JP2005140958A - Display device and portable equipment using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To refresh the display contents of respective pixels in a refresh period meeting the information holding time of liquid crystal display elements in a liquid crystal display device using the liquid crystal display elements of a long information holding time, and to immediately change the display contents in changing the pixel information and to reduce the management burden for the purpose of refresh management. <P>SOLUTION: In the liquid crystal display device using the liquid crystal display elements of the long information holding time, a refresh control means is so constituted as to periodically write image information at intervals of the refresh time Tref regardless of the presence or absence of the write of the image information by a change control means. As a result, the display contents of the respective pixels can be refreshed at the refresh period meeting the information holding time of the liquid crystal display elements, and when the image information is changed, the display contents can be immediately changed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a display device such as a liquid crystal display device using a liquid crystal element having a long image information retention time, and a portable device using the display device.

  A liquid crystal display device is widely used as a display device such as a television receiver, a computer terminal monitor, and a display unit of a mobile phone.

  Each of the liquid crystal display elements of the liquid crystal display device has a unique information retention time. This information holding time is applied by applying a predetermined voltage to the liquid crystal display element, for example, from the display-on state where the liquid crystal is twisted and reversed, and removing the applied voltage from the outside to return the twist and turning off the display, or This is the time until the contrast is in a state where the allowable value is divided.

  In the conventional liquid crystal display device, since the information holding time of the liquid crystal display element is as short as about several tens of milliseconds, for example, it is necessary to refresh (redisplay) the display information of the liquid crystal display device in a cycle corresponding to the information holding time. It has become.

  When the displayed image is a moving image, the image information itself is updated in a short cycle, so that there is no problem that the retention time of the liquid crystal display element is short depending on the degree.

  However, when displaying an image with little change, such as a display unit of a mobile phone or a monitor of a personal computer that performs a man-machine interface, detection is performed using data delayed by one frame as in Patent Document 1. Thus, the display information refresh cycle is made as long as possible, the number of refreshes is reduced, and power consumption as a display device is reduced.

  In addition, liquid crystal display elements with improved information retention characteristics and longer retention times have been researched and developed. For example, twisted nematic (TN) liquid crystal elements, etc., which have information retention times of several hundred ms to several seconds. Has been announced.

Even when a display device is configured using a liquid crystal display element having a long holding time, the display device is driven by a simple matrix method (multiplex method), an active matrix method, or the like that is usually employed. In any driving method, the refresh cycle Tref can be set longer in accordance with the information holding time Thold of the liquid crystal display element (where Told> Tref), and power consumption as a display device can be reduced. it can.
JP 7-239463 A

  For the pixels in which the image information has changed, it is necessary for viewing the image to change the display contents substantially simultaneously with the change. Therefore, as shown in FIG. 5, the elapsed time is counted starting from the display content change time (indicated by a circle in the figure) for each pixel, and the time of the refresh cycle Tref, that is, the refresh time Tref has elapsed. At that time (indicated by the mark ● in the figure), the display contents are refreshed. For pixels whose display contents have been changed before the refresh time Tref elapses, the count value is reset, and the elapsed time from that point is counted again toward the refresh time Tref.

  As described above, since it is necessary to manage the refresh cycle Tref for each pixel, there is a problem that the management burden increases.

  Accordingly, the present invention provides a display device such as a liquid crystal display device using a liquid crystal display element having a long information holding time, and refreshes the display contents of each pixel at a refresh cycle corresponding to the information holding time of the display element. The purpose is to immediately change the display contents when information is changed and to reduce the management burden for refresh management.

The display device according to claim 1 includes a display unit having display elements arranged corresponding to pixels;
An image memory for storing image information to be displayed on the display unit corresponding to the pixels;
Refresh control means for writing the image information stored in the image memory to the display elements corresponding to the respective pixels of the display section at a refresh time Tref having a time interval shorter than the information holding time Thold of the display elements; A change control means for writing the changed image information to the display element corresponding to the pixel whose information has changed, and a display control unit for performing display control,
Regardless of whether or not image information is written by the change control means, the refresh control means periodically writes image information at the interval of the refresh time Tref.

The display device according to claim 2 is the display device according to claim 1, wherein a flag area is provided at the same address as the image information of each pixel of the image memory,
The change control means sets a flag indicating that the image information has changed in the flag area of the same address as the image information when storing the changed image information in the image memory corresponding to the pixel,
Only the image information in which the flag is set is written to the corresponding display element, and the flag is reset.

  The display device according to claim 3 is the display device according to claim 2, wherein when the image information is stored in the image memory, the input image information and the already stored image information are compared for each pixel, The flag is set according to the mismatch.

  In the display device according to claim 4, in the display device according to claim 3, if the input image information has a display density slightly lower than the image information already stored as a result of the comparison, the flag is not set. The image information is stored in the image memory.

  According to a fifth aspect of the present invention, in the display device according to the second aspect, when image information is stored in the image memory, the input image information is regarded as changed image information, and a change control process is performed. Features.

  The portable device according to claim 6 uses the display device according to any one of claims 1 to 5.

  According to the display device of the first aspect, regardless of whether the image information is written by the change control means, the refresh control means periodically writes the image information at the interval of the refresh time Tref, so that the information holding time is long. In a display device using a display element, the display content of each pixel is refreshed at a refresh cycle corresponding to the information holding time of the display device, and the display content is immediately changed when the pixel information is changed, and the refresh cycle Tref is managed. Since all pixels can be performed collectively or for each group, the management burden can be reduced.

  According to the display device of claim 2, by writing only the image information in which the flag is set in the corresponding display element in the next drive cycle, the image information changed in the minimum change cycle can be displayed. If there is no change again by resetting the flag, the display is automatically updated only in the refresh cycle.

  According to the display device of claim 3, when all image information is input regardless of whether or not the image information is changed, only the display element corresponding to the pixel whose image information is changed is selectively changed. be able to.

  According to the display device of the fourth aspect, since the display density of the corresponding display element changes in a direction that naturally decreases with time, the frequency of change can be reduced accordingly. Further, since the changed image information is written in the image memory, it is updated with the changed image information at the next refresh.

  According to the display device of the fifth aspect, when only the image information corresponding to the changed pixel is inputted from the host side, the comparison process can be omitted, so that the processing speed can be increased.

  According to the portable device of the sixth aspect, since the current consumption can be reduced, the usage time can be extended.

  Embodiments of a display device according to the present invention will be described below with reference to the drawings as examples of a liquid crystal display device.

  FIG. 1 is a block diagram showing the overall configuration of the liquid crystal display device of the present invention, FIG. 2 is a diagram showing a timing chart for refreshing the liquid crystal display and changing display contents, and FIG. 3 is a partially enlarged timing chart. FIG. 4 is a diagram showing the memory structure of the image memory.

  In FIG. 1, a liquid crystal display unit 11 is a liquid crystal display element provided corresponding to each pixel and has a long information retention time (for example, several hundred ms to several seconds), and these liquid crystal display elements are arranged in a matrix. Has been.

  The liquid crystal display element group arranged in a matrix is driven by a simple multiplex method, an active multiplex method, or the like. The Y driver 12 and the X driver 13 supply scanning signals and information signals for matrix driving to the liquid crystal display unit 11 based on the control signals.

  The image memory 14 corresponds to the number of liquid crystal display elements of the liquid crystal display unit 11 and is composed of a RAM having storage elements corresponding to the display depth (gradation), and writing or reading is performed by each command signal. Is called.

  The display control unit 15 writes the image information supplied from the host 16 configured by the MPU or the like through the interface 17 to the image memory 14 or reads out the image information stored in the image memory, Control operations as a liquid crystal display device such as display content change control to the liquid crystal display unit 11, Y driver 12, and X driver 13, display control of refresh control, and counter control are performed.

  Now, image information to be displayed is output from the host 16 and supplied to the display control unit 15 via the interface 17. This image information is usually not significantly considered whether it has changed from the previous image information or the like, and one screen is regularly shorter than at least the information holding time Thold of the liquid crystal display element of the present invention. Supplied in cycles.

  The display control unit 15 sequentially compares the image information supplied from the host 16 and the image information read from the image memory 14 for each corresponding pixel, and determines whether they match or do not match. If they match, there is no change in the image information of the pixel, so the liquid crystal display is not changed for this pixel.

  However, if they do not match, the image information of the pixel is changed, so that the information of the pixel in the image memory 14 is newly rewritten with the changed image information, and the pixel of the liquid crystal display unit 11 at that time Is rewritten with new image information. This change control is repeated for every pixel of one screen every time image information is supplied from the host 16. Thus, the liquid crystal display element corresponding to the pixel whose image information has changed can be displayed with a new display density immediately after the change.

  The display control unit 15 also performs refresh control separately from change control for immediately rewriting a liquid crystal display element corresponding to a pixel whose image information has changed. In this refresh control, the image information stored in the image memory 14 is written to the liquid crystal display element corresponding to each pixel of the liquid crystal display unit 11 at a refresh cycle Tref having a time interval shorter than the information holding time Thold of the liquid crystal display element. In this refresh control, image information is periodically written at an interval of the refresh time Tref regardless of whether or not image information is written by change control.

  The timing chart of the above change control and refresh control is shown in FIG. In FIG. 2, change control for changing the display content is indicated by ○, and refresh control for updating the display content is indicated by ●. Since the liquid crystal display is driven in matrix, simultaneous or collective control actually requires time for scanning.

  In FIG. 2, for example, regarding pixel 1, each refresh period No. 1-No. Since there is no change control for changing the display contents in all three, refresh control is performed for each refresh period Tref. On the other hand, regarding the pixel 3, the first period No. No. 2 twice during the third period No. 1 Although the display content is changed once during 3, refresh control is performed for each refresh time Tref, as with other pixels, regardless of the change in the display content.

  In this manner, the liquid crystal display elements corresponding to all the pixels are updated at the refresh time interval regardless of whether or not the image information is written by the change control means. Accordingly, time management for refresh control can be performed simply by providing a single repetitive counter for all pixels in common, so a simple configuration is sufficient.

  In the example of FIG. 2, all the pixels are refreshed at the same time, but instead, all the pixels are divided into a plurality of groups (eg, m groups), and refresh control is performed for each group in time. You may make it carry out by shifting. In this case as well, time management for refresh control can be performed by providing one repetition counter in common for all pixels and assigning each count value (1 to m) to each group.

  Next, a more specific configuration example of the change control will be described with reference to FIGS.

  As shown in FIG. 3, one change period Tc includes an input period Ti and a drive period Td. This one change period Tc is a period that is significantly shorter than the refresh period Tref, and this change period Tc is repeated.

  FIG. 4 is a diagram showing a memory structure of the image memory 14, and is configured to store pixel image information and flag set / reset for each address A + 1 to A + n.

  When the image information from the host 16 is supplied to the display control unit 15 during the input period Ti, the image information is read from the corresponding addresses A + 1 to A + n of the image memory 14 according to the designation of the pixel address. Then, for each pixel, the supplied image data and the read image data are compared to determine whether they match or do not match.

  If they match, the same image information as before is stored in the address of the pixel in the image memory 14. On the other hand, in the case of mismatch, the image information supplied to the corresponding address in the image memory 14 is written and stored. Along with the storage of the image information, a flag indicating that the image information has been changed is set, attached to the image information, and stored. When the comparison / change detection / write processing is completed for one screen, display content change control is performed in the subsequent drive period Td.

  During this change control, image information is read from the image memory 14 for each address, only the liquid crystal display element corresponding to the address for which the flag is set is rewritten, and the flag is reset.

  In this way, the pixel changed during the input period Ti is written in the corresponding liquid crystal display element only in the image information for which the flag is set in the next drive cycle Td, so that the changed image information is minimized. The change period Tc can be displayed. Further, when the flag is reset, the display is automatically updated only in the refresh cycle Tref when there is no change again.

  In the example of FIG. 4, a memory area for a flag is provided in the image memory 14, but instead, a memory for a flag is provided separately from the image memory 14, and writing and reading are performed at the same address. May be controlled.

  Next, a modified example of the control method of the change control means will be described.

  The display density of the liquid crystal display element has a property that the density decreases with time after the applied voltage is removed. Using this property, the display content change control can be partially simplified.

  That is, when image information is stored in the image memory 14, the input image information and the already stored image information are compared for each pixel, and the flag is set according to the mismatch. In this case, as a result of the comparison, if the input image information has a display density (for example, one gradation) slightly lower than the image information that has already been stored, the flag of the image memory 14 is not set without setting the flag. Rewrite image information to input pixel information.

  In this case, since the flag is not set, the display information is not changed in the subsequent drive period Td, although the image information of the pixel changes slightly in the direction in which the display density decreases. This is because the display density of the liquid crystal display element has a property of decreasing with time, so that the frequency of change is reduced by that amount without changing the display contents. However, since the image information after the change is written in the image memory 14, it is updated with the image information after the change at the next refresh, so that it does not cause a big problem as an image to be displayed.

  Next, display control in the case of other methods for supplying image information supplied from the host 16 will be described.

  As a method of supplying image information to be displayed on the display control unit 15 from the host 16 via the interface 17, it is not necessary to consider whether or not it has changed from the previous image information as described above. In addition to a method in which image data is periodically supplied in a short cycle, the host side monitors whether there is a change in image information, and when any pixel in one screen changes, the image for that one screen There are a method of supplying information, and a method of supplying only image information corresponding to a changed pixel in one screen with a corresponding address.

  Among these, in the method in which the image information for one screen having changed is supplied, the liquid crystal display control is similarly performed by the display control method described above.

  In the method in which only the image information corresponding to the changed pixels in one screen is supplied, only the image information that has been confirmed on the host 16 side is supplied with an address because there is a change in display contents. There is no need to perform comparison and coincidence detection again on the display device side.

  Therefore, in each of the embodiments described above, when image information is stored in the image memory 14, the input image information can be regarded as changed image information and change control processing can be performed.

  According to this liquid crystal display device, when only image information corresponding to the changed pixel is input from the host side, the comparison processing and the like can be omitted, so that the processing speed can be increased.

  In the description so far, the display content change control and the refresh control are all processed in units of pixels. In the case of a color image, it is of course possible to similarly perform processing in units of pixels.

  However, in a color image, one color pixel is basically represented by three pixels of R, G, and B, so that display content change control and refresh control can be performed in units of color pixels.

  In the above description, only the liquid crystal display device has been described. However, other display devices such as electronic paper and electronic sheet may be used as long as the display device needs to perform refresh control.

The block diagram which shows the whole structure of the liquid crystal display device of this invention The figure which shows the timing chart of refresh of the liquid crystal display of this invention, and display content change Figure showing a partially enlarged timing chart Diagram showing the memory structure of the image memory The figure which shows the timing chart of the refresh of the conventional liquid crystal display, and display content change

Explanation of symbols

11 Liquid crystal display unit 12 Y driver 13 X driver 14 Image memory 15 Display control unit 16 Host 17 Interface Tref Refresh cycle Tc Change cycle

Claims (6)

A display unit having a display element arranged corresponding to the pixel;
An image memory for storing image information to be displayed on the display unit corresponding to the pixels;
Refresh control means for writing the image information stored in the image memory to the display element corresponding to each pixel of the display unit at a refresh time shorter than the information holding time of the display element; A change control means for writing the changed image information to the display element corresponding to the changed pixel, and a display control unit for performing display control,
Regardless of whether or not image information is written by the change control means, the refresh control means periodically writes the image information at the refresh time interval. A flag area is provided at the same address as the image information of each pixel of the image memory,
The change control means sets a flag indicating that the image information has changed in the flag area of the same address as the image information when storing the changed image information in the image memory corresponding to the pixel,
2. The display device according to claim 1, wherein only the image information in which the flag is set is written to a corresponding display element, and the flag is reset.   When the image information is stored in the image memory, the input image information and the already stored image information are compared for each pixel, and the flag is set according to the mismatch. The display device according to claim 2.   As a result of the comparison, when the input image information has a display density slightly lower than the image information already stored, the image information is stored in the image memory without setting the flag. The display device according to claim 3.   3. The display device according to claim 2, wherein when the image information is stored in the image memory, the input image information is regarded as changed image information, and change control processing is performed.   A portable device using the display device according to claim 1.

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