a specific one of the driving waveforms in dependence upon a length of the specific driving waveform. By having driving waveforms end, for example, in a specific one of the periods of time, instead of start in a specific one of the periods of time, the 'wave moving' effect can be enhanced.

The display may be a bistable display, e.g. an electrophoretic display or a reflective cholesteric display. This type of display, used in e-Books, seems to be most affected by the occurrence of optical flicker and flashing. However, the display could also be a conventional display, e.g. the one used in most televisions. A second aspect of the invention provides a display panel comprising the display driver.

A third aspect of the invention provides an electronic device comprising the display panel. The electronic device may be, for example, an e-Book, a PDA, a mobile phone, a television, or a computer monitor.

These and other aspects of the invention will be further elucidated and described with reference to the drawings, in which:

Fig. 1 is a diagrammatic cross-section of a portion of an electrophoretic display;

Fig. 2 shows diagrammatically an electronic device with an equivalent circuit diagram of a portion of the electrophoretic display of Fig. 1;

Fig. 3 is a schematic representation of an active matrix display; Fig. 4 illustrates a first embodiment of the method of the invention; Fig. 5 illustrates a second embodiment of the method of the invention;

Fig. 6 illustrates a third embodiment of the method of the invention; Fig. 7 illustrates a fourth embodiment of the method of the invention; Corresponding elements in the drawings are identified by the same reference numerals.

Fig. 1 is a diagrammatic cross-section of a portion of an electrophoretic display panel 1 which, for example, has the size of a few display elements. The electrophoretic display panel 1 comprises a base substrate 2, an electrophoretic film with an electronic ink which is present between two transparent substrates 3 and 4 of, for example, polyethylene. One of the substrates 3 is provided with transparent picture electrodes 5, 5' and the other substrate 4 is provided with a transparent counter electrode 6. The electronic ink comprises multiple microcapsules 7 of about 10 to 50 microns. The microcapsules 7 do not need to be ball-shaped; any other shape, such as, for example, predominantly rectangular, is possible. Each microcapsule 7 comprises positively charged black particles 8 and negatively charged white particles 9 suspended in a fluid. The dashed material is a polymeric binder. The particles 8 and 9 may have colors other than black and white. It is only important that the two types of particles 8, 9 have different optical properties and different charges, such that they act differently on an applied electric field. The layer 3 is not necessary, or could be a glue layer. When a negative voltage is applied to the counter electrode 6 with respect to the picture electrodes 5, an electric field is generated which moves the black particles 8 to the side of the microcapsule 7 directed to the counter electrode 6, and the display element will appear dark to a viewer. Simultaneously, the white particles 9 move to the opposite side of the microcapsule 7 where they are hidden from the viewer. By applying a positive field between the counter electrodes 6 and the picture electrodes 5, the white particles 9 move to the side of the microcapsule 7 directed to the counter electrode 6, and the display element will appear white to a viewer (not shown). When the electric field is removed, the particles 7 remain in the acquired state and the display exhibits a bistable character and consumes substantially no power.

Fig. 2 shows diagrammatically an equivalent circuit of the display panel 1 comprising an electrophoretic film laminated on the base substrate 2 provided with active switching elements 19, a row driver 16 and a column driver 10. The counter electrode 6 is preferably provided on the film comprising the encapsulated electrophoretic ink, but the counter electrode 6 could be alternatively provided on a base substrate if operation of the display is based on using in-plane electric fields. The display panel 1 is driven by active switching elements, which, for example, are thin- film transistors (TFTs) 19. The display panel 1 comprises a matrix of display elements at the area of intersecting row or selection electrodes 17 and column or data electrodes 11. The row driver 16 consecutively selects the row electrodes 17, while a column driver 10 provides data signals to the column electrodes 11 for the selected row electrode 17. Preferably, a processor 15 first processes incoming data 13 to the data signals to be supplied by the column electrodes 11.

The control lines 12 and 12' convey signals that control the mutual synchronization between the column driver 10 and the row driver 16. Select signals from the row driver 16 which are electrically connected to the row electrodes 17 select the pixel electrodes 22 via the gate electrodes 20 of the thin-film transistors 19. The source electrodes 21 of the thin- film transistors 19 are electrically connected to the column electrodes 11. A data signal present at the column electrode 11 is transferred to the pixel electrode 22 of the display element 18 (also referred to as pixel) coupled to the drain electrode of the TFT. In the embodiment shown, the display device of Fig.1 further comprises an optional capacitor 23 at the location of each display element 18. This optional capacitor 23 is connected between the pixel electrodes 22 of the associated pixel 18 and one or more storage capacitor lines 24. Instead of a TFT, other switching elements can be applied such as diodes, MIMs, etc. The processor 15 is operative to supply a plurality of driving waveforms for updating an image. The supply of respective ones of the plurality of driving waveforms is started in respective ones of successive periods of time. At least a subsequent subset of the plurality of driving waveforms is supplied for one or more subsequent pixels. Each of the one or more subsequent pixels is closer to an opposite side of the image than one or more previous pixels for which a previous one of the subsequent subset of driving waveforms was supplied. In an electronic device that comprises the display panel 1, an image-processing circuit 25 is present which receives the input data signal IV to supply images as the incoming data 13 to the processor 15.

Fig. 3 illustrates an active matrix display, consisting of m columns (e.g. 800 columns) and n lines (e.g. 600 lines). In an image refresh period, e.g. upon page turning, the active matrix display is scanned from the pixels Pl l to P12 ... Plm, P21, P22 ... Pnm, line by line in every frame with a typical frame time of 20ms, corresponding to a line time of about 33us (=20ms/6001ines). Multiple frames are usually required as the driving waveforms are typically 1000 to 2000ms long. These driving waveforms usually consist of multiple portions like pre-set pulses, over-reset pulses, resulting in a long waveform with flashing or optical flicker in an image update. Methods such as column or line inversion can be applied to reduce the amount of flashing, but these methods are found to be inadequate to achieve a level that consumers feel as really comfortable. Creating a 'wave moving' effect, e.g. a feature that is familiar to a user reading a conventional paper book, can reduce this flashing. A delay is intentionally introduced pixel by pixel or line by line in an image update, which is significantly longer than a natural line time available in the matrix display.

In a first embodiment, a line-by-line delay is introduced, which is schematically shown in Fig. 4. The image update starts from the first line by executing all waveforms for all pixels on the first line. The waveforms for all pixels on line 2 to line n are not executed in the subsequent scans. The waveforms for all pixels on line 2 start to be executed when the delay time thas elapsed and the waveforms for all pixels on line 3 to line n are not executed in the subsequent scans. The execution of waveforms for the pixels on line 1 is continued in every subsequent frame. Similarly, the waveforms for all pixels on line 3 start to be executed when the delay time 2xtL has elapsed and the waveforms for all pixels on line 4 to line n are not executed in the subsequent scans. The execution of waveforms for the pixels on line 1, line 2 is continued in every subsequent frame. The same procedure is repeated for subsequent lines until line n is treated. The update of the entire display is complete when the last frame of the longest waveforms for the pixels on the last line is updated. The waves thus start from the first line on the right and move gradually to the left across the page, as indicated in Fig. 4 (the lower part), when the display is used as a portrait book. Assuming that a total delay time of 1.2 seconds from right to left is requested by a user and the number of lines on the display is 600, a constant line delay time X_L will be about 2ms (=1200ms/6001ines). It is also possible to define variable delay times from line to line to create more user-desired features.

In a second embodiment, the wave moving effect is realized by delaying blocks of lines as illustrated in Fig. 5 with a fixed frame time. In this example, a block of 10 lines is used with a total delay time fa) of 20ms, i.e. one frame time, equivalent to a delay time of 2ms per line. The image update starts from the first block consisting of lines 1 to 10 by executing all waveforms for all pixels on the first 10 lines. The waveforms for all pixels on line 11 to line n are not executed in the subsequent scans. The waveforms for all pixels on lines 11 to 20 (second block of lines) start to be executed when the delay time tF has elapsed and the waveforms for all pixels on line 21 to line n are not executed in the subsequent scans. The execution of waveforms for the pixels on lines 1 to 10 is continued in every subsequent frame. Similarly, the waveforms for all pixels on lines 21 to 30 start to be executed when the delay time 2xtF has elapsed and the waveforms for all pixels on line 31 to line n are not executed in the subsequent scans. The execution of waveforms for the pixels on lines 1 to 10, lines 11 to 20 is continued in every subsequent frame. The same procedure is repeated for the next block of 10 lines till the line n is treated. In this way, the waves start from the first block of 10 lines on the right and move gradually to the left across the page, as indicated in Fig. 5 (the lower part). Assuming that a total delay time of 1.2 seconds from right to left is requested by a user and the number of lines on the display is 600, a constant delay time tF will be about 20ms for a block of 10 lines (=1200ms/60block), which, advantageously, is exactly one (standard) frame time. In a third embodiment, a pixel-by-pixel delay is introduced, which is schematically shown in Fig. 6. The image update starts from the first pixel Pl 1 by executing the waveform for the pixel in the top-right corner. The waveforms for all other pixels are not executed in the subsequent scans. The waveforms for pixels Pl 2 and P21 start to be executed when the delay time tphas elapsed and the waveforms for all other pixels, which have not been started in previous scans, are not executed in the subsequent scans. Similarly, the waveforms for pixels Pl 3, P31 and P22 start to be executed when the delay time 2xtphas elapsed and the waveforms for all other pixels, which have not been started in previous scans, are not executed in the subsequent scans. The same procedure is repeated for subsequent pixels till the last pixel Pnm is treated. The update of the entire display is complete when the last pixel is completely updated. The waves thus start from the top-right corner and move gradually to the bottom- left corner across the page, as indicated in Fig. 6 (the lower part), when the display is used as a portrait book. Assuming that a total delay time of 2 seconds from the top-right corner to the bottom- left corner is requested by a user and the number of pixels along the diagonal direction lines is 1000, a constant pixel delay time tp will be about 2ms (=2000ms/1000pixels). Alternatively, a sequential order PI l, P12, P13...PIm, P21, P22,

P23...P2m, P31, P32, P33...P3m, , Pnm may also be considered and used with a large sequential delay time between the pixels. It is also possible to define variable delay times from pixel to pixel, to create more user-desired features. In a fourth embodiment, the wave moving effect is realized by delaying blocks of pixels as illustrated in Fig. 7 with a fixed frame time. In this example, a block of 10 pixels along the diagonal direction is used with a total delay time fa) of 20ms, i.e. one frame time, equivalent to a delay time of 2ms per pixel. The image update starts from the first block of pixels BPl by executing the waveforms for the block of pixels in the top-right corner. The waveforms for all other pixels are not executed in the subsequent scans. The waveforms for pixels BP2 start to be executed when the delay time tF has elapsed and the waveforms for all other pixels, which have not been started in previous scans, are not executed in the subsequent scans. Similarly, the waveforms for pixel block BP3 start to be executed when the delay time 2xtF has elapsed and the waveforms for all other pixels, which have not been started in previous scans, are not executed in the subsequent scans. The same procedure is repeated for the next group or block of pixels till the last pixel group BP_nZ10 is treated. The waves start from the top-right corner and move gradually to the bottom- left corner across the page, as indicated in Fig. 7 (the lower part). Assuming that a total delay time of 2 seconds from the top-right corner to the bottom- left corner is requested by a user and the number of pixels along the diagonal direction lines is 1000, a constant delay time tF for a block of 10 pixels will be about 20ms (=2000ms/100blocks), which is, advantageously, exactly one normal frame time.

It is also possible to supply the waveforms without any delay for the pixels with an optical transition requiring the longest driving waveforms, so that the "wave moving" effect is created and the refresh time for updating the entire page is not significantly prolonged. Waveforms for image transitions towards a grey scale are usually the longest. It has been experimentally observed that in every page update, 50 to 60% of the entire display often requires the white-to-white transition. The length of the waveform for white-to-white transition is usually about half the longest driving waveform. It is therefore possible to only delay the update of the waveform for white-to-white transition, sequentially pixel by pixel, avoiding a significant increase of the refresh time.

While the invention has been described in connection with preferred embodiments, it will be understood that modifications thereof within the principles outlined above will be evident to those skilled in the art, and thus the invention is not limited to the preferred embodiments but is intended to encompass such modifications. The invention resides in each and every novel characteristic feature and each and every combination of characteristic features. Reference numerals in the claims do not limit their protective scope. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements other than those stated in the claims. Use of the article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

'Means', as will be apparent to a person skilled in the art, are meant to include any hardware (such as separate or integrated circuits or electronic elements) or software (such as programs or parts of programs) which perform in operation or are designed to perform a specified function, be it solely or in conjunction with other functions, be it in isolation or in co-operation with other elements. The invention can be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the apparatus claim enumerating several means, several of these means can be embodied by one and the same item of hardware. 'Control software' is to be understood to mean any software product stored on a computer-readable medium, such as a floppy disk, downloadable via a network, such as the Internet, or marketable in any other manner.

Claims

CLAIMS:

1. A display driver (15, 10, 16) comprising a processor (15) operative to supply a plurality of driving waveforms for updating an image, wherein the supply of respective ones of the plurality of driving waveforms is started in respective ones of successive periods of time, at least a subsequent subset of the plurality of driving waveforms being supplied for one or more subsequent pixels, each of the one or more subsequent pixels being closer to an opposite side of the image than one or more previous pixels for which a previous one of the subsequent subset of driving waveforms was supplied.

2. A display driver (15, 10, 16) as claimed in claim 1, wherein specific ones of the plurality of driving waveforms are supplied in one or more first ones of the successive periods of time, the specific ones being driving waveforms for image transitions towards a grey scale.

3. A display driver (15, 10, 16) as claimed in claim 1, wherein specific ones of the plurality of driving waveforms are supplied in one or more first ones of the successive periods of time, the specific ones being driving waveforms for image transitions occurring relatively infrequently.

4. A display driver (15, 10, 16) as claimed in claim 3, wherein the specific ones of the plurality of driving waveforms comprise driving waveforms for all image transitions except white-to-white image transitions.

5. A display driver (15, 10, 16) as claimed in claim 1, wherein the display driver (15, 10, 16) limits a duration of the successive periods of time based on a user-specified period of time.

6. A display driver (15, 10, 16) as claimed in claim 1, wherein the display driver (15, 10, 16) determines a period of time for starting the supply of a specific one of the driving waveforms in dependence upon a length of the specific driving waveform.

7. A display driver (15, 10, 16) as claimed in claim 1, wherein the display (1) is a bistable display.

8. A display panel comprising the display driver (15, 10, 16) of claim 1.

9. An electronic device comprising the display panel of claim 8.

10. A method of driving a display ( 1 ), comprising the step of supplying a plurality of driving waveforms for updating an image, wherein the supply of respective ones of the plurality of driving waveforms is started in respective ones of successive periods of time, at least a subsequent subset of the plurality of driving waveforms being supplied for one or more subsequent pixels, each of the one or more subsequent pixels being closer to an opposite side of the image than one or more previous pixels for which a previous one of the subsequent subset of driving waveforms was supplied.

11. Control software operative to enable a display driver to perform the method of claim 10.