CN102456320A - Electrophoretic display and picture updating method thereof - Google Patents

Abstract

The invention discloses an electrophoretic display, when updating the picture, firstly erasing the residual image of the old picture, then continuously starting a plurality of frames, each frame only changes one gray scale, thereby gradually adjusting all pixels to the respective required gray scale. The invention can simplify the updating of the picture, accelerate the speed of updating the picture and reduce the capacity of the search table. The invention can simplify the adjustment of the brightness by matching with the time length of the adjusting frame.

Description

Electrophoretic display and its screen update method

technical field

The present invention relates to an electrophoretic display (Electro Phoretic Display; EPD), in particular to an EPD screen updating method.

Background technique

Compared with other types of displays, EPD has the advantage of lower power consumption, but has the disadvantage of more complicated driving methods. For EPD, to change a pixel from a certain gray scale to another gray scale, its driving signal should not only consider the final gray scale, but also consider the initial gray scale, such as M.Johnson et al. "High Quality Images on Electronic Paper Displays", cf. SID 05 Digest 1666 (2005).

Taking the active matrix EPD shown in Figure 1 as an example, when controlling the EPD 10 to update the picture, the host 12 transmits the new picture to the timing controller 14, and the timing controller 14 uses the memory 16 to store the new and old pictures respectively, and then according to each The new and old grayscale values of a pixel are detected from the flash memory 18 to find the corresponding driving waveform, and then generate a control signal to the EPD panel 20, the column electrode 24 is sequentially driven by the column driver 22, and the row driver 26 provides a specific voltage to the row electrode 28. In the EPD panel 20, there is a pixel 30 at the intersection of each column electrode 24 and each row electrode 28, and each pixel 30 is configured with a thin film transistor 32, and its gate, source and drain are respectively connected to the column of the pixel 30 The electrodes 24 , the row electrodes 28 and the pixel electrodes can selectively apply voltages to the pixel 30 to generate an electric field to drive the electrophoretic particles of the pixel 30 to migrate, thus making the pixel 30 brighter or darker. Taking the microcapsule binary particle system shown in FIG. 2 as an example, a microcapsule 38 is sandwiched between two parallel electrodes 34 and 36, and there are suspended black particles 40 and white particles 42 inside. Therefore, applying a voltage V on the electrodes 34 and 36 can drive the black particles 40 and the white particles 42 to move in opposite directions respectively. When the black particles 40 are closer to the viewing side, for example, on the side of the electrode 34, the displayed color of the pixel 30 is blacker; on the contrary, when the white particles 42 are closer to the viewing side, the displayed color of the pixel 30 is whiter, thus Different gray scales can be represented by controlling the displacement of the black particles 40 and the white particles 42 . The displacement of the black particles 40 and the white particles 42, and thus the change of the derived optical state, is positively correlated with the integral of the voltage V to time (referred to as a voltage pulse), such as "Drive waveforms for active matrix electrophoretic" by R.Zehner et al. displays", cf. SID 03Digest 842 (2003). Returning to Fig. 1, the driving waveforms that change from any gray scale to another gray scale are stored in the memory 18 in the form of a look-up table for the timing controller 14 to read, for example, "High Performance" by H.Gates et al. ActiveMatrix Electrophoretic Display Controller", SID 08 Digest 693 (2008) cf. Taking the 16-gray-scale system shown in FIG. 3 as an example, there are 16 initial gray-scales and 16 final gray-scales, so there are 16×16=256 gray-scale changing methods, that is, 256 driving waveforms are required. In the existing EPD, as shown in Figure 4, the driving method is to migrate the electrophoretic particles from the current position to the position corresponding to the target gray scale through the driving of multiple frames. The process includes repeatedly driving the electrophoretic particles to make them gradually Reach the position corresponding to the target grayscale. This driving method is very complicated and time-consuming, and it consumes more power because of the large number of frames.

In addition, if the driving waveform of a frame needs 2 bits to be stored, then the look-up table needs 256×N×2÷8=64N bytes (byte) capacity, and it will increase significantly with the increase of the number of gray scales. Increase. Secondly, the characteristics of the material will change with the temperature, so the lookup table needs to store the driving waveforms at different temperatures, such as "High Performance Active Matrix Electrophoretic Display Controller" by H. Gates et al., referred to by SID 08Digest693 (2008), resulting in The key is larger.

Due to the difference in materials, the driving waveform for the same grayscale adjustment cannot be applied to all EPD panels, so each batch of products needs to reset the lookup table, which is not suitable for mass production.

The above-mentioned driving method also has an adverse effect on the brightness adjustment of the EPD panel, because the brightness is determined by the position of the electrophoretic particles. Once the brightness difference of each gray scale is to be changed, all driving waveforms must be updated.

Contents of the invention

One of the objectives of the present invention is to provide an EPD and its screen updating method.

One of the objectives of the present invention is to provide an EPD with faster picture updating and a picture updating method thereof.

One of the objectives of the present invention is to provide a relatively power-saving EPD and its screen update method.

One of the objectives of the present invention is to propose an EPD and a screen updating method thereof that reduce the capacity of the retrieval table.

One of the objectives of the present invention is to provide an EPD that simplifies brightness adjustment and an image updating method thereof.

According to the present invention, an EPD includes an EPD panel, a timing controller is connected to the EPD panel, a flash memory is connected to the timing controller, and the flash memory stores a driving waveform changing a gray scale in the form of a lookup table. When updating the picture, first erase the afterimage of the old picture on the EPD panel, and then open multiple frames continuously, and each frame only changes one gray level, so as to gradually adjust all pixels to their respective desired gray levels.

Since each frame only changes one gray level, the updating of the picture is simplified and the number of frames is reduced, thereby speeding up the speed of updating the picture and reducing power consumption. Since only the driving waveform changing one gray level is stored, the capacity of the lookup table is greatly reduced. Furthermore, using this driving method, the brightness difference of each gray scale can be adjusted by adjusting the frequency of the system clock.

Description of drawings

Figure 1 is a schematic diagram of an active matrix EPD;

Fig. 2 is a schematic diagram of a microcapsule binary particle system;

Fig. 3 is a schematic diagram of the gray scale change mode of the 16 gray scale system;

Fig. 4 is a schematic diagram of a conventional EPD driving mode;

Fig. 5 is a relationship diagram between different voltages and pulse lengths and brightness changes;

Fig. 6 is a method embodiment according to the present invention;

Fig. 7 is a schematic diagram of adjusting all pixels to the same gray scale;

Fig. 8 is the process of adjusting pixels to gray scale 15;

Fig. 9 is the process of adjusting pixels to gray scale 3;

Figure 10 is the process of adjusting pixels to gray scale 0;

Figure 11 is the process of bidirectionally adjusting the gray scale;

FIG. 12 is a schematic diagram of an EPD that can adjust the varying brightness of the gray scale; and

FIG. 13 is a schematic diagram of two kinds of system clock frequencies.

Description of main component symbols:

10EPD

12 hosts

14 timing controller

16 memory

18 flash memory

20EPD panel

22 column driver

24 columns of electrodes

26 row driver

28 rows of electrodes

30 pixels

32 Thin Film Transistors

34 electrodes

36 electrodes

38 microcapsules

40 black particles

42 white particles

44 grayscale 0

46 grayscale 15

48 grayscale 7

50 VCO

Detailed ways

As shown in Figure 2, the displacement dL of the electrophoretic particles 40 and 42 is a function of the voltage V and its application time length, such as "Drive waveforms for active matrix electrophoretic displays" by R.Zehner et al., referred to by SID 03Digest842 (2003), so The voltage pulse required for each change of one gray scale can be planned in advance. For example, Figure 5 shows the relationship between different voltages and pulse lengths and the brightness change dL ^* disclosed in "Towards video-rate microencapsulated dual-particle electrophoretic displays," SID 04 Digest 133 (2004) by T.Whitesides et al. The length indicates the length of time for which the voltage is applied, and L ^* is a lightness unit defined in the CIELAB standard. As can be seen from Figure 2 and Figure 5, the gray scale can be determined by

dL ^* ＝v×t＝kV×t Formula 1

Determined, where v is the moving speed of the electrophoretic particles 40 and 42 . Under ideal conditions, the brightness change dL ^* is proportional to the moving time t of the electrophoretic particles 40 and 42 , that is, k is a constant. But the characteristic curve of dL ^* on implementation is not linear, as shown in Fig. 5. However, from the characteristic curve of dL ^* , the voltage pulse required for each change of a gray scale can be determined, for example, the pulse length t required at a certain voltage V. Based on this, all the driving waveforms required to change one gray scale are stored in the flash memory 18 in FIG. 1 . When adjusting the grayscale of the pixel 30, multiple frames are continuously turned on, and corresponding driving waveforms are applied to the pixel 30. Each frame only changes one grayscale until the pixel 30 reaches the desired grayscale.

Figure 6 is an embodiment of a method according to the present invention. Referring to FIG. 1 and FIG. 6 , when updating the screen, the residual image of the current screen is erased first by step S1 . In this step, the timing controller 14 turns on several frames to apply a reset voltage pulse to all the pixels 30 of the EPD panel 20 , preferably including at least one black and white alternation. Then step S2 adjusts all the pixels 30 to the same gray scale. For example, referring to FIG. , as shown by the dashed line 48. Returning to FIG. 1 and FIG. 6 , the last step S3 is to continuously open multiple frames, each frame only changes one gray level, and gradually adjusts all the pixels 30 to their respective desired gray levels. For example, referring to Figure 8, to adjust a pixel to grayscale 15, no matter what its initial grayscale is, first erase it, then open 16 frames continuously, adjust to grayscale 0 after the first frame, and adjust to grayscale 0 in the second frame Finally adjust to grayscale 1, and so on, until the 16th frame is adjusted to grayscale 15. As shown in Figure 8, in a 16-gray-scale system, at most only 16 frames are needed to complete the gray-scale adjustment of all pixels, plus the previously erased frames, the total number of frames is less than the conventional driving method , so the screen update speed is faster, and it saves power. Referring to Figure 9, to adjust the pixel to grayscale 3, the process is the same as that in Figure 8, but grayscale 3 has been reached after the fourth frame, and no voltage is applied to the pixel in subsequent frames, and the pixel maintains grayscale 3 until the end of 16 frames. The same is true for pixels of other gray scales. Any pixel will not change after reaching its target gray scale, and only pixels that have not yet reached the target gray scale will continue to change one gray scale per frame in subsequent frames. This further saves power since the lower grayscale pixels stop changing their grayscale earlier. Figure 10 shows another situation. After erasing, all pixels are adjusted to grayscale 15, and then each frame is changed by one grayscale. The pixel targeted for grayscale 0 reaches grayscale 0 after 16 frames. In Figure 11, after erasing, all pixels are first adjusted to grayscale 7, and then multiple frames are turned on continuously. The pixels whose target is lower than grayscale 7 are lowered by one grayscale for each frame, and the target is higher than grayscale 7. The number of pixels is increased by one gray level per frame, thus further reducing the number of frames.

As mentioned earlier, the displacement of electrophoretic particles depends on voltage pulses. If the applied voltage is higher, the required pulse length is shorter and vice versa. And because of the non-linearity of the dL ^* characteristic curve, even if the same voltage is applied, the time required to change a gray level from different gray levels may not be the same. Therefore, the time lengths of different frames are not necessarily the same, and the driving voltages of different frames are not necessarily the same, and the time length and driving voltage of each frame are determined by the system designer. However, in a system, the time length of each frame is generated based on the system clock, so this feature can be used to adjust the gray scale difference of the EPD panel. Because each frame changes a gray level, under the same driving voltage, changing the time length of the frame means changing the brightness of a gray level change. For example, as shown in FIG. 12 , the timing controller 18 includes a voltage-controlled oscillator 50 to provide a system clock CLK, which is the basis for determining the time length of the frame. When the brightness of the EPD panel 20 is to be adjusted, the frequency of the system clock CLK can be adjusted, thereby changing the time length of each frame. For example as shown in Figure 13, the system clock pulse changes from CLK1 to CLK2, and its frequency increases, so the time length of each frame applied to the EPD panel 20 will be shortened, so the time for the electrophoretic particles to move during each frame becomes shorter, at the same Driven by a certain voltage, its displacement shortens. Referring to formula 1, the shortening of the time t will reduce the difference of the gray levels, so the fineness of each gray level can be changed by adjusting the frequency of the system clock CLK.

In different embodiments, the frequency of the system clock CLK is not changed, but the number of clock counts corresponding to each frame is changed. For example, the original time length of a frame is equivalent to 50 clock counts, which is reduced to 40 clock counts, that is, its time length is shortened by 20%.

Now check the capacity of the key. In a 16-gray-scale system, the look-up table only needs to store the driving waveforms of 16 frames. If the frequency level corresponding to each frame is stored in 4 bits, the lookup table needs a capacity of 16×4÷8=8 bytes, which is much lower than the capacity of the conventional lookup table.

Claims (10)

1. An electrophoretic display, characterized in that said display comprises: An electrophoretic display panel containing multiple pixels; a timing controller connected to the electrophoretic display panel; and A flash memory, connected to the timing controller, stores the driving waveform of the plurality of pixels changing one gray scale; Wherein, when updating the picture, the timing controller reads the required driving waveform from the flash memory, generates a control signal to the electrophoretic display panel, and adjusts at least one pixel among the plurality of pixels gray scale. 2. A method for updating a picture of an electrophoretic display, characterized in that, the method comprises the following steps: A. Erase the afterimage of the old picture; and B. Multiple frames are opened continuously, and each frame only changes one gray scale, so as to gradually adjust the pixels to be updated to their respective desired gray scales. 3. The image updating method according to claim 2, wherein said step A comprises applying a reset voltage pulse to all pixels of said electrophoretic display. 4. The image updating method according to claim 2, wherein said step B comprises first adjusting all pixels of said electrophoretic display to the same gray scale. 5. The image updating method according to claim 2, wherein said step B comprises first adjusting all pixels of said electrophoretic display to a full black gray scale. 6. The image updating method according to claim 2, wherein said step B comprises first adjusting all pixels of said electrophoretic display to full white grayscale. 7. The image updating method according to claim 2, wherein said step B comprises first adjusting all the pixels of said electrophoretic display to a gray scale between a full black gray scale and a full white gray scale. 8. The screen updating method according to claim 2, wherein said method further comprises adjusting the time lengths of said plurality of frames. 9. The screen updating method according to claim 2, further comprising adjusting the frequency of the system clock to adjust the time lengths of the plurality of frames. 10. The picture updating method according to claim 2, further comprising adjusting the number of clock counts corresponding to each frame, so as to adjust the time lengths of the plurality of frames.

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