Liquid crystal display device

Abstract

To provide a display device which consumes less electric power during a period of time for the retention of a written image.SOLUTION: A display device comprises a liquid crystal display panel driven by electric power supplied from a converter or a backup circuit. During a writing operation with large load, a fixed potential is supplied using the converter and a capacitor is charged. For an image retention time with small load, the fixed potential may be supplied preferentially from the capacitor without using the converter.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a display device and a driving method thereof. [Background technology]

[0002] As a result of the increasing integration of semiconductor elements and the improved processing power of computing elements, electronic devices have become smaller and lighter. The number of people using computers has increased, and people can now carry around highly functional electronic devices. In addition, by improving the information transmission infrastructure of society, it will become possible to use portable electronic devices even when out and about. It has become possible to handle large amounts of information using devices. Display devices that transmit information via displays have become increasingly important with the development of electronic devices.

[0003] On the other hand, portable electronic devices can be used continuously for long periods of time even in situations where it is difficult to receive power from the power line. In order to extend the operating time, it is desirable to increase the capacity of the battery. Therefore, there is a strong demand for reducing power consumption.

[0004] In addition, from the perspective of the current energy problem, reducing the power consumption of electronic devices is an urgent task. The technology to reduce power consumption is not limited to portable electronic devices, but also applies to television sets, which are becoming larger. Technique is required.

[0005] Conventional display devices display the same image at regular intervals even if the image data for consecutive periods is the same. The image data is written in the display device. For example, in a still image display, the screen is scanned once to write image data, and then the screen is unscanned. A technology has been reported in which a pause period is set longer than a scanning period (for example, see patent document 1). See reference 1 and non-patent document 1. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 7,321,353 [Non-patent literature]

[0007] [Non-Patent Document 1] K. Tsuda et al. IDW'02 Proc., p.295-298 Summary of the Invention [Problem to be solved by the invention]

[0008] The power consumption of a display device is determined by the power consumed by the display panel when writing data and the power consumed when the written image is displayed. This is the sum of the power consumed during the period when the image is held (also called the image holding period). This not only reduces the frequency of writing to the display panel of the display device, but also reduces the power consumption during the image retention period. also needs to be suppressed.

[0009] The present invention has been made under such technical background, and is directed to a method for reducing consumption during an image retention period. An object of the present invention is to provide a display device with reduced power consumption. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention provides a DC-DC converter for a power supply circuit provided in a drive circuit of a display panel. We focused on the power consumed by the C converter during the image retention period.

[0011] For example, the capacitance formed between the pixel electrode of each pixel and the common electrode on the liquid crystal display panel is In order to maintain high quality image information without degradation during the image retention period, the power supply circuit The fixed potential must be supplied to the common electrode. The power supply is generated by a DC-DC converter installed in the power supply circuit from the power provided by an external power source such as a Therefore, the conversion efficiency of the DC-DC converter affects the power consumed during the image retention period. do.

[0012] The conversion efficiency of a DC-DC converter is expressed as the ratio of the power it outputs to the power it consumes, and is: It is preferable to use a DC-DC converter that exhibits high conversion efficiency when a large load is connected. However, the conversion efficiency of a DC-DC converter varies depending on the size of the connected load. Therefore, a DC-DC converter that shows high conversion efficiency when the load is large is Sometimes you can't expect high conversion efficiency.

[0013] For example, when connecting an LCD panel as a load, a high fluctuation of about 75% occurs during writing. However, the power consumed during the image retention period is also important. The power consumption is 10 times that of the write operation. -1 Double to 10 -4 The image is about twice as large. The conversion efficiency of the DC-DC converter during the hold period may drop to around several tens of percent.

[0014] In this way, the power consumed by a DC-DC converter connected to a highly fluctuating load can be reduced. To achieve this, a DC-DC converter with high conversion efficiency is used when the load increases. The inventors have come up with the idea that when the load becomes small, a fixed potential can be supplied by another means.

[0015] Specifically, the liquid crystal display device is equipped with a converter that converts the power input into a specified DC power and a backup A backup circuit is provided, and a converter is used to supply a fixed potential during write operations when the load is large. The image retention time is reduced by supplying the image to the backup circuit and charging the capacitor. During this period, a fixed potential is preferentially supplied from a charged capacitor without using a converter. Just do that.

[0016] The backup circuit supplies power from the power source via a converter to the LCD panel and the The first mode supplies power to the capacitor, and the second mode stops power supply to the converter from the power supply. It has a second mode in which the power stored in the capacitor is supplied to the LCD panel.

[0017] That is, one aspect of the present invention is a converter that converts a power supply input into a predetermined DC power, A backup circuit having a capacitor for charging the power output by the converter or It is powered by power supplied from a backup circuit and has the function of retaining the same image for a certain period of time. The power consumption during image writing is 10 times or more than the power consumption during the image retention period. 4 Less than double The liquid crystal display panel has a power supply. A first mode of supplying power to the liquid crystal display panel and the capacitor, and a second mode of supplying power to the converter. and supplying the power stored in the capacitor to the liquid crystal display panel. In addition, a liquid crystal display device that supplies power to the liquid crystal display panel in the second mode during the image retention period. It is a device.

[0018] According to the above aspect of the present invention, the liquid crystal display panel is configured to hold the same image while the power is turned on. The converter that converts the power from the battery to a specified DC power stops, and the capacitor in the backup circuit becomes liquid. This provides a fixed potential to the LCD panel, which reduces the load area where the converter has poor conversion efficiency. Specifically, the converter is operated during the image retention period of the liquid crystal display panel, which is an area where the load is extremely small. Since the liquid crystal display device does not consume power during the image retention period, the power consumption during the image retention period is suppressed. We can provide it.

[0019] Another aspect of the present invention is a converter for converting a power supply input into a predetermined DC power; A backup circuit having a capacitor for charging the power output by the converter or the backup It is powered by power supplied from a backup circuit and has the function of retaining the same image for a certain period of time. The power consumption during image writing is 10 times or more than the power consumption during image retention. 4 Less than double The liquid crystal display panel is provided with a backup circuit that supplies power to the liquid crystal display panel via a converter. A first mode supplies a capacitor connected to a display panel and a limiter circuit; The power supply to the converter is stopped, and the power stored in the capacitor is supplied to the LCD panel. In addition, the liquid crystal display panel is supplied with power in the second mode during the image retention period. The liquid crystal display device supplies the power.

[0020] According to the above aspect of the present invention, during a period in which the liquid crystal display panel holds the same image, The power supply stops and the capacitor of the backup circuit with charge limiter supplies a fixed voltage to the LCD panel. This provides a load voltage that is low in the converter's conversion efficiency, specifically in the extremely low The converter does not consume power during the image retention period of the LCD panel, which is an area where the load is small. Therefore, it is possible to provide a liquid crystal display device in which the power consumption during the image retention period is suppressed.

[0021] Moreover, one aspect of the present invention includes a backup circuit with a charge limiter. The capacitor of the backup circuit is connected to the converter via a limiter circuit. If a capacitor that is not full of charge is connected to the converter, a sudden This can eliminate problems caused by charging.

[0022] In addition, one embodiment of the present invention is a method for displaying the same image signal on a liquid crystal display panel at intervals of 10 seconds or more and 600 seconds or less. The liquid crystal display device is configured as follows.

[0023] According to the above aspect of the present invention, it is possible to extend the stop period of the converter, and the consumption This has a significant effect on reducing power consumption.

[0024] In addition, one aspect of the present invention is a power supply device that is supplied through a converter that converts a power input into a predetermined DC power. The power generated is used to charge the capacitor in the backup circuit and the liquid crystal display panel. The image is written to the LCD panel, and the gate of the pixel transistor of the LCD panel is turned on at set intervals. The potential of the pixel transistor and the potential of the capacitor provided in the backup circuit are monitored. When the absolute value of the gate potential of the When the potential of the capacitor becomes greater than the second set potential, the power to the converter is cut off and the The liquid crystal display device repeats the above monitoring operation until the time has elapsed or the operation is interrupted by an interrupt command. This is a driving method for the device.

[0025] According to the above aspect of the present invention, the image is changed depending on the potential of the capacitor provided in the backup circuit. Select the fixed potential to be supplied to the LCD panel during the image retention period. The load region where the conversion efficiency is poor, specifically the region where the load is extremely small, is the image region of the liquid crystal display panel. The power consumed during the image retention period is reduced because the converter does not consume power during the image retention period. It is possible to provide a method for driving a liquid crystal display device in which the voltage is controlled.

[0026] According to the aspect of the present invention, the absolute value of the gate potential of the pixel transistor is smaller than the set potential. When the voltage drops below the set voltage, power is supplied to the converter, and the potential on the liquid crystal display panel side of the capacitor rises to the set voltage. If the voltage exceeds this limit, the power supply to the converter is cut off. This allows the backup circuit to It acts as a load on the converter and uses the area with high conversion efficiency to supply the capacitor of the backup circuit. It can be charged.

[0027] In one aspect of the present invention, the first set potential is 5 V or more. This is the method.

[0028] According to the above aspect of the present invention, a gate electrode of a pixel transistor provided in a pixel portion of a liquid crystal display panel is This keeps the absolute value of the power supply potential greater than 5V. The potential supplied to the pixel transistors can be kept in the off state, causing the retained image to be distorted. It can prevent elephants.

[0029] In one aspect of the present invention, the second set potential is 98% or less of the output potential of the converter. The liquid crystal display device is driven by a method.

[0030] According to the above aspect of the present invention, when the charge of the capacitor included in the backup circuit approaches full charge, If the load is too low, the load will be too small. By eliminating the charge in this low load region, the conversion efficiency can be improved. Therefore, the capacitor of the backup circuit can be charged by using the low-voltage region preferentially.

[0031] In this specification, the high power supply potential Vdd refers to a potential higher than the reference potential. The low power supply potential Vss is a potential lower than the reference potential. It is desirable that both power supply potentials Vss be at a potential at which the transistors can operate. The high power supply potential Vdd and the low power supply potential Vss are sometimes collectively referred to as the power supply voltage. In this specification, being connected means being electrically connected.

[0032] In this specification, the common potential Vcom is the potential of the image signal supplied to the pixel electrode. It is sufficient if the potential is a fixed potential that serves as a reference for the input terminal, and as one example, it may be the ground potential. Effect of the Invention

[0033] According to the present invention, it is possible to provide a display device in which the power consumption during an image retention period is reduced. [Brief description of the drawings]

[0034] [Figure 1] FIG. 1 is a block diagram illustrating a configuration of a liquid crystal display device according to an embodiment. [Diagram 2] FIG. 1 is a block diagram illustrating a configuration of a power supply circuit according to an embodiment. [Diagram 3] 1 is an equivalent circuit diagram illustrating a configuration of a liquid crystal display panel according to an embodiment. [Figure 4] 4 is a timing chart illustrating a method for driving a liquid crystal display device according to an embodiment. [Diagram 5] 4 is a timing chart illustrating a method for driving a liquid crystal display device according to an embodiment. [Figure 6] 4 is a timing chart illustrating a method for driving a liquid crystal display device according to an embodiment. [Figure 7] 1A to 1C are diagrams illustrating a method for driving a power supply circuit according to an embodiment; [Figure 8] 1A to 1C are diagrams illustrating a method for driving a power supply circuit according to an embodiment; [Figure 9] 1A to 1C illustrate a method for manufacturing a transistor according to an embodiment. [Figure 10] FIG. 1 is a block diagram illustrating a configuration of a liquid crystal display device according to an embodiment. [Figure 11] FIG. 2 is a circuit diagram illustrating a configuration of a backup circuit according to an embodiment. [Figure 12] 5A and 5B are diagrams for explaining the relationship between the image retention time and the drivable time of the liquid crystal display device according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The embodiment will be described in detail with reference to the drawings. However, the present invention is not limited to the following description. The present invention is not limited to the above embodiment, and various changes and modifications may be made in the form and details without departing from the spirit and scope of the present invention. It will be easily understood by those skilled in the art that the above-mentioned invention can be obtained by the following embodiments. The present invention should not be construed as being limited to the contents described below. The same reference numerals are used in different drawings to indicate the same parts or parts having similar functions. A repeated explanation will be omitted.

[0036] (Embodiment 1) In this embodiment, a converter or a buffer for converting an input power supply potential into a predetermined DC potential is used. A liquid crystal display device having a liquid crystal display panel driven by power supplied from a backup circuit This will be explained with reference to Figs. 1 and 2.

[0037] The configuration of a liquid crystal display device 100 exemplified in this embodiment will be described with reference to the block diagram shown in FIG. The liquid crystal display device 100 includes a driving circuit section 110, a liquid crystal display panel 120, and a storage device 14. 0, a power supply unit 150, and an input device 160. Note that the backlight unit 130 is not necessary. It can be set according to the above.

[0038] In the liquid crystal display device 100, power is supplied from a power supply unit 150 to a power supply circuit 116. The circuit 116 supplies a power supply potential to the display control circuit 113 and the liquid crystal display panel 120. The display control circuit 113 takes in electronic information stored in the storage device 140 and controls the liquid crystal display panel 1 20. In addition, when the backlight unit 130 is provided, the display control circuit 113 The power supply voltage and the control signal are output to the backlight unit 130 .

[0039] The drive circuit section 110 includes a switching circuit 112, a display control circuit 113, and a power supply circuit 116. The display control circuit 113 includes an arithmetic circuit 114, a signal generating circuit 115a, and a liquid crystal driving circuit 1 The power supply circuit 116 includes a power supply potential generating circuit 117, a first DC-DC converter 115b, and a second DC-DC converter 116c. a first DC-DC converter 118a, a second DC-DC converter 118b, and a third DC-DC converter 118c, a first backup circuit 119a, and a second backup circuit 119b. Prepare.

[0040] In the power supply circuit 116, the power supply potential supplied from the power supply unit 150 is supplied to the first DC-DC converter. The inverter 118a boosts the voltage through the first backup circuit 119a and supplies the second DC-DC converter The inverter 118b is inverted via the second backup circuit 119b, and the power supply potential generating circuit The power supply potential generating circuit 117 supplies the power supply potential (high power supply potential) to the display control circuit 113. A common potential Vcom is supplied to the liquid crystal display panel 120. The third DC-DC converter 118c reduces the power supplied from the power supply unit 150. The signal is then compressed and supplied to the arithmetic circuit 114 of the display control circuit 113.

[0041] The configuration of the first backup circuit 119a and the second backup circuit 119b is shown in FIG. The following description will be given using the block diagram shown in FIG. 2. Note that FIG. 2 is a block diagram of FIG. 1 with the power supply circuit 116 as the focus. The same reference numerals are used for the same components. Since the circuit 119a and the second backup circuit 119b have the same configuration, The first backup circuit 119a will be described.

[0042] The first backup circuit 119a connects a first DC-DC converter 118a to a terminal of the first DC-DC converter 118a. One terminal of the switch 190a is connected. The same terminal of the first limiter circuit 191a is connected to the same terminal of the first limiter circuit 18a. The other terminal of the input circuit 191a is connected to one terminal of a second switch 193a. The other terminal of the second switch 193a is connected to one terminal 195a of the capacitor 192a and to a third One terminal of the switch 194a is connected to the capacitor 192a, and the other terminal of the capacitor 192a is grounded. The other terminal of the first switch 190a and the other terminal of the third switch 194a are both A power supply potential generating circuit 117 is connected to the power supply potential generating circuit 117, and a potential supplied by the first DC-DC converter 118a is supplied to the power supply potential generating circuit 117. 2 via the power supply potential generating circuit 117. I am putting effort into it.

[0043] The first backup circuit 119a illustrated in this embodiment includes a first resistor in addition to a capacitor. Since it is equipped with a limiter circuit 191a, it can also be called a backup circuit with a charge limiter. The first limiter circuit 191a is a first limiter circuit that limits the charge of the capacitor 192a when the capacitor 192a is in a low charge state. The current flowing through the first DC-DC converter 118a is limited, and the first DC-DC converter The phenomenon of the potential output from the output terminal 118a dropping is suppressed, and the operation of the liquid crystal display device 100 is stabilized. It is also possible to adopt a configuration that does not use a limiter circuit.

[0044] The arithmetic circuit 114 monitors the power supply circuit 116. Specifically, the first backup circuit 1 The potential of the terminal 195a of the capacitor 192a in the second backup circuit 19a is The potential of the terminal 195b of the capacitor 192b in the power supply potential generating circuit 11 7 outputs power supply potentials (for example, Vdd and Vss). The charging state of the capacitor 192a and the capacitor 192b and the liquid crystal display panel You can see the display status of 120.

[0045] The arithmetic circuit 114 also controls the opening and closing circuit 112. The arithmetic circuit 114 also controls the capacitor 192. a, the charge state of the capacitor 192b (or the potentials of the terminals 195a and 195b), or The gate potential of the pixel transistor (or the potential electrically connected to the gate electrode of the pixel transistor) The first DC-DC converter 118a is turned on through the switching circuit 112 in response to the potential of the wiring connected to the , and the supply of power to the second DC-DC converter 118b.

[0046] In addition, the first switch 190a, the first switch 190b, and the second switch 190c provided in the backup circuit A switch 193a, a second switch 193b, a third switch 194a, and a third switch 19 The timing of connection and disconnection of the switching circuit 114b is synchronized with that of the switching circuit 112. When the power supply unit 150 and the power supply circuit 116 are connected via the first switch 190a, The first switch 190b, the second switch 193a, and the second switch 193b are all in a connected state. The third switch 194a and the third switch 194b are in a disconnected state. When the switching circuit 112 is in a disconnected state, the first switch 190a, the first switch 190b, the second switch The switch 193a and the second switch 193b are all in a disconnected state, and the third switch 194 The third switch 194a and the third switch 194b are in a connected state. A backup circuit can also be configured using this.

[0047] Power supply to the first DC-DC converter 118a and the second DC-DC converter 118b By controlling the power supply, the DC-DC converter can be used during write operations where the load is large. A fixed potential is supplied using a motor and a capacitor is charged, reducing the load on the image retention During this period, a fixed potential is preferentially supplied from the capacitor without using a DC-DC converter. can.

[0048] In the display control circuit 113 (see FIG. 1), the arithmetic circuit 114 takes out the The electronic data is analyzed, calculated, and processed. The processed image is displayed on the LCD together with the control signal. The liquid crystal display driver 115b outputs the image to the liquid crystal display panel 120. The signal generating circuit 115a converts the image signal into a signal that can be read by the arithmetic circuit 11 and outputs the converted image signal. In synchronization with 4, the control signal (start pulse SP and clock signal CK) is generated from the power supply potential. The arithmetic circuit 114 supplies the signal to the liquid crystal display panel 120. A control signal for making the potential of the electrode 128 floating is generated by the signal generating circuit 115. Alternatively, the signal may be output to the switching element 127 via a.

[0049] The image signal data can be generated by dot inversion driving, source line inversion driving, gate line inversion driving, The image signal may be appropriately inverted by a method such as frame inversion driving. If the image signal is analog, it must be converted to digital via an A / D converter, etc. The signal may be converted into a digital signal and supplied to the liquid crystal display device 100.

[0050] In addition, the arithmetic circuit 114 uses the switching circuit 112 to connect the first DC-DC converter to the power supply unit 150. 118a and the second DC-DC converter 118b. Furthermore, the arithmetic circuit 114 includes a first backup circuit 119a and a second backup circuit The charging state of the capacitor provided in the path 119b and the gate potential of the display panel are monitored.

[0051] The arithmetic circuit 114 analyzes, calculates, and processes the electronic data retrieved from the storage device. For example, the system analyzes electronic data to determine whether it is a video or a still image, and The control signal including the above can be output to the signal generating circuit 115a and the liquid crystal driving circuit 115b. The arithmetic circuit 114 extracts one frame of a still image from the image signal Data including the still image. , a control signal indicating a still image, and a signal generating circuit 115a and a liquid crystal driving circuit The arithmetic circuit 114 can output a moving image from the image signal Data including the moving image to the arithmetic circuit 115b. It detects the motion picture and displays successive frames along with a control signal indicating that it is a moving image on the LCD panel. It can output to 120.

[0052] The arithmetic circuit 114 outputs different signals to the liquid crystal display device 100 of this embodiment in response to the input electronic data. In this embodiment, the arithmetic circuit 114 judges the image to be a still image. The operation is performed in the still image display mode, and the operation circuit 114 judges the image to be a moving image. This operation is called a moving image display mode. In this specification, the image displayed during still image display is called a still image display mode. This is called a still image.

[0053] In addition, the arithmetic circuit 114 exemplified in this embodiment has a display mode switching function. The display mode switching function may be performed by the liquid crystal display device regardless of the judgment of the arithmetic circuit 114. A user of the device selects an operation mode of the liquid crystal display device manually or by using an external connected device, This function switches between video display mode and still image display mode.

[0054] The above-mentioned functions are examples of the functions of the arithmetic circuit 114, and various functions may be implemented depending on the application of the display device. Simply select and apply the image processing function.

[0055] The image signal converted into a digital signal is then processed (e.g., the difference between the image signals is detected, etc.) Since it is easy to do so, when the input image signal (image signal data) is an analog signal, Alternatively, an A / D converter or the like may be provided in the arithmetic circuit 114.

[0056] The storage device 140 includes a storage medium and a read device. It may also be composed of.

[0057] The power supply unit 150 includes a secondary battery 151 and a solar cell 155. The secondary battery uses a capacitor. The power supply unit 150 is not limited to this, and may be a battery, a power generation device, or the like. Alternatively, the power supply unit 150 may be an AC-DC converter connected to an electric lighting line.

[0058] The input device 160 may be a switch or a keyboard. A touch panel may be provided. The user uses the input device 160 to input data to the storage device 140. and inputs a command to display the electronic data stored in the LCD device 100.

[0059] The liquid crystal display panel 120 has a pair of substrates (a first substrate and a second substrate). The liquid crystal element 215 is formed by sandwiching the liquid crystal layer between a pair of substrates. The pixel circuit section 121, the pixel section 122, and the terminal section 126 are provided. A common electrode 128 (also called a common electrode) may be provided on the second substrate. In this embodiment, a common connection portion (also called a counter electrode) is provided. A contact (also called a "mon contact") is provided on the first substrate or the second substrate, and The connection portion is connected to a common electrode 128 on the second substrate.

[0060] The pixel section 122 includes a plurality of gate lines 124 (scanning lines) and source lines 125 (signal lines). A plurality of pixels 123 are surrounded by gate lines 124 and source lines 125. In the liquid crystal display panel 120 illustrated in this embodiment, In this case, the gate line 124 extends from the gate line side driving circuit 121A, and the source line 125 extends from the source It extends from the source line side driver circuit 121B.

[0061] The pixel 123 has a transistor 214 as a switching element, and the transistor 214 is connected The pixel includes a capacitor element 210 and a liquid crystal element 215.

[0062] The transistor 214 has a gate electrode connected to one of the gate lines 124 provided in the pixel section 122. One of the source electrodes or the drain electrodes is connected to one of the source lines 125. The other of the source electrode and the drain electrode is connected to one of the capacitor elements 210. The electrode is connected to one electrode (pixel electrode) of the liquid crystal element 215 .

[0063] In addition, it is preferable to use a transistor with reduced off-state current as the transistor 214. For example, the transistor described in Embodiment 3 is suitable. In this case, the transistor 214 in the off state stably supplies a current to the liquid crystal element 215 and the capacitor element 210. In addition, by using the transistor 214 whose off-state current is sufficiently reduced, Therefore, the pixel 123 can be configured without providing the capacitor element 210.

[0064] With this configuration, the pixel 123 is written before the transistor 214 is turned off. This allows the written state to be maintained for a long period of time, thereby reducing power consumption.

[0065] The liquid crystal element 215 is an element that controls the transmission or non-transmission of light by the optical modulation action of liquid crystal. The optical modulation of the liquid crystal is controlled by the electric field applied to the liquid crystal. The field direction varies depending on the liquid crystal material, driving method, and electrode structure, and can be selected appropriately. For example, when using a driving method in which an electric field is applied in the thickness direction (so-called vertical direction) of the liquid crystal, The pixel electrodes are provided on the first substrate and the common electrode is provided on the second substrate so as to sandwich the crystal. In addition, a driving method in which an electric field is applied to the liquid crystal in the in-plane direction of the substrate (so-called horizontal electric field) In the case of using a liquid crystal display, a pixel electrode and a common electrode may be provided on the same surface as the liquid crystal. The pixel electrodes and the common electrodes may have various opening patterns.

[0066] Examples of liquid crystals that can be used in liquid crystal elements include nematic liquid crystals, cholesteric liquid crystals, and smectic liquid crystals. tic liquid crystal, discotic liquid crystal, thermotropic liquid crystal, lyotropic liquid crystal, low molecular weight Liquid crystal, polymer dispersed liquid crystal (PDLC), ferroelectric liquid crystal, antiferroelectric liquid crystal, main chain liquid crystal, side chain Examples include polymer liquid crystal and banana-shaped liquid crystal.

[0067] The liquid crystal driving mode is TN (Twisted Nematic) mode, S TN (Super Twisted Nematic) mode, OCB (Optical ly Compensated Birefringence mode, ECB (Ele ctrically Controlled Birefringence) mode, F LC (Ferroelectric Liquid Crystal) mode, AFLC (AntiFerroelectric Liquid Crystal) mode, PD LC (Polymer Dispersed Liquid Crystal) mode, PNLC (Polymer Network Liquid Crystal) mode, Guest host mode can be used. In addition, IPS (In-Plane-Sw fringe field switching mode, FFS (Fringe Field Switching) mode mode, MVA (Multi-domain Vertical Alignment) mode mode, PVA (Patterned Vertical Alignment) mode, ASM(Axially Symmetric aligned Micro-cell Of course, in this embodiment, the optical modulation If the element controls the transmission or non-transmission of light by the action of the liquid crystal material, the driving method, and the voltage The pole structure is not particularly limited.

[0068] Note that the liquid crystal element exemplified in this embodiment has a pixel electrode provided on a first substrate and a The vertical electric field generated between the pixel electrodes on the substrate and the opposing common electrodes changes the alignment of the liquid crystal. The direction is controlled by changing the pixel electrode as appropriate depending on the liquid crystal material or the liquid crystal driving mode. It is also possible to configure the liquid crystal orientation to be controlled by a lateral electric field.

[0069] The terminal unit 126 receives a predetermined signal (high power supply potential Vdd, low power supply potential Vdd) output by the display control circuit 113. potential Vss, start pulse SP, clock signal CK, image signal Data, etc.), and 3 is an input terminal for supplying a common potential Vcom and the like to the pixel drive circuit unit 121.

[0070] The pixel driving circuit section 121 includes a gate line side driving circuit 121A and a source line side driving circuit 121B. The gate line side driving circuit 121A and the source line side driving circuit 121B each have a plurality of pixels. A shift register circuit (shift register It has a function called "data".

[0071] The gate line side driving circuit 121A and the source line side driving circuit 121B are connected to the pixel section 122. The second substrate may be formed on the same substrate as the first substrate, or may be formed on a different substrate.

[0072] The pixel driving circuit unit 121 is connected to a high power supply potential Vd d, a low power supply potential Vss, a start pulse SP, a clock signal CK, and an image signal Data are provided. will be provided.

[0073] When the switching element 127 is provided, a transistor can be used. The gate electrode of the switching element 127 is connected to the terminal 126A. In response to the control signal, a common potential Vcom is supplied to the common electrode 128 via the terminal 126B. The gate electrode and one of the source electrode and the drain electrode of the switching element 127 are The other end is connected to a terminal portion 126 and the other end is connected to a common electrode 128. A common potential Vcom may be supplied to the common electrode 128. The element 127 is formed on the same substrate as the pixel driving circuit section 121 or the pixel section 122. Alternatively, it may be formed on a separate substrate.

[0074] In addition, the switching element 127 may be, for example, a device having a reduced off-current, as described in the third embodiment. By using such a transistor, the potential applied to both terminals of the liquid crystal element 215 decreases with time. The bottom can be suppressed.

[0075] The common electrode 128 is a common electrode that provides a common potential Vcom supplied from the power supply potential generating circuit 117. It is electrically connected to the electric current carrying line at the common connection portion.

[0076] A specific example of the common connection portion is a conductive particle in which an insulating sphere is coated with a thin metal film. By this, an electrical connection between the common electrode 128 and the common potential line can be achieved. The common connection portion may be provided at a plurality of locations within the liquid crystal display panel 120.

[0077] The photometric circuit may be provided in the liquid crystal display device. The LCD display can detect the brightness of the environment in which it is placed. When it is found that the backlight 132 is turned on, the display control circuit 113 increases the light intensity of the backlight 132. By controlling the brightness of the LCD display, good visibility of the display screen is ensured. When it is determined that the display is being used under external light (for example, under direct sunlight outdoors), the display control circuit 1 13 controls the light intensity of the backlight 132 to reduce the amount of light consumed by the backlight 132. In this way, the display control circuit reduces the power consumption according to the signal input from the photometry circuit. 113 can control the driving method of light sources such as a backlight, a sidelight, etc.

[0078] The backlight unit 130 includes a backlight control circuit 131 and a backlight 132. The backlight 132 may be selected and combined according to the intended use of the liquid crystal display device 100. For example, a light emitting diode (LED) or the like can be used for the backlight 132. For example, a white light emitting element (such as an LED) can be arranged. A backlight signal for controlling the backlight from the display control circuit 113 and a power supply voltage are input to the display control circuit 113. Of course, the backlight unit 130 is not used, and the display can be viewed by external light. A liquid crystal display panel of this type is preferred because it consumes less power.

[0079] The backlight unit 130 and the pixel electrodes of the liquid crystal display panel 120 are provided with an area that transmits visible light. By providing the liquid crystal display device, a transmissive or semi-transmissive liquid crystal display device can be provided. A transmissive liquid crystal display device is convenient because the displayed image can be viewed even in a dimly lit place.

[0080] If necessary, optical films (polarizing films, retardation films, anti-reflection films, etc.) The backlight used in the semi-transmissive liquid crystal display device can be used in combination. The light source such as a light may be selected and combined according to the purpose of the liquid crystal display device 100. Cathode ray tubes and light emitting diodes (LEDs) can be used. Multiple LED light sources, Alternatively, a surface light source may be formed by using a plurality of electroluminescence (EL) light sources. As a surface light source, three or more types of LEDs may be used, or a white-emitting LED may be used. In addition, RGB light-emitting diodes are arranged in the backlight, and color display is performed in time division. When using the field sequential method, the color filter In some cases, a color filter that absorbs the backlight is not used. By applying the color mixing method, power consumption can be reduced.

[0081] According to the liquid crystal display device exemplified in this embodiment, the liquid crystal display panel holds the same image. During this period, the DC-DC converter can be stopped. During this time, the capacitor in the backup circuit supplies a fixed potential to the LCD panel, -The load range where the conversion efficiency of the DC converter is poor, specifically the range where the load is extremely light. The DC-DC converter does not consume power during the image retention period of the LCD panel, so the image It is possible to provide a display device in which the power consumption during the image retention period is reduced.

[0082] In addition, the liquid crystal display device exemplified in this embodiment is provided with a backup circuit with a charge limiter. The capacitor of the backup circuit with charge limiter is DC-DC Since the capacitor is connected to the DC-DC converter, the capacitor that is not filled with charge Even if the battery is connected to a power adapter, problems caused by sudden charging of the capacitor can be eliminated.

[0083] Note that this embodiment mode can be appropriately combined with other embodiment modes described in this specification. .

[0084] (Embodiment 2) In this embodiment, the power supplied from the DC-DC converter or the backup circuit is A method of driving a liquid crystal display device having a liquid crystal display panel to be driven will be described with reference to FIGS. 3 to 8. He explains.

[0085] A method for driving the liquid crystal display device 100 shown in FIG. 1 will be described with reference to FIGS. The method of driving the liquid crystal display device described in this embodiment is as follows, depending on the characteristics of the image to be displayed: By changing the refresh rate (or frequency) of the display panel, the load becomes heavier during writing operations. The DC-DC converter is used to supply a fixed potential and charge the capacitor. During the shorter image retention period, the capacitor takes priority without using a DC-DC converter. This is a display method in which a fixed potential is supplied to the display.

[0086] Specifically, when displaying an image (moving image) in which the image signals of successive frames are different, A display mode in which image signals are written for each frame is used. When the same image (still image) is displayed, a new image is displayed during the period when the same image is displayed. Image signals are not written or are written very infrequently, and no voltage is applied to the liquid crystal element. The potential of the pixel electrode and the common electrode is made to be in a floating state, and the liquid crystal element is applied with the potential. A display mode is used in which the voltage at the time of the power supply is maintained and a still image is displayed without supplying any new voltage. .

[0087] In addition, during write operations where the load is large, a DC-DC converter is used to provide a fixed potential. The DC-DC converter supplies power and charges the capacitor while displaying the same image. The power supply to the power supply is stopped, and a fixed potential is preferentially supplied from the capacitor.

[0088] The LCD device displays a combination of moving images and still images on the screen. By switching between multiple different images at high speed, the image appears as a moving image to the human eye. This refers to an image that can be recognized as a moving picture. Specifically, the image must be switched at least 60 times (60 frames) per second. By doing so, the human eye will perceive the image as a moving image with less flicker. Unlike moving images and partial moving images, it quickly switches between multiple images that are time-divided into multiple frame periods. Even if the operation is switched between the nth and (n+1)th frames, This refers to an image that does not change from frame to frame.

[0089] First, power is supplied to the liquid crystal display device 100. The power supply potential generating circuit 117 generates a common potential Vcom and a power supply potential (high power supply potential Vdd and low power supply potential Vdd) via the display control circuit 113 Vss) and control signals (start pulse SP and clock signal CK) are fed to the liquid crystal display panel. Supply to Nel 120.

[0090] The arithmetic circuit 114 of the liquid crystal display device 100 analyzes the electronic data to be displayed. The child data includes moving images and still images, and the arithmetic circuit 114 distinguishes between moving images and still images and performs A case where a process for outputting a different signal is performed will be described.

[0091] When the electronic data displayed by the arithmetic circuit 114 changes from a moving image to a still image, A still image is cut out, and a control signal indicating that it is a still image is output to the signal generating circuit 115a, When the electronic data changes from a still image to a moving image, the liquid crystal display driver 115b outputs the signal. The image signal including the moving image is input to the signal generating circuit 11 together with a control signal indicating that the image is a moving image. 5a, and also to the liquid crystal drive circuit 115b.

[0092] Next, the state of signals supplied to the pixels will be described with reference to the equivalent circuit diagram of the liquid crystal display device shown in FIG. 3 and the equivalent circuit diagram of the liquid crystal display device shown in FIG. The timing chart will be used for explanation.

[0093] FIG. 4 shows the clock signal GC In addition, the display control circuit 113 is a source line side driver circuit 121B. To explain the output timing of the clock signal, the waveform of the clock signal is shown in Figure 4 as a simple square wave. It is shown by a waveform.

[0094] FIG. 4 also shows the data line, the potential of the pixel electrode, and the potential of the common electrode. In the case where the switching element 127 is provided, the potential of the source line 125, the potential of the pixel electrode, 1 shows the potential of terminal 126A, the potential of terminal 126B, and the potential of the common electrode.

[0095] In FIG. 4, a period 1401 corresponds to a period for writing an image signal for displaying a moving image. During a period 1401, an image signal is supplied to each pixel of the pixel portion 122, and a common potential is supplied to the common electrode. In addition, because the write operations, which are heavy loads, are performed continuously, the DC-DC converter is A fixed potential is provided and a capacitor is charged using a motor.

[0096] The period 1402 corresponds to a period during which a still image is displayed (also called an image holding period). In the period 1402, the image signal Data to each pixel of the pixel section 122 is stopped, and the pixel transistor A potential that turns off the transistor is supplied to the gate line, and a common potential is supplied to the common electrode 128. During the image holding period 1402 when the load is small, a fixed potential is preferentially supplied from the capacitor. In the period 1402 shown in FIG. The configuration of supplying each signal to stop the operation of the The refresh rate prevents degradation of still images by periodically writing image signals. It is preferable to have a configuration that prevents this.

[0097] First, the timing chart for the period 1401 during which an image signal for displaying a moving image is written is In period 1401, a clock signal is constantly supplied as the clock signal GCK. A pulse corresponding to the vertical sync frequency is supplied as the start pulse GSP. In the period 1401, a clock signal SCK is constantly supplied. As the gate pulse SSP, a pulse corresponding to one gate selection period is supplied.

[0098] In addition, an image signal Data is supplied to the pixels of each row via a source line 125, and In response to the potential of the source line 125, the potential of the source line 125 is supplied to the pixel electrode.

[0099] In addition, the display control circuit 113 connects the switching element 127 to the terminal 126A. A potential is supplied to make 127 conductive, and a common potential is supplied to the common electrode via terminal 126B. do.

[0100] Next, a timing chart for the period 1402 during which a still image is displayed will be described. In 02, the clock signal GCK, the start pulse GSP, the clock signal SCK, and the start In addition, in a period 1402, the source pulse SSP supplied to the source line 125 is stopped. The image signal Data that was being transmitted stops. The clock signal GCK and the start pulse GSP During the period 1402 when both are stopped, the transistor 214 is in a non-conducting state, and the potential of the pixel electrode becomes floating.

[0101] Also, during the period 1402, the power supply potential generating circuit 117 supplies the common potential Vcom to the common electrode 1 28, and a potential is applied between the pixel electrode in a floating state and the common electrode 128 at the common potential Vcom. The liquid crystal element 215 having a liquid crystal layer can stably hold a still image. Image preservation is achieved by supplying a fixed potential from the capacitor without using a C converter. This reduces the amount of electricity consumed during the period of use.

[0102] In addition, when the liquid crystal display panel includes a switching element 127, the display control circuit 113 A voltage for turning off the switching element 127 is applied to the terminal 126A of the switching element 127. A potential can be supplied to the common electrode 128, and the potential of the common electrode 128 can also be left floating.

[0103] In the period 1402, the potentials of the electrodes at both ends of the liquid crystal element 215, that is, the pixel electrode and the common electrode, are floated. In the case where the switching element 127 is provided, a still image can be displayed. During a period 1402, the power supply potential generating circuit 117 supplies a common potential Vcom to the common electrode 128. This eliminates the need to supply the common potential Vcom to the power supply potential generating circuit 117, and the power supply potential generating circuit 117 can stop generating the common potential Vcom. By using the arithmetic circuit 114 to control the generation of the common potential Vcom, This is preferable because it allows reducing power consumption.

[0104] In addition, the clocks supplied to the gate line side driver circuit 121A and the source line side driver circuit 121B are By stopping the clock signal and the start pulse, it is possible to reduce power consumption. Furthermore, the supply of power to the DC-DC converter is stopped to turn on the first backup circuit 119a. , and the capacitor of the second backup circuit 119b is connected to the power supply potential generating circuit 1 In order to output a fixed potential to the liquid crystal display panel 120 via the Standby power consumption can be reduced.

[0105] In particular, the transistor 214 and the switching element 127 are transistors with reduced off-state current. The phenomenon in which the voltage applied to both terminals of the liquid crystal element 215 decreases over time due to the use of a capacitor. This is preferable because it can suppress the above.

[0106] Next, a period in which a moving image is switched to a still image (period 1403 in FIG. 4) and a period in which a still image is switched to a moving image are During the period when the display is switched to the other image or when the still image is rewritten (period 1404 in FIG. 4), The operation of the display control circuit will be described with reference to Figs. 5(A) and (B). Figs. 5(A) and (B) show the display control circuit. The control circuit outputs the high power supply potential Vdd, the clock signal (GCK in this case), and the start 12A shows the pulse signal (here GSP) and the potential at terminal 126A.

[0107] The operation of the display control circuit during the period 1403 during which a moving image is switched to a still image is shown in FIG. The display control circuit stops the start pulse GSP (E1 in FIG. 5(A), first step). Next, after the start pulse signal GSP stops, the pulse output is transferred to the final stage of the shift register. After reaching the threshold, the clock signals GCK are stopped (E2 in FIG. 5A, second step Next, the high power supply potential Vdd of the power supply potential is changed to the low power supply potential Vss (E in FIG. 5(A)). 3, third step).

[0108] If the liquid crystal display panel 120 includes a switching element 127, the terminal 12 6A is set to a potential at which the switching element 127 is in a non-conducting state (E in FIG. 5A). 4, the fourth step). Also, the arithmetic circuit 114 controls the power supply potential generating circuit 117 to The generation of the potential Vcom can be stopped.

[0109] Through the above procedure, the pixel driving circuit 121 can be driven without causing a malfunction. The signal supplied to the path 121 can be stopped. Since noise is retained as a still image, the display control circuit has fewer malfunctions. The liquid crystal display device can display still images with little degradation.

[0110] Display of the period 1404 during which the still image will be switched to a video or the still image will be rewritten The operation of the control circuit is shown in FIG. In the case where the display control circuit is provided with a display control circuit, the potential of the terminal 126A is set to a conductive state by the switching element 127. The potential is then set to a potential that puts the electrode into the positive electrode state (S1 in FIG. 5(B), the first step).

[0111] Next, regardless of the presence or absence of the switching element 127, the power supply potential is changed from the low power supply potential Vss to A high power supply potential Vdd is applied (S2 in FIG. 5B, second step). Then, the clock signal GCK is a pulse signal that is longer than the normal clock signal GCK and goes high first. After providing the clock signals GCK (S3 in FIG. 5B, the third step ). Next, a start pulse signal GSP is supplied (S4 in FIG. 5(B), the fourth step). .

[0112] By the above procedure, the pixel driving circuit 121 can be driven without causing a malfunction. The supply of the drive signal to the display unit 121 can be resumed. The potential of each wiring can be returned to the state when a moving image is displayed in an appropriate order. In this way, the pixel driving circuit unit 121 can be driven without malfunction.

[0113] FIG. 6 shows a period 601 in which a moving image is displayed or a period 602 in which a still image is displayed. , which shows the frequency of writing image signals for each frame period. In FIG. 6, "W" indicates the image signal "H" indicates the period during which the image signal is held. In addition, in FIG. 6, the period 603 represents one frame period, but it may be a different period. may be also possible.

[0114] In this way, in the configuration of the liquid crystal display device of this embodiment, the still image displayed in the period 602 The image signal of the image is written in the period 604, and the image signal written in the period 604 is written in the period 6 02 and other periods.

[0115] Next, a method for driving the power supply circuit 116 will be described with reference to FIGS. The liquid crystal display device 100 illustrated in FIG. 1 changes the liquid crystal display panel 120 in accordance with the characteristics of the image to be displayed. In addition to changing the rewrite frequency (or frequency) of the In addition, a DC-DC converter is used to supply a fixed potential and charge the capacitor, and the load is small. During the image retention period, the fixed voltage is preferentially supplied from the capacitor without using the DC-DC converter. A potential is supplied.

[0116] During a moving image display period in which images are frequently written, the power supply unit 150 supplies A fixed potential is supplied to the liquid crystal display panel 120 via the power supply potential generating circuit 117. In addition, the first backup circuit 119a and the second backup circuit 119b include The DC-DC converter is connected to the LCD panel. When a load that writes an image to the 120 and a load that charges a capacitor are connected, It is only necessary to select and use one that exhibits a high conversion efficiency.

[0117] In addition, the first backup circuit 119a and the second backup circuit 119b include If the charge level of the capacitor is too low, connect the capacitor to a DC-DC converter. As a result, the output potential of the DC-DC converter drops, and the power supply potential generating circuit 117 does not operate properly. This causes a problem in that a positive fixed potential cannot be output to the liquid crystal display panel. The backup circuit is equipped with a limiter circuit that limits the current flowing into the capacitor. This can prevent malfunctions caused by sudden charging of the capacitor.

[0118] During periods when images are written infrequently, such as during still image display periods (also known as image retention periods), A method for driving the power supply circuit in the embodiment will be described with reference to the flow chart shown in FIG.

[0119] During the image retention period, a still image is displayed on the liquid crystal display panel 120, and the arithmetic circuit 114 calculates the time. The status of the display device is monitored periodically (for example, every few seconds) while measuring (also called counter operation). Specifically, the first backup circuit 119a and the second backup circuit The potential of the capacitor provided in 119b and the gate potential of the pixel transistor are monitored. The monitoring operation will be described in detail later.

[0120] Also, when an image write command is received from the input device 160 during the counter operation, the arithmetic circuit 1 14 reads the electronic data from the memory device 140 and stops the counter operation.

[0121] Next, the arithmetic circuit 114 uses the switching circuit 112 to switch the first DC-DC converter 118a, and the second DC-DC converter 118b are connected to a power supply unit 150, and a power supply potential generating circuit 1 Power is supplied to the liquid crystal display panel 120 via 17.

[0122] The arithmetic circuit 114 converts the electronic data into an image signal, and the first DC-DC converter 118a and a liquid crystal display panel using the power supplied from the second DC-DC converter 118b. After writing the image data, the arithmetic circuit 114 monitors the state of the display device. do.

[0123] Then, the counter starts. The counting time is set by automatically counting the displayed image data. This corresponds to the writing interval, and can be set to a value ranging from a few seconds to a few tens of minutes. A value of 600 seconds or less is preferable, and a value of 10 seconds or more will have a significant effect on reducing power consumption. By setting the time to 600 seconds or less, degradation of the quality of the stored image can be prevented.

[0124] The arithmetic circuit 114 is connected to the power supply unit 150 at all times via the third DC-DC converter 11. Because it receives power from the 8c, it can respond to interrupt commands from users without delay. In addition, if the arithmetic circuit 114 goes into sleep mode during the time count operation, the power consumption Power consumption can be further reduced.

[0125] The monitoring operation of the arithmetic circuit 114 will be described with reference to the flow chart shown in FIG. During the time count operation, the circuit 114 periodically monitors the state of the display device and turns on the power supply unit 150. Connected to a first DC-DC converter 118a and a second DC-DC converter 118b The switching operation is controlled by using a switching circuit 112.

[0126] The arithmetic circuit 114 periodically (for example, every few seconds) refers to the gate potential of the pixel transistor and calculates the pixel When the absolute value of the gate potential of the element transistor becomes smaller than the set potential, the switching circuit 112 is used. The first DC-DC converter 118a and the second DC-DC converter 118b are supplied with power. The gate potential of the pixel transistor is connected to the gate electrode of the pixel transistor. The potential can be determined by referring to the potential of the wiring electrically connecting the The value should be 5V or more. The magnitude of the absolute value of the set potential is The off-current of the pixel transistor in the off-state is sufficiently low, and the transistor is prevented from being affected by noise or the like. It is sufficient to prevent the transistor from being erroneously turned on. A normally-off n-type transistor with a threshold voltage Vth of approximately 0 V is fabricated using a conductor layer as the channel formation region. When using a transistor as a pixel transistor, the gate potential should be kept below -5V. .

[0127] A first DC-DC converter 118a and a second DC-DC converter 118b are supplied with power. When the power supply is not provided, the first backup circuit 119a or the second backup The output potential of the capacitor included in the circuit 119b is the absolute value of the gate potential of the pixel transistor. The first backup circuit 119a or the second backup circuit 119b The capacitor is discharged by leakage current generated in the circuitry constituting the liquid crystal display device 100. And the output potential drops.

[0128] Therefore, the first backup circuit 119a or the second backup circuit 119b is provided The charge in the capacitor is insufficient, and the absolute value of the gate potential of the pixel transistor falls short of the set potential. If the voltage falls below the threshold, the arithmetic circuit 114 switches the power supply unit 150 to the first DC-D A power supply potential is generated by connecting the power supply 118 to a first DC-DC converter 118a and a second DC-DC converter 118b. The absolute value of the gate potential of the pixel transistor is maintained at a set potential or higher through the synthesis circuit 117. to.

[0129] In addition, the arithmetic circuit 114 periodically checks the first backup circuit 119a and the second backup circuit 119b. When the potential of the capacitor in the trip circuit 119b becomes greater than the set potential, the open / close circuit A first DC-DC converter 118a and a second DC-DC converter 118b are connected to the power supply 112. The capacitor 118b is disconnected from the power supply unit 150. For example, a capacitor is connected to set the potential. Output of the first DC-DC converter 118a or the second DC-DC converter 118b It is sufficient to set the potential at about 98%.

[0130] The first DC-DC converter 118a or the second DC-DC converter The load of the converter is realized by setting the potential to about 98% of the output potential of the converter 118b. It is possible to reduce power consumption while setting the range within which no problems arise in use.

[0131] According to the liquid crystal display device exemplified in this embodiment, the liquid crystal display panel holds the same image. During this period, the DC-DC converter can be stopped. During this time, the capacitor in the backup circuit supplies a fixed potential to the LCD panel, -The load range where the conversion efficiency of the DC converter is poor, specifically the range where the load is extremely light. The DC-DC converter does not consume power during the image retention period of the LCD panel, so the image It is possible to provide a liquid crystal display device in which the power consumption during the image retention period is suppressed.

[0132] In addition, the liquid crystal display device exemplified in this embodiment is provided with a backup circuit with a charge limiter. The capacitor of the backup circuit with charge limiter is DC-DC Since the capacitor is connected to the DC-DC converter, the capacitor that is not filled with charge Even if the battery is connected to a power adapter, problems caused by sudden charging of the capacitor can be eliminated.

[0133] In particular, in the liquid crystal display device of this embodiment, a transistor with reduced off-state current is provided in each pixel, By applying this to the switching element of the common electrode, it is expected that the potential can be held by the storage capacitor. This allows for a longer interval (time), dramatically reducing the frequency with which image signals need to be written. This makes it possible to reduce power consumption when displaying still images and to reduce eye fatigue. It has a remarkable effect.

[0134] Note that this embodiment mode can be appropriately combined with other embodiment modes described in this specification. .

[0135] (Embodiment 3) In this embodiment, an oxide used in the liquid crystal display device described in the first or second embodiment is An example of a transistor including a semiconductor layer and a manufacturing method thereof will be described in detail with reference to FIG. The same parts as those in the above embodiment or parts and steps having similar functions are the same as those in the above embodiment. The same explanation will be omitted. .

[0136] 9A to 9E show examples of cross-sectional structures of transistors. The transistor 510 shown in FIG. 1 is used in the liquid crystal display device described in Embodiment 1 or 2. The transistor in this embodiment is an inverted staggered transistor having a bottom gate structure. In the transistor having an oxide semiconductor layer in a channel formation region, The current flowing through the electrodes and drain current is extremely small, so the pixel transistors of the liquid crystal display panel By applying this to the image sensor, the degradation of image information written to the pixels during the image retention period is suppressed. can.

[0137] Hereinafter, a process of manufacturing a transistor 510 on a substrate 505 will be described with reference to FIGS. Explain.

[0138] First, a conductive film is formed on a substrate 505 having an insulating surface, and then a first photolithography process is performed. A gate electrode layer 511 is formed by a process. If the resist mask is formed by the inkjet method, a photomask is not used. This reduces manufacturing costs.

[0139] In this embodiment mode, a glass substrate is used as the substrate 505 having an insulating surface.

[0140] An insulating film serving as a base film may be provided between the substrate 505 and the gate electrode layer 511. The silicon nitride film, the silicon oxide film, and the like have a function of preventing the diffusion of impurity elements from the substrate 505. The insulating layer is made of one or more films selected from a silicon oxide film, a silicon nitride film, and a silicon oxynitride film. The insulating film can be formed by a laminate structure.

[0141] The material of the gate electrode layer 511 is molybdenum, titanium, tantalum, tungsten, or aluminium. Aluminum, copper, neodymium, scandium, and other metal materials, or alloys containing these as the main components The insulating film can be formed in a single layer or a laminated layer using a material.

[0142] Next, a gate insulating layer 507 is formed on the gate electrode layer 511. The gate insulating layer 507 is A silicon oxide layer, a silicon nitride layer, etc. are formed by using a plasma CVD method, a sputtering method, etc. , silicon oxynitride layer, silicon nitride oxide layer, aluminum oxide layer, aluminum nitride layer A single layer of aluminum oxide nitride, aluminum oxide nitride, or hafnium oxide is formed. can be formed by laminating.

[0143] The oxide semiconductor of this embodiment is an oxide semiconductor that is made into an i-type or substantially i-type by removing impurities. Such highly purified oxide semiconductors have low resistance to interface states and interface charges. Since the oxide semiconductor layer is extremely sensitive to the temperature, the interface between the oxide semiconductor layer and the gate insulating layer is important. Therefore, the gate insulating layer in contact with the highly purified oxide semiconductor is required to have high quality.

[0144] For example, high-density plasma CVD using microwaves (e.g., 2.45 GHz frequency) produces dense This is preferable because it allows the formation of a high-quality insulating layer with high dielectric strength. The close contact between the gate insulating layer and the high-quality gate insulating layer reduces the interface state density and improves the interface characteristics. This is because it can be made into something that is

[0145] Of course, if a good insulating layer can be formed as a gate insulating layer, sputtering is also possible. Other deposition methods such as the plasma CVD method and the like can be applied. Even if the insulating layer is one in which the film quality of the gate insulating layer and the interface characteristics with the oxide semiconductor are modified by In any case, the film quality as a gate insulating layer is good, and the oxidation Any material may be used as long as it can reduce the interface state density with the solid semiconductor and form a good interface.

[0146] In addition, the gate insulating layer 507 and the oxide semiconductor film 530 contain hydrogen, a hydroxyl group, and moisture as much as possible. In order to prevent the oxide semiconductor film 530 from being broken down, sputtering was performed as a pretreatment for the formation of the oxide semiconductor film 530. In the preheating chamber of the heating apparatus, the substrate 505 on which the gate electrode layer 511 is formed or the gate insulating layer 5 The substrate 505 on which the above-mentioned steps 107 are formed is preheated to remove hydrogen, moisture, etc. adsorbed on the substrate 505. It is preferable to desorb impurities and evacuate them. A pump is preferable. This preheating process can be omitted. Before the insulating layer 516 is formed, the source electrode layer 515a and the drain electrode layer 515b are heated. The same may be done with the formed substrate 505 .

[0147] Next, a film having a thickness of 2 nm to 200 nm, preferably 5 nm or more, is formed on the gate insulating layer 507. An oxide semiconductor film 530 having a thickness of 30 nm or less is formed (see FIG. 9A).

[0148] Note that before the oxide semiconductor film 530 is formed by a sputtering method, argon gas is introduced. The reverse sputtering is performed by introducing the metal into the gate insulating layer 507 to generate plasma. It is preferable to remove the powdery substances (also called particles or dust) that are stuck to the surface. In an argon atmosphere, a voltage is applied to the substrate using an RF power source to form plasma near the substrate. In addition, nitrogen, helium, oxygen, etc. can be used instead of argon atmosphere. Either may be used.

[0149] The oxide semiconductor used for the oxide semiconductor film 530 is a quaternary metal oxide, In-S n-Ga-Zn-O oxide semiconductors and In-Ga-Zn-O ternary metal oxides Oxide semiconductors, In-Sn-Zn-O oxide semiconductors, In-Al-Zn-O oxide semiconductors Conductor, Sn-Ga-Zn-O oxide semiconductor, Al-Ga-Zn-O oxide semiconductor, S n-Al-Zn-O oxide semiconductors and In-Zn-O oxides, which are binary metal oxides Semiconductors, Sn-Zn-O oxide semiconductors, Al-Zn-O oxide semiconductors, Zn-Mg- O-based oxide semiconductors, Sn-Mg-O-based oxide semiconductors, In-Mg-O-based oxide semiconductors, I n-Ga-O-based oxide semiconductors, In-O-based oxide semiconductors, Sn-O-based oxide semiconductors, Z nO-based oxide semiconductors can be used. Here, for example, the In-Ga-Zn-O-based oxide semiconductor may include indium It means an oxide film containing In, Gallium, and Zinc. The stoichiometric ratio is not particularly important. Also, elements other than In, Ga, and Zn may be included. In this embodiment, an In-Ga-Zn-O oxide target is used as the oxide semiconductor film 530. The cross section at this stage is shown in FIG.

[0150] Examples of targets for forming the oxide semiconductor film 530 by a sputtering method include The composition ratio is In2O3:Ga2O3:ZnO=1:1:1 [molar ratio] Using a target, an In-Ga-Zn-O film is formed. The composition is not limited to, for example, In2O3:Ga2O3:ZnO=1:1:2 [mol number An oxide target having a thickness of 1000 nm may be used.

[0151] The filling rate of the oxide target is 90% or more and 100% or less, preferably 95% or more and 99% or less. By using an oxide target with a high filling rate, the oxide semiconductor film formed The body membrane can be a dense membrane.

[0152] The oxide semiconductor film 530 is formed using a sputtering gas of hydrogen, water, a hydroxyl group, or hydrogen. It is preferable to use a high-purity gas from which impurities such as oxides have been removed.

[0153] The substrate is held in a film-forming chamber maintained in a reduced pressure state, and the substrate temperature is preferably set to 100° C. or more and 600° C. or less. The temperature is preferably 200° C. or higher and 400° C. or lower. In addition, the concentration of impurities in the oxide semiconductor film can be reduced. Damage caused by etching is reduced. The removed sputtering gas is introduced, and an oxide semiconductor is deposited on the substrate 505 using the target. In order to remove the residual moisture in the deposition chamber, a suction type vacuum pump, e.g. For example, it is preferable to use a cryopump, an ion pump, or a titanium sublimation pump. The exhaust means is preferably a turbo pump with a cold trap. The deposition chamber evacuated using a cryopump may be filled with, for example, hydrogen atoms, water (H2O), Compounds containing hydrogen atoms (and more preferably compounds containing carbon atoms) are exhausted. Therefore, the impurity concentration in the oxide semiconductor film formed in the deposition chamber can be reduced.

[0154] The atmosphere in which the sputtering method is performed is a rare gas (typically argon), oxygen, or a rare gas. The atmosphere may be a mixture of oxygen and oxygen.

[0155] As an example of the deposition conditions, the distance between the substrate and the target is 100 mm, and the pressure is 0.6 Pa. The conditions were: DC power supply 0.5kW, oxygen (oxygen flow rate 100%) atmosphere. In addition, when a pulsed DC power supply is used, the powdery substances (particles, etc.) generated during film formation are reduced. This is preferable because it can reduce the amount of adhesion (also referred to as the "friction") and make the film thickness distribution uniform.

[0156] Next, the oxide semiconductor film 530 is subjected to a second photolithography process to form an island-shaped oxide semiconductor In addition, a resist mask for forming an island-shaped oxide semiconductor layer is applied to the ink. If the resist mask is formed by the inkjet method, the photomask Since no disks are used, manufacturing costs can be reduced.

[0157] In addition, when a contact hole is formed in the gate insulating layer 507, the process is performed using an oxide semiconductor. This can be done simultaneously with the processing of the membrane 530 .

[0158] Note that the etching of the oxide semiconductor film 530 here may be dry etching or wet etching. For example, the oxide semiconductor film 530 may be subjected to wet etching. The etching solution used for etching is a mixture of phosphoric acid, acetic acid, and nitric acid. Alternatively, ITO07N (manufactured by Kanto Chemical Co., Ltd.) may be used.

[0159] Next, the oxide semiconductor layer is subjected to a first heat treatment. The conductor layer can be dehydrated or dehydrogenated. The temperature of the first heat treatment is 400° C. The temperature is set to 750°C or higher, or 400°C or higher but lower than the distortion point of the substrate. The substrate was placed in an electric furnace, which is one of the equipment used for the deposition of oxide semiconductor layers, and the temperature was raised to 450°C in a nitrogen atmosphere. After the heat treatment for 1 hour, the oxide semiconductor layer was cooled to room temperature and then cooled to room temperature. Thus, an oxide semiconductor layer 531 is obtained (see FIG. 9B).

[0160] The heat treatment device is not limited to an electric furnace, and may be a heat treatment device using heat conduction or heat from a heating element such as a resistance heating element. A device that heats the workpiece by radiation may be used. For example, a GRTA (Gas Reactor Transformer) apid Thermal Anneal) equipment, LRTA (Lamp Rapid T RTA (Rapid Thermal Anneal) equipment, etc. al) equipment can be used. The LRTA equipment can be a halogen lamp, a metal halide lamp, lamp, xenon arc lamp, carbon arc lamp, high pressure sodium lamp, high pressure mercury lamp This is a device that heats the workpiece by radiating light (electromagnetic waves) emitted from a lamp or other light source. The GRTA device is a device that uses high-temperature gas to perform heat treatment. Inert gases such as argon or nitrogen that do not react with the workpiece during heat treatment An active gas is used.

[0161] For example, the first heat treatment is performed by immersing the substrate in an inert gas heated to a high temperature of 650° C. to 700° C. The plate is moved and placed in the oven, heated for a few minutes, and then the substrate is moved and placed in an inert gas atmosphere heated to a high temperature. A GRTA may be conducted from the

[0162] In the first heat treatment, nitrogen or a rare gas such as helium, neon, or argon is used. It is preferable that the nitrogen introduced into the heat treatment device does not contain water, hydrogen, etc. Or the purity of rare gases such as helium, neon, and argon must be 6N (99.9999%) or higher. Preferably, the impurity concentration is 7N (99.99999%) or more (i.e., 1 ppm or less, It is preferable that the concentration of the ion exchange resin is 0.1 ppm or less.

[0163] After the oxide semiconductor layer is heated by the first heat treatment, high-purity oxygen gas, high-purity Introduce 100% N2O gas or ultra-dry air (dew point below -40℃, preferably below -60℃). It is preferable that the oxygen gas or N2O gas does not contain water, hydrogen, etc. Alternatively, the purity of the oxygen gas or N2O gas introduced into the heat treatment device is preferably 6N or more. Preferably, the impurity concentration in the oxygen gas or N2O gas is 1 ppm or less. It is preferable to set the concentration of the oxygen gas or N2O gas to 0.1 ppm or less. The oxidation rate is reduced by the removal of impurities through dehydration or dehydrogenation treatment. By supplying oxygen, which is the main component material of oxide semiconductors, the oxide semiconductor layer is highly It is purified and made into type I (authentic).

[0164] In addition, the first heat treatment of the oxide semiconductor layer is performed on the oxide semiconductor layer before it is processed into the island-shaped oxide semiconductor layer. The semiconductor film 530 may be subjected to the first heat treatment. In that case, the semiconductor film 530 may be heated by the heating device after the first heat treatment. The substrate is taken out and a photolithography process is performed.

[0165] In addition to the above, the first heat treatment may be performed after the oxide semiconductor layer is formed. After laminating a source electrode layer and a drain electrode layer on the insulating layer, or After forming an insulating layer on the drain electrode layer, the above-mentioned step may be performed.

[0166] In addition, when a contact hole is formed in the gate insulating layer 507, the process is performed using an oxide semiconductor. This may be done before or after the film 530 is subjected to the first heat treatment.

[0167] In addition, the oxide semiconductor layer is formed in two separate steps and heat-treated in two separate steps. Regardless of the material of the component, such as oxide, nitride, or metal, the thick crystalline region, i.e., the film An oxide semiconductor layer having a crystal region in which the c-axis is oriented perpendicular to the surface may be formed. For example, A first oxide semiconductor film having a thickness of 3 nm to 15 nm is formed, and nitrogen, oxygen, a rare gas, or In a dry air atmosphere, 450°C to 850°C, preferably 550°C to 750°C The first heat treatment is performed to obtain a first crystal having a crystalline region (including plate-like crystals) in a region including a surface. Then, a second oxide semiconductor film having a thickness larger than that of the first oxide semiconductor film is formed. The second film is formed at 450° C. or more and 850° C. or less, preferably 600° C. or more and 700° C. or less. heat treatment is performed to grow crystals upward using the first oxide semiconductor film as a seed for crystal growth; The entire second oxide semiconductor film is crystallized to form an oxide semiconductor film having a thick crystalline region. A semiconductor layer may be formed.

[0168] Next, a source electrode layer and a drain electrode layer are formed on the gate insulating layer 507 and the oxide semiconductor layer 531. A conductive film is formed to become the source electrode layer (including wiring formed in the same layer). The conductive film used for the gate electrode layer and the drain electrode layer is, for example, Al, Cr, Cu, Ta, T Metal film containing an element selected from I, Mo, and W, or metal nitride containing the above elements as components It is possible to use a film such as titanium nitride, molybdenum nitride, or tungsten nitride. In addition, Ti, Mo, W, etc. may be applied to either or both of the upper and lower sides of the metal film such as Al or Cu. High melting point metal films or their metal nitride films (titanium nitride film, molybdenum nitride film, titanium nitride film, etc.) In particular, a titanium film and a titanium tin film may be stacked on the side in contact with the oxide semiconductor layer. It is preferable to provide a conductive film containing

[0169] A resist mask is formed on the conductive film by a third photolithography process, and selective etching is performed. After forming the source electrode layer 515a and the drain electrode layer 515b by etching, a resist The mask is removed (see FIG. 9(C)).

[0170] In the third photolithography process, ultraviolet light or KrF laser is used for exposure when forming the resist mask. The source electrodes adjacent to each other on the oxide semiconductor layer 531 are preferably irradiated with a laser beam or an ArF laser beam. The width of the gap between the bottom end of the drain electrode layer and the bottom end of the drain electrode layer determines the width of the gap between the bottom end of the drain electrode layer and the bottom end of the drain electrode layer. The channel length L is determined. Note that when performing exposure with a channel length L of less than 25 nm, Extreme ultraviolet rays have extremely short wavelengths of several nm to several tens of nm. et) is used to perform exposure during resist mask formation in the third photolithography process. Extreme ultraviolet light exposure provides high resolution and a large depth of focus. The channel length L of the transistor can be set to 10 nm or more and 1000 nm or less. The operating speed of the circuit can be increased.

[0171] In order to reduce the number of photomasks and steps used in the photolithography process, The resist pattern is formed by a multi-tone mask, which is an exposure mask that allows the light to be projected at multiple intensities. The etching process may be performed using a resist mask formed using a multi-tone mask. The mask has a shape with multiple film thicknesses, and the shape can be further deformed by etching. This allows for multiple etching processes to be performed to create different patterns. Therefore, one multi-tone mask can handle at least two different patterns. Therefore, the number of exposure masks can be reduced. Since the corresponding photolithography process can also be eliminated, the process can be simplified.

[0172] Note that when the conductive film is etched, the oxide semiconductor layer 531 is etched and divided. It is desirable to optimize the etching conditions so as not to cause this. It is difficult to obtain a condition in which the oxide semiconductor layer 531 is etched without being etched at all. During etching of the conductive film, the oxide semiconductor layer 531 is only partially etched, and a groove is formed. In some cases, the oxide semiconductor layer may have a recess (concave portion).

[0173] In this embodiment, a Ti film is used as the conductive film, and an In-Ga- Since a Zn-O-based oxide semiconductor was used, ammonia hydrogen peroxide (NH3H2O) was used as an etchant. A mixture of water and hydrogen peroxide is used.

[0174] Then, a plasma treatment is performed using a gas such as N2O, N2, or Ar to remove the exposed Water or the like adsorbed on the surface of the oxide semiconductor layer may be removed by the plasma treatment. In this case, the insulating layer 5, which is a protective insulating film that is in contact with a part of the oxide semiconductor layer without being exposed to the air, is formed. Form 16.

[0175] The insulating layer 516 has a thickness of at least 1 nm. The insulating layer 516 can be formed by using a method that does not mix impurities such as hydrogen. When hydrogen is contained in the oxide semiconductor layer, the hydrogen penetrates into the oxide semiconductor layer, or the hydrogen penetrates into the oxide semiconductor layer. Oxygen in the layer is extracted, and the back channel of the oxide semiconductor layer becomes low-resistance (N-type). Therefore, the insulating layer 516 should be as thin as possible. It is important that the deposition process does not use hydrogen, resulting in a hydrogen-free film.

[0176] In this embodiment, a silicon oxide film having a thickness of 200 nm is formed as the insulating layer 516 by sputtering. The substrate temperature during film formation should be between room temperature and 300°C. In the present embodiment, the temperature is set to 100° C. The silicon oxide film is formed by sputtering using a rare gas (typically In general, under an atmosphere of argon, oxygen, or a mixture of rare gas and oxygen In addition, a silicon oxide target or a silicon target can be used as the target. For example, a silicon target can be used in an oxygen-containing atmosphere. A silicon oxide film can be formed on the oxide semiconductor layer by a sputtering method. The insulating layer 516 to be formed is made of water, hydrogen ions, and OH- It does not contain impurities such as An inorganic insulating film is used to block the intrusion of A silicon oxynitride film, an aluminum oxide film, an aluminum oxynitride film, or the like is used. .

[0177] In the same manner as in the formation of the oxide semiconductor film 530, moisture remaining in the deposition chamber for the insulating layer 516 is removed. For this purpose, it is preferable to use an adsorption type vacuum pump (such as a cryopump). The concentration of impurities contained in the insulating layer 516 formed in a deposition chamber evacuated using an opamp was reduced. In addition, the following exhaust means can be used to remove residual moisture in the deposition chamber for the insulating layer 516: A turbo pump plus a cold trap may also be used.

[0178] The insulating layer 516 is formed using a sputtering gas such as hydrogen, water, a hydroxyl group, or a hydride. It is preferable to use a high-purity gas from which impurities have been removed.

[0179] Next, a second heat treatment (preferably a second heat treatment) is performed under an inert gas atmosphere or an oxygen gas atmosphere. For example, the heating is performed in a nitrogen atmosphere. The second heat treatment is performed at 250° C. for 1 hour under atmospheric pressure. A portion of the layer (channel formation region) is heated while in contact with the insulating layer 516 .

[0180] Through the above steps, the oxide semiconductor film is subjected to the first heat treatment to remove hydrogen, Impurities such as moisture, a hydroxyl group, or hydride (also called a hydrogen compound) are intentionally removed from the oxide semiconductor layer. The oxide semiconductor is formed by eliminating impurities and reducing the impurity concentration. Therefore, the oxide semiconductor layer can be supplied with oxygen, which is one of the main components of the oxide semiconductor layer. It is purified and made into type I (authentic).

[0181] Through the above steps, a transistor 510 is formed (see FIG. 9D).

[0182] In addition, when a silicon oxide layer containing many defects is used for the insulating layer 516, The heat treatment reduces hydrogen, moisture, a hydroxyl group, hydride, or the like contained in the oxide semiconductor layer. Impurities are diffused into the oxide insulating layer, and the impurities contained in the oxide semiconductor layer are further reduced. This has the effect of

[0183] A protective insulating layer 506 may be further formed on the insulating layer 516. The protective insulating layer 506 may be, for example, For example, a silicon nitride film is formed by RF sputtering. RF sputtering is suitable for mass production. The protective insulating layer does not contain impurities such as moisture. First, inorganic insulating films are used to block these substances from entering from the outside, and silicon nitride films, In this embodiment mode, a protective insulating film is formed using a silicon nitride film or the like. A layer 506 is formed (see FIG. 9(E)).

[0184] In this embodiment, the substrate 505 on which the insulating layer 516 is formed is used as the protective insulating layer 506. The gas is heated to a temperature of 100℃ to 400℃, and hydrogen and moisture are removed from the gas. A silicon nitride film is formed by introducing a target gas and using a silicon semiconductor target. In this case, similarly to the insulating layer 516, the protective insulating layer 50 is formed while removing the residual moisture in the film formation chamber. It is preferable to deposit 6.

[0185] After the protective insulation layer is formed, it is further heated in air at 100°C to 200°C for 1 hour to 30 hours. This heat treatment may be performed at a constant heating temperature. In addition, the temperature is increased from room temperature to a heating temperature of 100°C or more and 200°C or less, and then decreased from the heating temperature to room temperature. The temperature drop at 0.5° C. may be repeated several times.

[0186] The transistor described in this embodiment has a source electrode and a drain electrode in an off state. Because the current that flows is extremely small, when used as a pixel transistor in a liquid crystal display panel, This can suppress the phenomenon in which the image information written to the pixels during the image retention period deteriorates. Since the retention period can be extended and the frequency of writing images can be reduced, the transmission method exemplified in this embodiment can be used. By using a liquid crystal display panel that uses transistors, it is possible to reduce power consumption. A fixed potential is supplied from the capacitor of the backup circuit during the image retention period. In addition, the DC-DC converter can be stopped. The charge stored in the capacitor does not leak through the It can be reduced.

[0187] Note that this embodiment mode can be appropriately combined with other embodiment modes described in this specification. . EXAMPLES

[0188] In this embodiment, the device is driven by power supplied from a DC-DC converter or a backup circuit. A liquid crystal display device having a liquid crystal display panel was manufactured, and still images were written at different frequencies. The results will be explained.

[0189] The configuration of the liquid crystal display device exemplified in this embodiment will be described with reference to the block diagram shown in FIG. The liquid crystal display device is made up of a solar cell, a lithium ion capacitor, a drive circuit, a conversion board, and a liquid crystal. Equipped with a display panel.

[0190] The drive circuit is a DC-DC converter that outputs +3.3V to the microprocessor, A DC-DC converter that outputs +14V to the power generation circuit via a back-up circuit, and It has a DC-DC converter that outputs -14V to the power generation circuit via a step-up circuit. The power generation circuit supplies power to the signal generation circuit, and supplies power to the liquid crystal display panel via the conversion board. Supply.

[0191] The microprocessor reads image data from the flash memory and outputs it to the LCD driver IC. The LCD driver IC transfers image data to the LCD panel via the conversion board. The solar cell also supplies power to charge the lithium-ion capacitor, which then The lithium ion capacitor supplies power to the drive circuit, which then transmits the liquid crystal display (LCD) to the liquid crystal display via a conversion board. Drives the display panel.

[0192] The configuration of the backup circuit provided in the liquid crystal display device exemplified in this embodiment is shown in FIG. a first circuit through which the power output from the -DC converter is supplied to a power supply generating circuit via a rectifier; The second stage is connected to the power supply generating circuit via the DC-DC converter and two rectifiers. A capacitor is connected between the two rectifying elements of the second circuit. The potential of the capacitor is monitored by a microprocessor.

[0193] The time during which a liquid crystal display device having the above-described configuration can be driven using a lithium ion capacitor In addition, a lithium-ion capacitor capable of storing 4.1mAh of power was used. The time it takes for the output voltage to drop from the initial value of 4V to 3.5V is measured using the The time during which the display device could be driven was measured, and the potential of the capacitor was monitored every 2 seconds.

[0194] The lithium ion capacitor can drive the liquid crystal display device during the image writing interval. The plot of the time that the image can be written is shown by the solid line in Fig. 12. If the time is increased to 00 seconds, the time during which the liquid crystal display device of this embodiment can be driven becomes approximately 6.7 times longer. The time during which the liquid crystal display device of this embodiment can be driven strongly depends on the interval between image writing. The DC-DC converter was stopped during the image retention period, resulting in reduced power consumption. .

[0195] (Comparative Example) A liquid crystal display device in which the backup circuit is removed from the liquid crystal display device described in the embodiment is used. The time that the lithium ion capacitor described in the example can be used was investigated. Two converters are connected so that they output a voltage directly to the synthesis circuit. I set it to +13V and -13V.

[0196] The lithium ion capacitor can drive the liquid crystal display device during the image writing interval. The plot of the time that the image can be written is shown by the dashed line in Fig. 12. When the time is increased to 00 seconds, the time for which the liquid crystal display device of this comparative example can be driven is increased by about 1.7 times. Ta.

[0197] Compared to the liquid crystal display device of this comparative example, the liquid crystal display device equipped with the backup circuit of the embodiment could operate for 3.46 times longer. [Explanation of symbols]

[0198] 100 LCD display device 110 Drive circuit section 112 Opening and closing circuits 113 Display control circuit 114 Arithmetic circuit 115a Signal generation circuit 115b Liquid crystal drive circuit 116 Power supply circuit 117 Power supply potential generation circuit 118a DC-DC converter 118b DC-DC Converter 118c DC-DC Converter 119a Backup circuit 119b Backup circuit 120 Liquid crystal display panel 121 Pixel driving circuit section 121A Gate line side driving circuit 121B Source line side driver circuit 122 Pixel section 123 pixels 124 Gate Line 125 source lines 126 Terminal section 126A Terminal 126B Terminal 127 Switching element 128 Common electrode 130 Backlight section 131 Backlight control circuit 132 Backlight 140 Storage device 150 Power supply section 151 Secondary battery 155 Solar Cells 160 Input Devices 190a First switch 190b First switch 191a First limiter circuit 192a Capacitor 192b Capacitor 193a Second switch 193b Second switch 194a Third switch 194b Third switch 195a Terminal 195b Terminal 210 Capacitive element 214 Transistor 215 Liquid crystal element 505 Board 506 Protective insulation layer 507 Gate Insulation Layer 510 Transistor 511 Gate electrode layer 515a Source electrode layer 515b Drain electrode layer 516 Insulating Layer 530 Oxide Semiconductor Film 531 Oxide Semiconductor Layer 601 period 602 period 603 period 604 period 1401 period 1402 period 1403 period 1404 period

Claims

[Claim 1] A converter that converts a power input into a predetermined DC power; a backup circuit having a capacitor for charging the power output by the converter; a liquid crystal display panel electrically connected to the converter and the backup circuit; the liquid crystal display panel has a function of retaining the same image for a certain period of time; The power consumption during image writing is 10 times or more than the power consumption during image retention. ４ It is less than double, the backup circuit has a first mode in which power is supplied to the liquid crystal display panel and the capacitor via the converter, and a second mode in which power supply to the converter is stopped and power stored in the capacitor is supplied to the liquid crystal display panel; The liquid crystal display device supplies power to the liquid crystal display panel in the second mode during the image retention period.

Images