JP2008039887A - Liquid crystal driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce power consumption in a two-color display mode. <P>SOLUTION: A liquid crystal driving device connected to a color liquid crystal panel in which a plurality of liquid crystal cells are arrayed to drive the color liquid crystal panel by scanning a source line drive signal and a gate line drive signal synchronously with a horizontal scanning period is provided with a source driver (20) having a mode for controlling the drive of the color liquid crystal panel so that the driving timings of all liquid crystal cells to be driven are synchronized in one horizontal scanning period. In the case that the driving timings of all the liquid crystal cells to be driven are synchronized, the operation period of a circuit can be reduced as compared with a case of non-synchronization of driving timings, and moreover any trouble is not generated in two-color display. Thereby, the reduction of power consumption in the two-color display mode can be achieved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal driving device, and more particularly to a technique effective when applied to a liquid crystal display control LSI (large-scale semiconductor integrated circuit).

  In recent years, as display devices for portable electronic devices such as cellular phones and PDAs (Personal Digital Assistants), dot matrix type liquid crystal panels in which a plurality of display pixels are two-dimensionally arranged in a matrix, for example, are used. A liquid crystal driving device for controlling the display of the liquid crystal panel is mounted inside.

  Low power consumption is important for display devices for portable electronic devices. As a low power consumption technology, when a liquid crystal display control device is provided with a drive duty selection register and a drive bias selection register that can be rewritten from a microprocessor, when switching from full-screen display of a liquid crystal panel to display of only a part of rows, the above By changing the set values of the drive duty selection register and the drive bias selection register, display is selectively performed on a part of the liquid crystal panel with low voltage and low duty drive (see Patent Document 1).

  In addition, a boosted voltage is formed by a charge pump circuit that receives a pulse formed by a frequency adjustment type oscillation circuit, and a detected voltage corresponding to the boosted voltage is compared with a reference voltage by a voltage comparison circuit to stabilize the boosted voltage. The control voltage supplied to the frequency adjustment type oscillation circuit is formed so that the display voltage is generated, the display voltage is generated by the display voltage generation circuit by the stabilized boosted voltage, and the display voltage corresponding to the display data is selected by the liquid crystal driver Thus, there is known a technique that realizes low power consumption by outputting the data (see Patent Document 2).

JP 2006-133804 A JP 2003-295830 A

  In a portable electronic device in which a liquid crystal panel is mounted, an 8-color display mode for primary color display and a 2-color display mode are attracting attention as functions for reducing power consumption. In the 8-color display mode, an unnecessary gradation level power supply is stopped during 8-color display, and in the 2-color display mode, an unnecessary gradation level power supply is stopped during 2-color display. Thus, power consumption can be reduced by stopping unnecessary gray level power.

  The inventors of the present invention have examined the reduction in power consumption of the liquid crystal panel. In either case of the 8-color display mode or the 2-color display mode, the source amplifier is operated by dividing one horizontal period into three corresponding to RGB. Thus, it was found that the power consumption in the two-color display mode is not much different from that in the eight-color display mode.

  An object of the present invention is to provide a technique for reducing power consumption in the two-color display mode.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  The following is a brief description of an outline of typical inventions disclosed in the present application.

  [1] Coupled to a color liquid crystal panel in which a plurality of liquid crystal cells are arranged, and for driving the color liquid crystal panel by scanning a source line driving signal and a gate line driving signal in synchronization with a horizontal scanning period. In the liquid crystal driving device, a source driver having a mode for driving and controlling the color liquid crystal panel is provided so that the driving timings of all the liquid crystal cells to be driven are aligned every horizontal scanning period.

  According to the above means, the source driver can drive and control the color liquid crystal panel so that the driving timings of all the liquid crystal cells to be driven are aligned every horizontal scanning period. When the drive timings of all the liquid crystal cells to be driven are aligned for each horizontal scanning period, the circuit operation period can be reduced compared to the case where it is not, and two-color display is achieved. There is no hindrance. This achieves a reduction in power consumption in the two-color display mode.

  [2] A plurality of gate lines, a plurality of source lines arranged so as to intersect with the gate lines, a liquid crystal cell disposed at a position where the gate lines intersect with the source lines, and the source lines selectively In a liquid crystal driving device for driving a color liquid crystal panel comprising a plurality of panel switches capable of supplying source line driving signals, each color of RGB is supported for each period during which the gate line is driven to a selected level. A source driver capable of controlling the operations of the plurality of panel switches is provided so that source line driving signals are supplied to the liquid crystal cell.

  According to the above means, the source driver is configured to supply the plurality of source line drive signals to the liquid crystal cells corresponding to the respective RGB colors in a period during which the gate line is driven to the selection level. Control the operation of the panel switch. When source line drive signals are supplied to the liquid crystal cells corresponding to each color of RGB, the operation period of the circuit can be reduced as compared with the case where the source line drive signals are not supplied, and there is no problem in two-color display. . This achieves a reduction in power consumption in the two-color display mode.

  [3] A plurality of gate lines, a plurality of source lines arranged so as to intersect with the gate lines, a liquid crystal cell arranged at a position where the gate lines and the source lines intersect, and the source lines selectively In a liquid crystal driving apparatus for driving a color liquid crystal panel comprising a plurality of panel switches capable of supplying a source line driving signal, the driving timing of the liquid crystal cell for each period during which the gate line is driven to a selected level. So that the plurality of panel switches are electrically connected.

  According to the above means, the source driver makes the plurality of panel switches conductive so that the driving timing of the liquid crystal cell is aligned every time the gate line is driven to the selection level. When the plurality of panel switches are turned on so that the drive timing of the liquid crystal cell is aligned every time the gate line is driven to the selection level, the operation period of the circuit is reduced as compared with the case where the panel switch is not turned on. In addition, there is no hindrance to the two-color display. This achieves a reduction in power consumption in the two-color display mode.

  [4] In the above [3], the source driver is arranged so that the liquid crystal output circuit capable of outputting the source line driving signal and the driving timing of the liquid crystal cell are aligned every period when the gate line is driven to a selected level. And a timing generation circuit for forming a control signal for conducting the plurality of panel switches.

  [5] In the above [4], the liquid crystal driving device includes a control circuit capable of switching between 8-color display and 2-color display, and the timing generation circuit is in accordance with an instruction of 2-color display from the control circuit. Can be configured to generate a control signal for conducting the plurality of panel switches so that the driving timing of the liquid crystal cell is aligned every time the gate line is driven to a selection level.

  The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.

  That is, power consumption in the two-color display mode can be reduced.

  FIG. 1 shows a liquid crystal display control LSI as an example of a liquid crystal driving device according to the present invention.

  The liquid crystal display control LSI 5 shown in FIG. 1 is not particularly limited, but is mounted on a portable electronic device together with a color liquid crystal panel, and can display an image by driving the color liquid crystal panel based on display image data. To do. Such a liquid crystal display control LSI 5 includes, but is not limited to, a power supply unit 10, a source driver 20, a control circuit 21, an external display interface 22, and a latch circuit 23. A single crystal is manufactured by a known semiconductor integrated circuit manufacturing technique. It is formed on one semiconductor substrate such as a silicon substrate.

  While the liquid crystal display control LSI 5 can operate at a voltage of 5 V or less, a driving voltage such as 5 to 40 V is required for the display driving of the color liquid crystal panel. Thus, it is necessary to generate a voltage for driving the color liquid crystal panel. The power supply circuit 10 includes an oscillator (OSC) 101, DC / DC converters 101 and 102 for boosting a power supply voltage (DC voltage) by a switching operation based on the oscillation output of the oscillator 101, and the DC / DC converter 101 , 102, and a gradation voltage generation circuit 104 for generating gradation voltages based on the outputs of. The gradation voltage generated by the gradation voltage generation circuit 104 is transmitted to the source driver 20.

  The control circuit 21 controls the entire operation of the liquid crystal display control LSI 5 based on a chip select signal CS, a serial synchronous clock signal SCL, and a serial data input signal SDI that are respectively input via external terminals.

  The external display interface 22 is provided for capturing a vertical synchronization signal (frame synchronization signal) VSYNC, a horizontal synchronization signal (line synchronization signal) HSYNC, a dot clock signal DOTCLK, and an enable signal ENABLE that are respectively input via external terminals. The output signal of the external display interface 22 is held in the latch circuit 23 at the subsequent stage.

  The source driver 20 includes a timing generation circuit 201 for controlling the driving timing of the liquid crystal panel, and a level shifter circuit 202 for converting an output signal of the timing generation circuit 201 into a signal level of the liquid crystal panel. The signals output from the level shifter circuit 202 include panel interface signals SOUT1 to SOUT3 and panel switch signals PSW1 to PSW3. Further, the source driver 20 is a selector 203 for selecting source output signal data by time division, and a gradation level selection circuit for selecting a gradation level to be output based on the output signal of the selector circuit 23. 204 and a liquid crystal output circuit 205 capable of outputting source line drive signals (source outputs) S1 to S240 based on the output signal of the gradation level selection circuit 204.

  FIG. 2 shows a color liquid crystal panel 30 driven by the liquid crystal display control LSI 5.

  The color liquid crystal panel 30 shown in FIG. 2 is not particularly limited, but includes a plurality of gate lines GL, a plurality of source lines SL arranged so as to intersect the plurality of gate lines GL, the gate lines GL, and the above-described gate lines GL. A liquid crystal cell 301 is provided at a location where the source line SL intersects. The liquid crystal cell 301 corresponds to the minimum element constituting an image, and includes a TFT (Thin Film Transistor) 301A and a liquid crystal 301B to which a voltage is applied via the TFT 301A. The other electrode of the liquid crystal 301B is fixed to a common potential Vcom level via a common line.

  Further, the liquid crystal panel 30 is provided with a gate circuit 302, and the plurality of gate lines GL are sequentially driven to a selection level by the gate circuit 302. Panel interface signals SOUT1 to SOUT3 are supplied from the source driver 20 to the gate circuit 302. The gate circuit 302 drives the gate line GL by sequentially setting the gate line driving signals G1 to G320 to a selection level based on the supplied panel interface signals SOUT1 to SOUT3.

  Three source lines adjacent to each other in the plurality of source lines SL correspond to RGB (Red-Green-Blue), and are coupled to the common source line SLcom via the panel switch 303. There are a total of 240 common source lines SLcom. Source line drive signals S1 to S240 are supplied from the source driver 20 to the common source line SLcom. The source line drive signals S1 to S240 are selectively transmitted to the source line SL via the corresponding panel switch 303. The panel switch 303 is ON / OFF controlled by panel switch signals PSW1 to PSW3 from the source driver 20.

  FIG. 3 shows the operation timing of the main part of the liquid crystal display control LSI 5.

  The color liquid crystal panel 30 is driven by scanning the source line driving signals (S1 to S240) and the gate line driving signals (G1 to G320) in synchronization with the horizontal scanning period. The driving of the color liquid crystal panel 30 in this example includes a divided driving mode and a synchronous driving mode.

  In the split drive mode, the source line SL is driven in a split manner. That is, the timing at which the panel switch signals PSW1, PSW2, and PSW3 are driven to the high level are shifted from each other as indicated by φ1, φ2, and φ3. Accordingly, the timing at which the source line drive signal is supplied to the liquid crystal cells corresponding to the respective RGB colors is also shifted accordingly. This divided drive mode is selected by the control circuit 21 in the case of 8-color display.

  On the other hand, in the simultaneous drive mode, the timing at which the panel switch signals PSW1, PSW2, and PSW3 are driven to the high level are aligned with each other as indicated by φ3, so that the source is supplied to the liquid crystal cell corresponding to each color of RGB. Line drive signals are supplied together. Such a simultaneous drive mode is selected by the control circuit 21 in the case of two-color display.

  Such timing control is performed by the timing generation circuit 201 under the control of the control circuit 21. That is, when the 8-color display mode is selected from the outside of the liquid crystal display control LSI 5, the timing control in the divided drive mode is performed under the control of the control circuit 21, and the 2 colors from the outside of the liquid crystal display control LSI 5. When the display mode is selected, the timing control in the simultaneous drive mode is performed under the control of the control circuit 21. The steady current is dominated by the output current of the liquid crystal output circuit 205. In the 8-color display mode, the ratio between the steady current and the charge / discharge current is approximately 5: 1. On the other hand, in the simultaneous drive mode, the operation period of the liquid crystal output circuit 205 is reduced to about 1/3 compared to the split drive mode. Therefore, power consumption in the two-color display mode can be reduced as compared with the eight-color display mode.

  According to the above example, the following effects can be obtained.

  (1) When the two-color display mode is selected, timing control in the simultaneous drive mode is performed, and the output current of the liquid crystal output circuit 205 is dominant. In the 8-color display mode, the ratio between the steady current and the charge / discharge current is approximately 5: 1. On the other hand, in the simultaneous drive mode, the operation period of the liquid crystal output circuit 205 is reduced to about 1/3 compared to the split drive mode. Power consumption in the two-color display mode can be reduced.

  (2) Since the liquid crystal display control LSI 5 can reduce the power consumption in the two-color display mode due to the function and effect of the above (1), a mobile phone equipped with such a liquid crystal display control LSI 5 is mounted. In an electronic device or the like, the operation time when using a battery as a power source can be extended.

  Although the invention made by the present inventor has been specifically described above, the present invention is not limited thereto, and it goes without saying that various changes can be made without departing from the scope of the invention.

  In the above description, the case where the invention made mainly by the present inventor is applied to the liquid crystal display control LSI, which is the field of use behind it, has been described. However, the present invention is not limited to this, and the liquid crystal driving device Can be widely applied to.

  The present invention can be applied on condition that the color liquid crystal panel is driven by scanning at least a source line driving signal and a gate line driving signal.

1 is a block diagram illustrating a configuration example of a liquid crystal display control LSI as an example of a liquid crystal driving device according to the present invention. FIG. 3 is a circuit diagram illustrating a configuration example of a main part of a color liquid crystal panel driven by the liquid crystal display control LSI 5; FIG. 6 is an operation timing chart of the main part of the liquid crystal display control LSI 5.

Explanation of symbols

5 Liquid crystal display control LSI
DESCRIPTION OF SYMBOLS 10 Power supply part 20 Source driver 21 Control circuit 22 External display interface 23 Latch circuit 201 Timing generation circuit 202 Level shifter 203 Selector circuit 204 Gradation level selection circuit 205 Liquid crystal output circuit 301 Liquid crystal cell 302 Gate circuit

Claims (5)

A liquid crystal drive device coupled to a color liquid crystal panel comprising a plurality of liquid crystal cells arranged, and driving the color liquid crystal panel by scanning a source line drive signal and a gate line drive signal in synchronization with a horizontal scanning period Because
A liquid crystal driving apparatus comprising: a source driver having a mode for controlling driving of the color liquid crystal panel so that driving timings of all the liquid crystal cells to be driven are aligned every horizontal scanning period. Multiple gate lines,
Multiple source lines arranged to intersect it,
A liquid crystal cell disposed at the intersection of the gate line and the source line;
A liquid crystal driving device for driving a color liquid crystal panel comprising a plurality of panel switches capable of selectively supplying a source line driving signal to the source line,
A source driver capable of controlling the operation of the plurality of panel switches so that source line drive signals are supplied to the liquid crystal cells corresponding to the respective RGB colors every period during which the gate line is driven to a selection level. A liquid crystal driving device comprising: Multiple gate lines,
Multiple source lines arranged to intersect it,
A liquid crystal cell disposed at the intersection of the gate line and the source line;
A liquid crystal driving device for driving a color liquid crystal panel comprising a plurality of panel switches capable of selectively supplying a source line driving signal to the source line,
A liquid crystal driving device comprising: a source driver for conducting the plurality of panel switches so that the driving timing of the liquid crystal cell is aligned every time the gate line is driven to a selection level. A liquid crystal output circuit capable of outputting the source line drive signal;
4. A timing generation circuit for forming a control signal for conducting the plurality of panel switches so that the drive timing of the liquid crystal cell is aligned every time the gate line is driven to a selection level. Liquid crystal drive device. The liquid crystal driving device includes a control circuit that enables switching between 8-color display and 2-color display,
In response to a two-color display instruction from the control circuit, the timing generation circuit makes the plurality of panel switches conductive so that the driving timings of the liquid crystal cells are aligned every time the gate line is driven to a selected level. 5. A liquid crystal driving device according to claim 4, wherein a control signal for generating the control signal is formed.

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