HK1222252B - A driving system for an electrophoretic displays - Google Patents

Abstract

The present invention relates to a driving system for electrophoretic displays. Said driving system comprises: a plurality of display pixels; a single image memory for storing image data; and a lookup table map generator for receiving new image data, wherein said lookup table map generator generates a lookup table map and a plurality of sub lookup tables based on the real-time comparison between said new image data and said stored image data, wherein each of the sub lookup tables represents one category of driving waveforms and each category has waveforms for driving a display pixel to each of the color states, and said plurality of sub lookup tables is configured to provide driving voltage data for driving said electrophoretic displays based on said lookup table map.

Description

Driving system for electrophoretic display

This application is a divisional application of the patent application on filing date 2012, 8/30, application number 201210316809.6, and entitled "driving system for an electrophoretic display", the entire contents of which are incorporated herein by reference.

Technical Field

The present invention relates to a driving system for an electrophoretic display.

Background

Typically, the electrophoretic display is driven by using a look-up table storing drive waveforms. The look-up table typically involves the use of two memories, one storing information for the current image and the other storing information for the new image (i.e. the image to be driven from the current image). A lookup table is then searched for a particular pixel based on the current image information and the new image information to find the appropriate waveform for updating the pixel.

The memory space required to store the image and the look-up table is large. For example, for an electrophoretic display capable of displaying 16 different grey levels, there should be two image memories, in addition to which the look-up table also requires 256 entries to store the drive waveforms.

Certain methods described and identified as "background" or "prior art" in certain portions of this disclosure are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Thus, unless otherwise indicated, it should not be assumed that any of the approaches described thus far qualify as prior art merely by virtue of their identification as "background" or "prior art".

Disclosure of Invention

One aspect of the invention relates to a driving method for updating pixels in a current image to a new image, the method comprising the steps of:

a) storing only one image in an image memory; and

b) the look-up map is generated when new image data is sent to the display controller and the image memory is updated with the new image data.

The method may further comprise:

c) selecting drive voltage data from the sub-lookup table on a frame-by-frame basis based on the new image data and the category identified by the lookup map; and

d) sending the driving voltage data in step c) to the display frame by frame.

In one embodiment, the number of sub-lookup tables is no more than 50% of the number of image gray levels.

In one embodiment, the class of waveforms required to drive the pixels to the desired color state in the new image is determined based on a real-time comparison of the current image and the new image.

In one embodiment, the image has 16 gray levels.

Another aspect of the invention relates to a driving system for an electrophoretic display, the system comprising:

a) only one of the image memories is used,

b) a plurality of sub-lookup tables, wherein the number of lookup tables does not exceed 50% of the number of gray levels, and each sub-lookup table has a corresponding waveform selector, an

c) A lookup map generator and a lookup map.

Yet another aspect of the present invention relates to an electrophoretic display controller, comprising: a display controller Central Processing Unit (CPU) including a plurality of waveform selectors coupled to a category selector and a look-up table graph generator; a plurality of sub lookup tables coupled to the display controller CPU; a first interface configured to couple to a host computer CPU; a second interface configured to be coupled to a display; a third interface configured to couple to an image memory; and a fourth interface configured to couple to the look-up table map.

Yet another aspect of the invention relates to an electrophoretic display controller comprising: a look-up table map generator having a first connection configured to couple to the image memory to receive the image data, and a second connection configured to couple to the look-up table map; two or more sub-lookup tables each having an input configured to receive a number of frames and an output coupled to a respective waveform selector; a category selector having a plurality of inputs coupled to the waveform selector and the look-up table map; and an interface configured to couple to a display.

The driving method and system of the present invention can reduce the memory space required for driving an electrophoretic display.

Drawings

Fig. 1 shows a typical electrophoretic display device.

Fig. 2 shows an example of an electrophoretic display with a dichroic system.

Fig. 3 shows a conventional drive system.

Figure 4 illustrates the present invention.

Fig. 5 shows exemplary waveforms for illustration purposes.

Figure 6 shows a drive arrangement incorporating the present invention.

Fig. 7a and 7b are exemplary drive waveforms that may be applied to the present invention.

Detailed Description

Fig. 1 shows an electrophoretic display 100 driven by the driving method presented herein. In fig. 1, the electrophoretic display units 10a, 10b and 10c are provided with a common electrode 11 (which is typically transparent and thus on the viewing side) on the front viewing side indicated with the eye pattern. On the opposite side (i.e., the rear side) of the electrophoretic display units 10a, 10b, and 10c, the substrate 12 includes respective independent pixel electrodes 12a, 12b, and 12 c. Each of the pixel electrodes 12a, 12b and 12c defines a single pixel of the electrophoretic display. Although the pixel electrodes are shown aligned with the display elements, in practice, multiple display elements may be associated with a single pixel.

It should also be noted that when the substrate 12 and the pixel electrode are transparent, the display device can be viewed from the rear side.

Each of the electrophoretic display units 10a, 10b, and 10c is filled with an electrophoretic liquid 13. The electrophoretic display cells 10a, 10b and 10c are all surrounded by display cell walls 14.

The movement of the charged particles 15 in the display element is determined by the difference in voltage potentials applied to the common and pixel electrodes associated with the display element filled with charged particles.

For example, the charged particles 15 may be positively charged such that they are attracted to one of the pixel electrode or the common electrode where the voltage potential is opposite to the potential of the charged particles. If the same polarity is applied to the pixel and common electrodes in the display cell, the positively charged pigment particles will be attracted to the electrode having the lower voltage potential.

The charged particles 15 may be white. Also, it will be apparent to those skilled in the art that the charged particles may be dark in color and dispersed in a light colored electrophoretic fluid 13 to provide sufficient contrast to be visually discernable.

In another embodiment, the charged pigment particles 15 may be negatively charged.

In yet another embodiment, the electrophoretic display fluid may also have a transparent or light colored solvent or solvent mixture and two contrasting colors of oppositely charged particles dispersed therein. For example, positively charged white pigment particles and negatively charged black pigment particles may be present, and both types of pigment particles are dispersed in a transparent solvent or solvent mixture.

The term "display unit" is intended to mean a micro-container individually filled with a display liquid. Examples of "display elements" include, but are not limited to, microcups, microcapsules, microchannels, other segmented display elements, and equivalents thereof. In the microcup type, the electrophoretic display units 10a, 10b, and 10c may be sealed using a top sealing layer. There may also be an adhesive layer between the electrophoretic display cells 10a, 10b and 10c and the common electrode 11.

In this application the term "drive voltage" is used to denote the voltage potential difference experienced by the charged particles in the pixel area. The driving voltage is a potential difference between a voltage applied to the common electrode and a voltage applied to the pixel electrode. For example, in a single particle type system, positively charged white particles are dispersed in a black solvent. When a zero voltage is applied to the common electrode and a voltage of +15V is applied to the pixel electrode, the "driving voltage" of the charged pigment particles in the pixel region will be + 15V. In this case, the driving voltage will move the positively charged white particles close to or to the common electrode, as a result of which the white color is seen through the common electrode (i.e. on the viewing side). Alternatively, when zero voltage is applied to the common electrode and a voltage of-15V is applied to the pixel electrode, the drive voltage in this case will be-15V, and at such a drive voltage of-15V, the positively charged white particles will move to or close to the pixel electrode, resulting in the color of the solvent (black) being seen at the viewing side.

When a pixel is driven from one color state to another, a drive waveform is applied and consists of a series of drive voltages.

The term "two-color system" refers to a color system having two extreme color states (i.e., a first color and a second color) and a series of intermediate color states between the two extreme color states.

Fig. 2a to 2c show examples of dichroic systems with white particles dispersed in a black solvent.

In fig. 2a, white is seen when the white particles are on the viewing side.

In fig. 2b, black is seen when the white particles are at the bottom of the display cell.

In fig. 2c, the white particles are dispersed between the top and bottom of the display cell; an intermediate color is seen. In fact, the particles spread over the entire depth of the cell, or some on the top and some on the bottom. In this example, the color seen will be gray (i.e., the intermediate color).

Fig. 2d to 2f show examples of dichroic systems, where two types of particles (black and white) are dispersed in a transparent and colorless solvent.

In fig. 2d, white is seen when the white particles are on the viewing side.

In fig. 2e, black is seen when the black particles are on the viewing side.

In fig. 2f, white and black particles are dispersed between the top and bottom of the display cell; an intermediate color is seen. In fact, both types of particles are diffused over the entire depth of the cell, or some are distributed at the top and some at the bottom. In this example, the color seen will be gray (i.e., the intermediate color).

It is also possible to have more than two types of pigment particles in the display liquid. Different types of pigment particles may carry opposite charges and/or charges of different intensity levels.

In the present application, black and white are used for illustration purposes, but it should be noted that the two colors may be any colors as long as they exhibit sufficient visual contrast. Thus, two colors in a two-color system may also be referred to as a "first color" and a "second color".

The intermediate color is a color between the first color and the second color. The intermediate colors have proportionally different degrees of intensity between the two extremes (i.e., the first and second colors). Taking gray as an example, it may have a gray scale of 8, 16, 64, 256, or more.

In the gray scale of 16, gray level 0(G0) may be a full black color, and gray level 15(G15) may be a full white color. Gray levels 1 through 14(G1-G14) are gray colors ranging from dark to light.

When each image in the display device is formed of a large number of pixels and a new image is driven from a current image, a drive waveform composed of a series of drive voltages is applied to each pixel. For example, a pixel of the current image may be in the G5 color state while the same pixel in the new image is in the G10 color state, and then, as the current image is driven into the new image, the pixel is applied with a drive waveform to be driven from G5 to G10.

Fig. 3 shows a diagram illustrating an existing drive system involving the use of a look-up table.

In the prior art system as shown in the figure, the display controller 32 includes a display controller CPU 36 and a look-up table 37.

While the image update is being performed, the display controller CPU 36 accesses the current image data and the new image data from the image memory 33. Memory 33a represents the memory for the current image data of all pixels and memory 33b represents the memory for the new image data of these pixels.

When updating a pixel from the current image to a new image, the display controller CPU 36 refers to the look-up table 37 to find the appropriate waveform for each pixel. More specifically, when driving a new image from a current image, an appropriate drive waveform is selected from the look-up table for each pixel according to the color state in two successive images of the pixel. For example, a pixel may be in the white state in the current image and in the G5 state in the new image, thereby selecting the waveform accordingly.

For a display device capable of 16 gray scale levels, there are 256(16 × 16) waveforms in the look-up table (LUT) for selection.

The selected drive waveform is sent to the display 31 to be applied to the pixels to drive the current image into a new image. However, the drive waveforms are sent to the display on a frame-by-frame basis.

Throughout this application, the terms "current image" and "new image" are used to denote the image currently being displayed and the next image to be displayed, respectively. In other words, the drive system updates the current image to a new image.

Fig. 4 shows a diagram illustrating the present invention.

1) A single image memory:

a first unique feature of the present invention is that only one image memory 47 is required. The single image memory stores only image data of a new image.

In accordance with the present invention, image memory 47 would require only 240 kbytes (i.e., 600 × 800 × 4 bits) of memory space for a display having 600 × 800 pixels and 16 levels of gray scale (i.e., 4 bits).

In contrast, in prior systems, the required memory space is doubled (480 kbytes) because there are two image memories, one for the current image and one for the new image.

2) Sub lookup table

A second unique feature of the present invention is that the look-up table is divided into sub look-up tables (s-LUTs).

In the example shown in fig. 4, there are four s-LUTs, 44a to 44 d.

Each s-LUT represents a class of drive waveforms and each class has waveforms that drive the pixel to each possible color state. Thus, the number of drive waveforms in each s-LUT may be the same as the number of possible grey levels displayed by the drive system. For example, for a 16 gray scale drive system, each s-LUT has 16 waveforms.

The decision of how many s-LUTs there are in the drive system depends on the system designer. But the rule is that the number of s-LUTs cannot exceed 50% of the number of grey levels. In a 16 gray scale drive system, there cannot be more than 8 s-LUTs in the system.

Deciding how the waveforms are classified also depends on the system designer.

In the context of the present application, a high gray level may be defined as any one of G8 through G15, and a low gray level may be defined as any one of G0 through G7.

However, regardless of how the waveform is classified, the s-LUT covers all possible combinations of current and new color states of the pixel.

An example of an s-LUT is given in the following section.

In the prior art system shown in fig. 3, the entire look-up table 37 would require approximately 16 kbytes (i.e., 16 × 16 × 256 × 2 bits) of memory space, assuming that each drive waveform has 256 frames and 4 choices of applied voltages per frame (i.e., 2 bits). The 16 x 16 in the calculation represents the possible combinations of current (16) and new (16) color states of the pixel. Fig. 5 shows the remaining calculations.

For illustrative purposes, FIG. 5 shows an exemplary waveform 50 for a single pixel. For this waveform, the vertical axis represents the intensity and polarity of the applied voltage, and the horizontal axis represents the driving time. The waveform has a drive waveform period 51. There are many frames in the waveform and the length of a frame is referred to as the frame period or frame time 52.

Typical frame periods range from 2msec to 100msec and there may be up to 1000 frames in the waveform period. The length of the frame period in the waveform is determined by the TFT drive system design. The number of frames in the waveform is determined by the time required to drive the pixel to the desired color state. In the above calculation, it is assumed that each waveform has 256 frames.

As mentioned, when driving an EPD on an active matrix backplane, an image is typically displayed in many frames. During a frame period, a certain voltage is applied to the pixels in order to update the image. For example, as shown in FIG. 5, during each frame period, there are at least three different available voltage options, namely, + V, 0, or-V. Thus, the data in each s-LUT needs to be at least 2 bits in size to store the three possible choices. The waveform is composed of frames with different voltages to be applied.

Based on the information provided in the example shown in fig. 4, each s-LUT of the present invention may require approximately 1 kbyte (i.e., 16 x 256 x 2 bits) of memory space. The number 16 in this calculation represents the 16 waveforms in the s-LUT.

Thus, the total memory space required for 4 s-LUTs would be about 4k bytes.

In utilizing the system of the present invention as shown in FIG. 4, the following aspects of operation are involved:

aspect 1:

first, when a desired new image is sent to the display controller 42, the image memory 47 containing the current image (i.e., the previous "new" image) and the LUT image generator 41 perform a real-time comparison of the current image and the new image, after which the current image data is overwritten by the new image data, and the new image data is stored in the image memory 47. In other words, only new image data is stored in the image memory 47, and the image memory 47 is continuously updated pixel by pixel as new images are provided into the display controller 42.

Based on a real-time comparison of the current and new image data, the look-up table map generator 41 determines, on a pixel-by-pixel basis, the waveform class required to drive the pixel from its current color state to the new color state. Such information is then stored in the look-up table map 43. The look-up table map 43 has class information for all pixels.

Aspect 2:

this aspect of the driving method is done frame by frame starting with the first frame of the waveform and ending in the last frame. The respective s-LUTs 44a to 44d are provided with the frame being updated.

After completing aspect 1 of the transfer of new image data to the image memory 47, an update command is sent to the display controller for updating the image.

The desired color state of the pixels in the new image is sent from the image memory 47 to the waveform selector (45a to 45 d).

Based on the desired color state of the pixels in the new image, the waveform selectors 45a to 45d select the drive voltage data from the s-LUT for the frame being updated. For example, a waveform (among 16 kinds of waveforms) that drives a pixel to a desired color state in the s-LUT 44a is identified by the waveform selector 45a, and then the waveform selector 45a transmits the drive voltage data of the frame being updated in the waveform to the category selector 46.

The processing described for s-LUT 44a and waveform selector 45a is performed similarly for each pair of s-LUTs (44b, 44c or 44d) and their corresponding waveform selectors (45b to 45 c).

As a result of this aspect, there are four drive voltage data sent to the class selector 46 for the frame being updated, each from one waveform selector.

Here the individual drive voltage data from the individual waveform selectors, sent to the class selector 46, is based only on the new color state and thus the data size is 2 bits.

Aspect 3:

based on the category information from the lookup table fig. 43, the category selector 46 selects one driving voltage data from the plurality of driving voltage data received from the waveform selectors 45a to 45 d. The category selector 46 then sends the selected drive voltage data for the frame being updated to the display (e.g., a driver chip).

In operation, the steps of aspect 2 always precede the steps of aspect 3 for each frame. For example, the steps of aspects 2 and 3 are performed for frame 1, followed by the steps of aspects 2 and 3 for frame 2, and so on.

Fig. 6 shows how the invention can be incorporated into a display controller. A single image memory 47 for storing new image data provides the desired color state of the pixel into the waveform selectors 45 a-45 d. The waveform selector selects and sends a plurality of drive voltage data to the category selector 46. The waveform selector and the s-LUT are included in the display controller.

In one embodiment, the s-LUT need not be within the display controller. For example, they may be in an external chip.

The memory space required to find fig. 43 is about 120 kbytes (600 × 800 × 2 bits) for an image of 600 × 800 pixels. Since there are 4 s-LUTs, the calculation includes "2 bits".

As discussed in this application, the following table summarizes how the present invention can reduce the required memory space.

Memory space	Existing system	The invention
			Image memory	480k	240k
Lookup table	16k	4k
			Look-up table diagram	0k	120k
Total of	496k bytes	364k bytes

Therefore, the driving method of the present invention for updating pixels from a current image to a new image can be summarized as comprising the steps of:

a) storing only one image in an image memory;

b) generating a look-up map when new image data is sent to the display controller and updating the image memory with the new image data;

c) selecting drive voltage data from the sub-lookup table frame by frame based on the new image data and the category identified by the check map;

d) sending the driving voltage data in step c) to the display frame by frame.

Almost all waveforms known to drive an electrophoretic display can be used in the present invention.

For illustrative purposes, a suitable set of waveforms is shown in fig. 7a and 7 b.

Regardless of the previous color state, it is assumed that the driving time length T in the figure is long enough to drive the pixel to a fully white or fully black state.

For illustrative purposes, fig. 7a and 7b show an electrophoretic fluid including positively charged white pigment particles dispersed in a black solvent.

For WG waveform, if duration t₁Is 0, the pixel will remain in the white state. If the duration t is₁If T, the pixel is driven to a full black state. If the duration t is₁Between 0 and T, the pixel will be in the gray state, and T₁The longer the grey.

For KG waveform, if duration t₂Is 0, the pixel will remain in the black state. If the duration t is₂Is T, the pixel will be driven to the full white state. If the duration t is₂Between 0 and T, the pixel will be in the gray state, and T₂The longer the grey.

In other words, according to t in FIG. 7a₁And t in fig. 7b₂Any of two waveforms may be used in the present invention to drive the pixels to different desired color states.

Example 1: sub lookup table

In this example there are three sub-lookup tables.

Sub-lookup table 1-for driving pixels from gray level (G0 to G15) to the same gray level, e.g., G0 → G0, G1 → G1, G2 → G2, etc

Sub-lookup table 2-for driving a pixel from a low gray level (G0 to G7) to any one of 16 gray levels, e.g., G0 → G1, G5 → G6, G7 → G13, etc

Sub-lookup table 3-for driving a pixel from a high gray level (G8 to G15) to any one of 16 gray levels, e.g., G8 → G1, G11 → G6, G15 → G14, etc

In this case, a set of 16 waveforms would be designed for s-LUT 1 and stored in s-LUT 1. Regardless of the starting color state (G0-G15), each of the 16 waveforms drives the pixel as G0, G1, · G15, respectively.

Similarly, there are 16 waveforms in s-LUT 2 or s-LUT 3.

While the invention has been described with reference to specific embodiments thereof, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, composition, process step or steps, to the objective, spirit and scope of the present invention. All such modifications are intended to be included within the scope of the claims appended hereto.

Claims (5)

1. A driving system for an electrophoretic display, the system comprising:

a plurality of display pixels;

a single image memory for storing data of an image;

a lookup table map generator for receiving data of a new image, wherein the lookup table map generator generates a lookup table map based on a real-time comparison between the data of the new image and data of a stored image, an

A plurality of sub-lookup tables, each sub-lookup table representing a class of drive waveforms and each class comprising waveforms for driving display pixels to a color state, the plurality of sub-lookup tables being configured to provide drive voltage data for driving the electrophoretic display based on the generated lookup table map.

2. The drive system of claim 1, further comprising a waveform selector to select drive voltage data from the plurality of sub-lookup tables.

3. A driving system for an electrophoretic display, the system comprising:

a plurality of sub-lookup tables, each sub-lookup table comprising a set of display drive waveforms and the number of display drive waveforms in each set being equal to the number of gray levels displayed by the drive system, the plurality of sub-lookup tables being configured to provide drive voltage data for updating a display;

a plurality of waveform selectors for selecting the driving voltage data from the plurality of sub lookup tables;

and

a category selector to select one of the drive voltage data from the plurality of waveform selectors and to provide the selected drive voltage data to the electrophoretic display.

4. A driving system according to claim 3, wherein the number of sub-look-up tables is no more than 50% of the number of grey levels that the electrophoretic display is capable of displaying.

5. A driving system for an electrophoretic display, the system comprising:

a plurality of display pixels;

a single image memory for storing data of an image;

a lookup table map generator for receiving data of a new image, wherein the lookup table map generator generates a lookup table map based on a real-time comparison between the data of the new image and data of a stored image, an

A plurality of waveform selectors for selecting drive voltage data based on a desired color state of the received data for the new image.