JP2004151222A - Liquid crystal display control unit and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display control unit which can be small-sized and with which power consumption can be reduced by controlling a refreshing rate in accordance with the state of an image. <P>SOLUTION: An image update detecting circuit part 123 detects a control command from a CPU 13 of a central arithmetic processing unit to a display controller 121 or write information from the display controller 121 to a display memory 122 to detect a display image being updated. When the update of the display image is detected, a normal high refreshing rate is set and the display image is updated in frame units. When no update of the display image is detected, the display image is displayed with a previously set number of frames and then the refreshing rate is switched to a previously set low refreshing rate. A pixel clock frequency dividing circuit 124 which divides the frequency of a pixel basic clock supplies a pixel clock corresponding to a desired frame rate from a frame rate control circuit part 125 to the display controller 121. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal display control device used for a display device such as an information device such as a mobile phone device or a PDA, and a communication device, and a liquid crystal display device using the same. The present invention relates to a required liquid crystal display control device and a liquid crystal display device using the same.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a TFT active matrix type liquid crystal display panel is used as a display unit in a display device such as a mobile phone device or a PDA which is used by being carried. In this liquid crystal display panel, a liquid crystal layer is sandwiched between a pair of electrode substrates, and a plurality of pixel portions are arranged in a matrix in a horizontal direction and a vertical direction, and a display voltage is selectively supplied to each pixel. A driving TFT is provided for each pixel. A power supply voltage is supplied from a battery to the liquid crystal display panel, and each pixel portion is selectively driven by a source signal drive circuit and a gate signal drive circuit to change the alignment state of liquid crystal molecules in each pixel portion. Accordingly, an image can be displayed by changing the transmission / scattering state of light incident on the liquid crystal layer of each pixel portion.
[0003]
FIG. 3 is a circuit diagram showing a main configuration of a conventional TFT active matrix type liquid crystal display panel.
[0004]
3, the liquid crystal display panel 100 includes a source signal line driving circuit 110 and a gate signal line driving circuit 120 disposed around a display section, a pixel array section 130 as a display section, and a common voltage generation circuit 140. And
[0005]
The source signal line driving circuit 110 includes a sampling circuit 111, a memory 112, a DAC (digital-to-analog converter) 113, and a clock unit 114, and converts image data (digital data) input from the outside into the sampling circuit 111. After sampling in the memory 112 and conversion into video data (analog data) by the DAC 113, the video data is sequentially output from the clock unit 114 to each source signal line 131 described later in synchronization with a predetermined clock timing. .
[0006]
The gate signal line drive circuit 120 sequentially selects each gate signal line 132 in synchronization with the horizontal period signal, and controls on / off of the TFT 133.
[0007]
In the pixel array section 130, a plurality of source signal lines 131 and a plurality of gate signal lines 132 are provided so as to intersect with each other, and a TFT 133 serving as a switching element is provided at a position near the intersection. The TFT 133 has a source connected to the source signal line 131, a gate connected to the gate signal line 132, and a drain connected to the RGB pixel electrode 134. A plurality of pixel electrodes 134 are arranged in a matrix. One electrode of a CS (auxiliary capacitance) 135 is connected to a counter electrode facing the pixel electrode 134.
[0008]
The common voltage generation circuit 140 is connected to the other electrode of the CS 135 via a common voltage line provided in parallel with the gate signal line 132, and applies a common voltage to the common voltage line.
[0009]
With the above structure, the video data output to each source signal line 131 via the TFT 133 of the gate signal line 132 selected by the gate signal line driving circuit 120 is written to the pixel electrode 134, and the pixel data is transferred from each pixel electrode 134 to the liquid crystal layer. A display voltage is applied.
[0010]
In this manner, by sequentially selecting the gate signal lines 132 from the first line in each horizontal cycle, data for one field can be displayed on the liquid crystal display panel 100, and this data is displayed in each vertical cycle. By repeating the operation, a still image or a moving image can be displayed on the display screen. Note that the polarity of the voltage applied from the pixel electrode 134 to the liquid crystal layer is inverted for each line and each field so that no DC component is applied to the liquid crystal.
[0011]
Incidentally, in order to suppress the power consumption of the liquid crystal display panel 100, two methods are conceivable. The first method is to lower the liquid crystal driving voltage, and the second method is to lower the refresh rate of the screen display.
[0012]
Conventionally, as a first method, for example, Japanese Unexamined Patent Publication No. 7-121137 (Patent Document 1) provides a memory for one field and a comparator, and displays the current display image and the previous field stored in the memory by the comparator. And a method of lowering the power supply voltage to the liquid crystal display panel when a comparison result is determined to be a still image with no change.
[0013]
Also, for example, in Japanese Patent Application Laid-Open No. 7-5860 (Patent Document 2), in a ferroelectric liquid crystal display panel having a slow response speed, a fast refresh rate (60 Hz) from a display controller that controls image display of the liquid crystal display panel is required. There is disclosed a technique for improving display quality by processing image data after thinning. However, this conventional technique does not control the refresh rate in consideration of low power consumption.
[0014]
[Patent Document 1]
JP-A-7-121137 (pages 3 to 4, FIG. 1)
[0015]
[Patent Document 2]
JP-A-7-5860
[Problems to be solved by the invention]
As described above, in order to suppress the power consumption of the liquid crystal display panel, the first method of lowering the liquid crystal driving voltage and the second method of lowering the refresh rate of the screen display can be considered.
[0017]
As a first method, according to the related art disclosed in Japanese Patent Application Laid-Open No. Hei 7-121137, a current display image is compared with a display image of a previous field by a comparator, and it is determined that the still image has no change. When the comparison is determined, the power consumption of the display unit is reduced by lowering the power supply voltage supplied to the liquid crystal display panel. However, basically, there is a problem that when the power supply voltage to the liquid crystal display panel is reduced in a still image state, the display characteristics are changed.
[0018]
In addition, when considering a small portable terminal device such as a mobile phone device or a PDA, the circuit size of the memory and comparator for one field becomes large, and the power consumption of that portion should be ignored as the power consumption of the small portable device. Can not be done. Further, when considering as a display control device for a small portable device, the circuit scale of the memory and the comparator for one field is large, and it is not easy to apply to a small portable device.
[0019]
In the second method, simply lowering the refresh rate may cause flicker.
[0020]
Generally, in an active matrix type liquid crystal display panel, the refresh frequency is 60 Hz. When the refresh rate is reduced, flicker can be made inconspicuous by increasing the auxiliary capacitance (Cs capacitance) provided for holding the liquid crystal applied voltage of the pixel portion for one field period to a certain level (40 Hz). it can. However, when the refresh rate is further reduced, in the conventionally used 1H line inversion driving, the contrast of the pixels for each line becomes conspicuous, and even if the same gradation is displayed, the contrast differs for each line. The display will be performed. Although it depends on the displayed image, in a video such as a map where vertical and horizontal lines are displayed, horizontal line flicker becomes noticeable when the refresh rate is on the order of 30 Hz.
[0021]
As a driving method for eliminating the flicker, a dot inversion driving method in which the polarity of a voltage applied to an adjacent dot (pixel) is inverted, or a pseudo dot inversion driving method in which RGB pixels are arranged in a staggered wiring are known. I have. According to these driving methods, flicker can be made inconspicuous even at a low refresh rate, and image quality can be improved.
[0022]
However, when displaying at a low refresh rate using such a driving method, power consumption can be reduced, but a moving image such as a video or a real-time game image cannot be satisfactorily displayed. Therefore, it is necessary to make the refresh rate variable so as to improve the display quality at a high refresh rate for moving images and to reduce the power consumption of the liquid crystal display panel at a low refresh rate for still images.
[0023]
Also, unlike a CRT using a picture tube, the polarity of the liquid crystal display panel is inverted for each line and each field so that a DC component is not applied to the liquid crystal layer. Therefore, the refresh rate is controlled in even frame units. It is necessary. Further, the switching of the refresh rate needs to be performed instantaneously before the display of the first vertical line at which the frame starts.
[0024]
The present invention has been made in view of such circumstances, and it is possible to reduce the size, and to reduce the power consumption by appropriately controlling the refresh rate according to the image state (whether or not the display image is updated). It is an object of the present invention to provide a liquid crystal display control device that can be used and a liquid crystal display device using the same.
[0025]
[Means for Solving the Problems]
The liquid crystal display control device of the present invention is a display control unit that controls image display based on a refresh rate of a screen display, an image update detection unit that detects whether or not a display image has been updated, and outputs image update detection information, Rate control means for controlling a refresh rate of the display control means based on the image update detection information, and when the update of the display image is not detected by the image update detection means, the rate control means controls the refresh rate of the screen display. Is set to a low refresh rate, thereby achieving the above object.
[0026]
Preferably, the liquid crystal display control device of the present invention further includes a display memory accessible from the display control means, and the image update detecting means includes a control command to the display control means and a write command to the display memory. By detecting at least one of them, whether or not the display image has been updated is detected.
[0027]
Further, preferably, the rate control means in the liquid crystal display control device of the present invention controls the refresh rate for the display control means to be low by dividing the pixel basic clock.
[0028]
Furthermore, preferably, in the liquid crystal display control device of the present invention, when the update of the display image is not detected by the image update detection unit, the rate control unit sets the refresh rate for the display control unit to a low refresh rate from the next frame. Set.
[0029]
Still preferably, in the liquid crystal display control device according to the present invention, when the update of the display image is not detected by the image update detection unit, the rate control unit displays the refresh rate for the display control unit after displaying a predetermined number of frames. To a low refresh rate.
[0030]
Furthermore, preferably, in the liquid crystal display control device of the present invention, when the update of the display image is detected by the image update detection means, the rate control means sets the refresh rate for the display control means to a high refresh rate.
[0031]
Still preferably, in a liquid crystal display control device according to the present invention, the rate control means switches the refresh rate with respect to the display control means in even frame units.
[0032]
Further, preferably, the rate control means in the liquid crystal display control device of the present invention switches the refresh rate to the display control means at the start of the vertical display cycle.
[0033]
A liquid crystal display device according to the present invention includes the liquid crystal display control device according to any one of claims 1 to 8, and a liquid crystal display panel whose image display is controlled by the liquid crystal display control device. Objective is achieved.
[0034]
Preferably, in the liquid crystal display device of the present invention, a dot inversion driving method for inverting the polarity of a display voltage applied to each adjacent pixel portion or a three primary color RGB for the display portion of the liquid crystal display panel. Display driving is performed by a pseudo dot inversion driving method in which the pixel portion has a staggered wiring.
[0035]
The operation of the present invention having the above configuration will be described below.
[0036]
According to the present invention, in a liquid crystal display control device for controlling image display for a TFT active matrix type liquid crystal display panel, for example, which enables display driving at a low refresh rate by dot inversion driving or pseudo dot inversion driving, The presence or absence of the update of the display image can be detected by detecting the control command to the display control means from / for example, and / or the presence / absence of writing from the display control means to the display memory by the image update detection means. Further, by dividing the pixel basic clock by a frequency dividing circuit or the like, the refresh rate can be reduced to レ ー ト, ３, ４,.
[0037]
When the update of the display image is detected (for example, a moving image), a normal high refresh rate is set and the display image is updated in frame units. When the update of the display image is not detected (for example, a still image), the preset number of frames is displayed, and then the display is switched to the preset low refresh rate.
[0038]
The display control means (display controller) sets the refresh rate of the liquid crystal display panel to a high refresh rate as usual during the display of a moving image and a low refresh rate during the display of a still image. The power consumption of both the liquid crystal display panel and the display control means can be reduced dynamically as compared with the prior art in which the voltage is reduced.
[0039]
Also, since the update of the display image can be detected by the write signal to the display memory and the IO access signal from the CPU, compared with the conventional technology of detecting the moving image using the display memory for one field and the comparator. Thus, the circuit configuration can be significantly reduced in size.
[0040]
In a liquid crystal display panel, since the polarity is inverted for each line and each field so that no DC component is applied to the liquid crystal layer, it is preferable to control the refresh rate in even frame units. In addition, since it is necessary to switch the refresh rate in units of even frames immediately, it is preferable to switch the refresh rate immediately before the display of the first vertical line where the frame starts.
[0041]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0042]
FIG. 1 is a block diagram showing a configuration of a liquid crystal display device according to one embodiment of the present invention.
[0043]
1, a liquid crystal display device 10 includes a liquid crystal display panel 11, a liquid crystal display control device 12 for controlling a screen display of the liquid crystal display panel 11, and a CPU 13 for supplying video data and control commands to the display control device 12. ing.
[0044]
The liquid crystal display panel 11 is a TFT active matrix type liquid crystal display panel in which a plurality of pixel portions are arranged in a matrix in a horizontal direction and a vertical direction. In the present embodiment, a resolution of 176 × 220 dots is used for a mobile phone device. Alternatively, the resolution is 240 × 320 dots for PDA use. Also, a dot inversion driving method in which the polarity of a display voltage applied to an adjacent dot (pixel) is inverted so that flicker is not noticeable at a low refresh rate, or a pseudo dot inversion driving in which each pixel of RGB is staggered wiring. Driven by the law.
[0045]
The display control device 12 includes a display controller 121 as a display control unit, a display memory 122, an image update detection circuit unit 123 as an image update detection unit, a pixel clock frequency division circuit unit 124 as a rate control unit, and a frame rate. And a control circuit unit 125.
[0046]
The display controller 121 controls display of information from the CPU 13 on the liquid crystal display panel 11. The display controller 121 reads out data from the display memory 122 and causes the liquid crystal display panel 14 to display the data at the time of drawing processing and screen refreshing by the CPU 13. Further, the display controller 121 is supplied by the CPU 13 with video data displayed on the liquid crystal display panel 11 and control commands relating to display.
[0047]
In the display memory 122, data is read or written by the display controller 121, image update information is written in the display memory 122 when displaying a moving image, and writing is performed in the display memory 122 when there is no image update information when displaying a still image. Is not done. In FIG. 1, the display controller 121 and the display memory 122 are represented as respective functional blocks. However, when the display resolution is small, the display controller 121 and the display memory 122 are integrated by one integrated circuit (LSI). You may comprise.
[0048]
The image update detection circuit unit 123 detects whether or not the display image on the liquid crystal display panel 11 has been updated. The image update detection circuit section 123 needs to be configured with a minimum circuit configuration when driven by a small-capacity battery such as a mobile phone device or a PDA. 2. Description of the Related Art Conventionally, there is a technique of providing a memory for one field in order to obtain image update information, comparing data of a display image of a previous field with data of a current display image by a comparator, and determining image update. However, in this conventional technique, the circuit scale becomes large, and the power consumption in that part becomes large. Therefore, in the present embodiment, in order to configure the image update detection circuit unit 123 with a small-scale circuit, the image update detection circuit unit 123 detects an image update using the following two units.
[0049]
First, a write signal from the display controller 121 to the display memory 122 is detected. At the time of displaying a still image, there is no image update information from the CPU 13 to the display controller 121, so that data writing from the display controller 121 to the display memory 122 is not performed. Therefore, by detecting an access from the display controller 12 to the display memory 122 on a field-by-field basis, the update of the display image can be detected.
[0050]
Second, a control command from the CPU 13 to the display controller 121 is detected. For example, when there is a display command from the CPU 13 to the display controller 121 so that the display position of the first line on the liquid crystal display panel 11 is updated for each frame, such as a scroll display, the display on the liquid crystal display panel 11 is performed. The image is updated. Therefore, by providing the decoding circuit in the image update detection circuit section 123, a write signal from the CPU 13 to the internal register of the display controller 121 can be detected as display image update information for each frame.
[0051]
With the above-described method, the image update detection circuit unit 123 can be configured by a relatively small circuit.
[0052]
The pixel clock dividing circuit section 124 divides the basic pixel clock in order to reduce the refresh rate to １ ／, ３, ４,. For example, a display of 640 × 480 dots and a refresh rate (frame rate) of 60 Hz requires a basic pixel clock of about 25 MHz according to the VESA display timing specification. By dividing the basic pixel clock by half, the refresh rate can be easily halved without changing the circuit inside the display controller 12. As described above, FIG. 1 shows a circuit that divides the pixel clock into 、, ３, and ４ in order to reduce the refresh rate to 、, ３, and ４. However, it is also possible to set an arbitrary number of frame rates by the PLL oscillation circuit.
[0053]
The frame rate control circuit 125 sets a pixel clock to be output to the display controller 121 based on the image update detection signal (image update detection information) from the image update detection circuit 123.
[0054]
When the image update detection circuit 123 does not detect the image update information, the frame rate control circuit 125 changes the current high refresh rate to display the display data of a preset number of frames. maintain. Thereafter, in order to lower the refresh rate, the frequency is divided according to the frame frequency to be lowered (which one of the rates １ ／, 、 and 選 択 may be set in advance). The pixel clock is output to the display controller 121. When an image update is detected by the image update detection circuit unit 123, the frame rate control circuit unit 125 outputs an undivided basic pixel clock to the display controller 121, and the frame rate control circuit unit 125 Set a high refresh rate.
[0055]
Note that the liquid crystal display panel 11 employs a so-called AC driving method in which a display voltage whose polarity is inverted for each frame is applied to the liquid crystal layer. As a result, in order to improve the reliability, the frame rate needs to be variably controlled at the start of the vertical display timing in even frame units.
[0056]
FIG. 2 is a flowchart illustrating a frame rate control procedure performed by the frame rate control circuit unit 125 of FIG.
[0057]
First, when a write signal from the display controller 121 to the display memory 122 is detected by the image update detection circuit unit 123 during the current display frame period (step S1; YES), the frame rate control unit 125 starts the image update detection. Based on the image update detection signal from the circuit unit 123, after the display of the current frame is completed (step S3), a high refresh rate (high frame rate) is set (step S3).
[0058]
If the image update detection circuit 123 does not detect a write signal from the display controller 121 to the display memory 122 during the current display frame period (step S1; NO), a control command from the CPU 13 to the display controller 121 (display controller) When the register writing to the register 121 is detected (step S2; YES), the frame rate control circuit unit 125, based on the image update detection signal from the image update detection circuit unit 123, displays the current frame after completion of display. (Step S3), a high refresh rate (high frame rate) is set (Step S4).
[0059]
Until the end of the current display frame, if there is no writing from the display controller 121 to the display memory 122 or a control command from the CPU 13 to the display controller 121 (register writing into the display controller) (step S5; YES), It is possible to determine the still image state. In this case, after the preset number of frames is displayed (step S6: YES), the frame rate control unit 125 sets the low frame rate from the next frame (step S7).
[0060]
As described above, according to the present embodiment, the image update detection circuit unit 123 detects a control command from the CPU 13 of the central processing unit to the display controller 121 or information written from the display controller 121 to the display memory 122. Then, whether or not the display image has been updated is detected. When an update of the display image is detected (determined as a moving image), a normal high refresh rate is set and the display image is updated in frame units. When the update of the display image is not detected (determined as a still image), the display is switched to the preset low refresh rate after displaying the preset number of frames. A pixel clock corresponding to a desired frame rate is converted into a frame rate control circuit by a pixel clock frequency dividing circuit 124 that divides the pixel basic clock into one of 、, ３, １ ／,. 125 to the display controller 121. As a result, the size can be reduced as compared with the related art, and the power consumption can be reduced by appropriately controlling the refresh rate according to the image state (for example, whether the image is a moving image or a still image).
[0061]
【The invention's effect】
As described above, according to the present invention, at the time of displaying a moving image, a high refresh rate is displayed on the liquid crystal display panel to display a high-quality moving image, and at the time of displaying a still image, the image is displayed on the liquid crystal display panel. Display is performed at a low refresh rate, and power consumption can be reduced because of battery driving. Further, by detecting a control command from the CPU or the like to the display control means or writing information from the display control means to the display memory and detecting the update of the display image, the circuit configuration is downsized, and the small portable terminal device is provided. And a liquid crystal display device using the same.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration example of a main part of a liquid crystal display device according to an embodiment of the invention.
FIG. 2 is a flowchart showing a procedure of controlling a frame rate by a frame rate control circuit section of FIG. 1;
FIG. 3 is a circuit diagram showing a configuration example of a conventional liquid crystal display panel.
[Explanation of symbols]
Reference Signs List 10 liquid crystal display control device 11 liquid crystal display panel 12 liquid crystal display control device 121 display controller 122 display memory 123 image update detection circuit unit 124 image clock frequency division circuit unit 125 frame rate control circuit 13 CPU

Claims (10)

Display control means for controlling image display based on a screen display refresh rate;
Image update detection means for detecting the presence or absence of update of the display image and outputting image update detection information,
Rate control means for controlling a refresh rate of the display control means based on the image update detection information,
A liquid crystal display control device for setting the refresh rate of the screen display to a low refresh rate when the update of the display image is not detected by the image update detecting means. A display memory that can be accessed from the display control means,
The liquid crystal according to claim 1, wherein the image update detection unit detects whether the display image has been updated by detecting at least one of a control command to the display control unit and information written to the display memory. Display control device. 2. The liquid crystal display control device according to claim 1, wherein the rate control means controls the refresh rate of the screen display to be low by dividing the pixel basic clock. 4. The method according to claim 1, wherein when no update of the display image is detected by the image update detection unit, the rate control unit sets a refresh rate for the display control unit to a low refresh rate from a next frame. The liquid crystal display control device as described in the above. The rate control means sets a refresh rate for the display control means to a low refresh rate after a predetermined number of frames are displayed when no update of the display image is detected by the image update detection means. 3. The liquid crystal display control device according to any one of 3. The liquid crystal display according to claim 1, wherein when an update of a display image is detected by the image update detection unit, the rate control unit sets a refresh rate for the display control unit to a high refresh rate. Control device. The liquid crystal display control device according to claim 1, wherein the rate control unit switches a refresh rate with respect to the display control unit on an even frame basis. 8. The liquid crystal display control device according to claim 1, wherein said rate control means switches a refresh rate to said display control means at a start of a vertical display cycle. A liquid crystal display control device according to any one of claims 1 to 8,
A liquid crystal display device comprising: a liquid crystal display panel whose image display is controlled by the liquid crystal display control device. A dot inversion driving method for inverting the polarity of a display voltage applied to each adjacent pixel unit with respect to the display unit of the liquid crystal display panel, or a pseudo dot inversion driving method in which each of the three primary color RGB pixel units is staggered. The liquid crystal display device according to claim 9, wherein the display is driven by:

Images