JP2012173380A - Liquid crystal display device with touch panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device with a touch panel capable of reducing power consumption according to a state of a displayed image or the like.SOLUTION: A source driver 20 turns a source wiring 14 to a high impedance state over a predetermined period when contact to a touch panel 50 is not detected, and an image by an input image signal is a still image, and a gate driver 30 stops drive of a gate wiring 13 over the predetermined period. Preferably, the predetermined period is a period corresponding to a frame number set according to a period until a voltage holding ratio of a liquid crystal reaches a predetermined value when a state without application of a data voltage continues after applying the data voltage to the source wiring 14.

Description

  The present invention relates to a liquid crystal display device with a touch panel in which a touch panel is provided on the front surface of a liquid crystal display panel.

  In a liquid crystal display device in which a plurality of scanning wirings and a plurality of data wirings are arranged so as to cross each other and a scanning signal is sequentially supplied to the scanning wirings to display a still image and a moving image, an image of a certain frame in the moving image is displayed. There is a liquid crystal display device configured to stop the supply of a scanning signal when performing a static display (see, for example, Patent Document 1). In the liquid crystal display device described in Patent Document 1, the supply of the scanning signal is stopped for a few seconds. By performing such control, the power consumption of the liquid crystal display device is reduced.

  In addition, there is a liquid crystal display device in which a pause period is set between a certain frame and the next frame, and data wiring is set in a high impedance state during the pause period (see, for example, Patent Document 2). In the liquid crystal display device described in Patent Document 2, after the data wiring is set to a high impedance state, power supply to an analog circuit (for example, a source driver) in the drive circuit is further stopped to reduce power consumption.

JP-A-3-219287 JP 2001-31253 A

  The liquid crystal display device described in Patent Document 2 reduces power consumption by performing control such as setting the data wiring in a high impedance state during the idle period, but always performs such control. Therefore, it cannot be denied that the display quality is deteriorated to some extent.

  In the liquid crystal display device described in Patent Document 1, power consumption can be reduced by stopping the supply of a scanning signal when an image of a certain frame in a moving image is statically displayed, but the image is statically displayed. Unless an artificial request occurs, control that can reduce power consumption is not executed. The purpose of the invention described in Patent Document 1 is to stop and display a desired image in a moving image.

  An object of the present invention is to provide a liquid crystal display device with a touch panel that reduces power consumption in accordance with the state of an image to be displayed.

  A liquid crystal display device with a touch panel according to the present invention includes a liquid crystal display panel in which a plurality of gate lines and a plurality of source lines cross each other, a gate driver for sequentially applying a gate voltage to the gate lines, and data on the source lines. A liquid crystal display device with a touch panel comprising a source driver for applying a voltage (source voltage) and a touch panel provided on the viewing side of the liquid crystal display panel, wherein the source driver does not detect contact with the touch panel, and When the image by the input image signal is a still image, the source wiring is set to a high impedance state for a predetermined period, and when the touch to the touch panel is detected, the high impedance state of the source wiring is released. .

  The predetermined period is a frame set in accordance with a period until the voltage holding ratio of the liquid crystal reaches a predetermined value when a state in which the data voltage is not applied continues after the data voltage is applied to the source wiring. It is preferable that the period corresponds to the number. According to such a configuration, it is possible to reduce power consumption without reducing the visibility of the display screen of the liquid crystal display panel.

  It is preferable that the gate driver stops driving the gate wiring for a predetermined period. According to such a configuration, power consumption can be further reduced.

  In the case where the source driver has an output buffer circuit and the output buffer circuit can drive the source wiring with any one of the plurality of driving capabilities, a plurality of the driving drivers are provided over a predetermined period. It is preferable to set the output buffer circuit in a state in which the source wiring is driven with the lowest driving capability. According to such a configuration, power consumption can be further reduced.

  The liquid crystal display device with a touch panel is configured to include a motion detection unit that determines whether an image based on an input image signal is a still image or a moving image, and a touch detection unit that determines whether there is a touch on the touch panel. It may be.

  According to the present invention, it is possible to reduce power consumption in accordance with the state of an image to be displayed.

The block diagram which shows the structural example of the liquid crystal display device with a touch panel. The block diagram which shows an example of the internal structure of a source driver, a gate driver, and a timing control circuit, and the state of the input-output signal in them. FIG. 9 is a timing chart illustrating an operation example of a latch circuit. Explanatory drawing which shows an example of a current gain. Explanatory drawing which shows an example of the voltage retention of a liquid crystal. Explanatory drawing which shows typically operation | movement of a source driver.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration example of a liquid crystal display device with a touch panel according to the present invention. In the liquid crystal display device with a touch panel shown in FIG. 1, the liquid crystal display panel 10 has a large number of pixels 12 formed in a matrix. In order to form a pixel, a large number of gate lines 13 are provided in the horizontal direction (row direction), and a large number of source lines 14 are provided in the column direction so as to intersect the gate lines 13. A TFT 15 is formed at the intersection between the gate line 13 and the source line 14. The drain electrode 16 of the TFT 15 is connected to the pixel electrode.

  In general, a counter substrate (not shown) is provided at a position facing the substrate on which the gate wiring 13, the source wiring 14 and the pixel 12 are formed, and liquid crystal is provided between the substrate on which the pixel 12 is formed and the counter substrate. Is pinched. A common electrode (common electrode) is formed on the counter substrate. The common electrode is set to a common potential. Note that since the liquid crystal can be regarded as an element having a capacitance electrically, FIG. 1 shows a capacitor 17 in which one end is connected to the pixel electrode and the other end has a common potential. .

The gate driver 30 drives the gate lines 13 line-sequentially based on a signal output from the timing control circuit 40. The pixel electrode in the pixel connected to the selected gate line 13, that is, the gate line 13 to which the gate-on voltage V _GH is applied is applied to the data voltage (voltage corresponding to the data signal) by the source driver 20 via the source line 14. ) V _D is applied.

  Note that the source driver 20, the gate driver 30, and the timing control circuit 40 shown in FIG. 1 are components of a driving device for a liquid crystal display panel.

  The touch panel 50 by the resistance film method, the capacitance method, or other methods is installed on the surface side (viewing side) of the liquid crystal display panel 10. The touch panel 50 outputs a coordinate specifying signal that can specify the touched position to the control unit 60.

  The control unit 60 inputs an image signal and outputs the image signal to the timing control circuit 40. The image signal includes, in addition to image data, a horizontal synchronization signal and a vertical synchronization signal, or signals corresponding to them. The control unit 60 includes a motion detection unit 61 and a touch detection unit 62.

  The motion detector 61 uses the image signal to determine whether the image based on the currently input image signal is a still image or a moving image. If the motion detection unit 61 determines that the image is a moving image, the motion detection unit 61 sets the state of the motion detection signal output to the timing control circuit 40 to a significant state (for example, high level).

  The touch detection unit 62 determines whether or not there is a touch on the touch panel 50 based on the coordinate specifying signal. When the touch detection unit 62 determines that there is a touch on the touch panel 50, the touch detection unit 62 sets the state of the touch signal output to the timing control circuit 40 to a significant state (for example, high level).

  In addition, although the control part 60 may be incorporated in the liquid crystal display device with a touch panel, it may be provided outside the liquid crystal display device with a touch panel.

  FIG. 2 is a block diagram showing an example of the internal configuration of the source driver 20, the gate driver 30, and the timing control circuit 40 and the states of signals inputted to and outputted from them.

  The timing control circuit 40 includes a latch circuit 42 in addition to the timing generator 41. The latch circuit 42 latches the signal A corresponding to the logical sum of the touch signal and the motion detection signal when the vertical synchronization signal (V-sync) is turned on, and outputs the latch signal as the output enable signal OE. To do.

  FIG. 3 is a timing diagram illustrating an operation example of the latch circuit 42. As shown in FIG. 3, when V-sync rises (see “a” in FIG. 3) when the touch signal is in the on state (high level in this example), the output enable signal OE is in the on state (in this example). Then, it becomes low level). FIG. 3 illustrates the touch signal, but the latch circuit 42 also turns on the output enable signal OE even when the motion detection signal is turned on.

  In the present embodiment, the output enable signal OE is low active. The output enable signal OE is supplied to the source driver 20 and the gate driver 30.

  The timing generator 41 includes an image data signal (not shown), a data shift clock signal CLK, a horizontal start pulse STH corresponding to a signal indicating the start of a selection period, and a latch signal designating latching of one row of data. LP is output to the source driver 20. Further, the timing generator 41 outputs to the gate driver 30 a gate start pulse STV corresponding to a signal indicating the start of one frame and a shift clock signal CLKV which is a signal equivalent to a latch signal.

  The timing generator 41 stops outputting the signal for several frames (for example, seven frames) that are started after the output enable signal OE changes from the on state to the off state. Specifically, for example, the output signal is set to a high impedance state.

  The source driver 20 includes a source signal generation unit 21 and an output buffer circuit 22. The source signal generator 21 generates a data signal for driving each source line 14 based on the image data signal or the like. The source driver 20 includes a DA converter and outputs a data signal to the output buffer circuit 22 as an analog signal.

  The output buffer circuit 22 amplifies the output of the DA converter and applies it to each source line 14. In the present embodiment, it is assumed that the current amplification factor (drive capability) of the output buffer circuit 22 is variable.

  FIG. 4 is an explanatory diagram showing an example of the current amplification factor. As illustrated in FIG. 4, the driving capability includes 130% (output P), 100% (output Q), 80% (output R), and the signal itself (output S) from the DA converter. There is. The driving capacities of 130% and 80% correspond to the relative maximum output current based on the driving capability of the output Q. Further, it is assumed that the driving capability based on the signal from the DA converter is lower than the driving capability of the output R.

  Next, the operation of the liquid crystal display device with a touch panel will be described. FIG. 5 is an explanatory diagram showing an example of the voltage holding ratio of the liquid crystal. In the example shown in FIG. 5, it is assumed that the voltage holding ratio (Voltage Holding Ratio: the rate at which the charge accumulated in the pixel is held during one frame (16.7 ms)) is 99.4%. Further, it is assumed that a voltage of 5 V is applied to the liquid crystal when data is written to the pixel. In FIG. 5, black circles correspond to the charge retention rate at the time when n frames (n: natural number) have elapsed since the data was written to the pixels in the selection period of the first frame (the pixels were charged). . 100% is a charge retention rate in the selection period.

The voltage holding ratio when one frame has elapsed is expressed as follows.
(5 * EXP (−16.7 / CR)) / 5 × 100 (C and R are capacitance and resistance values related to the pixel)

In addition, the voltage holding ratio when the time after two frames has elapsed is expressed as follows.
Retention ratio = 0.994 ⁿ × 100 (n: number of frames)

  Then, after the data is written in a certain frame (the frame indicated by “1” in the example shown in FIG. 5), when the data is not rewritten for the subsequent 7 frames, the voltage holding ratio is It becomes about 95%. Even if the retention rate is 95%, the viewer can sufficiently view the still image. Therefore, in the present embodiment, the drive device performs control so that data is not rewritten for 7 frames after data is written when a predetermined condition is satisfied.

  During a period in which data is not rewritten, when the data voltage is not applied after the data voltage is applied to the source wiring 14, the liquid crystal voltage retention rate is a predetermined value (in this example, , A value that does not fall below 95%), and a period according to the number of frames set according to the period. Therefore, when a liquid crystal whose voltage holding ratio is not 99.4% is used, or when a liquid crystal whose period until the holding ratio reaches 95% is not 7 frames, data is not rewritten. The period may be different from 7 frames.

  In this embodiment, control is performed so that the voltage holding ratio of the pixel does not fall below 95%. However, even if the holding ratio is about 92%, the viewer can view a still image, and the holding ratio is about 92%. Can be increased, the number of frames in which data is not rewritten can be greater than seven.

  Hereinafter, a case where the source line inversion driving (column inversion driving) method is used will be described as an example. In the column inversion driving method, in one frame, for example, the data voltage is positive (the potential of the source electrode is higher than the common voltage) and negative (common voltage) from the left source wiring (column) to the right column. (The potential of the source electrode is lower than that of the source electrode), positive polarity, negative polarity,... (Odd columns drive positive, even columns drive negative), and the data voltage of each column in the next frame This is a driving method in which the polarity of is reverse to the polarity in the immediately preceding frame.

  The touch control unit 62 turns on the touch signal when a coordinate specifying signal capable of specifying the touched position is input. The on state is maintained for a predetermined period (for example, 3 seconds) after the touch signal is turned on.

  The motion detector 61 uses the input image data to determine whether the image based on the currently input image signal is a still image or a moving image. As an example, the motion detection unit 61 includes a memory capable of storing image data for at least one frame, and compares the input image data with the image data of the immediately preceding frame stored in the memory, Perform motion detection. Any known method may be used as the motion detection method.

  The motion detection unit 61 turns on the motion detection signal when it is determined by motion detection that a moving image is input.

  When the touch signal from the control unit 60 is in the on state (when the touch sensor 20 is touched) or when the motion detection signal is in the on state (when it is a moving image), the output enable signal OE is The source driver 20 and the gate driver 30 perform a normal driving operation. The normal driving operation of the gate driver 30 is an operation of applying a gate-on voltage to the gate wiring 13 line-sequentially. A normal driving operation of the source driver 20 is an operation of applying a data voltage to each source line 14.

  In the timing control circuit 40, the latch circuit 42 turns on the output enable signal OE when the touch signal or the motion detection signal is on.

  When the output enable signal OE is turned off (high level in this example), the output buffer circuit 22 in the source driver 20 sets the output to the high impedance state over 7 frames started thereafter. That is, each source wiring 14 is set to a high impedance state. Therefore, the source driver 20 does not pass a current through the source line 14. As a result, in the period of 7 frames, the power consumption of the source driver 20 is reduced compared to when performing a normal drive operation.

  The output buffer circuit 22 preferably has the lowest driving capability (output R in the example shown in FIG. 4) when the output enable signal OE is in the off state. This is because the output of the output buffer circuit 22 is in a high impedance state, but even in this state, the output buffer circuit 22 itself consumes power, and the power consumption when the drive capability is the lowest is the smallest.

  In addition, when the output enable signal OE is turned off, the gate driver 30 does not drive each gate line 13 over seven frames that are started thereafter. That is, a gate off voltage (for example, −6 V) is applied to each gate wiring 13. By preventing the gate wiring 13 from being driven, the power consumption of the gate driver 30 is reduced as compared with the case of performing the normal driving operation.

  If the output enable signal OE returns to the on state before the 7 frame period elapses, the source driver 20 and the gate driver 30 return to the state in which the normal drive operation is performed from the frame that starts immediately after. .

  Further, when the output enable signal OE continues to be off even after the period of 7 frames elapses, the source driver 20 and the gate driver 30 perform the normal driving operation in the 8th frame, and the 7th frame from the next frame. The source driver 20 sets the output to a high impedance state over the frame, and the gate driver 30 does not drive each gate line 13.

  FIG. 6 is an explanatory diagram schematically showing the operation of the source driver 20. In FIG. 6A, after the output enable signal OE is in the off state (high level) and the source driver 20 performs the normal driving operation in the first frame (1F), the subsequent 6 frames (2 to 6F) are displayed. 7F), the output is set to the high impedance state, but the output enable signal OE is turned on (low level) in the seventh frame (7F). That is, the high impedance state is canceled in 7 frames. Thereafter, as shown in FIG. 6A, the source driver 20 performs a normal driving operation in the eighth and subsequent frames.

  In FIG. 6, “odd output” schematically shows an odd column data voltage in each frame, and “even output” schematically shows an even column data voltage in each frame. The point indicated by the tip of the arrow indicates the frame in which the source wiring 14 is actually driven, and the source wiring 14 in the frame without the arrow and the source frame of the arrow is actually driven. Not (high impedance state).

  FIG. 6B shows an example in which the output enable signal OE is kept off for a long time. In this case, after the source driver 20 performs a normal driving operation in the first frame (1F), the output is set to a high impedance state in the subsequent seven frames (2 to 8F), and is again normal in the ninth frame (9F). After the driving operation, the output is set to a high impedance state in the 10th frame and thereafter.

  FIG. 6C shows a conventional example. In the example shown in FIG. 6C, the source driver 20 performs a normal drive operation in all frames.

  Note that the gate driver 30 applies a gate-off voltage to the gate wiring 13 when the source driver 20 sets the output to a high impedance state. The state of each signal input to the source driver 20 and the gate driver 30 is also in a high impedance state.

  In the present embodiment, the source driver 20 does not drive the source wiring 14 when the touch operation on the touch panel 50 is not detected and the input image signal is a still image. Power consumption is reduced. Further, since the gate driver 30 does not drive the gate wiring 13 when the touch operation on the touch panel 50 is not detected and the input image signal is a still image, the power consumption of the gate driver 30 in that case is reduced. To do.

  Note that, when the normal drive operation is not performed over 7 frames after the normal drive operation is performed in a certain frame as in the above embodiment, the power consumption related to the drive during that period is 1/8. To reduce.

  Further, in the present embodiment, control is performed not only to drive the source wiring 14 in the case of a moving image, but also to drive the source wiring 14 when a touch operation on the touch panel 50 is detected. To do. Therefore, in a device that switches the display of the liquid crystal display panel 10 when a touch operation is performed on the touch panel 50 and in which a liquid crystal display device with a touch panel is incorporated, the normal drive operation is not performed earlier. It is possible to shift to a state where the normal driving operation is executed. That is, as soon as the touch signal shown in FIG. 2 is detected, the high impedance state of the source wiring 14 can be canceled and preparation for the normal drive operation can be made, so that the transition can be made quickly without waiting for the motion detection signal. That is, since a touch operation on the touch panel 50 is detected before a moving image (including switching of display content of a still image) is detected, an early state transition is possible.

  In the above embodiment, the case where the column inversion driving method is used has been described as an example. However, the present invention can also be applied to the case where another inversion driving method is used. Further, the present invention can also be applied to an IPS (In Plane Switching) type liquid crystal display device.

  The present invention can be suitably applied to devices such as a tablet terminal and an electronic book terminal equipped with a touch panel and a liquid crystal display device.

10 Liquid crystal display panel 12 Pixel 13 Gate wiring 14 Source wiring 15 TFT
16 drain electrode 17 capacitor 20 source driver 21 source signal generation unit 22 output buffer circuit 30 gate driver 40 timing control circuit 41 timing generator 42 latch circuit 50 touch panel 60 control unit 61 motion detection unit 62 touch detection unit

Claims (5)

A liquid crystal display panel arranged such that a plurality of gate lines and a plurality of source lines cross each other; a gate driver that sequentially applies a gate voltage to the gate lines; a source driver that applies a data voltage to the source lines; A liquid crystal display device with a touch panel comprising a touch panel provided on the viewing side of the liquid crystal display panel,
The source driver sets the source wiring to a high impedance state for a predetermined period when contact with the touch panel is not detected and an image based on an input image signal is a still image, and the touch to the touch panel is not performed. When detected, the high impedance state of the source wiring is released. A liquid crystal display device with a touch panel. The predetermined period is set according to a period until the voltage holding ratio of the liquid crystal reaches a predetermined value when the state in which the data voltage is not applied continues after the data voltage is applied to the source wiring. The liquid crystal display device with a touch panel according to claim 1, wherein the period is in accordance with the number of frames. The liquid crystal display device with a touch panel according to claim 1, wherein the gate driver stops driving of the gate wiring over the predetermined period. The source driver has an output buffer circuit,
The output buffer circuit drives the source wiring with any one of a plurality of driving capabilities,
4. The output buffer circuit according to claim 1, wherein the output buffer circuit is set in a state in which a source wiring is driven with the lowest driving capability among the plurality of driving capabilities over the predetermined period. 5. Liquid crystal display with touch panel. 5. A motion detection unit that determines whether an image based on an input image signal is a still image or a moving image, and a touch detection unit that determines whether or not there is a touch on the touch panel. A liquid crystal display device with a touch panel according to claim 1.

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