WO2004107305A1

WO2004107305A1 - Electrophoretic display unit

Info

Publication number: WO2004107305A1
Application number: PCT/IB2004/050745
Authority: WO
Inventors: Guofu Zhou; Roger P. A. Delnoij; Johannes P. Van De Kamer; Neculai Ailenei; Mark T. Johnson
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2003-06-03
Filing date: 2004-05-19
Publication date: 2004-12-09
Also published as: TW200510892A

Abstract

The electrophoretic display unit (1) comprises drivers (60,61) for driving pixels (11) groups (70,71) of lines in parallel during data-independent parts of frame periods. During data-independent parts of frame periods, the groups (70,71) of lines are driven with common data and during data-dependent frame periods, the groups (70,71) of lines are driven with specific data. Preferably, the drivers (60,61) are row drivers, with the groups (70,71) of lines being groups of rows. During data-independent parts of frame periods, especially when shaking pulses are applied, the frame period can be reduced.

Description

Electrophoretic display unit

The invention relates to an electrophoretic display unit, to a display device comprising an electrophoretic display unit, to a method for driving an electrophoretic display unit, to a processor program product for driving an electrophoretic display unit, and to driving circuitry.

Examples of display devices of this type are: monitors, laptop computers, personal digital assistants (PDAs), mobile telephones and electronic books, electronic newspapers, and electronic magazines.

A prior art electrophoretic display unit is known from international patent application WO 99/53373. This patent application discloses an electronic ink display comprising two substrates, with one of the substrates being transparent and having a common electrode (also known as counter electrode) and with the other substrate being provided with pixel electrodes arranged in rows and columns. A crossing between a row electrode and a column electrode is associated with a pixel. The pixel is formed between a part of the common electrode and a pixel electrode. The pixel electrode is coupled to the drain of a transistor, of which the source is coupled to the column electrode and of which the gate is coupled to the row electrode. This arrangement of pixels, transistors and row and column electrodes jointly forms an active matrix. A row driver (select driver) supplies a selection signal for selecting a row of pixels and a column driver (data driver) supplies data signals to the selected row of pixels via the column electrodes and the transistors. The data signals correspond to data to be displayed, and form, together with the selection signal, a (part of a) driving signal for driving one or more pixels.

Furthermore, an electronic ink is provided between the pixel electrode and the common electrode provided on the transparent substrate. The electronic ink comprises multiple microcapsules of about 10 to 50 microns in diameter. Each microcapsule comprises positively charged white particles and negatively charged black particles suspended in a fluid. When a positive field is applied to the pixel electrode, the white particles move to the side of the microcapsule directed to the transparent substrate, and the pixel becomes visible 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 field 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 pixel appears dark to a viewer. Simultaneously, the white particles move to the pixel electrode at the opposite side of the microcapsule where they are hidden from the viewer. When the electric fields are removed, the display device remains in the acquired state and exhibits a bi-stable character.

To reduce the dependency of the optical response of the electrophoretic display unit on the history of the pixels, preset data signals are supplied before the data- dependent signals are supplied. These preset data signals comprise pulses representing energies which are sufficient to release the electrophoretic particles from a static state at one of the two electrodes, but which are too low to allow the particles to reach the other electrode. Because of the reduced dependency on the history, the optical response to identical data will be substantially equal, regardless of the history of the pixels. The underlying mechanism can be explained by the fact that, after the display device is switched to a predetermined state, for example a black state, the electrophoretic particles come to a static state. When a subsequent switching to the white state takes place, the momentum of the particles is low because their starting speed is close to zero. This results in a high dependency on the history, which requires a long switching time to overcome this high dependency. The application of the preset data signals increases the momentum of the electrophoretic particles and thus reduces the dependency (and allows a shorter switching time).

Independently of whether data-independent signals or data-dependent signals are to be supplied to the pixels, a row driver sequentially selects the rows of pixels and the column driver supplies data-independent or data-dependent signals to the selected row of pixels via the column electrodes and the transistors. As several frame periods are required to update an image to be displayed, the total time required to update the image is relatively long.

The known electrophoretic display unit is disadvantageous, inter alia, due to the updating of an image on the electrophoretic display unit requiring a relatively long time.

It is an object of the invention, inter alia, to provide an electrophoretic display unit having a relatively short time for updating the image. The invention is defined by the independent claims. The depencent claims define advantageous embodiments.

The electrophoretic display unit according to the invention comprises : - a display panel comprising a first group of lines and a second group of lines;

- a first driver for driving the first group of lines ;

- a second driver for driving the second group of lines; and

- a controller for controlling the first and second drivers for driving a line of the first group and a line of the second group in parallel during at least a data- independent part of a frame period.

By introducing at least two drivers for driving at least two groups of lines (at least two groups of rows or at least two groups of columns), with the controller during at least a data-independent part of a frame period driving the groups of lines in parallel (meaning that one or more lines of the first group and one or more lines of the second group are driven simultaneously, whereby data-independent signals corresponding to a data-independent part of an image are (to be) supplied during a data-independent part of a frame period; a data- independent part of an image either corresponds to one or more data-independent sections of an image, like for example in a picture-in-picture situation a static area surrounding the picture-in-picture image, or corresponds to a whole data-independent frame period), the efficiency of the driving has been increased. During at least a data-dependent part of a frame period, the controller does not drive the groups of lines in parallel (meaning that firstly all lines of the first group are driven, for example one after the other, and secondly all lines of the second group are driven, for example one after the other etc., whereby during a data- dependent part of a frame period, data-dependent signals are (to be) supplied to the data- dependent part of a frame period; a data-dependent part of a frame period either correspond to one or more data-dependent parts of a frame period, like for example the picture-in-picture image in a picture-in-picture situation, or corresponds to a whole data-dependent frame period). A simple, low cost driver drives one line at a time and is unflexible. By using two or more of these simple low cost drivers for driving two or more groups of lines either in parallel or not, the flexibility of the driving is increased, without needing to develop and/or search for a more complex, more expensive driver which is more flexible. The invention however is not limited to simple, low cost drivers and may be used in combination with more complex, more expensive drivers as well.

Usually, but not exclusively, a frame period corresponds to a time-interval used for driving all pixels in the electrophoretic display unit once (by driving each row one after the other and by driving all columns once per row, or vice versa). In other words, during a frame period all lines of pixels are addressed one by one. By driving the first and second groups of lines in parallel during at least a data-independent part of a frame period, less time is needed for driving the lines during this part of a frame period. As a result, for this frame period, the frame rate is increased (the duration of the frame period is reduced), and for a sequence of frame periods of an image update cycle, the average frame rate is increased, due to, for example, some frame periods of the sequence of frame periods comprising mainly data-independent parts, and other frame periods of the sequence comprising mainly data- dependent parts. An increased (average) frame rate results in a reduced visibility of flicker.

An embodiment of an electrophoretic display unit according to the invention is defined by claim 2. By driving the line of the first group and the line of the second group with common data during at least a data-independent part of a frame period (meaning that pixels in one or more lines of the first group and pixels in one or more lines of the second group are driven with identical data), each two (or more) lines are driven with the same information. By driving the line of the first and the line of the second group with specific data during at least a data-dependent part of a frame period (meaning that pixels in each line of each group are driven uniquely with specific data which may be equal to or different from data (to be) supplied to pixels in other lines), each line is driven with unique information.

An embodiment of an electrophoretic display unit according to the invention is defined by claim 3. By letting the first and second drivers correspond to row drivers (select drivers), with the first and second groups of lines corresponding to a first and a second group of rows (of pixels), during at least a data-independent part of a frame period, a row of the first group and a row of the second group are driven in parallel. This is more advantageous than the parallel driving of groups of columns, because each row driver, when driving a row of pixels, brings all transistors coupled to the pixel electrodes of the pixels in this row in a conducting state, after which the column drivers (data drivers) can supply the data to the pixels in that row substantially simultaneously. This effectively further reduces the duration of the frame period.

An embodiment of an electrophoretic display unit according to the invention is defined by claim 4. Shaking pulses, for example, may form the preset data signals discussed before. During at least a data-independent part of a frame period, the driving signals (data signals) may further comprise reset pulses (in addition to the shaking pulses), which reset pulses precede the driving pulses to further improve the optical response of the electrophoretic display unit, by defining a fixed starting point (fixed black or fixed white) for the driving pulses. Alternatively, during an at least data-dependent part of a frame period, the driving signals (data signals) may further comprise the reset pulses (in addition to the driving pulses), which reset pulses precede the driving pulses to further improve the optical response of the electrophoretic display unit, by defining a flexible starting point (black or white, to be selected in dependence on and closest to the gray value to be defined by the following driving pulses) for the driving pulses. The display device as claimed in claim 5 may be an electronic book, while the medium for storing information may be a memory stick, integrated circuit, a memory or other storage device for storing, for example, the content of a book to be displayed on the display unit.

Embodiments of a method according to the invention and of a processor program product according to the invention correspond to the embodiments of an electrophoretic display unit according to the invention.

The invention is based upon an insight, inter alia, that the driving of prior art electrophoretic display units is done irrespective of whether data-independent signals or data- dependent signals are to be supplied to the pixels, and is based on a basic idea, inter alia, that an electrophoretic display unit is to be divided into groups of lines, whereby the groups of lines are to be driven in parallel during at least a data-independent part of a frame period.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments(s) described hereinafter.

In the drawings:

Fig. 1 shows (in cross-section) a pixel;

Fig. 2 shows diagrammatically an electrophoretic display unit;

Fig. 3 shows two waveforms for driving an electrophoretic display unit; and Fig. 4 shows diagrammatically an electrophoretic display unit according to the invention.

The pixel 11 of the electrophoretic display unit shown in Fig. 1 (in cross- section) comprises a base substrate 2, an electrophoretic film (laminated on base substrate 2) with an electronic ink which is present between two transparent substrates 3,4 of, for example, polyethylene. One of the substrates 3 is provided with transparent pixel electrodes 5 and the other substrate 4 is provided with a transparent common electrode 6. The electronic ink comprises multiple microcapsules 7 of about 10 to 50 microns diameter. Each microcapsule 7 comprises positively charged white particles 8 and negatively charged black particles 9 suspended in a fluid 10. When a positive field is applied to the pixel electrode 5, the white particles 8 move to the side of the microcapsule 7 directed to the common electrode 6, and the pixel becomes visible to a viewer. Simultaneously, the black particles 9 move to the opposite side of the microcapsule 7 where they are hidden from the viewer. By applying a negative field to the pixel electrode 5, the black particles 9 move to the side of the microcapsule 7 directed to the common electrode 6, and the pixel appears dark to a viewer (not shown). When the electric field is removed, the particles 8,9 remain in the acquired state and the display exhibits a bi-stable character and consumes substantially no power. The electrophoretic display unit 1 shown in Fig. 2 comprises a display panel

DP comprising a matrix of pixels 11 at the area of crossings of row or selection electrodes 41,42,43 and column or data electrodes 31,32,33. These pixels 11 are all coupled to a common electrode 6, and each pixel 11 is coupled to its own pixel electrode 5. The electrophoretic display unit 1 further comprises a row driver 40 coupled to the row electrodes 41,42,43 and a column driver 30 coupled to the column electrodes 31,32,33 and comprises an active switching element 12 for each pixel 11. The electrophoretic display unit 1 is driven by these active switching elements 12 (in this example (thin-film) transistors). The row driver 40 consecutively selects the row electrodes 41,42,43, while the column driver 30 provides data signals to the column electrode 31,32,33. Preferably, a controller 20 first processes incoming data arriving via input 21 and then generates the data signals. Mutual synchronisation between the column driver 30 and the row driver 40 takes place via drive lines 23 and 24. Selection signals from the row driver 40 select the pixel electrodes 5 via the transistors 12 of which the drain electrodes are electrically coupled to the pixel electrodes 5 and of which the gate electrodes are electrically coupled to the row electrodes 41,42,43 and of which the source electrodes are electrically coupled to the column electrodes 31,32,33. A data signal present at the column electrode 31,32,33 is transferred to the pixel electrode 5 of the pixel 11 coupled to the drain electrode of the transistor 12. Instead of transistors, other switching elements can be used, such as diodes, MIMs, etc. The data signals and the selection signals together form (parts of) driving signals. Incoming data, such as image information receivable via input 21 is processed by controller 20. Thereto, controller 20 detects an arrival of new image information about a new image and in response starts the processing of the image information received. This processing of image information may comprise the loading of the new image information, the comparing of previous images stored in a memory of controller 20 and the new image, the interaction with temperature sensors, the accessing of memories containing look-up tables of drive waveforms etc. Finally, controller 20 detects when this processing of the image information is ready.

Then, controller 20 generates the data signals to be supplied to column driver 30 via drive lines 23 and generates the selection signals to be supplied to row driver 40 via drive lines 24. These data signals comprise data-independent signals which are the same for all pixels 11 and data-dependent signals which may or may not vary per pixel 11. The data- independent signals comprise shaking pulses forming the preset pulses, with the data- dependent signals comprising a reset pulse and a driving pulse. These shaking pulses comprise pulses representing energy which is sufficient to release the electrophoretic particles 8,9 from a static state at one of the two electrodes 5,6, but which is too low to allow the particles 8,9 to reach the other one of the electrodes 5,6. Because of the reduced dependency on the history, the optical response to identical data will be substantially equal, regardless of the history of the pixels. So, the shaking pulses reduce the dependency of the optical response of the electrophoretic display unit on the history of the pixels. The reset pulse precedes the driving pulse to further improve the optical response, by defining a flexible starting point for the driving pulse. This starting point may be a black or white level, to be selected in dependence on and closest to the gray value defined by the following driving pulse. Alternatively, the reset pulse may form part of the data-independent signals and may precede the driving pulse to further improve the optical response of the electrophoretic display unit, by defining a fixed starting point for the driving pulse. This starting point may be a fixed black or fixed white level.

In Fig. 3, two waveforms representing voltages across a pixel (11) as a function of time t are shown for driving an electrophoretic display unit 1. These waveforms are generated using the data signals supplied via the column driver 30. A first waveform

(upper graph) comprises shaking pulses Sho, followed by a reset pulse R and a driving pulse Dr. A second waveform (lower graph) comprises first shaking pulses Shi, followed by a reset pulse R, second shaking pulses Sh₂, and a driving pulse Dr. For example for an electrophoretic display unit with four gray levels, sixteen different waveforms are stored in a memory, like for example, a look-up table memory etc. forming part of and/or coupled to controller 20. In response to data received via input 21, controller 20 selects a waveform for one or more pixels 11, and supplies the corresponding selection signals and data signals via the corresponding drivers 30,40 to the corresponding transistors 12 and the corresponding one or more pixels 11. A frame period corresponds to a time-interval used for driving all pixels 11 in the electrophoretic display unit 1 once, by driving each row one after the other and by driving all columns once per row. During a data-independent (part of a) frame period, the data- independent signals are supplied to pixels 11, and during a data-dependent (part of a) frame period, the data-dependent signals are supplied to pixels 11. Therefore, in Fig. 3, each pulse, shown as a specific voltage level between two subsequent transitions, represents a separate frame period.

For supplying data-dependentor data-independent signals to the pixels 11, column driver 30 is controlled in such a way by controller 20 that all pixels 11 in a row receive these data-dependent or data- independent signals simultaneously. This is done row by row, with controller 20 controlling row driver 40 in such a way that the rows are selected one after the other by bringing all transistors 12 in the selected row into a conducting state. So, during data-independent (parts of) frame periods, the row driver 40 is selecting each row one after the other, with the column driver 30 supplying the same data-independent signal to the pixels 11 in the selected row for one row after the other. This inefficiency is reduced by the electrophoretic display unit 11 according to the invention as shown in Fig. 4.

The electrophoretic display unit 11 shown in Fig. 4 comprises a main column driver 31 (corresponding to column driver 30 in Fig. 2) and a main row driver 41 (corresponding to row driver 40 in Fig. 2). Main column driver 31 comprises a first column driver 50, a second column driver 51 and a third column driver 52, which receive first driving signals via drive lines 23. Main row driver 41 comprises a first row driver 60, a second row driver 61 and a third row driver 62, which receive second driving signals via drive lines 24. The electrophoretic display unit 11 is partitioned into a first group of lines 70 driven by first row driver 60, a second group of lines 71 driven by second row driver 61, and a third group of lines 72 driven by third row driver 62. Each one of the groups 70-72 comprises lines with a plurality of pixels 11.

The processor 20, the first row driver 60, and the second row driver 61 together form the driving circuitry 60,61,20. This driving circuitry may be formed by one or more integrated circuits, which may be combined with other components as an electronic unit.

During one or more data-independent (parts of) frame periods (during a data- independent (part of a) frame period, data-independent signals are (to be) supplied), the groups of lines 70-72 are driven in parallel (meaning that one or more lines of the first group 70 and one or more lines of the second group 71 and one or more lines of the third group 72 are driven simultaneously). As a result of the combined driving during the data-independent (parts of) frame periods, the duration of these frame periods has been reduced. During one or more data-dependent (parts of) frame periods (during a data-dependent (part of a) frame period, data-dependent signals are (to be) supplied), the groups of lines 70-72 are not driven in parallel (meaning that, for example, firstly all lines of the first group 70 are driven, for example one after the other, and secondly all lines of the second group 71 are driven, for example one after the other, and thirdly all lines of the third group 72 are driven, for example one after the other etc.). By driving the groups of lines 70-72 in parallel during at least one data-independent (part of a) frame period, less time is used for driving the lines during this (part of the) frame period. As a result, for this frame period, the frame period rate is increased, and for a sequence of frame periods of an image update cycle, the average frame rate is increased, due to, for example, some frame periods of the sequence comprising mainly data-independent parts, and other frame periods of the sequence comprising mainly data- dependent parts. An increased (average) frame rate results in a reduced flicker. During one or more data-independent (parts of) frame periods, the groups of lines 70-72 are driven with common data (meaning that one or more lines of the first group 70 and one or more lines of the second group 71 and one or more lines of the third group 72 are driven with identical data, with pixels 11 in these lines receiving the same data- independent signal), in which case each three (or more) lines are driven with the same information. During one or more data-dependent frame periods, the groups of lines 70-72 are driven with specific data (meaning that each line of each group 70-72 is driven uniquely with specific data which may possibly be equal to but is usually different from data (to be) supplied to other lines, with pixels 11 in each line receiving possibly the same but usually a different data-dependent signal compared to pixels 11 in other lines), in which case each line is driven with unique information.

Of course, with the previous paragraphs describing the parallel driving of groups of horizontal lines (rows) during one or more frame periods, groups of vertical lines (columns) can be driven in parallel as well, and the invention is not limited to groups of horizontal lines (rows) being driven in parallel during one or more (parts of) frame periods. Preferably, to increase the possible frame rate of the electrophoretic display unit 11, for data-independent signals (like, for example, the shaking pulses and possibly the reset pulses etc.), groups of lines 70-72 should be driven in parallel and with identical data, and for data-dependent signals (like for example driving pulses etc.), the groups of lines 70- 72 are not driven in parallel, but with specific data. It is preferred if, in particular, the row drivers 60-62 are driven in parallel. By driving, for example, two row drivers in parallel, the frame rate may be halved. These extremely short frame periods are particularly beneficial to the shaking pulses.

In case of the drive lines 23 (24) being three separate drive lines, either these three separate drive lines are coupled directly to controller 20 or they are coupled indirectly to controller 20 via for example a multiplexer. By providing the driving signals flowing via the three separate drive lines with information resulting in a parallel driving or not of the groups of lines, the groups of lines are driven either at the same moments in time or one after the other. In case of the three drive lines 23 (24) where one is a physical drive line, one or more indications will have to be added to the driving signals indicating for which driver 50- 52 (60-62) the driving signals are intended and indicating whether there should be parallel or non-parallel driving. Such indications may comprise codes and/or predefined time-intervals etc. For the driving signals supplied from controller 20 to the multiplexer, the same indications may be used, with the multiplexer then multiplexing in dependence on these indications. The information and/or the indications may alternatively be supplied separately (in time and/or in place) from the driving signals to the drivers 50-52 (60-62).

As a minimum there will be two column drivers 50,51 and one row driver 60, or one column driver 50 and two row drivers 60,61. As a maximum there will be as many column drivers as there are columns of pixels 11, and as many row drivers as there are rows of pixels 11.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. An electrophoretic display unit (1) comprising:

- a display panel (DP) comprising a first group of lines and a second group of lines;

- a first driver (60) for driving the first group (70) of lines ;

- a second driver (61) for driving the second group (71) of lines; and - a controller (20) for controlling the first and second drivers (60,61) for driving a line of the first group and a line of the second group (70,71) in parallel during at least a data- independent part of a frame period.

2. An electrophoretic display unit (1) as claimed in claim 2, wherein the controller (20) is adapted to drive the line of the first group (70) and the line of the second group (71) with common data during at least a data-independent part of a frame period and to drive the line of the first group (70) and the line of the second group (71) with individual data during at least a data-dependent part of a frame period.

3. An electrophoretic display unit (1) as claimed in claim 1, wherein the first and second drivers (60,61) comprise row drivers, the first and second groups of lines (70,71) comprising a first and a second group of rows.

4. An electrophoretic display unit (1) as claimed in claim 1, wherein the first (60) and the second driver (61) are adapted to provide shaking pulses during at least a data- independent part of a frame period, and driving pulses during at least a data-dependent part of a frame period.

5. A display device comprising an electrophoretic display unit (1) as claimed in claim 1, and a medium for storing information to be displayed on the display unit (1).

6. A method for driving an electrophoretic display unit (1) comprising a display panel (DP) comprising a first group of lines and a second group of lines, the method comprising the steps of: - driving the first group of lines (70) in response to a first driving signal;

- driving the second group of lines (71) in response to a second driving signal; and

- controlling the driving of a line of the first group (70) and a line of the second group (71) in parallel during at least a data-independent part of a frame period.

7. A computer program product for driving an electrophoretic display unit (1) comprising a display panel (DP) comprising a first group (70) of lines and a second group (71) of lines, the product comprising the functions of:

- driving the first group of lines (70) in response to a first driving signal; - driving the second group of lines (71) in response to a second driving signal; and

8. Driving circuitry for an electrophoretic display unit (1) comprising a display panel (DP) comprising a first group of lines and a second group of lines, the driving circuitry

(60,61,20) comprising:

- a first driver (60) for driving the first group (70) of lines ;

- a second driver (61) for driving the second group (71) of lines; and

- a controller (20) for controlling the first and second drivers (60,61) for driving a line of the first group and a line of the second group (70,71) in parallel during at least a data- independent part of a frame period.