BACKGROUND

Technical Field

The following disclosure relates to a liquid crystal display device and particularly relates to a liquid crystal display device including a liquid crystal panel with a built-in touch panel.

A touch panel has attracted attention as an input device for performing operations in a computer system or the like in the related art. For example, in a capacitive touch panel, a position of an object to be detected such as a finger of a user (operator) or a touch pen is detected based on a change in electrostatic capacitance. Such a touch panel has been used by being superimposed on a display panel such as a liquid crystal panel in the related art. Such a touch panel provided on the display panel is referred to as an “out-cell type touch panel”.

However, in the out-cell type touch panel, an increase in the weight and the thickness of the entire device including the display panel and the touch panel, and an increase in the power required to drive the touch panel have been problems. Thus, in recent years, development of display devices having a configuration in which the display panel and the touch panel are integrated has advanced. The touch panels having the configuration integrated with the display panel mainly include those referred to as “on-cell type touch panels” and those referred to as “in-cell type touch panels”. In the on-cell type touch panels, a sensor electrode is provided between one of two glass substrates constituting the display panel and a polarizer. In the in-cell type touch panels, the sensor electrode is provided inside the two glass substrates.

As described above, the touch panels include several types, but in recent years, the in-cell type touch panels have become mainstream in the market. In the in-cell type touch panels, rectangular sensor electrodes segmented into a plurality of rows×a plurality of columns are typically used, and touch detection (detection of touch position on the touch panel) is performed by a self capacitance method. Note that the self capacitance method is a method for measuring a position of an object to be detected by detecting that electrostatic capacitance has increased due to contact or approach of the object to be detected with or to the touch panel.

Some in-cell type touch panels employ a configuration in which the sensor electrode described above and a common electrode which is an electrode used for displaying an image are shared. In such a configuration, one electrode is used as the sensor electrode for performing the touch detection, and is also used as the common electrode for image display. By sharing the sensor electrode and the common electrode in this manner, a reduction in thickness and weight of the device are realized.

In recent years, liquid crystal display devices provided with memory circuits in pixel circuits have been developed in order to reduce power consumption. Such a liquid crystal display device is referred to as a “memory liquid crystal display”. In general, in the memory liquid crystal display, one bit of data can be held for each pixel, and in a case where an image of the same content or an image with a small change is displayed for a long period of time, image display using the data held in the memory circuit is performed. In the memory liquid crystal display, once the data is written to the memory circuit, the contents of the data written to the memory circuit are held until the next rewrite. Thus, little power is consumed in periods other than the periods before and after the contents of the image change. Thus, low power consumption can be achieved.

FIG. 22is a diagram illustrating a configuration of a pixel circuit900of a known memory liquid crystal display. As illustrated inFIG. 22, the pixel circuit900includes an input switch910, a memory circuit920, a voltage selection circuit930, and a liquid crystal capacitance940constituted by a pixel electrode941and a common electrode942. A first scanning signal GLA, a second scanning signal GLB, a data signal SL, a black voltage VA, which is a voltage for black display, and a white voltage VB, which is a voltage for white display, are supplied to the pixel circuit900.

A state of the input switch910is controlled by the first scanning signal GLA and the second scanning signal GLB. When the input switch910is in an on state, the data signal SL is supplied to the memory circuit920. Note that the data signal SL is binary data. The memory circuit920stores the binary data based on the data signal SL. The voltage selection circuit930selects either the black voltage VA or the white voltage VB in accordance with a value of the binary data stored in the memory circuit920. The voltage selected by the voltage selection circuit930is then applied to the pixel electrode941, which is reflected in a display state of the pixel.

Note that, in connection with the present case, JP 2015-96935 A and JP 2017-83530 A disclose technologies related to a memory liquid crystal display provided with a touch panel.

However, the memory liquid crystal display provided with the in-cell type touch panel is not realized for the reasons below. Note that in the following, a common electrode voltage is denoted by a reference sign VCOM, and a pixel electrode voltage is denoted by a reference sign Vp. In the following, focusing on a normally-white type, it is assumed that a liquid crystal application voltage is 0 V when the white display is performed, and the liquid crystal application voltage is 5 V or −5 V when the black display is performed.

FIG. 23is a waveform diagram when the black display is performed by a known memory liquid crystal display (by one pixel of interest). For the common electrode voltage VCOM, 5 V and 0 V appear alternately. Specifically, the common electrode voltage VCOM is 5 V in a period in which the black voltage VA is 0 V, and the common electrode voltage VCOM is 0 V in a period in which the black voltage VA is 5 V. By selecting the black voltage VA by the voltage selection circuit930, the pixel electrode voltage Vp is equal to the black voltage VA. As described above, the liquid crystal application voltage is −5 V in a period in which the common electrode voltage VCOM is 5 V, and the liquid crystal application voltage is 5 V in a period in which the common electrode voltage VCOM is 0 V. As a result, the black display is performed.

FIG. 24is a waveform diagram when the black display is performed, assuming that the known memory liquid crystal display is provided with the in-cell type touch panel. Note that a touch detection period (a period for detecting a touched position on the touch panel) is denoted by a reference sign Td. A pulse signal for touch detection is supplied to the common electrode942in the touch detection period Td. Accordingly, in the touch detection period Td, as illustrated inFIG. 24, the common electrode voltage VCOM varies between 0 V and 5 V. Here, in a period in which the common electrode voltage VCOM is 0 V among periods T91and T93in which the common electrode voltage VCOM is supposed to be maintained at 5 V, the common electrode voltage VCOM and the pixel electrode voltage Vp are equal to each other, so the liquid crystal application voltage is 0 V. In addition, in a period in which the common electrode voltage VCOM is 5 V among periods T92and T94in which the common electrode voltage VCOM is supposed to be maintained at 0 V, the common electrode voltage VCOM and the pixel electrode voltage Vp are also equal to each other, so the liquid crystal application voltage is 0 V. In this way, the white display is inserted in the period in which the black display is supposed to be performed.

FIG. 25is a waveform diagram when the white display is performed by the known memory liquid crystal display. For the common electrode voltage VCOM, 5 V and 0 V appear alternately. Specifically, the common electrode voltage VCOM is 5 V in a period in which the white voltage VB is 5 V, and the common electrode voltage VCOM is 0 V in a period in which the white voltage VB is 0 V. By selecting the white voltage VB in the voltage selection circuit930, the pixel electrode voltage Vp is equal to the white voltage VB. As described above, the liquid crystal application voltage is 0 V both in the period in which the common electrode voltage VCOM is 5 V and in the period in which the common electrode voltage VCOM is 0 V. As a result, the white display is performed.

FIG. 26is a waveform diagram when the white display is performed, assuming that the known memory liquid crystal display is provided with the in-cell type touch panel. Similar to the example illustrated inFIG. 24, in the touch detection period Td, as illustrated inFIG. 26, the common electrode voltage VCOM varies between 0 V and 5 V. Here, in a period in which the common electrode voltage VCOM is 0 V among periods T95and T97in which the common electrode voltage VCOM is supposed to be maintained at 5 V, the pixel electrode voltage Vp is maintained at 5 V, so the liquid crystal application voltage is 5 V. In addition, in a period in which the common electrode voltage VCOM is 5 V among periods T96and T98in which the common electrode voltage VCOM is supposed to be maintained at 0 V, the pixel electrode voltage Vp is maintained at 0 V, so the liquid crystal application voltage is −5 V. In this way, the black display is inserted in the period in which the white display is supposed to be performed.

As described above, in the case where the in-cell type touch panel is provided in the known memory liquid crystal display, a display defect (inversion of black and white) occurs due to the pulse signal for touch detection being supplied to the common electrode942.

SUMMARY

Thus, the following disclosure is directed to realizing the memory liquid crystal display provided with the in-cell type touch panel.

(1) A liquid crystal display device according to some embodiments of the disclosure is a liquid crystal display device including a liquid crystal panel with a built-in touch panel, the liquid crystal display device including a plurality of pixel circuits each including a liquid crystal capacitance constituted by a pixel electrode and a common electrode, a memory circuit configured to store binary data, and a voltage selection circuit configured to supply either a first voltage or a second voltage to the pixel electrode in accordance with a value of the binary data stored in the memory circuit; a common electrode drive circuit configured to drive the common electrode; and a state control circuit configured to switch a state of the pixel electrode between a floating state and a non-floating state, wherein the touch panel uses the common electrode as an electrode for touch detection, the common electrode drive circuit supplies a pulse signal for touch detection to the common electrode in a touch detection period for detecting a touched position on the touch panel, and the state control circuit switches the state of the pixel electrode from the non-floating state to the floating state before a start of the touch detection period, and switches the state of the pixel electrode from the floating state to the non-floating state after an end of the touch detection period.

According to such a configuration, even when the pulse signal for touch detection is supplied to the common electrode in the touch detection period in the memory liquid crystal display, the pixel electrode voltage also changes in accordance with the change in the common electrode voltage. Thus, the liquid crystal application voltage is maintained at the desired voltage throughout the touch detection period. Thus, the display defect (inversion of black and white) due to the pulse signal for touch detection being supplied to the common electrode does not occur. As described above, the memory liquid crystal display provided with the in-cell type touch panel is realized.

(2) The liquid crystal display device according to some embodiments of the disclosure includes the above-described configuration (1), wherein the state control circuit is a switch circuit provided between the voltage selection circuit and the pixel electrode, and the switch circuit electrically disconnects the voltage selection circuit and the pixel electrode from each other before the start of the touch detection period, and electrically connects the voltage selection circuit and the pixel electrode to each other after the end of the touch detection period.

(3) The liquid crystal display device according to some embodiments of the disclosure includes, in addition to the above-described configuration (2), a plurality of scanning signal lines configured to supply a scanning signal to each of the plurality of pixel circuits; a scanning signal line drive circuit configured to apply the scanning signal to each of the plurality of scanning signal lines; a plurality of data signal lines configured to supply a data signal to each of the plurality of pixel circuits; a data signal line drive circuit configured to apply the data signal to each of the plurality of data signal lines; a plurality of first voltage supply wiring lines configured to supply the first voltage to each of the plurality of pixel circuits; a plurality of second voltage supply wiring lines configured to supply the second voltage to each of the plurality of pixel circuits; a display voltage generation circuit configured to generate the first voltage and the second voltage; a scanning signal supply control switch circuit provided in a region outside a display region where the plurality of pixel circuits are formed, the scanning signal supply control switch circuit being configured to control an electrical connection state between the scanning signal line drive circuit and the plurality of scanning signal lines in the display region; a data signal supply control switch circuit provided in the region outside the display region, the data signal supply control switch circuit being configured to control an electrical connection state between the data signal line drive circuit and the plurality of data signal lines in the display region; and a display voltage supply control switch circuit provided in the region outside the display region, the display voltage supply control switch circuit being configured to control an electrical connection state between the display voltage generation circuit and the plurality of first voltage supply wiring lines in the display region and an electrical connection state between the display voltage generation circuit and the plurality of second voltage supply wiring lines in the display region, wherein the scanning signal supply control switch circuit electrically disconnects the scanning signal line drive circuit and the plurality of scanning signal lines in the display region from each other before the start of the touch detection period, and electrically connects the scanning signal line drive circuit and the plurality of scanning signal lines in the display region to each other after the end of the touch detection period, the data signal supply control switch circuit electrically disconnects the data signal line drive circuit and the plurality of data signal lines in the display region from each other before the start of the touch detection period, and electrically connects the data signal line drive circuit and the plurality of data signal lines in the display region to each other after the end of the touch detection period, and the display voltage supply control switch circuit electrically disconnects the display voltage generation circuit and the plurality of first voltage supply wiring lines in the display region from each other and electrically disconnects the display voltage generation circuit and the plurality of second voltage supply wiring lines in the display region from each other before the start of the touch detection period, and electrically connects the display voltage generation circuit and the plurality of first voltage supply wiring lines in the display region to each other and electrically connects the display voltage generation circuit and the plurality of second voltage supply wiring lines in the display region to each other after the end of the touch detection period.

(4) The liquid crystal display device according to some embodiments of the disclosure includes the above-described configuration (1), wherein the voltage selection circuit includes a first voltage supply control switch circuit configured to control an electrical connection state between a first voltage supply wiring line configured to supply the first voltage and the pixel electrode, and a second voltage supply control switch circuit configured to control an electrical connection state between a second voltage supply wiring line configured to supply the second voltage and the pixel electrode, the first voltage supply control switch circuit electrically connects the first voltage supply wiring line and the pixel electrode to each other when a first voltage supply control signal provided from the memory circuit is at an on level, and electrically disconnects the first voltage supply wiring line and the pixel electrode from each other when the first voltage supply control signal is at an off level, the second voltage supply control switch circuit electrically connects the second voltage supply wiring line and the pixel electrode to each other when a second voltage supply control signal provided from the memory circuit is at the on level, and electrically disconnects the second voltage supply wiring line and the pixel electrode from each other when the second voltage supply control signal is at the off level, and the state control circuit is a switching circuit provided in the memory circuit and configured to switch a level of the first voltage supply control signal between the on level and the off level and switch a level of the second voltage supply control signal between the on level and the off level, the switching circuit maintaining the level of the first voltage supply control signal and the level of the second voltage supply control signal at the off level in the touch detection period.

(5) The liquid crystal display device according to some embodiments of the disclosure includes, in addition to the above-described configuration (4), a plurality of scanning signal lines configured to supply a scanning signal to each of the plurality of pixel circuits; a scanning signal line drive circuit configured to apply the scanning signal to each of the plurality of scanning signal lines; a plurality of data signal lines configured to supply a data signal to each of the plurality of pixel circuits; a data signal line drive circuit configured to apply the data signal to each of the plurality of data signal lines; a display voltage generation circuit configured to generate the first voltage and the second voltage; a scanning signal supply control switch circuit provided in a region outside a display region where the plurality of pixel circuits are formed, the scanning signal supply control switch circuit being configured to control an electrical connection state between the scanning signal line drive circuit and the plurality of scanning signal lines in the display region; a data signal supply control switch circuit provided in the region outside the display region, the data signal supply control switch circuit being configured to control an electrical connection state between the data signal line drive circuit and the plurality of data signal lines in the display region; and a display voltage supply control switch circuit provided in the region outside the display region, the display voltage supply control switch circuit being configured to control an electrical connection state between the display voltage generation circuit and the plurality of first voltage supply wiring lines in the display region and an electrical connection state between the display voltage generation circuit and the plurality of second voltage supply wiring lines in the display region, wherein the scanning signal supply control switch circuit electrically disconnects the scanning signal line drive circuit and the plurality of scanning signal lines in the display region from each other before the start of the touch detection period, and electrically connects the scanning signal line drive circuit and the plurality of scanning signal lines in the display region to each other after the end of the touch detection period, the data signal supply control switch circuit electrically disconnects the data signal line drive circuit and the plurality of data signal lines in the display region from each other before the start of the touch detection period, and electrically connects the data signal line drive circuit and the plurality of data signal lines in the display region to each other after the end of the touch detection period, and the display voltage supply control switch circuit electrically disconnects the display voltage generation circuit and the plurality of first voltage supply wiring lines in the display region from each other and electrically disconnects the display voltage generation circuit and the plurality of second voltage supply wiring lines in the display region from each other before the start of the touch detection period, and electrically connects the display voltage generation circuit and the plurality of first voltage supply wiring lines in the display region to each other and electrically connects the display voltage generation circuit and the plurality of second voltage supply wiring lines in the display region to each other after the end of the touch detection period.

(6) The liquid crystal display device according to some embodiments of the disclosure includes, in addition to the above-described configuration (1), a display voltage generation circuit provided outside the liquid crystal panel, the display voltage generation circuit being configured to generate the first voltage and the second voltage; a first voltage supply wiring line configured to supply the first voltage from the display voltage generation circuit to the voltage selection circuit; and a second voltage supply wiring line configured to supply the second voltage from the display voltage generation circuit to the voltage selection circuit, wherein the state control circuit is a switch circuit provided between the display voltage generation circuit and the first voltage supply wiring line and between the display voltage generation circuit and the second voltage supply wiring line, the switch circuit being configured to electrically disconnect the display voltage generation circuit and the first voltage supply wiring line from each other and electrically disconnect the display voltage generation circuit and the second voltage supply wiring line from each other before the start of the touch detection period, and electrically connect the display voltage generation circuit and the first voltage supply wiring line to each other and electrically connect the display voltage generation circuit and the second voltage supply wiring line to each other after the end of the touch detection period.

(7) A liquid crystal display device according to some embodiments of the disclosure includes, in addition to the above-described configuration (6), a plurality of scanning signal lines configured to supply a scanning signal to each of the plurality of pixel circuits; a scanning signal line drive circuit configured to apply the scanning signal to each of the plurality of scanning signal lines; a plurality of data signal lines configured to supply a data signal to each of the plurality of pixel circuits; a data signal line drive circuit configured to apply the data signal to each of the plurality of data signal lines; a scanning signal supply control switch circuit provided in a region outside a display region where the plurality of pixel circuits are formed, the scanning signal supply control switch circuit being configured to control an electrical connection state between the scanning signal line drive circuit and the plurality of scanning signal lines in the display region; and a data signal supply control switch circuit provided in the region outside the display region, the data signal supply control switch circuit being configured to control an electrical connection state between the data signal line drive circuit and the plurality of data signal lines in the display region, wherein the scanning signal supply control switch circuit electrically disconnects the scanning signal line drive circuit and the plurality of scanning signal lines in the display region from each other before the start of the touch detection period and electrically connects the scanning signal line drive circuit and the plurality of scanning signal lines in the display region to each other after the end of the touch detection period, and the data signal supply control switch circuit electrically disconnects the data signal line drive circuit and the plurality of data signal lines in the display region from each other before the start of the touch detection period and electrically connects the data signal line drive circuit and the plurality of data signal lines in the display region to each other after the end of the touch detection period.

(8) A liquid crystal display device according to some embodiments of the disclosure includes the above-described configuration (6), wherein the display voltage generation circuit and the switch circuit are provided in one integrated circuit.

(9) A liquid crystal display device according to several embodiments of the disclosure includes any one of the above-described configurations (1) to (8), wherein each of the plurality of pixel circuits includes auxiliary capacitance provided in parallel to the liquid crystal capacitance.

(10) A method for driving a liquid crystal display device according to some embodiments of the disclosure is a method for driving a liquid crystal display device including a liquid crystal panel with a built-in touch panel, the liquid crystal display device including a plurality of pixel circuits each including a liquid crystal capacitance constituted by a pixel electrode and a common electrode, a memory circuit configured to store binary data, and a voltage selection circuit configured to supply either a first voltage or a second voltage to the pixel electrode in accordance with a value of the binary data stored in the memory circuit; and a common electrode drive circuit configured to drive the common electrode, the touch panel using the common electrode as an electrode for touch detection, the method sequentially executing: a step of switching a state of the pixel electrode from a non-floating state to a floating state; a step of supplying, by the common electrode drive circuit, a pulse signal for touch detection to the common electrode to detect a touched position on the touch panel; and a step of switching the state of the pixel electrode from the floating state to the non-floating state.

These and other objects, features, aspects, and advantages of the disclosure will become more apparent from the following detailed description of the disclosure with reference to the accompanying drawings.

