JP6038475B2 - Display device, information processing device, display driving method, display driving program, and computer-readable recording medium - Google Patents

Description

  The present invention mainly relates to a display device that performs screen refresh and a display driving method that controls the manner of screen refresh.

  In recent years, thin, lightweight, and low power consumption display devices typified by liquid crystal display devices have become extremely popular. A typical mounting form of such a display device is, for example, a mobile phone, a smartphone, a notebook PC (Personal Computer), or the like. In the future, electronic paper, which is a thinner display device, is expected to develop and spread rapidly. Under such circumstances, it is currently a common problem to reduce power consumption in various display devices.

  In a conventional CG (Continuous Grain) silicon TFT liquid crystal display panel, an amorphous silicon TFT liquid crystal display panel, or the like, an AC drive method is adopted, and it is necessary to perform screen refresh at 60 Hz. Therefore, attempts have been made to realize a refresh rate lower than 60 Hz in order to save power in the conventional liquid crystal display panel.

  For example, in Patent Document 1 below, a low blanking period is set for one vertical scanning period, and the analog circuit of the driver of the data signal line is stopped by setting the long blanking period as a pause period. A driving method of a display device that realizes power consumption is disclosed.

  Further, in Patent Document 2 listed below, while image data stored in a memory for displaying a still image on a display panel is intermittently read out in units of one screen (one field or one frame), A read stop period is provided for a certain period (one field or one frame). Patent Document 2 discloses that power consumption can be significantly reduced because driving of the image sensor and reading of image data from the memory can be stopped during the reading stop period.

  Further, in Patent Document 3 listed below, an image signal encoded by MPEG4-LSI constituting a host side device of a portable terminal is sent to a display driver built in the liquid crystal display device of the portable terminal. The update status of the image signal is detected in the display driver, and a signal for stopping the transmission of the display signal or the transmission of the display signal is requested from the display driver to the MPEG4-LSI in accordance with the update status of the image signal. A display driving method for sending a signal is disclosed.

JP 2001-31253 A (released on November 09, 2001) Japanese Patent Laid-Open No. 11-338425 (published on Dec. 10, 1999) JP2003-036046 (published on Feb. 07, 2003)

  However, in each of the above prior arts that attempted to reduce the refresh rate, the host control unit that generates image data for displaying an image on the liquid crystal display panel refreshes the screen even if the image data is updated. Or there is a problem that screen rewriting may be delayed.

  This problem will be specifically described with reference to FIG. 11 and FIG.

(60Hz refresh)
First, as shown in FIG. 11, in a conventional CG silicon TFT liquid crystal display panel, an amorphous silicon TFT liquid crystal display panel, or the like, screen refresh is performed at 60 Hz, so that the image data A generated by the host controller is 60 Hz. Transferred to the LCD driver. Even when the image A data is updated to the image B data in the host control unit, the transfer timing does not change, and the image B data is transferred to the liquid crystal driver at 60 Hz.

  The transfer timing of 60 Hz is given by the vertical synchronization signal. Further, as the liquid crystal driver, for example, a so-called COG driver mounted on a glass substrate of a liquid crystal display panel by COG (Chip on Glass) is taken as an example.

  Based on the image data transferred from the host controller to the liquid crystal driver and the vertical synchronization signal, the liquid crystal driver drives the liquid crystal display panel. Thereby, the screen of the liquid crystal display panel is refreshed at 60 Hz, and the display quality of the image A and the image B is kept good.

  Note that the example of FIG. 11 shows a case where the liquid crystal driver does not have a frame memory for holding the transferred image data, so the liquid crystal driver drives the liquid crystal display panel as soon as the image data is transferred. It is like that.

  Thus, if image data is transferred at 60 Hz and the liquid crystal driver drives the liquid crystal display panel at 60 Hz, the power consumption cannot be reduced.

(Low rate refresh)
Therefore, as shown in FIG. 12, if the transfer of the image data is thinned out and the transfer rate of the image data is lowered, a pause period can be given to at least one of the host control unit and the liquid crystal driver, so that power consumption can be reduced. become.

  In the example shown in FIG. 12, image data transfer is thinned out every other period (one frame) of the vertical synchronization signal, and as a result, image data is transferred at 30 Hz, and similarly, screen refresh is performed at 30 Hz. Can do.

  The techniques disclosed in the above-mentioned Patent Documents 1 to 3 are basically the same as the example shown in FIG.

  In this case, the host control unit assumes that the image A data is updated to the image B data at the time t1 shown in FIG. 12, and the time t1 coincides with the timing for thinning the transfer of the image B data. Suppose you did.

  Then, the actual transfer of the image B data is executed at a time t2 that is delayed by one frame from the time t1, and based on the transfer, the liquid crystal driver drives the liquid crystal display panel. Therefore, since the screen refresh is executed later than the update timing of the data of the image B, the display responsiveness deteriorates.

(Use of frame memory-delay of screen refresh)
Next, a problem that occurs when the liquid crystal driver includes a frame memory will be described with reference to FIG.

  In the liquid crystal driver, as shown in FIGS. 13A and 13B, a vertical synchronizing signal and a horizontal synchronizing signal are generated. The image data transferred from the host control unit to the liquid crystal driver is temporarily stored in the frame memory. As shown in FIGS. 13E and 13F, the liquid crystal driver receives the same image data from the frame memory at 60 Hz. Reading is repeated, the liquid crystal display panel is driven, and the screen is refreshed.

  Accordingly, since the screen refresh is performed at 60 Hz as in FIG. 11, the display quality can be maintained in a good state, while the effect of reducing the power consumption can be obtained as compared with the example of FIG. This is because, as shown in FIG. 13D, the host control unit does not need to transfer the image data every frame, that is, 60 Hz, and only when the image data is updated, the image data A or the image data B Is transferred to the liquid crystal driver.

  However, as in the example of FIG. 12, there arises a problem that the screen refresh may be delayed from the update timing of the image data. The reason is as follows.

  Since the liquid crystal driver includes a frame memory, a state in which reading of image data (memory read) from the frame memory is completed becomes a state in which transfer of new image data can be accepted. The liquid crystal driver notifies the host control unit that it has become acceptable by sending a transfer request signal shown in FIG. 13C to the host control unit.

  The transfer of the image A data or the image B data shown in (d) of FIG. 13 is executed in response to the rise of the transfer request signal (time t1 or t5).

  Assume that the host controller updates the image A data to the image B data at time t4 between times t1 and t5. As shown in FIG. Assume that it belongs to the period of frame 2.

  In this case, since the next timing when the transfer request signal is sent from the liquid crystal driver to the host controller is time t5, transfer of the image data B starts after time t5. For this reason, the memory read must be started from time t6 belonging to the period of frame 3.

  As described above, even when the liquid crystal driver includes a frame memory, the screen refresh may be executed with a delay of one frame from the update of the image data.

(Use of frame memory-broken display image)
If the liquid crystal driver has a frame memory and the image data is transferred when the image data is updated without using the transfer request signal, the display image is broken (discontinuity). Another problem occurs. This problem will be described below with reference to FIG.

  FIG. 14 shows that the memory read starts from time 0 and ends at time Te, and that data transfer of image A starts from Ta and ends at time Tae. Represents. The memory read speed (straight line) indicated by the solid line is smaller than the image data transfer speed (straight line) indicated by the broken line.

  Therefore, when the transfer of the image B data starts from the time Tb in the middle of the memory read and ends in the middle of the memory read, the memory read is performed at the time Tx (Tb <Tx <Te). Will be overtaken by the transfer of.

  In this case, if the display of the data of the image A shown in (b) of FIG. 14 is updated to the display of the data of the image B shown in (c) of FIG. 14, the display of the data of the image A at the time Tx. Switches to the display of the data of image B. As a result, the display image cracks (screen cracks) as shown in FIG. 14D occur, and the display quality deteriorates.

  In order to solve this problem, the transfer speed of image data is lowered and the operation performance is lowered, or the liquid crystal driver generates the transfer request signal and the transfer of the image B data is completed by the memory read. Whether to start after the time Te is adopted. In any case, a comfortable display operation cannot be provided to the user.

(Liquid crystal display panel in which TFT is constituted by an oxide semiconductor using In, Ga, Zn )
Recently, indium (In), gallium (Ga), the development of liquid crystal display panels in the oxide semiconductors to result TFT using a zinc (Zn) has been promoted intensively.

An oxide semiconductor using In, Ga, and Zn has an electron mobility that is about 20 to 50 times higher than that of amorphous silicon. Therefore, a TFT can be reduced in size, and the pixel aperture ratio is improved accordingly. be able to. In addition, unlike the conventional CG silicon TFT liquid crystal display panel or amorphous silicon TFT liquid crystal display panel, it is not necessary to refresh the screen at 60 Hz, and the refresh rate can be reduced to about 1 Hz. Have.

The present invention has been made in view of the above-mentioned problems and the technical level, and its main purpose is high-speed screen update and low refresh using a TFT composed of an oxide semiconductor using In, Ga, and Zn. An object of the present invention is to provide a display device that can achieve both driving.

In order to solve the above problems, a display device according to the present invention provides
(a) a display unit having a screen;
(b) a display driving unit that drives the display unit to cause the screen to perform display based on display data;
(c) a host controller that transfers updated display data for one screen to the display driver when the display data is updated;
(d) The display driver is
(1) At the latest, while the updated display data is being transferred from the host control unit to the display driving unit, the driving of the display unit is started.
(2) Drive that terminates driving of the display unit based on the updated display data by the display drive unit from a transfer end time at which transfer of the updated display data ends from the host control unit to the display drive unit. The timing for driving the display unit is controlled so that the end time is later.

  According to the above configuration, the updated display data is transferred from the host control unit to the display driving unit when the display data is updated, and there is no change in the display content of one screen. The display data is not basically transferred.

  Further, when the update display data is transferred, the display drive unit starts driving the display unit during the transfer of the update display data at the latest. To drive.

  Note that “at the latest” means that the display drive unit may start driving the display unit at the same time or almost simultaneously with the transfer of the updated display data.

  Further, since the display driving unit drives the display unit so that the driving end time is later than the transfer end time, a display before updating and a display after updating exist simultaneously on one screen. A good display can be obtained by quickly responding to the update of the update display data without causing a problem of screen breakage.

  As a result, it is possible to reduce the refresh rate of the screen while maintaining good display quality, and thus it is possible to provide a display device that achieves both high-speed display update and low power consumption.

The display drive unit of the display device according to the present invention includes:
(a) a memory for storing the updated display data for at least one screen;
(b) The update display data stored in the memory is read after a predetermined time has elapsed from the drive end time, and the screen is refreshed using the read update display data.

  According to the above configuration, the screen is refreshed by the display driving unit after a predetermined time has elapsed from the driving end time even in a period in which the display data is not updated.

  Therefore, even if a period in which the display data is not updated continues, it is possible to prevent the display quality of the screen from deteriorating.

  In this case, since the host control unit is not involved in the screen refresh at all, the host control unit can be kept in a dormant state during a period when the display data is not updated.

In the display device according to the present invention,
(a) The update display data stored in the memory is referred to as stored update display data.
(b) While the display drive unit refreshes the screen using the stored update display data, the display data is updated, and new update display data for one screen is controlled by the host. Transferred to the above memory,
(c) The display driver is
(c-1) after finishing the driving of the display unit based on the stored update display data,
(c-2) The driving of the display unit based on the new update display data is completed from the transfer end time when the transfer of the new update display data is completed from the host control unit to the display drive unit. So that the driving end time is later
(c-3) The readout of the new updated display data from the memory is delayed.

  According to the above configuration, even when the display data is updated while the display driving unit is refreshing the screen using the stored updated display data, the display quality is lowered. And the screen display can be updated at high speed.

  That is, first, the new update display data is read from the memory, and the display unit based on the stored update display data starts to drive the display unit using the read new update display data. This is after the driving of the part is finished.

  Therefore, it is possible to prevent the screen from being broken by simultaneously performing the display based on the stored update display data from the middle of the display based on the stored update display data.

  Secondly, since the reading of the new update display data from the memory is delayed so that the drive end time is later than the transfer end time, the transfer of the new update display data (to the memory) is delayed. Can be prevented from occurring when the drive of the display unit (reading of the memory) is overtaken.

In the display device according to the present invention,
(a) The update display data stored in the memory is referred to as stored update display data.
(b) While the display drive unit refreshes the screen using the stored update display data, the display data is updated, and new update display data for one screen is controlled by the host. Transferred from the memory, written to the memory,
(c) And when the speed at which the updated display data is transferred from the host controller to the display driver is faster than the speed at which the display is driven based on the updated display data,
(d) The display drive unit displays the display based on the stored update display data before the drive of the display unit based on the stored update display data is overtaken by transfer of the new update display data. The driving of the display unit is interrupted, and the driving of the display unit is switched based on the new updated display data.

  According to the above configuration, while the display driving unit is refreshing the screen using the stored updated display data, the display data is updated and the updated display data is transferred. If the display speed is faster than the speed at which the display unit is driven, the display unit is driven based on the stored update display data (reading from the memory) and the new update display data is transferred ( There is a risk of screen breakage due to overtaking of (writing to the memory).

  Therefore, the display drive unit is configured to display the display unit based on the stored update display data before the drive of the display unit based on the stored update display data is overtaken by transfer of the new update display data. Is controlled to switch to driving the display unit based on the new updated display data.

  As a result, the screen display based on the stored update display data is switched to the screen display based on the new update display data as soon as the display data is updated, without causing a screen break. Therefore, it is possible to ensure high-speed display updating without degrading display quality.

The host control unit of the display device according to the present invention includes:
(a) a host-side memory for storing the updated display data for at least one screen;
(b) The update display data stored in the host-side memory is read after a lapse of a certain time from the transfer end time, and the read update display data is transferred to the display driver.

  According to the above configuration, the screen is refreshed based on the updated display data read and transferred from the host-side memory after a fixed time has elapsed from the drive end time even in a period in which the display data is not updated. The

  Therefore, even if a period in which the display data is not updated continues, it is possible to prevent the display quality of the screen from deteriorating.

In the display device according to the present invention,
(a) The host control unit includes a host-side memory for storing the updated display data for at least one screen,
(b) The display drive unit sends a transfer request signal to the host control unit after a lapse of a fixed time from the drive end time,
(c) The host control unit reads the update display data stored in the host-side memory in response to receiving the transfer request signal from the display drive unit, and reads the read update display data to the display drive. It transfers to the part.

  According to the above configuration, the screen is read and transferred from the host-side memory in response to a request from the display driving unit after a predetermined time has elapsed from the driving end time even in a period in which the display data is not updated. Refreshed based on the updated display data.

  Therefore, even if a period in which the display data is not updated continues, it is possible to prevent the display quality of the screen from deteriorating.

  In the screen refresh in this case, the host control unit may transfer the updated display data when requested by the display driving unit. In other words, since the host control unit can be kept dormant during a period when there is no request from the display drive unit, an effect of suppressing power consumption can be obtained.

The display drive unit of the display device according to the present invention includes:
(a) In the period when the display data is not updated, the fixed time is gradually set longer,
(b) The update display data read from the memory is used to gradually delay the timing for refreshing the screen.

  Thereby, when the predetermined time is suddenly set longer and the refresh rate is suddenly lowered, adverse effects on the display such as a change in color can be prevented.

  The host control unit gradually delays the fixed time set for reading the update display data stored in the host-side memory after a lapse of a fixed time from the transfer end time. The refresh timing may be gradually delayed.

  Further, the fixed time set for sending the transfer request signal from the display driver to the host controller may be gradually delayed, thereby gradually delaying the timing for refreshing the screen.

In the display unit of the display device according to the present invention,
(a) A plurality of pixels are arranged two-dimensionally,
(b) a switching element for turning on and off the application of a voltage corresponding to the display data to the pixel is provided corresponding to at least one of the pixels;
(c) The switching element is a TFT formed of an oxide semiconductor using In, Ga, and Zn .

According to the above configuration, a display device provided with a TFT formed of an oxide semiconductor using In, Ga, and Zn as a switching element can suppress a screen display refresh rate to about 1 Hz. It is possible to sufficiently achieve the object of the present invention, that is, compatibility between high-speed updating and low power consumption.

  Note that an information processing apparatus equipped with any of the above display devices is also included in the scope of the present invention.

  The information processing apparatus is an apparatus that places particular emphasis on portability, such as a mobile phone, a smartphone, a notebook PC, a tablet terminal, an electronic book reader, or a PDA (Personal Digital Assistant).

  Since such an information processing apparatus is equipped with any of the display devices described above, the battery consumption time is kept long and the display responsiveness is improved, so that the comfort of the user who uses the information processing apparatus is improved. Can do.

A display driving method according to the present invention includes:
(a) A display driving method by a display driving unit that drives the display unit so as to display on the screen of the display unit based on display data,
(b) when the display data is updated, receiving updated display data for one screen;
(c) in the middle of receiving the updated display data at the latest, starting to drive the display unit;
(d) The display unit is driven so that a driving end time for ending driving of the display unit based on the updated display data is later than a reception end time at which reception of the updated display data ends. And a step of controlling timing.

  As described above, the screen refresh rate can be reduced while maintaining good display quality, as described above, thereby achieving the object of the present invention to achieve both high-speed display update and low power consumption. Can do.

  A display driving program for causing a computer to execute each step in the display driving method and a computer-readable recording medium storing the display driving program are also included in the scope of the present invention.

  According to the present invention, when the display control data is updated, the host control unit transfers the update display data for one screen to the display drive unit, and the display drive unit receives update display data from the host control unit at the latest. In the middle of the transfer, the drive of the display unit is started, and the display drive unit displays the display based on the update display data from the transfer end time when the transfer of the update display data ends from the host control unit to the display drive unit. The timing for driving the display unit is controlled so that the driving end time for ending the driving of the unit is delayed.

  Therefore, it is possible to reduce the refresh rate of the screen while maintaining good display quality, and it is possible to provide a display device that can achieve both high-speed display update and low power consumption.

3 is a timing chart showing an embodiment of a display driving method according to the present invention. It is a block diagram which shows the structure as one Embodiment of the display apparatus which concerns on this invention. It is explanatory drawing which shows an example of the relationship between the timing of an image update, and the timing of a display drive. It is explanatory drawing which shows the other example of the relationship between the timing of image update, and the timing of a display drive. It is a timing chart which shows the form which a host control part takes the lead regarding the screen refresh control performed during the interval of an image update. It is a timing chart which shows the form which a host control part and a display drive part perform in cooperation regarding the screen refresh control performed during the interval of an image update. It is explanatory drawing which shows a screen crack countermeasure in case the display drive speed is faster than an image update speed in the screen refresh control which a display drive part performs independently. It is explanatory drawing which shows the countermeasure against a screen crack when a display drive speed is slower than an image update speed in the screen refresh control which a display drive part performs independently. An example of step-wise rate reduction refresh control is shown. 10 is a timing chart illustrating a reference example in which low-rate refresh control is performed by detecting image update. It is a timing chart which shows an example of the refresh control in the conventional display apparatus. It is a timing chart which shows an example of the low-rate refresh control in the conventional display apparatus. It is a timing chart which shows an example of the low-rate refresh control in the conventional display apparatus provided with the frame memory. It is explanatory drawing which shows the generation | occurrence | production mechanism of a screen crack.

  An embodiment of the present invention will be described below with reference to the drawings.

(Configuration of display device)
FIG. 2 is a block diagram showing a configuration as one embodiment of the display device according to the present invention.

  As shown in FIG. 2, the display device 1 roughly includes a display unit 10, a display driving unit 20, and a host control unit 30.

The display unit 10 includes a screen, and is configured by a liquid crystal display panel in which TFTs are configured by an oxide semiconductor using In, Ga, and Zn as an active matrix liquid crystal display panel, for example.

A liquid crystal display panel in which a TFT is formed of an oxide semiconductor using In, Ga, and Zn is a switching element provided corresponding to at least one of a plurality of pixels arranged two-dimensionally as described above. This is a liquid crystal display panel that employs a TFT composed of an oxide semiconductor using In, Ga, and Zn .

By adopting a TFT composed of an oxide semiconductor using In, Ga, and Zn as the switching element, the pixel aperture ratio can be improved and the refresh rate of the screen display can be reduced to about 1 Hz. be able to. The improvement in the pixel aperture ratio brings about an effect of brightening the display or a power saving effect by reducing the amount of light of the backlight when the display brightness is the same as that of the CG silicon liquid crystal display panel.

  The display drive unit 20 is, for example, a so-called COG driver that is mounted on the glass substrate of the display unit 30 with COG (Chip on Glass), and the display unit 10 is displayed on the screen so as to perform display based on display data. To drive.

The display driving unit 20 includes a MIPI receiving circuit 21, a RAM 22 (memory), a timing generator (hereinafter abbreviated as TG) 23, a source driver 24, and a display refresh control unit 25. Further, as an option, the display driving unit 20 may include an image detection unit 26 described later.

The display unit refresh control unit 25 has a built-in storage unit 27 (computer-readable recording medium) that stores a display drive program for controlling the operation of the display drive unit 20.

  MIPI is an abbreviation for Mobile Industry Processor Interface, and means an open standard established by a non-profit organization for mobile application processor interfaces.

  The MIPI receiving circuit 21 receives display data converted and sent from the host control unit 10 using, for example, MIPI data transfer specifications, and returns the display data before conversion.

  The RAM 22 stores display data output from the MIPI receiving circuit 21.

The TG 23 reads the display data stored in the RAM 22 according to the timing instructed from the display unit refresh control unit 25, sends it to the source driver 24, and generates the drive timing for the display unit 10.

  The source driver 24 applies a display voltage corresponding to the display data to the pixels of the display unit 10 according to the drive timing.

  More specific operation of each part of the display driving unit 20 will be described in detail later.

  The host control unit 30 includes a screen update detection unit 31, a CPU 32, a VRAM 33 (Video Random Access Memory), an I / O interface 34, and a host TG 35.

  The screen update detection unit 31 detects whether it is necessary to update the display on the screen of the display unit 10. For example, when an application activated and executed in the display device 1 notifies the screen update detection unit 31 of the display update, the user of the display device 1 updates the display via the input unit. The screen update detection unit 31 needs to update the display of the screen to the CPU 32 when the screen update detection unit 31 is notified of a display update due to data streaming or broadcast waves via the Internet. Inform that there is.

  In response to this, the CPU 32 acquires the update display data for one screen, and rewrites the display data stored in the VRAM 33 with the update display data.

  The host TG 35 transfers the display data or the update display data to the display driver 20 and the MIPI receiving circuit 21 using, for example, the MIPI data transfer specification. The TG 35 may transfer the synchronization signal together with the display data.

Further, the TG 23 can independently generate the display drive timing, and the display unit refresh control unit 25 can also generate the timing independently. However, the TG 23 can generate the display drive timing or the display unit refresh control unit 25. A synchronization signal sent from the host TG 35 may be used to generate timing.

  In addition, as an information processing apparatus suitable for mounting the display device 1, for example, a mobile phone, a smartphone, a notebook PC, a tablet terminal, an electronic book reader, a PDA, or the like, particularly an information processing apparatus that emphasizes portability. Can be mentioned.

(Point of display drive method)
FIG. 1 is a timing chart showing an embodiment of a display driving method according to the present invention.

  As shown in FIG. 1A, in response to detection of an image update by the screen update detection unit 31, update display data for one screen is transferred from the host TG 35 to the TG 21. Next, the update display data is sent from the host TG 35 to the TG 21 when the display data A (image A in FIG. 1) is updated to display data B (image B in FIG. 1).

  In other words, the display device 1 basically transfers display data from the host control unit 30 to the display driving unit 20 only when the image is updated. In other words, the display data transfer method of the display device 1 is a conventional method in which the same display data is transferred for screen refresh every vertical scanning period (for example, 60 Hz) or every other vertical scanning period (for example, 30 Hz). It is completely different from the transfer method.

  Subsequently, in the display driving unit 20, when the MIPI receiving circuit 21 receives the display data A, the display data A is written in the RAM 22. While the display data A is being written to the RAM 22, the TG 23 synchronizes the display data A from the RAM 22 with FIFO (First-In, First-Out) at a timing synchronized with the vertical synchronization signal ((b) in FIG. 1). Reading is performed by the method, and the display unit 10 is driven by the source driver 24 ((d) in FIG. 1).

  Thus, in the display device 1, the first point is that when the image is updated, the updated display data is transferred from the host control unit 30 to the display driving unit 20. The second point is that driving of the display unit 10 based on the updated display data is started within the same frame (same vertical scanning period) as the frame to which the updated display data is transferred.

Along with the first point, in the period in which the image is not updated, the host control unit 30 and the display driving unit 20 can have a pause period during which the operation is paused, so that the effect of low power consumption is great. In addition, since the display unit 10 uses the TFT formed of the above-described oxide semiconductor using In, Ga, and Zn , the screen refresh rate can be significantly reduced to about 1 Hz compared to the related art. Thereby, the effect of low power consumption can be further increased.

  Further, the second point brings about the effect of high-speed updating of the screen.

(Basic timing of screen update)
(1. When the display drive speed is slower than the image update speed)
Next, it is an important point to appropriately set the timing for starting the driving of the display unit 10 and the timing for ending the driving so as not to cause screen breakage. This point will be described below with reference to FIGS.

  FIG. 3 is an explanatory diagram illustrating an example of a relationship between image update timing and display drive timing. In particular, FIG. 3 shows that when the speed at which the display driving unit 20 drives the display unit 10 is compared with the speed at which the host control unit 30 detects update of the image and transfers it to the display driving unit 20, the former is greater than the latter. The slow case is shown.

  Note that the speed at which the display driving unit 20 drives the display unit 10 is represented by the time from when the source driver 24 starts driving the display unit 10 based on the updated display data to when it finishes driving. Hereinafter, the speed at which the display driving unit 20 drives the display unit 10 is referred to as a display driving speed.

  The speed at which the host control unit 30 detects the update of the image and transfers it to the display driving unit 20 is expressed by the time from when the host TG 35 starts to transfer the updated display data to the MIPI receiving circuit 21 until the transfer ends. Suppose that Hereinafter, the speed at which the host control unit 30 detects the update of the image and transfers it to the display driving unit 20 is referred to as an image update rate.

  As shown in FIGS. 3A to 3C, when the display drive speed is slower than the image update speed, the TG 23 generates a vertical synchronization signal immediately after the start of transfer of the update display data, and the source driver 24 performs display drive. Can start. However, the end of display driving is later than the end of transfer of display data.

  FIG. 3D shows the relationship between the image update timing and the display drive timing more easily by a graph.

  The vertical axis of the graph represents the amount of data, and the horizontal axis represents time. In order to help conceptual understanding, it is assumed that the data amount to be updated and the data amount used for display driving are the same data amount E.

  Then, as shown in FIG. 3D, when the display drive speed is slower than the image update speed, the display drive is performed simultaneously with the image update in order to achieve the purpose of executing the display update on the display unit 10 at a high speed. It is preferable to start at almost the same time. However, the display drive end time te is later than the image update end time tE.

  In this case, the phenomenon that the image update and the display drive intersect does not occur. Therefore, in this case, as long as the display driving is started at the same time as the start of the image update or later, there is no possibility that the problem of the screen cracking described with reference to FIG. 14 will occur.

(2. Display drive speed is faster than image update speed)
On the other hand, FIG. 4 is an explanatory diagram showing another example of the relationship between the image update timing and the display drive timing, and particularly shows the case where the display drive speed is faster than the image update speed.

  As shown in FIGS. 4A to 4C, it is preferable to start the display drive in the middle of the image update in order to update the display unit 10 at high speed. As shown, it is important that the display drive end time te is always later than the image update end time tE.

  If the display drive end time te ′ is earlier than the image update end time tE, as indicated by the virtual straight line K in FIG. 4D, the display drive overtakes the image update at the time tx. Become.

  In this case, display data before update (stored update display data) stored in the RAM 22 is rewritten to update display data up to a data amount G (0 <G <E), and then the data amount (EG). Corresponding display data before update is read by the TG 23 and used to drive the display unit 10.

  In this case, the display on the display unit 10 is, contrary to the display shown in FIG. 14D, a triangle image based on the updated display data is displayed on the upper half, and a circle based on the display data before the update is displayed on the lower half. Type of screen breakage occurs.

  As can be seen from the above description based on FIG. 4D and FIG. 14A, the display drive and the image update intersect temporally regardless of the magnitude relationship between the display drive speed and the image update speed. This is a condition for avoiding screen cracks.

Therefore, with respect to the display drive control executed by the display drive unit 20, the requirements for achieving both high-speed display update and prevention of screen breakage are summarized as follows.
(1) The drive of the display unit 10 is started during the transfer of updated display data from the host control unit 30 to the display drive unit 20 at the latest.
(2) End of driving to end the driving of the display unit 10 based on the updated display data by the display driving unit 20 from the transfer end time tE when the transfer of the updated display data ends from the host control unit 30 to the display driving unit 20 The timing for driving the display unit 10 is controlled so that the time te is delayed.

(FIFO delay time)
When the display drive speed is faster than the image update speed, the display drive always overtakes the image update if the display drive is started simultaneously with the image update. Therefore, when the display drive speed is faster than the image update speed, timing control is required to delay the display drive start time ts from the image update start time 0, as shown in FIGS. become.

  In order to create a delay time for delaying the display drive start time, the TG 23 sets the delay time. That is, the TG 23 delays the start of data reading from the RAM 22 from the start of image update. The time for delaying the reading of the RAM 22 is called a FIFO delay time.

(How to determine FIFO delay time)
The TG 23 knows in advance the time required for image update Tr (see FIG. 4A) and the time required for display driving for one screen Td as constants. Therefore, the image update end time tE can be obtained by adding the required time Tr to the image update start time, and the display drive start time (ts) can be obtained by adding the required time Td to the display drive start time (ts). The end time te can be obtained.

  As a result, the TG 23 determines the shortest FIFO delay time so that the display drive end time te is later than the image update end time tE, and generates a vertical synchronization signal simultaneously with the end of the FIFO delay time. Can do.

  Since the start timing of the screen update may change, the FIFO delay time shown in FIG. 4B is not a constant but a variable variable.

(Display drive unit single low refresh control)
Next, as shown in FIGS. 1C and 1D, a mode in which the display driving unit 20 independently performs low-rate refresh control will be described below.

For example, in a display device using the above-described TFT formed of an oxide semiconductor using In, Ga, and Zn as an active switching element, the screen refresh rate of the display unit 10 is about 1 Hz (refreshed once per second). Can be dropped. However, when a still image is displayed for a while, the interval until the display data A is updated to the display data B may exceed 1 second as shown in FIG.

  In such a case, even if there is no image update, a process for refreshing the screen and maintaining high display quality is required.

Therefore, the display refresh control unit 25 measures the elapsed time from the end time of the previous display drive by the built-in timer, and when the elapsed time reaches a certain reference time, the display refresh control unit 25 performs FIG. A memory read instruction signal shown in (c) of FIG.

  In response to receiving the memory read instruction signal, the TG 23 reads the display data A stored in the RAM 22, and the source driver 24 refreshes the image A displayed on the display unit 10. Therefore, in this embodiment, the TG 23 can refresh the screen by generating a vertical synchronization signal in synchronization with the memory read instruction signal.

  The first merit of this form is that the control executed by the display drive unit 20 and the host control unit 30 is simplified, and the second merit is that the power saving effect of the display device 1 is great.

The reason why the first merit is obtained is that the display driving unit 20 can be configured by a hardware circuit as a driver dedicated to a liquid crystal display panel in which TFTs are configured by an oxide semiconductor using In, Ga, Zn , for example. It is. Since the hardware circuit automatically executes the refresh control process, the control load on the display drive unit 20 is reduced and the host control unit 30 does not need to perform the refresh control process. Does not require a control load for refresh.

  The reason why the second merit is obtained is that the host control unit 30 can be paused during a period when there is no image update. The power saving effect due to the suspension of the host control unit 30 is very large.

  In this embodiment, the memory capacity of the RAM 22 requires one frame. From the viewpoint of reducing the area occupied by the display drive unit 22 or reducing the cost, the memory capacity of the RAM 22 is preferably small.

(Host-led low refresh control)
A second form of control for refreshing the screen even when there is no image update will be described below with reference to FIG.

  FIG. 5 is a timing chart showing a form led by the host control unit 30 regarding the screen refresh control performed during the image update interval.

  In the host control unit 30, the CPU 32 measures the elapsed time from the end time of the previous image update using a built-in timer, and when the elapsed time reaches a certain reference time, the host TG 35 is not illustrated. A memory read instruction signal is given. The elapsed time may not be measured by the CPU 32 but may be replaced by the host TG 35.

  As shown in FIGS. 5A and 5B, in response to the reception of the memory read instruction signal, the host TG 35 reads the display data A stored in the VRAM 33 at a timing synchronized with the vertical synchronization signal, and MIPI Transfer to the receiving circuit 21.

  Then, as shown in FIGS. 5C and 5D, when the display data A is transferred, the display driver 20 displays the source driver 24 at the timing synchronized with the vertical synchronization signal generated by the TG 23. 10 is driven to refresh the image A displayed on the display unit 10.

  The merit of this form is that the control load of the display drive unit 20 is reduced. This is because the display drive unit 20 needs to drive the display unit 10 only when display data is transferred from the host control unit 30.

  Instead, the host control unit 30 must measure the elapsed time during the image update interval, and cannot pause. For this reason, the power saving effect is smaller than the refresh control of the display drive unit 20 alone.

(Cooperative refresh control)
A third form of control for refreshing the screen even when there is no image update will be described below with reference to FIG.

  FIG. 6 is a timing chart illustrating a mode in which the host control unit 30 and the display driving unit 20 perform in cooperation with respect to the screen refresh control performed during the image update interval.

In this embodiment, first, the display unit refresh control unit 25 measures the elapsed time from the end time of the previous display drive by the built-in timer, and when the elapsed time reaches a certain reference time, the host control unit A transfer request signal shown in FIG.

  This transfer request signal is sent to the CPU 32 via the I / O interface 34. In response to this, as described above, the CPU 32 gives a memory read instruction signal (not shown) to the host TG 35.

  As shown in FIGS. 6A and 6B, the host TG 35 receives the display data A stored in the VRAM 33 at a timing synchronized with the transfer vertical synchronization signal in response to the reception of the memory read instruction signal. Read and transfer to the MIPI receiving circuit 21.

  Next, as shown in FIGS. 6D and 6E, when the display data A is transferred, the display driver 20 displays the source driver 24 at a timing synchronized with the vertical synchronization signal generated by the TG 23. The image A displayed on the part 10 is refreshed.

  The merit of the third form is that the control load of the host control unit 30 is lighter than that of the second form. This is because the host control unit 30 does not need to perform the time management described in the second mode during the image update interval. Therefore, the power saving effect is greater than that of the second mode.

(Display drive unit single low refresh control-Screen cracking countermeasure 1)
It has already been described with reference to FIG. 1 that the display driving unit 20 independently performs the screen refresh during the image update interval.

  In this embodiment, the screen refresh performed independently by the display driving unit 20 and the image update detected by the host control unit 30 are independent. For this reason, depending on the timing of image update, the image may be updated while the display drive unit 20 is refreshing the screen.

  Then, as described with reference to FIG. 4D, when the display drive speed is faster than the image update speed, a state in which the display drive overtakes the image update may occur.

  Alternatively, as described with reference to FIG. 14A, when the display drive speed is slower than the image update speed and the transfer of the image data B starts from the time Tb during the display drive, the display drive is performed. A state of overtaking may occur at time Tx.

  In any of the above cases, the above-described screen breakage occurs. Therefore, when the display driving unit 20 performs the screen refresh alone, it is necessary to take measures to reliably avoid the occurrence of the screen breakage. preferable.

  Therefore, first, screen breakage countermeasure 1 when the display drive speed is faster than the image update speed will be described.

  FIG. 7 is an explanatory diagram showing a countermeasure for screen breakage when the display drive speed is faster than the image update speed in the screen refresh control performed independently by the display drive unit 20.

  As shown in FIGS. 7A, 7C, and 7D, the screen refresh using the stored update display data in the RAM 22 is executed from time 0 to time te, and the image update starts from time t1 in the middle. Consider a case in which display driving corresponding to the image update is executed from time t2.

  In this case, since the TG 23 knows the image update speed, the display drive speed, and the image update start time t1, the screen refresh end time te, the image update end time tE, and the image update shown in FIG. The display drive end time te ′ when the display drive start time t2 is determined can be obtained.

  Therefore, the TG 23 has a FIFO delay based on the time t1 so that the display drive start time t2 is after the screen refresh end time te and the display drive end time te ′ is after the image update end time tE. Time can be determined.

  The FIFO delay time is not a constant but a variable because it changes with the image update start time t1. Although there is no upper limit in setting the FIFO delay time, it is preferable to set the FIFO delay time as short as possible so as not to violate the purpose of high-speed image update. In the example of FIG. 7, the display drive start time t2 is determined at a timing synchronized immediately after the screen refresh end time te.

  Thereby, screen breakage can be prevented and high-speed screen update can be realized.

(Display drive unit single low refresh control-Screen crack countermeasure 2)
On the other hand, when the display drive speed is slower than the image update speed, a screen crack countermeasure 2 different from the screen crack countermeasure 1 is necessary.

  FIG. 8 is an explanatory diagram showing a countermeasure for screen breakage when the display drive speed is slower than the image update speed in the screen refresh control performed independently by the display drive unit 20.

  As shown in FIG. 8D, when the image update start time t1 is located in the middle of the screen refresh start time 0 to the screen refresh end time te and the display drive speed is slower than the image update speed, the time tx In (t1 ≦ tx <te), a state in which the display drive is overtaken by the image update may occur.

As a countermeasure in this case, the ongoing screen refresh is canceled at time tx. Specifically, the screen refresh is canceled by using a gate drive cancel function for stopping the gate drive for turning on TFTs formed of oxide semiconductors using In, Ga, and Zn in the display portion 10 in a line sequential manner. .

  8A to 8C, the image update start time t1 and the time tx are made to coincide with each other, and when the screen update detection unit 31 detects an image update during the screen refresh, the screen refresh is canceled immediately. The control form (I) is shown.

  However, the present invention is not limited to this control mode, and as shown in FIG. 8D, the time when the TG 23 uses the display drive speed, the image update speed, and the image update start time t1 to overtake the display drive by the image update. A control mode (II) in which tx is obtained by calculation and the screen refresh is canceled at the obtained time tx may be employed.

  Thereby, for example, the image A is being displayed on the screen, and the image B that is the updated image is overwritten from the beginning of the screen in the middle of the refresh of the image A. As soon as there is, the image A is rewritten to the image B. Accordingly, screen breakage can be prevented and high-speed screen updating can be realized.

(Display drive unit single low refresh control-supplement)
Even when the display drive speed is slower than the image update speed, there is a case where the above-mentioned screen breakage countermeasure 1 using the FIFO delay time can be applied instead of the above-mentioned screen breakage countermeasure 2. This case will be supplemented below.

  As shown in FIG. 8E, even if the image update starts at time t1 in the middle from the screen refresh start time 0 to the screen refresh end time te, the image update end time tE is greater than the screen refresh end time te. Consider the case later.

  In this case, since the image update does not overtake the screen refresh, the display drive corresponding to the image update can be continuously executed as soon as the screen refresh is completed.

  The display drive start time t2 corresponding to the image update can be set by the FIFO delay time. That is, the TG 23 can obtain the FIFO delay time that is after the display drive start time t2 from the screen refresh end time te with the image update start time t1 as a base point.

  To summarize the above, the TG 23 obtains the screen refresh end time te and the image update end time tE, and if te ≦ tE, selects the image update start time t1 + FIFO delay time setting control (screen breakage countermeasure 1), If te> tE, the gate drive cancellation (screen breakage countermeasure 2) may be selected.

(Gradual rate reduction refresh control)
For example, consider a case where the display is switched to a still image or an image with little motion while the display unit 10 is displaying a moving image. During the display of the moving image, for example, the screen is updated at 60 Hz. On the other hand, during the display of a still image or an image with little motion, screen refresh is performed at a cycle of, for example, about 1 Hz by applying the present invention.

  Therefore, when the moving image is switched to a still image or the like, the screen update rate drops sharply from 60 Hz to 1 Hz, for example. A sudden change in the screen update rate may adversely affect the display, such as changing the color of the image.

  Considering this point, it is preferable to gradually decrease the screen update rate, in other words, the screen refresh rate.

  Therefore, as shown in FIG. 9A, when a long interval occurs after the image A is transferred from the host control unit 30 to the display driving unit 20 and until the next image update, ( As shown in b) to (d), the refresh rate of the screen is gradually lowered. This stepwise rate reduction refresh control is performed by the TG 23.

  For example, when the display drive unit 20 performs low-rate refresh alone, the TG 23 reduces the refresh rate, that is, the cycle of reading display data from the RAM 22 in stages, such as 60 Hz, 30 Hz, 15 Hz, 5 Hz, and 1 Hz. To go.

  As a result, when the refresh rate is suddenly reduced, it is possible to prevent adverse effects on the display such as a change in the color of the image.

  In the step-wise rate reduction refresh control described here, the display drive unit 20 performs low rate refresh independently (FIG. 1), and the host control unit 30 performs low rate refresh (FIG. 5). The display drive unit 20 and the host control unit 30 can be applied in any manner (FIG. 6) in which low rate refresh is performed in cooperation.

(Reference example)
By the way, there is a system that has to transfer an image at 60 Hz from the host controller to the display driver even for a still image, such as when the performance of the host controller is low. Even in such a system, it is possible to achieve both low-rate refresh and high-speed image update. An example of refresh control applied to such a system will be described last as a reference example.

  First, as for the configuration of the display device 1, as shown in FIG. 2, an image detection unit 26 is provided in the display drive unit 20. The image detection unit 26 receives display data of the current frame from the MIPI receiving circuit 21 and reads stored display data from the RAM 22, that is, display data one frame before the current frame. In short, the image detection unit 26 compares the display data of the current frame with the display data of the previous frame, and determines whether the image has been updated.

The determination result is sent from the image detection unit 26 to the display unit refresh control unit 25. In response to this, the display unit refresh control unit 25 gives the TG 23 a memory read instruction signal shown in FIG. As a result, as shown in FIG. 10E, screen refresh using display data read out from the RAM 22 by the TG 23 is executed.

  When the image detection unit 26 detects an image update, the detection signal may be given to the TG 23 and the TG 23 may read the display data from the RAM 22 using the detection signal as a trigger.

Further, as shown in FIG. 10E, when the image detection unit 26 detects an image update, the display unit refresh control unit 25 or the TG 23 sets a flag indicating update detection in the RAM 22 and sets the flag. Display driving may be started at the timing synchronized with the vertical synchronization signal corresponding to the next frame. In this way, the control of the display drive start timing is not complicated.

  The configuration of the display device 1 in this reference example is organized as follows.

The display device according to the reference of the present invention,
(a) a display unit having a screen;
(b) a display driving unit that drives the display unit to cause the screen to perform display based on display data;
(c) a host control unit that transfers display data for one screen to the display drive unit at a constant cycle (for example, every vertical scanning period);
An update detection unit that detects whether or not there is an update in the display data transferred from the host control unit to the display drive unit,
(d) The display driver is
When the update detection unit does not detect the update of the display data, a pause period is provided in which the display unit is stopped based on the display data.
(e) The display drive unit refreshes the display of the screen at least when the update detection unit detects an update of the display data.

(Supplement)
Finally, each block of the display device 1, particularly each block of the display drive unit 20, may be configured by hardware logic, or a program code (execution format program) of a control program that is software that realizes each function described above. , Intermediate code program, source program) can also be achieved by reading out from the storage unit 27 and executing it.

The recording medium recorded so as to be readable by the computer is not limited to the form of the storage unit 27 built in the display unit refresh control unit 25, and may be a recording medium that can be externally attached to the display device 1. Examples of such a recording medium include a tape system such as a magnetic tape and a cassette tape, a magnetic disk such as a floppy (registered trademark) disk / hard disk, and an optical disk such as a CD-ROM / MO / MD / DVD / CD-R. A disk system including an IC card (including a memory card) / optical card or a semiconductor memory system such as a mask ROM / EPROM / EEPROM (registered trademark) / flash ROM can be used.

  The display device 1 may be configured to be connectable to a communication network, and the program code may be supplied via the communication network. The communication network is not particularly limited. For example, the Internet, intranet, extranet, LAN, ISDN, VAN, CATV communication network, virtual private network, telephone line network, mobile communication network, satellite communication. A net or the like is available.

  Further, the transmission medium constituting the communication network is not particularly limited. For example, even in the case of wired such as IEEE 1394, USB, power line carrier, cable TV line, telephone line, ADSL line, etc., infrared rays such as IrDA and remote control, Bluetooth ( (Registered trademark), 802.11 wireless, HDR, mobile phone network, satellite line, terrestrial digital network, and the like can also be used.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The present invention can be used for a display device that requires low power consumption or an information processing apparatus equipped with the display device.

DESCRIPTION OF SYMBOLS 1 Display apparatus 10 Display part 20 Display drive part 22 RAM (memory)
27 Storage unit (computer-readable recording medium)
30 Host control unit 33 VRAM (host side memory)

Claims (6)

A display unit with a screen;
A display driving unit for driving the display unit to cause the display to perform display based on display data;
A host controller that transfers updated display data for one screen to the display driver when the display data is updated;
The display driver is
(1) to the display driver from the host control unit, in the course of being transferred on the Symbol updated display data, starts the driving of the display unit based on the update display data,
(2) Drive that terminates driving of the display unit based on the updated display data by the display drive unit from a transfer end time at which transfer of the updated display data ends from the host control unit to the display drive unit. Control the timing to drive the display unit so that the end time is later ,
The display driver is
A memory for storing the updated display data for one screen;
After a lapse of a certain time from the drive end time, the updated display data stored in the memory is read out, the updated display data is used to refresh the screen,
The update display data stored in the memory is referred to as stored update display data,
While the display driver is refreshing the screen using the stored updated display data, the display data is updated, and new updated display data for one screen is transferred from the host controller. Is written to the above memory,
And when the speed at which the updated display data is transferred from the host controller to the display driver is faster than the speed at which the display is driven based on the updated display data,
The display driver is
The drive of the display unit based on the stored update display data for one screen is interrupted before the drive of the display unit based on the stored update display data is overtaken by the transfer of the new update display data. And switching to driving of the display unit based on the new updated display data . The host control unit
A host-side memory for storing the updated display data for at least one screen;
2. The update display data stored in the host-side memory is read after a lapse of a predetermined time from the transfer end time, and the read update display data is transferred to the display driver. Display device. The host control unit includes a host side memory for storing the updated display data for at least one screen,
The display driving unit sends a transfer request signal to the host control unit after a lapse of a fixed time from the driving end time,
The host control unit reads the update display data stored in the host-side memory in response to receiving the transfer request signal from the display drive unit, and transfers the read update display data to the display drive unit. The display device according to claim 1. The information processing apparatus equipped with a display device according to any one of claims 1 to 3. A display driving method by a display driving unit for driving the display unit so as to cause display on the screen of the display unit to perform display based on display data,
A step of receiving updated display data for one screen when the display data is updated;
In the middle of receiving the upper Symbol updated display data, comprising the steps of starting driving of the display unit based on the update display data,
The timing for driving the display unit is controlled so that the driving end time for ending the driving of the display unit based on the updated display data is delayed from the receiving end time for receiving the updated display data. the method comprising the steps of,
With respect to the memory that stores the updated display data for one screen, after the elapse of a certain time from the driving end time, the updated display data stored in the memory is read out, and the read updated display data is used to read the updated display data. Refreshing the screen, and
The update display data stored in the memory is referred to as stored update display data,
During the step of refreshing the screen using the stored updated display data, the display driving unit updates the display data, receives new updated display data for one screen, and stores it in the memory. writing,
And when the speed at which the updated display data is received is faster than the speed at which the display unit is driven based on the updated display data,
Before the drive of the display unit based on the stored update display data is overtaken by the reception of the new update display data, the drive of the display unit based on the stored update display data for one screen is interrupted. The display drive method further includes a step of switching to drive of the display unit based on the new updated display data . 6. A display driving program for causing a computer to execute each step in the display driving method according to claim 5 .

Images