JP4259775B2 - Active matrix display device and control device thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a display device that switches between a moving image mode that displays video signals that are input as needed and a still image mode that displays video signals stored in a frame memory.
[0002]
[Prior art]
With the spread of personal digital assistants (PDAs) such as mobile phones and notebook computers in recent years, display devices such as liquid crystal display devices (LCD) and electroluminescence (EL) display devices are used as display devices with low power consumption. ing.
[0003]
FIG. 4 shows an active matrix LCD as an example of a conventional display device. The active matrix display device is configured by connecting a control circuit 200 to a liquid crystal panel 100.
[0004]
The liquid crystal panel 100 includes liquid crystal sealed between a first substrate on which a plurality of pixel electrodes 1 are formed and a second substrate on which one common electrode 10 facing the plurality of pixel electrodes is formed. On the first substrate, a plurality of pixel electrodes 1 and switching elements 2 made of, for example, thin film transistors (TFTs) corresponding to each of the pixel electrodes 1 are arranged in a matrix. Corresponding to the matrix of pixel electrodes 1, gate lines 3 are arranged in the row direction and data lines 4 are arranged in the column direction. A gate line 3 is connected to the gate of each pixel TFT 2, and a data line 4 is connected to the drain. The gate line 3 is connected to a gate line shift register 5 arranged around the display area. The data line 4 is connected to the data bus line 7 via the data line selection TFT 6, and the gate of the data line selection TFT 6 is connected to the output of the data line shift register 8. The data line selection TFT 6 and the data line shift register 8 constitute a data line driver that sequentially selects the data lines 4 and supplies data signals. In each pixel, an auxiliary capacitor 9 is arranged in parallel with the liquid crystal capacitor in order to hold the pixel voltage.
[0005]
The control circuit 200 includes a data processing unit 21, a CPU interface 22, a timing controller 23, and a digital analog converter (DAC) 24. When the video signal is an analog signal, the data processing unit 21 first samples the video signal at an appropriate timing and converts it to a digital signal, adjusts brightness and contrast, and applies gamma correction. Thus, an optimal signal for the liquid crystal panel 100 is created. The CPU interface 22 receives a command (command) of a CPU (not shown) that controls a device on which an LCD such as a PDA or a mobile phone is mounted, and transmits a control signal to each unit according to the command. The timing controller 23 outputs various timing signals to the liquid crystal panel 100 based on the vertical start signal and the horizontal synchronization signal extracted from the video signal. The DAC 24 converts the RGB digital data output from the data processing unit into a voltage optimum for the pixel voltage of the liquid crystal panel 100 and outputs the converted voltage.
[0006]
Next, the operation of the active matrix LCD will be described along with drive control signals. 5 and 6 are timing charts showing several timing signals. The vertical synchronization signal Vsync is a clock that is output high once every start of the vertical synchronization period, and indicates the start of the frame period. The vertical start signal STV is input to the gate line shift register 5. The gate line shift register 5 is a shift register, and starts its operation in response to the vertical start signal STV. The gate line clock CKG is input to the gate line shift register 5, and the shift register is next switched for each gate line clock CKG to sequentially supply gate signals to the gate lines 3. The half cycle of the gate line clock CKG corresponds to the horizontal synchronization period. All the pixel TFTs 2 connected to the gate line 3 to which the gate signal is supplied are turned on. The horizontal start signal STH is input to the data line shift register 8 of the data line driver, with a clock slightly delayed by a double cycle of the gate line clock CKG. The data line shift register 8 receives the horizontal start signal STH and starts operation. The data line clock CKD is input to the data line shift register 8, and the shift register is next switched every data line clock CKD, and the data line selection TFT 6 is sequentially supplied with the data line selection signal. The data line selection TFT 6 to which the data line selection signal is supplied is turned on, and the data signal DATA is supplied from the data bus line 7 to the pixel electrode 1 through the data line 4 and the pixel TFT 2. As shown in the figure, there are cases where a plurality of data bus lines 7 are provided and the same gate signal is input to the corresponding data line selection TFT 6 to simultaneously apply pixel voltages to the plurality of pixel electrodes 1. When the data line shift register 8 finishes selecting all the data lines 4, the gate line clock CKG is input again, and the next gate line 3 is selected. Similarly, when the gate line shift register 5 finishes selecting all the gate lines 3, one screen is completely displayed. There is a horizontal blanking period in which data is not input for a certain period each time data for one row, for example, data for 176 pixels, is written. In addition, every time data for all the pixels, for example, 220 rows, is written, there is a vertical blank period in which data is not input for a certain period (about several horizontal periods). During the vertical blanking period, the next vertical synchronization signal Vsync is input, the next frame is started, and the above operation is repeated from the beginning.
[0007]
By the way, in a PDA such as a cellular phone, it is important to reduce power consumption in order to secure an operation time. Therefore, a mobile phone or the like often uses a display device that is equipped with a frame memory having a capacity for storing video data for one screen and displays the data stored in the frame memory. FIG. 7 shows a display device equipped with a frame memory. The same components as those of the display device shown in FIG. The frame memory 25 is an SRAM in which digital image data of all the pixels of the liquid crystal panel 100 is input via the CPU interface 22 and is held. The video data held in the frame memory 25 is converted into a pixel voltage by the DAC 24 and supplied to each pixel electrode.
[0008]
When video data stored in the frame memory 25 is displayed, a timing signal such as the vertical synchronization signal Vsync is not supplied from the outside, so that it is necessary to create a timing signal. The oscillator 26 creates a basic clock and supplies it to the timing controller 23. The timing controller 23 multiplies the basic clock to generate the data line clock CKD. By counting the basic clock by a counter in the timing controller, a pulse is generated at a rate of once per predetermined number of data line clocks CKD, and a horizontal start signal STH, a gate line clock CKG, and the like are generated. Then, the basic clock is counted by another counter to generate the vertical start signal STV and the like.
[0009]
[Problems to be solved by the invention]
Since the display device having the frame memory 25 does not need to input display data from the outside, there is an advantage in that power consumption is low. However, since it is necessary to store the video data in the frame memory 25 once and this storage takes time, there is not a sufficient drawing speed for displaying a moving image.
[0010]
Therefore, an object of the present invention is to provide a display device that can display a moving image and consumes less power.
[0011]
[Means for Solving the Problems]
The present invention has been made to solve the above problems, and includes a plurality of gate lines, a plurality of data lines intersecting the gate lines, a switching element disposed at the intersection of the gate lines and the data lines, and switching. A plurality of pixel electrodes connected to each of the elements, supplying a video signal from the data line to all the pixel electrodes every one frame period, in accordance with a pixel voltage generated between the pixel electrode and the common electrode In an active matrix display device that performs display, a moving image mode that performs display according to the output of a data processing unit that performs predetermined processing on a video signal that is input as needed, and an output of a memory that holds video signals of a plurality of pixels When a static switching signal for switching from the still image mode to the moving image mode is received during a certain frame period, Until the frame period ends will continue to still image mode, an active matrix type display device and a control system switches from the next frame period moving image mode.
[0012]
Furthermore, in the video mode, the operation is based on an external vertical synchronization signal that is a timing signal that is output at the beginning of the frame period in synchronization with an externally input video signal. In the still image mode, the internal vertical synchronization signal Is generated inside the display device, and when a static switching signal is received during a certain frame period during still image mode display, the still image mode is continued until the end of the frame period, and the next internal vertical sync signal is generated. Instead, when the external vertical synchronization signal is input next after the end of the frame period, display in the moving image mode is started.
[0013]
Furthermore, the switching timing from the moving image mode to the still image mode is different from the switching timing from the still image mode to the moving image mode.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a display device according to an embodiment of the present invention. Constituent elements similar to those of the prior art are given the same numbers, and description thereof is omitted. The liquid crystal panel 100 of this embodiment is exactly the same as the conventional one. In the control circuit 200 of the present embodiment, both the data processing unit 21 and the frame memory 25 are arranged, and a selector 27 is provided to select and switch between these outputs, and the moving image mode and the still image mode are switched and displayed. Different from conventional ones. In the moving image mode, the data processing unit 21 adjusts the brightness and contrast of the video signal that is input at any time, applies gamma correction, and creates and outputs an optimal signal to the liquid crystal panel 100 at any time. Display accordingly. In the still image mode, display is performed according to the video signal stored in the frame memory.
[0015]
In this embodiment, when displaying a moving image, it is possible to switch between a moving image mode with a high drawing speed, usually a still image mode with a low drawing speed but low power consumption, thereby improving user convenience. A display device with less power consumption can be obtained without loss. For example, the CPU that controls the PDA or mobile phone on which the display device is mounted starts from the still image mode when the display is normally performed in the still image mode and a moving image signal is received or the user performs a key operation. Set to output a switching signal to switch to the movie mode, and switch from the CPU to the still image mode again after a certain period of time has elapsed after the movie display ends in the movie mode or the user ends the key operation. Set to output signals. A switching signal from the CPU is output to the timing controller 23 via the CPU interface 22, and the timing controller 23 switches the selector 27 based on the switching signal. As a result, the output from the data processing unit 21 and the output from the frame memory 25 are switched, and the moving image mode and the still image mode are switched.
[0016]
In any mode, during the operation mode, the display operation is performed in the same manner as in the past by the timing signals shown in FIGS. However, in the moving image mode, each timing signal is an external timing signal created using a clock extracted from an externally input video signal. In the still image mode, the timing signal is output from the oscillator 26 connected to the timing controller 23. An internal timing signal created based on the basic clock is used. These timing signals are essentially similar signals, but in this specification, a timing signal extracted from an external signal is an external timing signal, and a timing signal created from an output of the built-in oscillator 26 is an internal timing. In some cases, the signals are described separately. For example, in the vertical synchronization signal Vsync, a signal extracted from an external signal may be distinguished from an external vertical synchronization signal, and a signal based on the output of the oscillator 26 may be distinguished from an internal vertical synchronization signal.
[0017]
The display device according to the present embodiment can be basically operated in the same manner as the conventional one, but further ingenuity is required when switching the operation mode. This is because the external timing signal and the internal timing signal are generated completely independently of each other, and for example, the external vertical synchronization signal and the internal vertical synchronization signal are not synchronized at all. A switching signal for switching the mode is input from the CPU of the device through the CPU interface, and this command is also issued regardless of both timing signals.
[0018]
First, a first embodiment relating to mode switching will be described. In the first embodiment, when the mode switching signal is input, the horizontal counter and vertical counter of the timing controller are forcibly reset, and display is started from the first row and the first column in the mode switched immediately. Specifically, the timing controller 23 outputs the vertical start signal STV and the horizontal start signal STH at the time when the mode switching signal is input, and operates the shift register from the beginning. In this case, the timing controller 23 has a built-in counter for counting the gate line clock CKG and the data line clock CKD, and grasps the pixel voltage supplied to the pixel in which row and column. This counter needs to be reset.
[0019]
However, this first embodiment has the following problems. Since the mode switching signal is not synchronized with the vertical synchronization signal Vsync, it is usually input during the frame period. However, during the frame period, the gate line shift register 5 and the data line shift register 8 have already started operation. Now, it is assumed that the pixel voltage is supplied to the pixel electrode of n rows and m columns. Therefore, when a mode switching signal is input, the pixel voltage is forcibly reset and the pixel voltage is supplied again from the first row and first column, but the shift register simultaneously selects the first row and first column and the nth row and m + 1 column. It becomes. As a result, in the frame in which the mode is switched, the second row, the n + 1th row, the third row, and the n + 2 row are simultaneously selected, and the same image is displayed on the upper and lower portions of the screen, which is unsightly. .
[0020]
Next, a more excellent second embodiment relating to mode switching will be described. First, switching from the moving image mode to the still image mode will be described. FIG. 2 is a timing chart when switching from the moving image mode to the still image mode. As described above, when the display is performed in the moving image mode, the operation is performed based on the external timing signal input from the outside. When the video signal is digital, the external timing signal is input as the timing signal itself. When the video signal is an analog signal such as NTSC or PAL, the external timing signal is extracted from the video signal and input. . In some cases, the signal is extracted inside the control circuit 200, but here is collectively referred to as an external timing signal. Now, assume that a switching signal for switching from the moving image mode to the still image mode is received during a certain frame period (in particular, there is a case where the switching signal from the moving image mode to the still image mode is distinguished from the dynamic / static switching signal). The vertical counter built in the timing controller is reset by the vertical start signal STV and counts the gate clock, and the horizontal counter is reset by the horizontal start signal STH and counts the data line clock. It is a count value (n, m). Therefore, this count value indicates the coordinates of the pixel that is supplying the pixel voltage at that time. Therefore, if the video signal is read from the address of the frame memory 25 corresponding to the count value, the video signal corresponding to the next pixel electrode can be read from the frame memory 25. Therefore, when the movement / static switching signal is input to the timing controller 23 via the CPU interface 22, the timing controller 23 does not reset the count values of the vertical counter and the horizontal counter based on the basic clock output from the oscillator 26. The output of the internal timing signal is started, the selector 27 is switched to select the frame memory 25, and the mode is immediately switched to the still image mode. A video signal from a corresponding address in the frame memory 25 is supplied to the next pixel electrode. By switching in this way, two gate lines are not selected at the same time, so that the display is not unsightly when switching modes.
[0021]
Here, the data clock (basic clock) of the external timing signal and the basic clock output from the oscillator 26 are not synchronized, but no problem occurs. This is because the counter built in the timing controller is not reset, and when the mode is switched, the operation is merely stopped for about one cycle of the basic clock. In the present embodiment, the timing controller 23 does not output a clock of less than one cycle of the basic clock because it causes a malfunction. Therefore, when the mode is switched, the basic clock is displayed during the period Δt shown in the figure. The operation is stopped for one or more cycles.
[0022]
Next, switching from the still image mode to the moving image mode will be described. FIG. 3 is a timing chart when switching from the still image mode to the moving image mode. When a switching signal from the still image mode to the moving image mode is received in a certain frame period (in particular, it may be expressed as a static switching signal), the operation is not particularly switched, and the oscillator 26 is used until the frame period ends. The operation by the internal timing signal based on the output of, and still image mode are continued. The next internal vertical synchronizing signal is not output. After that, when the period Δt2 elapses, the external vertical synchronization signal is input, so that the video frame mode based on the external timing signal is switched from the next frame period after the external vertical synchronization signal. By switching in this way, the mode is continued until one frame period is completed, so that two gate lines are not selected at the same time, and the display is not unsightly at the time of mode switching.
[0023]
It is not necessary to supply a clock during the period Δt2 between the still image mode and the moving image mode. However, since it is difficult to stably supply each external timing signal at the same time as the external vertical synchronization signal is input, the external timing signal is several basic clocks ahead of the input of the external vertical synchronization signal. It is good to start to output. In the period Δt2, even if the timing signal is supplied, neither the vertical start signal STV nor the horizontal start signal STH is supplied, so that the shift registers 5 and 8 do not start operation. Of course, switching to the external timing signal may be performed immediately after the frame period of the still image mode is completed.
[0024]
In the still image mode, the supply of the video signal and the supply of the timing signal are closed by the control circuit 200, whereas in the moving image mode, the video signal is supplied from the outside, and the display operation must be performed in synchronization therewith. I don't get it. Therefore, as described above, in the second embodiment, the switching timing from the still image mode to the moving image mode is different from the switching timing from the moving image mode to the still image mode, and the mode is optimized according to each switching. Switching can be performed to further improve the display quality.
[0025]
In the above embodiment, the liquid crystal display device has been described as an example of the active matrix display device. However, the present invention is not limited to this, and the present invention can be similarly applied to an EL display device, an LED display device, a vacuum fluorescent display device, and the like. .
[0026]
【The invention's effect】
As described above in detail, according to the present invention, a moving image mode in which display is performed as needed according to the output of the data processing unit, and a still image mode in which display is performed according to the output of a memory that holds a video signal of a plurality of pixels. Since the display is switched, display with low power consumption and high display quality can be achieved.
[0027]
Furthermore, when a static switching signal for switching from the still image mode to the moving image mode is received in a certain frame period, the still image mode is continued until the end of the frame period, and by switching from the next frame period to the moving image mode, When switching from the still image mode to the moving image mode, the mode can be switched without performing an unsightly display.
[0028]
Furthermore, when a static switching signal is received during a certain frame period in which the still picture mode is displayed, the still picture mode is continued until the end of the frame period, the next internal vertical synchronization signal is not generated, and the frame period The present invention can be implemented with a relatively simple configuration by starting the display in the moving image mode when the external vertical synchronization signal is next input after the end.
[0029]
In addition, the switching timing from the video mode to the still image mode is different from the switching timing from the still image mode to the video mode, so the display quality can be improved by switching the mode according to the procedure optimized for each switching. it can.
[Brief description of the drawings]
FIG. 1 is a diagram showing an active matrix display device according to an embodiment of the present invention.
FIG. 2 is a timing chart for explaining switching from a moving image mode to a still image mode according to the present invention.
FIG. 3 is a timing chart for explaining switching from a still image mode to a moving image mode according to the present invention.
FIG. 4 is a diagram showing a conventional active matrix display device.
FIG. 5 is a timing chart for explaining the operation of the active matrix display device;
FIG. 6 is a timing chart for explaining the operation of the active matrix display device;
FIG. 7 is a diagram showing a conventional active matrix display device.
[Explanation of symbols]
1: Pixel electrode 2: Pixel switching element (TFT)
3: Gate line 4: Data line 5: Shift register 6: Data line selection switching element (TFT)
7: Data bus line 8: Shift register 9: Auxiliary capacitor 10: Common electrode 21: Data processing unit 22: CPU interface 23: Timing controller 24: Digital / analog converter 25: Frame memory 26: Oscillator 27: Switching means (selector)

Claims (4)

Multiple gate lines,
A plurality of data lines intersecting the gate line;
A switching element disposed at an intersection of the gate line and the data line;
A plurality of pixel electrodes connected to each of the switching elements,
In an active matrix display device that supplies a video signal from the data line to all the pixel electrodes every one frame period and performs display in accordance with a pixel voltage generated between the pixel electrode and the common electrode.
In accordance with the output of the data processing unit that performs predetermined processing on the video signal that is input at any time, it is synchronized with the video signal and displayed at any time based on the external vertical synchronization signal that is a timing signal that is pulsed at the beginning of the frame period Video mode to perform
According to the output of the memory that holds the video signal of multiple pixels, the display is switched between the still image mode that creates and displays the internal vertical sync signal inside the display device ,
When a static switching signal for switching from the still image mode to the moving image mode is received in a certain frame period, the still image mode is continued until the end of the frame period, the next internal vertical synchronization signal is not generated, and the frame period An active matrix display device which starts display in the moving image mode when an external vertical synchronization signal is input next after the end . When receiving the switching Ru movements switching signal from the moving image mode to the still image mode in a certain frame period, active matrix display device according to claim 1, characterized in that switch immediately to a still image mode. Multiple gate lines,
A plurality of data lines intersecting the gate line;
A switching element disposed at an intersection of the gate line and the data line;
A plurality of pixel electrodes connected to each of the switching elements,
A control device that controls an active matrix display device that performs display in accordance with a pixel voltage generated between the pixel electrode and the common electrode;
A data processing unit that performs predetermined processing on a video signal that is input at any time and outputs it at any time, a memory that holds and outputs a video signal of a plurality of pixels, and
Switching means for selecting and switching the output of the data processing unit and the output of the memory;
A timing controller that outputs a timing signal including a vertical synchronization signal that outputs a pulse every frame period;
An oscillator connected to the timing controller ;
When the data processing unit is selected, it synchronizes with an externally input video signal and operates based on an external timing signal including an external vertical synchronization signal pulsed at the beginning of a frame period,
When the memory is selected, the timing controller operates based on an internal timing signal including an internal vertical synchronization signal created based on the output of the oscillator,
Wherein the frame period in which to select the output of the memory, when the static and dynamic stresses switching signal for switching from said memory to said data processing unit is entered, until the frame period ends continues to select the output of said memory, said The timing controller continues to create the internal timing signal until the end of the frame period, and does not create the next internal vertical synchronization signal, and when the external vertical synchronization signal is input next after the end of the frame period, A control device for an active matrix type display device, wherein the operation based on an external timing signal is started by switching to the output of the data processing section . When the from the output of the data processing unit receives the switching Ru movements switching signal to the output of the memory in a certain frame period, the control of an active matrix display device according to claim 3, characterized in that to switch immediately to the still image mode apparatus.

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