Abstract:
A display controller system with a memory controller and buffers is described. The system enables transferring data from the main memory of the CPU to the image memory without interfering with the image updating. As a result, the present invention may allow continuously updating the image display and continuously writing new image data from CPU to the image memory, which improves overall system performance.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. non-Provisional application Ser. No. 13/828,370, filed Mar. 14, 2013 (Publication No. 2013/0222404), which is itself a continuation-in-part of U.S. non-Provisional application Ser. No. 12/882,094, filed Sep. 14, 2010 (Publication No. 2011/0063314, now abandoned) which claims priority to U.S. Provisional Application No. 61/242,680, filed Sep. 15, 2009; the contents of all the preceding applications are incorporated herein by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a display controller system and a method of transferring data from the main memory of a CPU to a display device, in particular, an electrophoretic display. 
       BACKGROUND OF THE INVENTION 
       [0003]    An electrophoretic display (EPD) is a non-emissive device based on the electrophoresis phenomenon of charged pigment particles suspended in a solvent. The display usually comprises two plates with electrodes placed opposing each other, separated by using spacers. One of the electrodes is usually transparent. A suspension composed of a colored solvent and charged pigment particles is enclosed between the two plates. When a voltage difference is imposed between the two electrodes, the pigment particles migrate to one side and then either the color of the pigment or the color of the solvent can be seen according to the polarity of the voltage difference. 
         [0004]    In order to obtain a desired image, driving waveforms are required for an electrophoretic display. A driving waveform consists of a series of voltages applied to a pixel to allow migration of the pigment particles in the electrophoretic fluid. For an image of 600×800 pixels, there is a tremendous amount of image data and waveforms that need to be processed in a given time period. While the images are being constantly updated, in the method currently used, the central processing unit of a computer must wait until an image update is completed before the display controller can receive additional image data. This method has the disadvantage of delaying processing the image data, thus causing slow-down of the entire system. 
       SUMMARY OF THE INVENTION 
       [0005]    The first aspect of the present invention is directed to a display controller system for transferring image data to a display wherein the display controller comprises a memory controller, a first buffer and a second buffer, and the memory controller transfers data from one of the buffers which is full, to an image memory. 
         [0006]    In one embodiment, the memory controller determines if image data from a CPU memory is transferred to the first buffer or the second buffer. In one embodiment, the two buffers operate as ping-pong buffers. In one embodiment, the display controller further comprises a display controller CPU and a look-up table. In one embodiment, the image memory has at least three spaces. 
         [0007]    The second aspect of the present invention is directed to a method of transferring data for a display device, which method comprises:
       (A) accessing current and next image data from an image memory and comparing the two images,
           (ii) finding the appropriate driving waveforms, one for each of the pixels in a given line, from a lookup table,   (iii) forwarding to a display voltage data to be applied to each of the pixels in said given line; and   
           (B) transferring image data from a buffer which is full to the image memory, and
           both steps A and B are completed within a line updating time period.   
               
 
         [0013]    In one embodiment, during multiple line updating time periods, Steps A and B repeat and are carried out in an interleaving manner. In one embodiment, in a line updating time period, Step B is skipped. In one embodiment, the display is an electrophoretic display. In one embodiment, the line updating time period is calculated from a frame time divided by the number of lines of pixels. 
         [0014]    The third aspect of the present invention is directed to a display system comprising:
       an electrophoretic display;   a display controller comprising a memory controller and two buffers; and   an image memory.       
 
         [0018]    The display controller system and method of the present invention enables transferring data from the main memory of the CPU to the image memory without interfering the image updating. As a result, the present invention may allow continuously updating the display image and continuously writing new image data from CPU to the image memory, which improves overall system performance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a cross-section view of a typical electrophoretic display device. 
           [0020]      FIG. 2  illustrates the structure of a pixel. 
           [0021]      FIG. 3  illustrates an active matrix backplane. 
           [0022]      FIG. 4  illustrates a driving waveform. 
           [0023]      FIG. 5A  illustrates an operating system for a display device. 
           [0024]      FIG. 5B  illustrates the current display controller system. 
           [0025]      FIG. 6  illustrates a display controller with a memory controller in accordance with an embodiment of the present invention. 
           [0026]      FIGS. 7A-7C  illustrate methods of the present invention for transferring image data. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]      FIG. 1  illustrates a typical electrophoretic display  100  comprising a plurality of electrophoretic display cells  10   a ,  10   b  and  10   c . In  FIG. 1 , the electrophoretic display cells  10   a ,  10   b ,  10   c , on the front viewing side indicated with the graphic eye, are provided with a common electrode  11  (which is usually transparent and therefore on the viewing side). On the opposing side (i.e., the rear side) of the electrophoretic display cells  10   a ,  10   b  and  10   c , a substrate ( 12 ) includes discrete pixel electrodes  12   a ,  12   b  and  12   c , respectively. Each of the pixel electrodes defines an individual pixel of the electrophoretic display. In practice, a single display cell may be associated with one discrete pixel electrode or a plurality of display cells may be associated with one discrete pixel electrode. 
         [0028]    An electrophoretic fluid  13  comprising charged pigment particles  15  dispersed in a solvent is filled in each of the display cells. The movement of the charged particles in a display cell is determined by the voltage potential difference applied to the common electrode and the pixel electrode associated with the display cell in which the charged particles are filled. For example, in a binary system where positively charged white particles are dispersed in a black solvent, when no voltage is applied to a common electrode and a voltage of +15V is applied to a pixel electrode, the driving voltage for the charged pigment particles in the area of the pixel would be +15V. In this case, the driving voltage would move the white particles to be near or at the common electrode and as a result, the white color is seen through the common electrode (i.e., the viewing side). Alternatively, when no voltage is applied to a common electrode and a voltage of −15V is applied to a pixel electrode, the driving voltage in this case would be −15V and under such −15V driving voltage, the positively charged white particles would move to be at or near the pixel electrode, causing the color of the solvent (black) to be seen at the viewing side. 
         [0029]    If there is only one type of pigment particles in the electrophoretic fluid, the pigment particles may be positively charged or negatively charged. In another embodiment, the electrophoretic display fluid may have a transparent or lightly colored solvent or solvent mixture and charged particles of two different colors carrying opposite particle charges, and/or having differing electro-kinetic properties. 
         [0030]    The display cells may be of a conventional walled or partition type, a microencapsulated type or a microcup type. In the microcup type, the electrophoretic display cells may be sealed with a top sealing layer. There may also be an adhesive layer between the electrophoretic display cells and the common electrode. 
         [0031]    The term “display cell” is intended to refer to a micro-container which is individually filled with a display fluid. Examples of “display cell” include, but are not limited to, microcups, microcapsules, micro-channels, other partition-typed display cells and equivalents thereof. 
         [0032]    In a practical implementation of EPD, the desired images may be black, white, and a number of grey levels (e.g. 2, 4, 16, or 256 grey levels). The black and white colors may be, in general, referred to as first and second color states. The grey levels may be, in general, referred to as intermediate color states. 
         [0033]    The amount of data required to define an image is the number of lines in the image times the number of pixel per line times the number of bits required to defined the color. One example is a display with 600 lines×800 pixels per line times 8 bits. The 8 bits defines 256 gray levels. However, the present invention may apply to a display with different combinations of desired pixel images. 
         [0034]    An active matrix driving mechanism is often used to drive a display device. In general, an active matrix display device includes a display unit on which the pixels are arranged in a matrix form. A diagram of the structure of a pixel is illustrated in  FIG. 2 . Each individual pixel such as element  250  on the display unit is disposed in each of intersection regions defined by two adjacent scanning signal lines (i.e., gate signal lines)  252  and two adjacent image signal lines (i.e., source signal lines)  253 . The plurality of scanning signal lines  252  extending in the column-direction are arranged in the row-direction, while the plurality of image signal lines  253  extending in the row-direction intersecting the scanning signal lines  252  are arranged in the column-direction. Gate signal lines  252  couple to gate driver ICs and source signal lines  253  couple to source driver ICs. 
         [0035]    More specifically, a thin film transistor (TFT) array is composed of a matrix of pixels and ITO region  251  (a transparent electric conducting film) each with a TFT device  254  and is called an array. A significant number of these pixels together create an image on the display. For example, an EPD may have an array of 600 lines by 800 pixels/line, thus 480,000 pixels/TFT units. 
         [0036]    A TFT device  254  is a switching device, which functions to turn each individual pixel on or off, thus controlling the number of electrons flow into the ITO zone  251  through a capacitor  255 . As the number of electrons reaches the expected value, TFT turns off and these electrons can be kept within the ITO zone. 
         [0037]      FIG. 3  illustrates an active matrix backplane  380  for an EPD. In an active matrix backplane, the source driver  381  is used to give the proper voltages to the line of the pixels. And the gate driver  382  is used to trigger the update of the pixel data for each line  383 . 
         [0038]    In practice, charged particles corresponding to a pixel are driven to a desired location by a series of driving voltages which is often referred to as a driving waveform. 
         [0039]    Typically, a driving waveform period is 100 msec to 10 seconds, depending upon the quality of a display device, age of the display device, and environmental conditions (e.g., temperature, humidity or lighting conditions). 
         [0040]      FIG. 4  shows an example waveform  450  for a single pixel. For driving waveform  450 , the vertical axis denotes the intensity of the applied voltages whereas the horizontal axis denotes the driving time. The length of  453  is the driving waveform period. 
         [0041]    There are frames within the driving waveform  450  as shown in  FIG. 4  and the length of the frame is referred to as a frame period  451 . 
         [0042]    When driving an EPD on an active matrix backplane, it usually takes many frames for the image to be displayed. The term “frame period” or “frame time” is intended to refer to the interval time during which a voltage is applied to a pixel in order to update an image. For example, during the frame period  451 , a voltage of +V is applied to the pixel. 
         [0043]    The typical frame time ranges from 2 msec to 100 msec. Therefore, there may be as many as 1000 frames in a waveform period, but typically there are 20-40 frames in a waveform period. A typical frame period is 20 msec (millisecond) and therefore for a driving waveform having a length of 2000 msec, the voltages are applied 100 times to each single pixel. 
         [0044]    An image update is carried out line by line. In an example, an EPD may comprise an active matrix of 600 lines of 800 pixels per line. During each frame time, all of the pixels in the image are updated. Hence, there are 600 line updating time periods in a frame period and during each line updating time period, there are 800 pixels to be updated. Therefore the term “line updating time period” is intended to refer to the frame time divided by the number of lines in a display device. If the frame period is 20 msec, then the line updating time period for an image of 600 lines×800 pixels per line would be equal to 20/600=33 μsec (microsecond). 
         [0045]    As stated, an EPD requires a series of applied voltages to drive the pigment particles to a desired state. As described, the display controller transmits voltage information, frame by frame, to the TFT backplane of the display, e.g., the source driver IC and the gate driver IC. The gate driver IC selects which line to charge, and the source driver IC provides the appropriate voltage level. 
         [0046]      FIG. 5A  shows a system  500  which comprises a CPU (computer processing unit)  505 , CPU memory  504 , a display  501 , a display controller  502 , image memory  503 , and computer bus  506 . 
         [0047]    The CPU  505  is able to read to or write to CPU memory  504  via computer bus  506 . CPU memory  504  is sometimes referred to as the “main memory” in the system. 
         [0048]    In a display application, the images are stored in the CPU memory  504 . When an image is to be displayed, the CPU  505  sends a request to the display controller  502 . CPU  505  then instructs the CPU memory  504  to transfer the image data via computer bus  506  to the display controller  502 . 
         [0049]    In the current display controller system as shown in  FIG. 5 b   , the display controller  502  comprises a CPU of the display controller  512  and a lookup table  510 . 
         [0050]    When an image update is being carried out, the display controller CPU  512  accesses the current image and the next image from the image memory  503  and compares the two images. Based on the comparison, the display controller CPU  512  consults the lookup table  510  to find the appropriate waveform for each pixel. More specifically, when driving from the current image to the next image, a proper driving waveform is selected from the look up table for each pixel, depending on the color states of the two consecutive images of that pixel. For example, a pixel may be in the white state in the current image and in the level 5 grey state in the next image, a waveform is chosen accordingly. 
         [0051]    The selected driving waveforms are sent to the display  501  to be applied to the pixels to drive the current image to the next image. The driving waveforms however are sent, frame by frame, to the display. 
         [0052]    In this system, while the display controller  512  is busy constantly updating the images, it cannot receive additional new image data from the CPU memory  504  because the memory cannot be read or written to at the same time. The CPU memory  504  has to wait until the display controller  512  finishes updating before the additional new image data may be transmitted. This causes significant slow-down of the entire system. 
         [0053]      FIGS. 6 and 7  illustrate the present invention. 
         [0054]    In the present invention, a memory controller  611  and two buffers  608  and  609  are incorporated to solve the delay issue. 
         [0055]    As shown in  FIG. 6 , the display controller  602  of the present invention comprises the display controller CPU  612 , memory controller  611 , two buffers  608  and  609  and a look-up table  610 . 
         [0056]    According to the present invention, the new image data may be transmitted to the buffers  608  or  609  as determined by the memory controller  611 . Buffer 0   608  and buffer 1   609  are “ping-gong” or “double” buffers and are implemented to receive image data from the CPU memory  604 . The size of the buffer is significantly smaller than the size of data for a single image. For example, it may be about 0.001% to about 10% of the size of the data of a single image. 
         [0057]    In practice, while Buffer 0   608  is read, buffer 1   609  can be written to, and while buffer 1   609  is read, Buffer 0   608  can be written to. Hence, if buffer 0   608  is full, then buffer 1   609  may be available to receive image data from the CPU memory  604 . With the ping-pong buffers, data in one buffer may be processed while the next set of image data is read into the other buffer. 
         [0058]    Once one of the buffers is full, the data in that buffer is available to be processed and transferred to image memory  603 . The transferring of the data from the buffer  608  or  609  to the image memory  603  occurs during an idle time which is after the voltages for a line of pixels have been sent to the display and before the waveforms of the next line of pixels are processed. 
         [0059]    For the purpose of this invention, the image memory  603  has at least three spaces, e.g., A, B and C. Image memory Spaces A and B are occupied by the images that are being updated. The new image data are then transmitted to image memory Space C. There may be more than three spaces in the image memory. 
         [0060]    In summary, the present invention allows the following two steps (A and B) to be sequentially carried out within a “line updating time period”. 
         [0061]    Step A:
       i. accessing current and next image data from an image memory and comparing the two images,   ii. finding the appropriate driving waveforms, one for each of the pixels in a given line, from a lookup table,   iii. forwarding to a display the voltage data to be applied to each of the pixels in said given line; and       
 
         [0065]    Step B:
       i. transferring image data from a buffer which is full to the image memory.       
 
         [0067]    The current and next images may be referred to as the first and second images. 
         [0068]    In Step A(iii), the display controller CPU  612  provides the voltage data to the source driver IC and the gate driver IC of the display  601 . 
         [0069]    If neither of the buffers is full, Step B may be skipped. 
         [0070]    As described previously, the term “line updating time period” in the present invention is defined as the frame period divided by the number of lines in an image. For example, for an image of 600 lines×800 pixels per line and the frame period is 20 msec, the line updating time would be 33 μsec. 
         [0071]    The frame time is an inherent feature of an active matrix TFT driving system and it is usually set at 20 msec. 
         [0072]    As shown in  FIG. 7A , both Steps A and B are completed within a line updating time period of 33 μsec. In this example, Step A takes only 14 μsec to complete. The speed of Step A is dependent on the bandwidth of the image memory, the display controller processing time, etc. and it is significantly faster than the line updating time, 33 μsec. The present invention takes advantage of the idle time of 19 μsec to transfer the image data from buffer 0   608  or buffer 1   609  to the image memory  603  per Step B. In other words, there are 19 μsec available in each line updating time period for memory controller  611  to transfer new image data from buffer 0   608  or buffer 1   609 , whichever is full, to the image memory  603 . Step B must be completed within 19 μsec. 
         [0073]    With the aforementioned approach, CPU  605  may send the data to the buffer 0   608  or buffer 1   609  at any time and the image data in the buffers may move to the image memory  603  at a regular interval. 
         [0074]    As stated above, the data in a buffer is transferred to the image memory only when the buffer is full. In  FIG. 7B , it is shown that if in every line updating time period, there is one buffer that is full, the Steps A and B will be carried out in an interleaving manner (i.e., alternating order). If during a line updating time period, none of the two buffers is full, Step B is skipped, as shown in  FIG. 7C . 
         [0075]    The method as shown in  FIGS. 7B  (Steps A and B carried out in a interleaving manner) and  7 C (Step B is skipped in a line updating time period) may be carried out in more than one frame time or more than one waveform driving period. 
         [0076]    It is understood that it is also possible to transfer data from a buffer to the image memory when it is not full. However, in practice, it is less preferred. 
         [0077]    In order to avoid both buffers being full at the same time, the writing speed from CPU  605  to the buffers must be calculated and controlled. 
         [0078]    Although the foregoing disclosure has been described in some detail for purposes of clarity of understanding, it will be apparent to a person having ordinary skill in that art that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing both the method and system of the present invention. Accordingly, the present embodiments are to be considered as exemplary and not restrictive, and the inventive features are not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.