JP2013117641A - Liquid crystal display apparatus, and television receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display apparatus that controls the image refresh timing more accurately.SOLUTION: A liquid crystal display apparatus according to this invention comprises: a control unit 11 for controlling a scan line driver circuit 12 and a signal line driver circuit 13; and a comparator 15 for comparing a voltage of a monitor pixel electrode 152 with a predetermined threshold value. The control unit 11 controls the image refresh timing in accordance with a comparison result of the comparator 15.

Description

  The present invention relates to a liquid crystal display device. The present invention also relates to a voltage comparator provided in the liquid crystal display device and a television receiver provided with the liquid crystal display device.

  In recent years, the size of liquid crystal panels included in television receivers (hereinafter also referred to as televisions) has been increasing. Along with this, power consumption in liquid crystal panels is increasing, and reduction of power consumption is an issue.

  Furthermore, in recent years, the development of a television (a so-called 4K2K television) having a liquid crystal panel having a high resolution of about 4000 × 2000 is being promoted. With the development of such a high-definition television, there is an opportunity to display not only moving images represented by broadcast programs and content recorded in video, but also still images and moving images with little image change on the television. It is increasing.

  On the other hand, when the image displayed on the liquid crystal panel is a moving image, the display image is rewritten at a predetermined rewriting cycle (so-called refresh rate), but the still image and the moving image have little change in the image. In this case, a technology has been developed that reduces power consumption by reducing the refresh rate and reducing the number of times of rewriting the display image.

  Here, the voltage applied to each pixel included in the liquid crystal panel to display an image on the display panel is held in a capacitor (for example, a capacitor) included in each pixel. In addition, the voltage held by the capacitor is gradually reduced by a leakage current of a switching element (for example, a TFT (thin film transistor)) included in each pixel.

  Therefore, in the case of a still image and a moving image with little change in the image, it is necessary to rewrite (refresh) the display image before the displayed image changes due to a change in the pixel voltage due to the leakage current. is there.

  In Patent Document 1, when the image information displayed on the liquid crystal panel is not changed for a certain period of time, the drive voltage and the drive frequency of the information signal applied to the information electrode included in each pixel are lowered, and the temperature of the liquid crystal panel is set. A technique for controlling the drive voltage and drive frequency of an information signal according to the above is disclosed.

JP 9-5710 A (published on January 10, 1997)

  However, the leakage current in each switching element differs not only due to temperature change, but also due to variations in characteristics at the time of manufacture, and changes in characteristics with the passage of years of use (aging). That is, the leakage current changes due to variation in characteristics in addition to the temperature change of each switching element due to the temperature change of the liquid crystal panel. For this reason, in the technique described in Patent Document 1, although the refresh rate can be changed according to the temperature change of the liquid crystal panel, the change in the leakage current due to the variation in characteristics of each switching element and the secular change, etc. It cannot be properly controlled accordingly.

  Further, the technique described in Patent Document 1 controls the refresh rate according to the temperature change of the liquid crystal panel as described above, not the temperature change of each pixel. For this reason, when the temperature change of a part of the liquid crystal panel is more significant than the temperature change of other parts, the image displayed on the pixel of the part may change.

  Therefore, the technique described in Patent Document 1 has a problem that the refresh rate cannot be controlled with high accuracy.

  The present invention has been made to solve the above-described problems, and a main object of the present invention is to provide a liquid crystal display device capable of controlling the rewrite timing of an image (that is, refresh timing) with higher accuracy. It is to provide.

  In order to solve the above problems, a liquid crystal display device according to the present invention includes a plurality of in-region pixels arranged in a display region for displaying an image and at least one out-of-region arranged outside the display region. A display panel having pixels, a scanning signal supply circuit for supplying a scanning signal to the pixels in the region and the pixels outside the region, and an image signal for each pixel electrode provided in the pixels in the region and the pixels outside the region In a liquid crystal display device comprising: an image signal supply circuit that supplies a scanning signal supply circuit; and a control unit that controls the scanning signal supply circuit and the image signal supply circuit. And a control circuit for controlling the refresh timing of the image in accordance with a comparison result by the comparison circuit.

  According to said structure, the said control part controls the refresh timing of an image according to the said comparison result.

  Here, the voltage of the pixel electrode included in the out-of-region pixel is provided in the out-of-region pixel, and an electrical connection between the image signal line and the pixel electrode for supplying the image signal according to the scanning signal Is attenuated by a leakage current of a TFT (thin film transistor) that turns on and off. Further, the leakage current of the TFT changes due to a change in temperature of the TFT caused by driving the out-of-region pixel, a variation in characteristics at the time of manufacturing the TFT, a deterioration in the characteristics of the TFT due to continuous use, and the like.

  Therefore, the liquid crystal display device can control the refresh timing of the image in the control unit according to the comparison result (that is, the change in the voltage of the pixel electrode due to the leakage current of the TFT). As a result, the liquid crystal display device can control the refresh timing of the image with high accuracy.

  The voltage of the pixel electrode provided in the out-of-region pixel is used as a change of the voltage of the pixel electrode provided in the in-region pixel (so-called sample), and the refresh timing of the image is controlled according to the comparison result. The refresh timing of the image can be controlled in accordance with the characteristics of the pixel electrode and TFT of the pixel in the area. As a result, the characteristics of the pixel electrode provided in the pixel in the region change due to connecting the comparison circuit to directly compare the voltage of the pixel electrode provided in the pixel in the region with the threshold voltage. (In other words, it is possible to prevent the displayed image from changing).

  In the liquid crystal display device according to the present invention, the controller may refresh the image when the absolute value of the voltage of the pixel electrode included in the out-of-region pixel is equal to or less than the absolute value of the threshold value. preferable.

  According to the above configuration, the control unit does not start refreshing the image when the absolute value of the voltage of the pixel electrode is larger than the absolute value of the threshold value. According to this, for example, when the image displayed in the display area is not an image that always needs to be refreshed (for example, when the image is a still image), the number of refreshes can be reduced.

  Therefore, the liquid crystal display device can reduce the power consumed for refreshing the image. In addition, since the liquid crystal display device can reduce the number of times a scanning signal is supplied to the pixels in each region by reducing the number of refreshes, the deterioration of the characteristics of the TFTs provided in the pixels in each region is minimized. Can be suppressed.

  In the liquid crystal display device according to the present invention, the display panel includes a plurality of pixels outside the region, and the control unit has the lowest voltage among the absolute values of the voltages of the pixel electrodes included in the pixels outside the region. It is preferable to refresh the image when the absolute value is equal to or less than the absolute value of the threshold value.

  According to said structure, the said control part controls refresh of an image based on the absolute value of the lowest voltage among the absolute values of the voltage of each said pixel electrode. As a result, the liquid crystal display device can control the refresh of the image based on the voltage of the pixel electrode provided in the out-of-region pixel having the TFT having the largest leakage current.

  In addition, the larger the display panel, the greater the variation in the TFT characteristics of the out-of-region pixels generated depending on where the display panel is formed at the time of manufacture. Therefore, the liquid crystal display device can control the timing of image refreshing with higher accuracy even when the variation in characteristics of each TFT is large.

  In the liquid crystal display device according to the present invention, the control unit attenuates from the time when the image refresh is started until the absolute value of the voltage of the pixel electrode included in each of the pixels outside the region becomes equal to or less than the absolute value of the threshold value. It is preferable to measure time and set the refresh rate of the image based on each decay time.

  According to said structure, the said liquid crystal display device can set the optimal refresh rate according to the change of the voltage of the said pixel electrode by measuring the said decay time at least once. Of course, the decay time can be repeatedly measured, and the refresh rate can be reset every time the decay time is measured. According to this, the liquid crystal display device can always set an optimum refresh rate according to a change in the voltage of the pixel electrode.

  In the liquid crystal display device according to the present invention, the control unit divides the display area into a plurality of sub display areas based on each decay time, and controls the refresh timing for each of the sub display areas. It is preferable.

  According to the above-described configuration, the liquid crystal display device can respond to the variation even when the TFT characteristics of the out-of-region pixel are varied depending on where the display panel is formed at the time of manufacture. The display area is divided into a plurality of sub display areas, and the refresh timing is controlled for each of the divided sub display areas. Accordingly, it is possible to refresh the image only in the sub display area to which the out-of-area pixel having the pixel electrode in which the absolute value of the voltage is equal to or less than the absolute value of the threshold. Therefore, even when the absolute value of the voltage of the pixel electrode included in some of the pixels outside the region is equal to or less than the absolute value of the threshold value, it is necessary to refresh the image displayed on all the pixels included in the display panel. Therefore, power consumed in refresh can be reduced.

  In the liquid crystal display device according to the present invention, the comparison circuit is formed on the display panel, and includes a source connected to the voltage input node and a drain connected to one end of the capacitor. And a first transistor having a gate connected to a first control signal input node, a source connected to the other end of the capacitor, a drain connected to an intermediate node, and the first control. A second transistor having a gate connected to the signal input node; a source connected to the intermediate node; a drain connected to the output node; and a gate connected to the second control signal input node. A third transistor, a source connected to the output node, a grounded drain, and a gate connected to the intermediate node. A fifth transistor having a source connected to the intermediate node, a grounded drain, and a gate connected to a third control signal input node; a source connected to a reference voltage power supply; A sixth transistor having a drain connected to the other end of the first resistor having one end connected to the output node, a gate connected to the second control signal input node, and the reference voltage power supply; A second resistor having one end connected and the other end connected to the output node, the voltage of the pixel electrode of the out-of-region pixel being input to the voltage input node, and the comparison from the output node It is preferable that an output voltage indicating the result is output.

  According to the above configuration, since the comparison circuit including each of the above elements is formed on the display panel, the components constituting the liquid crystal display device are compared with the case where the comparison circuit is provided outside the display panel. The number can be reduced.

  In the liquid crystal display device according to the present invention, it is preferable that each of the plurality of in-region pixels and the at least one out-of-region pixel includes a TFT having an oxide semiconductor as a semiconductor layer.

  According to the above configuration, in the display device, the refresh rate is changed by adopting a TFT having an oxide semiconductor having excellent on and off characteristics as a semiconductor layer for each in-region pixel and out-of-region pixel. It becomes easy to make.

  A comparison circuit according to the present invention is formed on a display panel of a liquid crystal display device, and is a comparison circuit for comparing an input voltage with a predetermined threshold voltage, and includes a source connected to a voltage input node and one end of a capacitor. A drain connected to the first control signal input node; a source connected to the other end of the capacitor; a drain connected to an intermediate node; and A second transistor having a gate connected to the first control signal input node; a source connected to the intermediate node; a drain connected to the output node; and a second transistor connected to the second control signal input node A third transistor having a gate, a source connected to the output node, a grounded drain, and a gate connected to the intermediate node; And a fourth transistor having a source connected to the intermediate node, a grounded drain, and a gate connected to the third control signal input node, and a reference voltage power supply. A sixth transistor having a source, a drain connected to the other end of the first resistor connected at one end to the output node, and a gate connected to the second control signal input node; A second resistor having one end connected to the voltage power source and the other end connected to the output node, and is provided outside the image display region in the display panel having a plurality of pixels, and has an input voltage applied to the voltage input node. Is output, and an output voltage indicating the comparison result is output from the output node.

  By forming the comparison circuit as described above, a circuit in which a driving voltage is not continuously applied to each transistor forming the comparison circuit can be realized. Accordingly, the voltage comparator can be formed on the display panel even when the display panel included in the display device is formed of, for example, a glass substrate.

  Note that a television receiver provided with the reproducing apparatus also falls within the scope of the present invention.

  As described above, the liquid crystal display device according to the present invention includes a plurality of in-region pixels arranged in a display region for displaying an image and at least one out-of-region pixel arranged outside the display region. A display panel, a scanning signal supply circuit for supplying a scanning signal to the pixels in the region and the pixels outside the region, and an image signal to each pixel electrode included in the pixels in the region and the pixels outside the region An image signal supply circuit; a control unit that controls the scan signal supply circuit and the image signal supply circuit; a comparison circuit that compares a voltage of a pixel electrode included in the out-of-region pixel and a predetermined threshold; The control unit is characterized in that it controls the refresh timing of the image according to the comparison result by the comparison circuit.

  Therefore, the liquid crystal display device can control the timing of image refreshing with high accuracy.

It is a figure which shows the outline of the whole structure of the television which concerns on one Embodiment of this invention. It is a timing chart which shows operation | movement of a television in the case of displaying a moving image on the display area with which the television concerning one Embodiment of this invention is provided. It is a timing chart which shows operation | movement of a television in the case of displaying a still image on the display area with which the television concerning one Embodiment of this invention is provided. It is a timing chart which shows operation | movement of the television which measures a leak time, when displaying a still image on the display area with which the television concerning one Embodiment of this invention is provided. It is a timing chart which shows the operation | movement of the television which changes the voltage and supply time of a scanning signal based on leak time, when displaying a still image on the display area with which the television which concerns on one Embodiment of this invention is equipped. It is a timing chart which shows operation | movement of the television which comprises one frame by several fields, when displaying a still image on the display area with which the television concerning one Embodiment of this invention is equipped. It is a figure which shows the outline of the display panel with which the television which concerns on one Example of one Embodiment of this invention is provided. It is a figure which shows the outline of the display panel with which the television which concerns on the other Example of one Embodiment of this invention is provided. It is a figure which shows the outline of the display panel with which the television which concerns on the other Example of one Embodiment of this invention is provided. It is a circuit diagram which shows the structure of the comparator with which the television concerning other embodiment of this invention is provided. It is a timing chart which shows operation | movement of the comparator with which the television concerning other embodiment of this invention is provided.

<Embodiment 1>
A liquid crystal display device according to an embodiment of the present invention will be described with reference to FIGS. However, unless otherwise specified, the configuration described in this embodiment is not merely intended to limit the scope of the present invention, but is merely an illustrative example. In addition, since the liquid crystal display device according to the present embodiment is realized by a television receiver (hereinafter also referred to as a television), it is hereinafter referred to as a television.

  Hereinafter, a case where the liquid crystal display device is a television will be described as an example, but the present invention is not limited to this. The liquid crystal display device according to the present invention may be, for example, a personal computer, a PDA (Personal Digital Assistants), a tablet PC, a mobile phone, and a smartphone.

[Configuration of TV]
The configuration of the television 1 according to the present embodiment will be described with reference to FIG. FIG. 1 is a diagram showing an outline of the overall configuration of a television 1 according to this embodiment. As shown in FIG. 1, the television 1 includes a display panel 10, a control unit 11, and a comparator (comparison circuit) 15.

(Display panel)
The display panel 10 includes a scanning line driving circuit (scanning signal supply circuit) 12, a signal line driving circuit (image signal supply circuit) 13, and a display area 14 for displaying an image by driving a plurality of pixels. . Note that the scanning line driving circuit 12 and the signal line driving circuit 13 are provided in a non-display area (so-called frame area) outside the display area.

  The display panel 10 has a total of P rows (where P is an integer of 1 or more) scanning lines and a total number of Q columns (Q is an integer of 1 or more) arranged to intersect each scanning line in the display area 14. ) And a plurality of pixels (in-region pixels) provided at the intersections between the scanning lines and the signal lines.

  In addition, each pixel is provided with a pixel electrode 142 and includes a TFT (switching element) 141 that turns on and off the electrical connection between the pixel electrode 142 and the signal line by a scanning signal supplied to the scanning line. ing. The TFT 141 has a gate electrode connected to the scanning line, a source terminal connected to the signal line, and a drain terminal connected to the pixel electrode 142.

  Further, the display panel 10 is provided on the side of the signal line driving circuit 13 in the non-display area, at one line of the scanning scanning line m and the intersection of the monitoring scanning line m and the total number of Q signal lines. And a plurality of monitor pixels (out-of-region pixels).

  Each monitor pixel is provided with a monitor pixel electrode 152, and a monitor that turns on / off the electrical connection between the monitor pixel electrode 152 and the signal line by a scanning signal supplied to the monitor scanning line m. TFT (switching element) 151 is provided. The monitor TFT 151 has a gate electrode connected to the monitor scanning line m, a source terminal connected to the signal line, and a drain terminal connected to the monitor pixel electrode 152.

  In the present embodiment, the monitor pixels are not used for displaying an image, but are used for monitoring changes in TFT characteristics during the operation of the television 1, as will be described later. Of course, the present invention is not limited, and may be used to display an image.

  For convenience of explanation, among the three terminals provided in the TFT 141 and the monitor TFT 151, for two terminals other than the gate terminal, the terminal connected to the signal line is called a source terminal, and the pixel electrode 142 and the monitor pixel electrode 152 are connected. The terminal connected to is referred to as a drain terminal, but may be reversed.

  The semiconductor layers of the TFT 141 and the monitor TFT 151 are generally formed of, for example, a-Si (amorphous silicon), but are not limited thereto.

  Note that the image displayed in the display area 14 may be a moving image or a still image. Examples of the case where a still image is displayed in the display area include a case where a moving image is temporarily stopped.

(Control part)
The control unit 11 controls the scanning line driving circuit 12 and the signal line driving circuit 13 to control the refresh timing of the image displayed in the display area 14 of the display panel 10. Specifically, a synchronization signal and a gate clock signal sent from the outside are acquired, and a control signal for displaying an image in the display area 14 is output. The control unit 11 outputs a scanning control signal, a gate clock signal, a gate start pulse signal, and the like to be performed later to the scanning line driving circuit 12. In addition, the control unit 11 outputs a source clock signal, a source start pulse signal, a latch strobe signal, a polarity inversion signal, and the like to the signal line driver circuit 13.

  In addition, when the image displayed in the display area 14 is a still image or a moving image with little change in the image, the control unit 11 scans the scanning line driving circuit 12 and the signal line driving circuit 13 so that the refresh rate is lowered. To control.

  Further, as will be described later, the control unit 11 outputs a voltage indicating a predetermined threshold value, and acquires a comparison result by the comparator 15. When the comparison result input from the comparator 15 indicates a predetermined threshold value, the control unit 11 controls the scanning line driving circuit 12 and the signal line driving circuit 13 to refresh the image regardless of the set refresh rate. Control. For example, the control unit 11 may control the scanning line driving circuit 12 and the signal line driving circuit 13 by supplying a refresh signal indicating that the image is refreshed to the scanning line driving circuit 12 and the signal line driving circuit 13. .

  Note that threshold data indicating the value of the predetermined threshold voltage may be stored in advance in a memory (not shown) included in the television 1. A method for setting the threshold data will be described later.

(Scanning line drive circuit)
The scanning line driving circuit 12 supplies a scanning signal to the pixels and the monitor pixels. Specifically, scanning of the scanning line is started with the gate start pulse signal received from the control unit 11 as a cue.

  When the scanning line driving circuit 12 starts supplying the scanning signal, the scanning line driving circuit 12 sequentially applies the scanning voltage from the scanning line of the first row in the display area in accordance with the gate clock signal and the gate output control signal received from the control unit 11. A scan voltage is applied to all the scan lines in the row. Further, the scanning line driving circuit 12 applies a scanning voltage to the monitoring scanning line m provided in the non-display area. Thereby, the scanning line driving circuit 12 sequentially supplies a scanning signal having a scanning voltage for turning on the TFT 141 and the monitoring TFT 151 provided in the pixels on the scanning line to each scanning line. Note that supplying a scanning signal (that is, applying a scanning voltage) to turn on the TFT 141 and the monitor TFT 151 for each scanning line is hereinafter referred to as scanning the scanning line.

(Signal line drive circuit)
The signal line driver circuit 13 supplies pixel signals to the pixel electrode 142 included in the pixel and the monitor pixel electrode 152 included in the monitor pixel. Specifically, the signal line driving circuit 13 stores the input image signal of each pixel in a register (not shown) according to the source clock signal based on the source start pulse signal received from the control unit 11. Further, the signal line driving circuit 13 supplies an image signal indicating image data to each signal line of the display panel 10 in accordance with the next source latch strobe signal, and the pixel electrode 142 and the monitor provided in the pixel including each signal line. The pixel electrode 152 is charged.

  Based on the input image signal, the signal line driving circuit 13 calculates a voltage value to be output to each pixel on the selected scanning line, and outputs the voltage of that value to each signal line. As a result, image data is supplied to each pixel and monitor pixel on the selected scanning line.

  Further, the signal line driving circuit 13 sets the polarity of the image signal applied to the selected pixel, which is a pixel selected in a certain field, according to the polarity inversion signal received from the control unit 11 in the row direction and the column direction, respectively. And the polarity of the image signal applied to each selected pixel in a certain field is set to the image signal applied to the selected pixel in the field immediately before the certain field. Inverts with respect to the polarity.

(Comparator)
The comparator 15 compares the voltage of the monitor pixel electrode 152 (hereinafter also referred to as monitor voltage) with a voltage indicating a predetermined threshold supplied from the control unit 11 (hereinafter also simply referred to as threshold voltage). . Specifically, the comparator 15 determines the timing at which the absolute value of the voltage held in the monitor pixel electrode 152 becomes equal to or lower than the absolute value of the threshold when the absolute value of the voltage decreases due to the leakage current of the monitor TFT 151.

  The comparator 15 can be realized by a comparator, for example, but is not limited to this in the present invention.

  Note that the threshold voltage supplied from the control unit 11 to the comparator 15 is similarly “+” when the polarity of the voltage held in the monitor pixel electrode 152 is “+”. Good. Further, the threshold voltage may be similarly “−” when the polarity of the voltage held in the monitor pixel electrode 152 is “−”.

  The comparator 15 outputs a monitor determination signal when the absolute value of the monitor voltage becomes equal to or less than the absolute value of the threshold value.

(Threshold data setting)
Here, an example of a threshold data setting method will be described.

  For example, by providing a test mode in the television 1 that displays a test image and measuring the voltage of each pixel in a state where the test image is displayed in the display area 14, the image displayed on each pixel is the most. The voltage at the time when the image changes in a pixel that changes quickly (becomes defective) is measured. Next, the control unit 11 stores data indicating the value of the measured voltage in the memory as threshold data.

  As described above, by setting the threshold data in the test mode, the control unit 11 can supply the optimum threshold voltage to the comparator 15. By setting the threshold data before the television 1 is shipped, the user can set the threshold data in accordance with the characteristics of the pixels, the TFT 141, the pixel electrode 142, and the like included in the television 1 in advance. 1 can be used.

  The threshold data stored in the memory may be rewritable (reset). For example, the user may be able to set by operating the remote controller.

  According to the above-described configuration, threshold data can be set optimally and can be reset, so that a degree of freedom can be given to the comparison between the monitor voltage and the threshold voltage in the comparator 15.

  Note that the control unit 11 according to the present embodiment may include a D / A converter (not shown) in order to supply the threshold voltage with reference to the threshold data stored in the memory.

[TV operation]
Next, the operation of the television 1 according to the present embodiment will be described with reference to FIGS. Here, the operation of the television 1 when displaying a still image and a moving image with little image change will be described by taking the operation of the television 1 when displaying a still image as an example.

(Video display)
First, a case where a normal moving image (that is, a moving image with little image change) is displayed in the display area 14 will be described with reference to FIG. FIG. 2 is a timing chart showing the operation of the television 1 when a moving image is displayed in the display area 14.

  When displaying a moving image, as shown in FIG. 2, in the first field, the scanning line driving circuit 12 first starts supplying scanning signals to the monitor scanning line m. When the scanning signal driving circuit 12 finishes supplying the scanning signal to the monitor scanning line m, the scanning line driving circuit 12 starts to supply the scanning signal to the first scanning line provided in the display area 14. Further, when the supply of the scanning signal to the first scanning line is completed, the supply of the scanning signal to the second scanning line is started. In this way, the scanning signal is sequentially supplied to each scanning line up to the Pth row.

  Further, the signal line driving circuit 13 supplies an image signal to each signal line from the first column to the Q column while each scanning line is scanned.

  When the supply of the scanning signal to the monitor scanning line m and the P-th scanning line (hereinafter also simply referred to as the P + 1-th scanning line) is completed, the first field is completed. Next, in the second field, the scanning line driving circuit 12 sequentially supplies a scanning signal to the P + 1-th scanning line again. As a result, the images are refreshed sequentially, and the moving images are displayed in the display area 14.

  In the present embodiment, the case where the scanning line driving circuit 12 supplies a scanning signal to the monitor scanning line m when displaying a normal moving image has been described as an example. It is not limited to this. For example, when displaying a normal moving image, the scanning line driving circuit 12 may adopt a configuration in which a scanning signal is not supplied to the monitor scanning line m.

(Still image display)
Next, a case where a still image is displayed in the display area 14 will be described with reference to FIG. FIG. 3 is a timing chart showing the operation of the television 1 when a still image is displayed in the display area 14.

  In the case of displaying a still image, as shown in FIG. 3, the scanning line driving circuit 12 supplies a scanning signal to the monitoring scanning line m in the first field, and each of the first to Pth rows. A scanning signal is sequentially supplied to the scanning lines. Further, the signal line driving circuit 13 supplies an image signal to each signal line from the first column to the Q column while each scanning line is scanned.

  The scanning line driving circuit 12 stops the supply of the scanning signal when the supply of the scanning signal to all the scanning lines of the P + 1th row is completed. Further, when the supply of the image signal to each signal line is completed while the P-th scanning line is being scanned, the signal line driving circuit 13 stops the supply of the image signal.

  When the monitor determination signal is input from the comparator 15, that is, when the absolute value of the monitor voltage is equal to or less than the absolute value of the threshold, the control unit 11 supplies a refresh signal to the scanning line driving circuit 12 and the signal line driving circuit 13. To be notified. Note that when the monitor determination signal is input to the control unit 11, the first field ends and the second field starts.

  When the refresh signal is notified in the second field, the scanning line driving circuit 12 and the signal line driving circuit 13 resume supply of the scanning signal to the scanning line and supply of the image signal to the signal line, and the image is refreshed. Is done.

  According to the above-described configuration, when displaying a still image and a moving image with little change in the image, the television 1 reduces the number of refreshes by not refreshing the image until the monitor voltage becomes equal to or lower than the threshold value due to the leakage current. Can do. For this reason, the television 1 can reduce the power consumed for refreshing. In addition, the television 1 can reduce the number of times the scan signal is supplied to the TFT 141 included in each pixel by reducing the number of refreshes, and can minimize deterioration in characteristics of each TFT 141.

  Therefore, the television 1 can control the refresh timing of the image according to a temperature change in each pixel, a variation in leakage current of each TFT, deterioration of characteristics, and the like.

(Refresh rate setting for still image display)
Next, when displaying a still image in the display area 14, a case where a leak time that is a decay time of the monitor voltage is measured from the time when refresh is started at a certain time until the monitor voltage becomes equal to or lower than the threshold voltage is shown in FIG. This will be described with reference to FIG. FIG. 4 is a timing chart showing the operation of the television 1 that measures the leak time when a still image is displayed in the display area 14.

  In the case of displaying a still image, as shown in FIG. 3, the scanning line driving circuit 12 supplies a scanning signal to the monitoring scanning line m in the first field, and each of the first to Pth rows. A scanning signal is sequentially supplied to the scanning lines. Further, the signal line driving circuit 13 supplies an image signal to each signal line from the first column to the Q column while each scanning line is scanned.

  The scanning line driving circuit 12 stops the supply of the scanning signal when the supply of the scanning signal to all the scanning lines of the P + 1th row is completed. Further, when the supply of the image signal to each signal line is completed while the P-th scanning line is being scanned, the signal line driving circuit 13 stops the supply of the image signal.

  The control unit 11 refreshes the scanning line driving circuit 12 and the signal line driving circuit 13 when the monitor determination signal is input from the comparator 15, that is, when the absolute value of the monitoring voltage is equal to or lower than the absolute value of the threshold value. Notify the signal.

  When the refresh signal is notified, the scan line driver circuit 12 and the signal line driver circuit 13 resume supply of the scan signal to the scan line and supply of the image signal to the signal line, and the image is refreshed. Note that when the monitor determination signal is input to the control unit 11, the first field ends and the second field starts.

  Further, the control unit 11 ends the supply of the scanning signal to all of the scanning lines in the P + 1 row from the time when the supply of the scanning signal to the monitoring scanning line m is started, and the monitor determination signal is input from the comparator 15. The leak time required until the time is measured using a clock signal. The control unit 11 sets the measured leak time as a refresh rate when a still image is displayed in the display area 14.

  That is, after the second field, the control unit 11 controls the scanning line driving circuit 12 and the signal line driving circuit 13 so as to refresh the image based on the refresh rate set according to the leak time measured in the first field. . According to the above-described configuration, the television 1 can set an optimum refresh rate corresponding to the change in the monitor voltage by measuring the leak time once.

  The control unit 11 may employ a configuration in which the leak time is repeatedly measured and the refresh rate is reset every time the leak time is measured. According to this, the television 1 can always set an optimum refresh rate according to the change in the monitor voltage.

(Change of scanning signal in still image display)
Next, a case where the scanning voltage of the scanning signal and the supply time (that is, the scanning time of the scanning line) are changed based on the leak time when a still image is displayed on the display area 14 will be described with reference to FIG. . FIG. 5 is a timing chart showing the operation of the television 1 that changes the scanning voltage and the supply time based on the leak time when a still image is displayed in the display area 14.

  First, the control unit 11 measures the leak time as described above, and sets the measured leak time as a refresh rate when a still image is displayed in the display area 14.

  Next, the control unit 11 changes the scanning voltage (amplitude) and the supply time (pulse width) based on the set refresh rate. For example, the control unit 11 may set the scanning voltage low as shown in FIG. In this case, in order to obtain an on-voltage for turning on each TFT 141 and the monitor TFT 151 and to sufficiently supply the voltage of the image signal supplied through the signal line to each pixel electrode 142 and the monitor pixel electrode. In order to charge 152, the supply time of the scanning signal may be set longer. Note that, as shown in FIG. 5, the length of time for supplying the scanning signal needs to be set within a range in which the supply of the scanning signal to all the scanning lines of the (P + 1) th row is completed during one field period (one cycle of the refresh rate). There is.

  According to the above-described configuration, when displaying a still image and a moving image with little image change, the number of times that a high voltage is applied to each TFT 141 can be reduced, so that deterioration of characteristics of each TFT 141 is minimized. Can be suppressed.

  Moreover, the control part 11 may set the voltage of a scanning signal high. In this case, since the ON voltage and the voltage of the image signal can be sufficiently obtained, the supply time of the scanning signal can be set long.

  Note that, as described above, the control unit 11 may reset the refresh rate every predetermined period. In this case, the control unit 11 can optimally reset the scanning voltage and the supply time every predetermined period in accordance with the reset refresh rate. As a result, when the television 1 displays a still image and a moving image with little image change, the characteristics of the TFTs 141 during the operation of the television 1 due to temperature changes of the TFTs 141, deterioration of characteristics, and the like. The scanning voltage and the supply time can be appropriately set every time the refresh rate is reset so as to cope with the dynamic change.

(One frame is composed of multiple fields)
Next, a case where one frame is constituted by a plurality of fields when a still image is displayed in the display area 14 will be described with reference to FIG. FIG. 6 is a timing chart showing the operation of the television 1 that configures one frame by a plurality of fields when a still image is displayed in the display area 14.

  In order to form one frame by a plurality of fields, the same number of monitor scanning lines as the number of fields constituting one frame and monitor pixels corresponding to each monitor scanning line are provided in the non-display area. Is preferred. In the present embodiment, a case where one frame is constituted by two fields will be described as an example where two monitor scanning lines m1 and monitor scanning lines m2 are provided.

  When displaying a still image, as shown in FIG. 6, the scanning line driving circuit 12 first supplies a scanning signal to the monitoring scanning line m1 in the first field, and is further provided in the display area 14. A scanning signal is sequentially supplied to each odd-numbered scanning line from the first scanning line to the (P-1) th scanning line. The signal line driving circuit 13 supplies image signals to the signal lines from the first column to the Qth column while the monitor scanning line m1 and the odd-numbered scanning lines are being scanned.

  The scanning line driving circuit 12 stops the supply of the scanning signal when the supply of the scanning signal to the scanning line m1 for monitoring and each of the odd-numbered scanning lines provided in the display area 14 is completed. Further, when the supply of the image signal to each signal line is completed while the P-th scanning line is being scanned, the signal line driving circuit 13 stops the supply of the image signal to each signal line.

  The scanning line driving circuit 12 supplies a scanning signal to the monitoring scanning line m2 in the second field, and further, an even number from the second scanning line to the Pth scanning line provided in the display area 14. A scanning signal is sequentially supplied to each scanning line in the row. The signal line driving circuit 13 supplies image signals to the signal lines from the first column to the Q-th column while the monitor scanning line m2 and the even-numbered scanning lines are being scanned.

  The scanning line driving circuit 12 stops supplying the scanning signal when the supply of the scanning signal to the scanning line m2 for monitoring and each of the even-numbered scanning lines provided in the display area 14 is completed. Further, when the supply of the image signal to each signal line is completed while the P-th scanning line is being scanned, the signal line driving circuit 13 stops the supply of the image signal to each signal line. As a result, one image (one frame) is displayed in the display area 14.

  In addition, in any one of the first field and the second field, the control unit 11 receives the monitor determination signal from the comparator 15, that is, the absolute value of the monitor voltage is equal to or less than the absolute value of the threshold value. In this case, the refresh signal is notified to the scanning line driving circuit 12 and the signal line driving circuit 13.

  When the refresh signal is notified, the scanning line driving circuit 12 and the signal line driving circuit 13 start refreshing the still image. Specifically, when the refresh signal is notified in the first field, the scanning line driving circuit 12 and the signal line driving circuit 13 interrupt the first field and execute the second field in the current frame. , Start the first field in the next frame. Further, when the refresh signal is notified in the second field, the scanning line driving circuit 12 and the signal line driving circuit 13 interrupt the second field and start the first field in the next frame.

  As described above, when one frame is constituted by a plurality of fields, if the absolute value of the monitor voltage is equal to or smaller than the absolute value of the threshold in any field, the operation in the current frame is interrupted and refresh is started (that is, the next frame Start operation).

  Further, in the present embodiment, the configuration in which the scanning lines scanned in each field are switched every row (even rows and odd rows) has been described as an example, but the present invention is not limited to this. Absent. For example, a configuration may be adopted in which the scanning lines scanned in each field are switched every n (n is a natural number) rows. For example, when n = 2, the first and second scanning lines may be scanned in the first frame, and the third and fourth scanning lines may be scanned in the second frame. In the case of n = 1, the configuration is as described above.

  Further, the value of n is preferably determined according to the number of scanning lines supplied to each scanning line and the polarity of the scanning signal being inverted. For example, when the polarity of the scanning signal is inverted every row, n = 1 is preferable, and when the polarity of the scanning signal is inverted every two rows, n = 2 is preferable.

  In the present embodiment, the scanning line scanning in the first field and the scanning line scanning in the second field have been described as examples. However, the present invention is limited to this. It is not a thing. For example, scanning of the scanning line in the first field and scanning of the scanning line in the second field are independent, and before the monitor determination signal is input to the control unit 11 in the first field (or the refresh rate is indicated). Scanning of the scanning line in the second field may be started before the period of one field has elapsed.

  When the monitor determination signal is input to the control unit 11 in the first field (or when the period of one field indicated by the refresh rate has elapsed), before the monitor determination signal is input to the control unit 11 in the second field ( Alternatively, before the period of one field indicated by the refresh rate elapses, scanning of the scanning line in the first field in the next frame (that is, the field scanned with the same scanning line as the scanning line scanned in the first field) is performed. May be started.

  According to the above-described configuration, since the scanning signal supplied to the scanning line has the same polarity in each field, the television 1 supplies a scanning signal in which the polarity is inverted every n scanning lines in one field. Compared to the case, power consumption can be reduced.

  Further, according to the above-described configuration, when displaying a still image and a moving image with little change in the image, the television 1 displays images in each field constituting one frame until each monitor voltage becomes equal to or lower than a threshold value due to a leak current. By not refreshing, the number of refreshes in each field can be reduced. For this reason, the television 1 can reduce the power consumed for refreshing, and can reduce the number of times the scanning signal is supplied to each TFT 141, so that the deterioration of the characteristics of each TFT 141 is minimized. Can be suppressed.

(Drive by area)
Further, the control unit 11 may measure the leak times of the plurality of monitor TFTs 151 in the same manner as the leak time measurement described above. At this time, the control unit 11 divides the display area 14 into a plurality of areas (sub display areas) based on each leak time. Further, the control unit 11 controls the refresh timing for each divided area according to the corresponding leak time.

  According to the above-described configuration, the television 1 divides the display area 14 into a plurality of areas according to variations in characteristics of the TFTs 141 and the monitor TFTs 151 generated depending on where the display panel 10 is formed at the time of manufacture. The refresh timing is controlled for each area. As a result, it is possible to individually refresh the image only in the area to which the monitor pixel having the monitor pixel electrode in which the absolute value of the monitor voltage is equal to or smaller than the absolute value of the threshold value. Accordingly, even when the absolute values of the voltages of some of the monitor pixel electrodes are equal to or less than the absolute value of the threshold value, it is not necessary to refresh the images displayed on all the pixels included in the display panel 10. It is possible to reduce the power consumed in the operation.

  In the present embodiment, the case where one comparator 15 is provided has been described as an example. However, the present invention is not limited to this, and for example, a plurality of comparators 15 are provided. Also good. When a plurality of comparators 15 are provided, each comparator 15 compares the absolute value of the monitor voltage different from the absolute value of the threshold voltage. In this case, the control unit 11 follows the monitor determination signal input earliest from each comparator 15, that is, in accordance with the change in the characteristics of the monitor TFT 151 whose absolute value of the monitor voltage is the earliest or lower threshold voltage. What is necessary is just to control the operation | movement mentioned above.

  Further, in this embodiment, the voltage of the monitor pixel electrode 152 is used as a change of the voltage of the pixel electrode 142 (so-called sample), and the refresh timing of the image is controlled according to the comparison result, thereby the pixel electrode 142. The refresh timing of the image according to the characteristics of the TFT 141 can be controlled. As a result, the characteristics of the pixel electrode 142 and the TFT 141 change due to the direct connection of the comparator 15 in order to directly compare the voltage of the pixel electrode 142 with the threshold voltage (that is, the displayed image is changed). Change).

  With the above-described configuration, the television 1 according to the present embodiment can control the timing of image refreshing with high accuracy.

<Modification 1>
Next, a modification of the present embodiment will be described with reference to FIG. As shown in FIG. 7, the television 1a according to the present modification has one line of the monitor scanning line m ′ and the monitor scanning on the side opposite to the signal line driving circuit 13 side of the non-display area of the display panel 10a. The configuration is the same as that of the television 1 according to the first embodiment except that a plurality of monitor pixels (out-of-region pixels) provided at intersections between the line m ′ and the signal lines in the total number Q columns are provided.

  Each monitor pixel is provided with a monitor pixel electrode 152a, and the electrical connection between the monitor pixel electrode 152a and the signal line is turned on and off by a scanning signal supplied to the monitor scanning line m ′. And a monitoring TFT (switching element) 151a. The gate electrode of the monitor TFT 151a is connected to the monitor scanning line m ', the source terminal is connected to the signal line, and the drain terminal is connected to the monitor pixel electrode 152a.

  For convenience of explanation, of the three terminals provided in the monitor TFT 151a, of the two terminals other than the gate terminal, the terminal connected to the signal line is referred to as a source terminal, and the terminal connected to the monitor pixel electrode 152a is referred to. Although called a drain terminal, the reverse may be possible.

  The operation of the television 1a when displaying a still image in the present modification is performed by scanning the monitor scanning line m ′ after the scanning line provided in the display area 14 is scanned by the scanning line driving circuit 12. Since the operation is the same as that of the television 1 in the first embodiment, the description thereof is omitted here.

<Modification 2>
Next, another modification of the present embodiment will be described with reference to FIG. As shown in FIG. 8, the television 1b according to the present modification is replaced with the monitor scanning line m, and a line of monitor signal lines l on the side opposite to the scanning line driving circuit side of the non-display area of the display panel 10b. In addition, the embodiment 1 includes a plurality of monitor pixels (out-of-region pixels) provided at intersections of the monitor signal line l and the total number of P scanning lines. The configuration is the same as that of the television 1.

  Each monitor pixel is provided with a monitor pixel electrode 152b, and the electrical connection between the monitor pixel electrode 152b and the monitor signal line 1 is turned on and off by a scanning signal supplied to each scanning line. And a monitor TFT (switching element) 151b. The gate electrode of the monitor TFT 151b is connected to the scanning line, the source terminal is connected to the monitor signal line l, and the drain terminal is connected to the monitor pixel electrode 152b.

  For convenience of explanation, of the three terminals provided in the monitor TFT 151b, of the two terminals other than the gate terminal, the terminal connected to the monitor signal line l is called a source terminal and is connected to the monitor pixel electrode 152b. These terminals are referred to as drain terminals, but may be reversed.

[TV operation]
Next, the operation when displaying a still image in the display area 14 of the television 1b according to this modification will be described.

(Still image display)
When displaying a still image, the scanning line driving circuit 12 sequentially supplies a scanning signal to each scanning line from the first row to the P-th row in the first field. At this time, the signal line driving circuit 13 supplies the image signal to each signal line from the first column to the Qth column and the monitor signal line l while each scanning line is scanned.

  The scanning line driving circuit 12 stops the supply of the scanning signal when the supply of the scanning signal to all the scanning lines in the P row is completed. Further, the signal line driving circuit 13 stops the supply of the image signal when the supply of the image signal to all the signal lines in the Q column and the monitor signal line 1 is completed while the P-th scanning line is being scanned. .

  When the monitor determination signal is input from the comparator 15, that is, when the absolute value of the monitor voltage is equal to or less than the absolute value of the threshold, the control unit 11 supplies a refresh signal to the scanning line driving circuit 12 and the signal line driving circuit 13. To be notified. Note that when the monitor determination signal is input to the control unit 11, the first field ends and the second field starts.

  When the refresh signal is notified in the second field, the scanning line driving circuit 12 and the signal line driving circuit 13 resume supply of the scanning signal to the scanning line and supply of the image signal to the signal line, and the image is refreshed. Is done.

  According to the above-described configuration, when displaying a still image and a moving image with little change in the image, the television 1b reduces the number of refreshes by not refreshing the image until the monitor voltage becomes equal to or lower than the threshold value due to the leakage current. Can do. For this reason, the television 1b can reduce the power consumed for refreshing. In addition, the television 1b can reduce the number of times the refresh signal is supplied to the TFT 141 included in each pixel by reducing the number of refreshes, and can minimize deterioration of the characteristics of each TFT 141.

  Therefore, the television 1b can control the refresh timing of the image according to the temperature change in each pixel, the variation in leakage current of each TFT, the deterioration of characteristics, and the like.

(Refresh rate setting for still image display)
The controller 11 starts supplying scanning signals to the first scanning line until the scanning signals are supplied to all the scanning lines of the P row and the monitor determination signal is input from the comparator 15. The leakage time required for the measurement is measured using a clock signal. The control unit 11 sets the measured leak time as a refresh rate when displaying a still image.

  That is, after the second field, the control unit 11 controls the scanning line driving circuit 12 and the signal line driving circuit 13 so as to refresh the image based on the refresh rate set according to the leak time measured in the first field. . The control unit 11 adopts a configuration that controls the scanning line driving circuit 12 and the signal line driving circuit 13 according to the refresh rate set according to the leak time measured in the first field in all the fields after the second field. Also good. Further, the control unit 11 may adopt a configuration in which the refresh rate is reset every predetermined period by measuring the leak time every predetermined period.

(Change of scanning signal in still image display)
Further, the control unit 11 changes the scanning voltage (amplitude) and the supply time (pulse width) based on the refresh rate set as described above. For example, the control unit 11 may set the scanning voltage low. In this case, an on-voltage for turning on each TFT 141 is obtained, and a voltage of an image signal supplied through each signal line and the monitor signal line l is sufficiently increased for each pixel electrode 142 and the monitor. In order to charge the pixel electrode 152b, the supply time of the scanning signal may be set long. Note that the length of the scanning signal supply time needs to be set within a range in which the supply of the scanning signal to all the scanning lines of the P rows ends within one field period.

  According to the above-described configuration, when displaying a still image and a moving image with little image change, the number of times that a high voltage is applied to each TFT 141 can be reduced, so that deterioration of characteristics of each TFT 141 is minimized. Can be suppressed.

  Moreover, the control part 11 may set the voltage of a scanning signal high. In this case, since the ON voltage and the voltage of the image signal can be sufficiently obtained, the supply time of the scanning signal can be set long.

  Note that, as described above, the control unit 11 may reset the refresh rate every predetermined period. In this case, the control unit 11 can optimally reset the scanning voltage and the supply time every predetermined period in accordance with the reset refresh rate. Thus, when the television 1b displays a still image and a moving image with little image change, the characteristics of the TFTs 141 during the operation of the television 1b due to temperature changes of the TFTs 141, degradation of the characteristics, and the like. The scanning voltage and the supply time can be appropriately set every time the refresh rate is reset so as to cope with the dynamic change.

(One frame is composed of multiple fields)
Further, a case where one frame is constituted by a plurality of fields when a still image is displayed in the display area 14 will be described. When one frame is constituted by a plurality of fields, at least as many comparators 15 as the number of fields constituting one frame are provided for each monitor pixel electrode 152b corresponding to the scanning line scanned in each field. It is preferable that they are connected.

  When displaying a still image, first, the scanning line driving circuit 12 sequentially supplies scanning signals to the odd-numbered scanning lines from the first scanning line to the P-1th scanning line in the first field. To do. Further, the signal line driving circuit 13 applies an image to each of the signal lines from the first column to the Qth column provided in the monitor signal line l and the display area 14 while each odd-numbered scanning line is scanned. Supply signal.

  When the scanning signal supply to the odd-numbered scanning lines provided in the display area 14 is completed, the scanning line driving circuit 12 stops the supply of the scanning signal. Further, when the supply of the image signal to each signal line is completed while the P-th scanning line is being scanned, the signal line driving circuit 13 stops the supply of the image signal to each signal line.

  The scanning line driving circuit 12 and the signal line driving circuit 13 operate in the same manner as in the first field except that the scanning line driving circuit 12 sequentially scans even-numbered scanning lines in the second field. As a result, one image (one frame) is displayed in the display area 14.

  In addition, in any one of the first field and the second field, the control unit 11 receives the monitor determination signal from the comparator 15, that is, the absolute value of the monitor voltage is equal to or less than the absolute value of the threshold value. In this case, the refresh signal is notified to the scanning line driving circuit 12 and the signal line driving circuit 13.

  When one frame is composed of a plurality of fields, when a refresh signal is notified (that is, when the absolute value of the monitor voltage becomes equal to or smaller than the absolute value of the threshold in any field), the operation in the current frame is interrupted, and the next Operation on the frame is started. Note that the operation of the television 1b that is notified of the refresh signal is the same as the operation of the television 1 according to the first embodiment, and thus the description thereof is omitted here.

  According to the above-described configuration, when displaying a still image and a moving image with little change in the image, the television 1 refreshes the image in each field constituting one frame until each monitor voltage becomes equal to or less than a threshold value due to a leak current. By not doing so, the number of refreshes in each field can be reduced. For this reason, the television 1 can reduce the power consumed for refreshing, and can reduce the number of times the scanning signal is supplied to each TFT 141, so that the deterioration of the characteristics of each TFT 141 is minimized. Can be suppressed.

<Modification 3>
Next, still another modification of the present embodiment will be described with reference to FIG. As shown in FIG. 9, the television 1c according to the present modification includes a row of monitor signal lines l ′ on the scan line driving circuit side in the non-display area of the display panel 10c, instead of the monitor scan lines m. In addition, according to the first embodiment, except that the monitor signal line l ′ and a plurality of monitor pixels (out-of-region pixels) provided at intersections of the total number P of scanning lines are provided. The configuration is the same as that of the television 1.

  Each monitor pixel is provided with a monitor pixel electrode 152c, and the electrical connection between the monitor pixel electrode 152c and the monitor signal line l ′ is turned on / off by a scan signal supplied to each scan line. And a monitoring TFT (switching element) 151c. The gate electrode of the monitor TFT 151c is connected to the scanning line, the source terminal is connected to the monitor signal line l, and the drain terminal is connected to the monitor pixel electrode 152c.

  For convenience of explanation, of the three terminals provided in the monitor TFT 151c, two terminals other than the gate terminal are connected to the monitor signal line l ′ as a source terminal and connected to the monitor pixel electrode 152c. The connected terminal is called a drain terminal, but it may be reversed.

  Note that the operation of the television 1c when displaying a still image in the present modification is the same as the operation of the television 1b in the second embodiment, and thus the description thereof is omitted here.

<Embodiment 2>
Another embodiment of the present invention will be described as follows. Note that the television 2 according to the present embodiment is described in the first embodiment, except that the comparator 2 formed on the display panel 10 is provided instead of the comparator 15 provided outside the display panel 10. This is the same configuration as the TV 1.

(Comparator circuit configuration)
Here, the comparator according to the present embodiment will be described with reference to FIG. FIG. 10 is a circuit diagram illustrating a configuration of the comparator 25 included in the television 2 according to the present embodiment.

  As shown in FIG. 10, the comparator (comparison circuit) 25 includes a power source V1 (reference voltage power source), V2 (ground), control signal input terminals S1 to S3 (first control signal input node to third control signal). Input node), monitor voltage input terminal (voltage input node) I, output terminal (output node) O, transistors T1 to T6 (first transistor to sixth transistor), resistors R1 (first resistor), R2 ( A second resistor) and a capacitor C. In the present embodiment, the power source V2 may be a GND (ground) terminal, for example.

  The monitor voltage input terminal I is connected to the source terminal of the transistor T1. The gate terminal of the transistor T1 is connected to the control signal input terminal S1, and the drain terminal is connected to one end Net1 of the capacitor C. The other end Net2 of the capacitor C is connected to the source terminal of the transistor T2, the source terminal gate terminal of the transistor T2 is connected to the control signal input terminal S1, and the drain terminal is connected to the terminal Net3 (intermediate node). ing.

  The gate terminal of the transistor T3 is connected to the control signal input terminal S2, the source terminal is connected to the terminal Net3, and the drain terminal is connected to the output terminal O. The transistor T5 has a gate terminal connected to the control signal input terminal S3, a source terminal connected to the terminal Net3, and a drain terminal connected to the power supply V2.

  The transistor T6 has a gate terminal connected to the control signal input terminal S2, a source terminal connected to the power source V1, and a drain terminal connected to one end of the resistor R1. The other end of the resistor R1 is connected to the output terminal O.

  One end of the resistor R2 is connected to the power source V1, and the other end is connected to the output terminal O. The gate terminal of the transistor T4 is connected to the terminal Net3, the source terminal is connected to the output terminal O, and the drain terminal is connected to the power supply V2.

  Note that the transistors T4 and T6 and the resistors R1 and R2 form an inverter circuit, and the terminal Net3 can be regarded as an input terminal of the inverter circuit.

  In the present embodiment, the case where the transistors T1 to T6 are all Nch TFTs (thin film transistors) will be described as an example. However, the present invention is not limited to this.

  In this embodiment, the control signal input terminals S1 to S3 and the output terminal O are connected to the control unit 11, and the power supplies V1 and V2 are connected to a power supply circuit (not shown) included in the television 1. The monitor voltage input terminal I may be connected to the monitor pixel electrode 152.

  In the first and second embodiments, TFTs using so-called oxide semiconductors can be employed as the TFT 141, the monitoring TFT 151, and the transistors T1 to T6.

(TFT characteristics using oxide semiconductor)
A TFT using an oxide semiconductor has an electron mobility of about 20 to 50 times higher in an on state than a TFT using a-Si, and has excellent on characteristics. .7 ms or less, that is, it is easy to set the refresh rate to 60 Hz or more.

  The display panel 10 according to the first and second embodiments can drive a pixel with a smaller TFT by using a TFT using an oxide semiconductor with excellent on-state characteristics for each pixel. Thereby, the display panel 10 can reduce the ratio of the area occupied by the TFT in each pixel. That is, the aperture ratio in each pixel can be increased, and the backlight transmittance can be increased. As a result, a backlight with low power consumption can be adopted or the luminance of the backlight can be suppressed, so that power consumption can be reduced.

  In addition, since the on-characteristics of the TFT are excellent, the writing time of the source signal to each pixel can be shortened, so that the frame period of the display panel 10 can be easily shortened (that is, the refresh rate can be easily increased). Can be high).

  In addition, a TFT using an oxide semiconductor has a leakage current in an off state that is about one-hundredth that of a TFT using a-Si. Is. Thus, since the off characteristics are very excellent, it is easy to set the frame period to 33 ms or more, that is, the refresh rate to 30 Hz or less.

  The display panel 10 according to the first to fifth embodiments employs a TFT using such an oxide semiconductor having excellent off characteristics for each pixel, whereby each source signal of a plurality of pixels included in the display panel 10 is used. Can be maintained for a long period of time, so that the frame period of the display panel 10 can be easily lengthened (that is, the refresh rate can be easily lowered).

  Note that even a TFT using such an oxide semiconductor generates a considerable leakage current. Therefore, by using the comparator 25 including the circuit according to the present embodiment, the deterioration of the TFT is further minimized. be able to.

(Comparator operation)
Next, the operation of the comparator 25 will be described with reference to FIG. FIG. 11 is a timing chart showing the operation of the comparator 25 provided in the television 2 according to the present embodiment.

  As shown in FIG. 11, the voltage of the output terminal O at the time before time t1 is an H level voltage, and specifically, the voltage applied to the resistor R2 has dropped from the voltage applied to the power supply V1. Voltage.

  At time t1, as shown in FIG. 11, scanning of the monitor scanning line m is started (the scanning voltage transitions to a high level (H level)), and at the same time, it is input to the control signal input terminals S1 and S2. Both control signals transition to the H level. When an H level control signal is input to the control signal input terminal S1, the transistors T1 and T2 are turned on. Further, when an H level control signal is input to the control signal input terminal S2, the transistors T3 and T6 are turned on.

  When the transistor T3 is turned on, the input terminal (that is, the terminal Net3) and the output terminal O of the inverter circuit including the transistors T4 and T5 and the resistors R1 and R2 are short-circuited. Therefore, as shown in FIG. 11, the input voltage (that is, the voltage at the terminal Net3) of the inverter circuit and the output voltage (that is, the voltage at the output terminal O) are equal to the threshold voltage A of the inverter circuit. Since the transistor T6 is in the on state, the threshold voltage A is (1) the on-resistance of the transistor T6, the resistor R1 connected in series to the transistor T6, and the resistor connected in parallel with the transistor T6 and the resistor R1. It is determined by the ratio between the combined resistance value of R2 and (2) the resistance value of the on-resistance of the transistor T4.

  In this embodiment, as shown in FIG. 11, the threshold voltage B is used as a threshold when determining whether the absolute value of the monitor voltage is equal to or smaller than the absolute value of the predetermined threshold after time t4. Specifically, when the voltage at Net3 is larger than the threshold voltage B, an output signal having an L level voltage is output from the output terminal O, and when the voltage at Net3 is equal to or lower than the threshold voltage B, the output signal is output. An output signal having an H level voltage is output from the terminal O.

  At time t4, at the time when the voltage input to the monitor voltage input terminal I is compared with the threshold voltage, the control signal input terminal S2 is at the L level and the transistor T6 is in the OFF state. Therefore, the threshold voltage B is determined by the ratio of the resistance value between the on-resistance of the transistor T4 and the resistor R2. Therefore, the difference between the threshold voltage A and the threshold voltage B is a value for determining the amount of change in the potential charged in the pixel electrode.

  Since the transistors T1 and T2 are in the on state, the monitor voltage input from the monitor voltage input terminal I is applied to one end Net1 of the capacitor C, and the threshold voltage A of the terminal Net3 is applied to the other end Net2. The As a result, a differential voltage between the monitor voltage and the threshold voltage A is applied to the capacitor C.

  At time t2, the scanning voltage transitions to the low level (L level), and at the same time, the control signals input to the control signal input terminals S1 and S2 both transition to the L level. When an L level control signal is input to the control signal input terminals S1 and S2, the transistors T1 and T2 are turned off. The differential voltage between the monitor voltage and the threshold voltage A is held in the capacitor C by turning off the transistors T1 and T2.

  At time t3, the control signal input to the control signal input terminal S3 changes to H level, and the transistor T5 is turned on. When the transistor T5 is turned on, the terminal Net3 and the power source V2 are short-circuited, and the voltage at the terminal Net3 becomes the same L level (ground potential) as that of the power source V2. Since the voltage at the terminal Net3 applied to the gate terminal of the transistor T4 becomes the L level, the deterioration of characteristics due to the continuous application of the H level voltage to the transistor T4 can be minimized.

  Further, when the voltage at the terminal Net3 applied to the gate terminal of the transistor T4 becomes L level, the transistor T4 is turned off, and the voltage at the output terminal O returns to the initial voltage at the time before the time t1. . Hereinafter, an operation in which the voltage of the output terminal O returns to the initial voltage when the H level control signal is input to the control signal input terminal S3 is also referred to as resetting the voltage of the output terminal O.

  As shown in FIG. 11, the monitor voltage input to the monitor voltage input terminal I is attenuated by the leak current during a period from time t2 to t4.

  At time t4, the control signal input to the control signal input terminal S1 transitions to the H level, and the transistors T1 and T2 are turned on. When the transistors T1 and T2 are turned on, the voltage at one end Net1 and the other end Net2 of the capacitor C decreases by the same value as the monitor voltage attenuated during the period from time t2 to t4. As a result, the voltage at the terminal Net3 decreases by the same value as the value at which the monitor voltage is attenuated.

  At time t5, both the control signals input to the control signal input terminal S1 transition to the L level, and the transistors T1 and T2 are turned off. When the transistors T1 and T2 are turned off, the capacitor C holds a voltage that is decreased from the voltage held at the time t2 by the same value as the monitor voltage attenuated during the period from the time t2 to the time t4. become.

  As shown in FIG. 11, since the voltage at the terminal Net3 is higher than the threshold voltage B in the period from time t4 to t6, the output terminal O outputs an output having an L level voltage as the output of the comparator 25. Output a signal.

  At time t6, the control signal input to the control signal input terminal S3 changes to H level, and the transistor T5 is turned on. When the transistor T5 is turned on, the terminal Net3 and the power source V2 are short-circuited, and the voltage at the terminal Net3 becomes the same L level as that of the power source V2.

  Further, when the voltage at the terminal Net3 applied to the gate terminal of the transistor T4 becomes L level, the transistor T4 is turned off, and the voltage at the output terminal O is reset.

  As shown in FIG. 11, the monitor voltage input to the monitor voltage input terminal I is attenuated by the leak current during the period from time t5 to t7.

  At time t7, the control signal input to the control signal input terminal S1 transitions to H level, and the transistors T1 and T2 are turned on. When the transistors T1 and T2 are turned on, the voltage at one end Net1 and the other end Net2 of the capacitor C decreases by the same value as the monitor voltage attenuated during the period from time t5 to t7, and the voltage at the terminal Net3 is also the same. Decreases by the value.

  At time t8, both the control signals input to the control signal input terminal S1 transition to the L level, and the transistors T1 and T2 are turned off. When the transistors T1 and T2 are turned off, the capacitor C holds a voltage that is decreased from the voltage held at the time t5 by the same value as the monitor voltage attenuated during the period from the time t4 to the time t6. become.

  As shown in FIG. 11, since the voltage at the terminal Net3 is lower than the threshold voltage B in the period from time t7 to t9, the output terminal O outputs an output having an H level voltage as the output of the comparator 25. Output a signal.

  At time t9, the control signal input to the control signal input terminal S3 changes to H level, and the transistor T5 is turned on. When the transistor T5 is turned on, the terminal Net3 and the power source V2 are short-circuited, and the voltage at the terminal Net3 becomes the same L level as that of the power source V2.

  Further, when the voltage at the terminal Net3 applied to the gate terminal of the transistor T4 becomes L level, the transistor T4 is turned off, and the voltage at the output terminal O is reset.

  Note that the control unit 11 according to the present embodiment scans to refresh the displayed image when an output signal having an H level voltage (that is, a monitor determination signal) is input from the comparator 25. The line driver circuit 12 and the signal line driver circuit 13 may be controlled.

  Note that the operation of the television 2 according to the present embodiment is the same as the operation of the television 1 according to the first embodiment, and thus description thereof is omitted here.

  In addition, by configuring the comparator 25 as described above, it is possible to realize a circuit in which the driving voltage is not continuously applied to the transistors T1 to T6 included in the comparator 25 for a long time. Accordingly, the comparator 25 can be formed on the display panel 10 realized by, for example, a glass substrate.

  It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The display device according to the present invention can be suitably applied to a television receiver, a personal computer, a car navigation system, a mobile phone, a PDA, a smartphone, a tablet PC, a digital camera, a digital video camera, and the like.

1, 1a, 1b, 1c, 2 TV (liquid crystal display device)
10, 10a, 10b, 10c Display panel 11 Controller 12 Scan line drive circuit (scan signal supply circuit)
13 Signal line drive circuit (image signal supply circuit)
14 Display area 15, 25 Comparator (comparison circuit)
141 TFT
142 Pixel electrode 151, 151a, 151b, 151c Monitor TFT
152, 152a, 152b, 152c Monitor pixel electrode

Claims (9)

A display panel having a plurality of in-region pixels arranged in a display region for displaying an image and at least one out-of-region pixel arranged outside the display region;
A scanning signal supply circuit for supplying a scanning signal to the pixels in the region and the pixels outside the region;
An image signal supply circuit for supplying an image signal to each pixel electrode included in the in-region pixel and the out-of-region pixel;
In a liquid crystal display device comprising: a control unit that controls the scanning signal supply circuit and the image signal supply circuit;
A comparison circuit that compares the voltage of the pixel electrode included in the out-of-region pixel with a predetermined threshold voltage;
The control unit controls the refresh timing of the image according to the comparison result by the comparison circuit.
A liquid crystal display device characterized by the above. The control unit refreshes the image when the absolute value of the voltage of the pixel electrode included in the out-of-region pixel becomes equal to or less than the absolute value of the threshold voltage.
The liquid crystal display device according to claim 1. The display panel includes a plurality of the out-of-region pixels,
The control unit refreshes the image when the absolute value of the lowest voltage among the absolute values of the voltage of the pixel electrode included in each of the pixels outside the region is equal to or less than the absolute value of the threshold voltage.
The liquid crystal display device according to claim 1 or 2. The control unit measures the decay time from the start of image refresh until the absolute value of the voltage of the pixel electrode included in each out-of-region pixel becomes equal to or less than the absolute value of the threshold voltage, and based on each decay time. To set the refresh rate of the above image,
The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a liquid crystal display device. The control unit divides the display area into a plurality of sub display areas based on each decay time, and controls the refresh timing for each of the sub display areas.
The liquid crystal display device according to claim 4. The comparison circuit is formed on the display panel,
A first transistor having a source connected to the voltage input node, a drain connected to one end of the capacitor, and a gate connected to the first control signal input node;
A second transistor having a source connected to the other end of the capacitor, a drain connected to an intermediate node, and a gate connected to the first control signal input node;
A third transistor having a source connected to the intermediate node, a drain connected to an output node, and a gate connected to a second control signal input node;
A fourth transistor having a source connected to the output node, a grounded drain, and a gate connected to the intermediate node;
A fifth transistor having a source connected to the intermediate node, a grounded drain, and a gate connected to a third control signal input node;
A first source having a source connected to a reference voltage power source, a drain connected to the other end of the first resistor connected to the output node, and a gate connected to the second control signal input node. 6 transistors,
A second resistor having one end connected to the reference voltage power source and the other end connected to the output node;
The voltage of the pixel electrode included in the out-of-region pixel is input to the voltage input node,
An output voltage indicating the comparison result is output from the output node.
The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a liquid crystal display device. Each of the plurality of in-region pixels and the at least one out-of-region pixel includes a TFT having an oxide semiconductor as a semiconductor layer.
The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a liquid crystal display device. A comparison circuit formed on a display panel of a liquid crystal display device for comparing an input voltage with a predetermined threshold voltage,
A first transistor having a source connected to the voltage input node, a drain connected to one end of the capacitor, and a gate connected to the first control signal input node;
A second transistor having a source connected to the other end of the capacitor, a drain connected to an intermediate node, and a gate connected to the first control signal input node;
A third transistor having a source connected to the intermediate node, a drain connected to an output node, and a gate connected to a second control signal input node;
A fourth transistor having a source connected to the output node, a grounded drain, and a gate connected to the intermediate node;
A fifth transistor having a source connected to the intermediate node, a grounded drain, and a gate connected to a third control signal input node;
A first source having a source connected to a reference voltage power source, a drain connected to the other end of the first resistor connected to the output node, and a gate connected to the second control signal input node. 6 transistors,
A second resistor having one end connected to the reference voltage power source and the other end connected to the output node;
The input voltage is input to the voltage input node,
An output voltage indicating a comparison result is output from the output node.
A comparison circuit characterized by that. The liquid crystal display device according to claim 1 is provided.
Television receiver characterized by that

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