Electronic appliance

Abstract

To provide a display device in which power to be consumed in a period of keeping a written image is suppressed.SOLUTION: A display device includes a liquid crystal display panel that is driven with power supplied from a converter or a backup circuit. At the time of writing operation in which a load is large, a fixed potential is supplied using a converter and a capacitor is charged. In an image keeping period in which the load is small, the fixed potential may be supplied with priority 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 the integration of semiconductor elements progresses and the processing power of computing elements improves, electronic devices become smaller and lighter. As a result, it became possible to carry around and use highly functional electronic devices. Furthermore, by providing a sufficient information transmission infrastructure for 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 a display 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 a power line. To extend the operating time, it is desirable to increase the battery capacity. 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. This technology is not limited to portable electronic devices, but is also used to reduce power consumption in increasingly large television sets and other devices. Technique is required.

[0005] Conventional display devices display the same image data 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 image data is written. A technique has been reported in which a pause period longer than the scanning period is set (for example, patent document 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 based on the idea of ​​reducing consumption during an image retention period. An object of the present invention is to provide a display device that consumes less power. [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 deterioration during the image retention period, The fixed potential to be supplied to the common electrode is the same as that of the battery. It 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 output to the power consumed, 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 high conversion efficiency cannot be expected.

[0013] For example, when connecting an LCD panel as a load, a high fluctuation of about 75% occurs during writing. However, the DC-DC converter that has the highest conversion efficiency is used. The power consumption is 10 times that of a write operation. -1 From double to 10 -4 The image is about doubled 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 load with large fluctuations 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 LCD display device is equipped with a converter that converts the power input into a specified DC power supply and a backup power supply. A backup circuit is provided, and a converter is used to supply a fixed potential during write operations when the load becomes large. The image retention time is reduced by supplying power and charging the capacitor in the backup circuit. During this period, a fixed potential is preferentially supplied from the charged capacitor without using a converter. Just do that.

[0016] The backup circuit supplies power from the power supply via a converter to the LCD panel and The first mode supplies power to the capacitor, and the second mode stops power from the power supply to the converter. It has a second mode in which 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 that charges 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 the power consumption during the image retention period. 4 Less than double The backup circuit has a liquid crystal display panel. The first mode supplies power to the LCD panel and the capacitor, and the second mode supplies power to the converter. and a second mode in which the power stored in the capacitor is supplied to the LCD 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 display a display image while the power is turned on. The converter that converts the power into 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 designed to operate during the image retention period of the liquid crystal display panel, which is an area where the load is extremely small. Since the image retention period is reduced, the LCD device consumes less power. 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 the power consumption during image retention. 4 is less than double The LCD panel includes a backup circuit that supplies power to the LCD panel via a converter. A first mode supplies a voltage to a capacitor connected to a display panel and a limiter circuit; The power supply to the inverter 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. It is a liquid crystal display that supplies power.

[0020] According to the above aspect of the present invention, the conversion is performed during the period in which the liquid crystal display panel holds the same image. The capacitor in the backup circuit with a charge limiter will supply a fixed voltage to the LCD panel. This allows the converter to operate in a load region where the conversion efficiency is poor, specifically in an extremely 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 that consumes less power during the image retention period.

[0021] Furthermore, 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. Even if a capacitor that is not full of charge is connected to the converter, a sudden This can solve the problem of charging.

[0022] Furthermore, 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 to write data to the liquid crystal display device.

[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] Furthermore, one aspect of the present invention is a power supply device that is supplied via a converter that converts a power supply 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. and writes an image to the LCD panel, and at set intervals, The potential of the capacitor provided in the backup circuit is monitored, and the pixel transistor When the absolute value of the gate potential of the When the potential of the capacitor exceeds the second set potential, the power to the converter is cut off. 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 a fixed potential to be supplied to the LCD panel during the image retention period. The load area where conversion efficiency is poor, specifically the area where the load is extremely low, is the image area of ​​the liquid crystal display panel. The converter does not consume power during the image retention period, so the power consumed during the image retention period is reduced. 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 LCD panel side of the capacitor rises to the set voltage. If the voltage becomes too high, the power supply to the converter is cut off. This causes the backup circuit to It acts as a load on the converter and utilizes the area with high conversion efficiency to It can be charged.

[0027] Furthermore, one aspect of the present invention is a driving method of the liquid crystal display device, wherein the first set potential is 5 V or more. It is a 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 voltage greater than 5V. The potential supplied to the pixel transistor can keep the pixel transistor 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 the method.

[0030] According to the above aspect of the present invention, when the charge of the capacitor provided in the backup circuit approaches full charge, If the load is too low, the load will be too small. By eliminating charging in this low load range, 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 may be a fixed potential that serves as a reference for the other potentials, and may be ground potential as an example. [Effects of the Invention]

[0033] According to the present invention, it is possible to provide a display device that consumes less power during an image retention period. [Brief explanation 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. [Figure 2] FIG. 1 is a block diagram illustrating a configuration of a power supply circuit according to an embodiment. [Figure 3] 1 is an equivalent circuit diagram illustrating a configuration of a liquid crystal display panel according to an embodiment. [Figure 4] 3 is a timing chart illustrating a method for driving a liquid crystal display device according to an embodiment. [Figure 5] 3 is a timing chart illustrating a method for driving a liquid crystal display device according to an embodiment. [Figure 6] 3 is a timing chart illustrating a method for driving a liquid crystal display device according to an embodiment. [Figure 7] 1A to 1C illustrate a method for driving a power supply circuit according to an embodiment. [Figure 8] 1A to 1C illustrate 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 the configuration of a backup circuit according to an embodiment. [Figure 12] 5A and 5B are diagrams illustrating 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 INVENTION

[0035] The embodiments 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 embodiments, and various changes and modifications may be made in the form and details thereof without departing from the spirit and scope of the present invention. It will be readily understood by those skilled in the art that the present invention can be achieved by the following embodiments. It should not be construed as being limited to the contents of the description. The same reference numerals are used in different drawings to denote 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 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 drive circuit unit 110, a liquid crystal display panel 120, a memory device 14, and a display unit 16. 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 need.

[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 the 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 outputs a power supply potential and a control signal 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 116a. The power supply circuit 116 includes a power supply potential generating circuit 117, a first DC-DC converter 118, a second DC-DC converter 119, a third DC-DC converter 120, a fourth DC-DC converter 121, a fifth DC-DC converter 122, a sixth DC-DC converter 123, a sixth DC-DC converter 124, a sixth DC-DC converter 125, a sixth DC-DC converter 126, a sixth DC-DC converter 1 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 voltage to 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 supplied to the arithmetic circuit 114 of the display control circuit 113.

[0041] The configurations of the first backup circuit 119a and the second backup circuit 119b are shown in FIG. 2 is a block diagram of the power supply circuit 116 in FIG. 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 the first DC-DC converter 118a to the terminals 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 first limiter circuit 191a. The other terminal of the switch 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 the 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 The power supply potential generating circuit 117 is connected to the power supply potential generating circuit 117, and the potential supplied by the first DC-DC converter 118a is is output to a liquid crystal display panel 120 (not shown in FIG. 2) via a power supply potential generating circuit 117. I'm putting in effort.

[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 limits the first limit 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 118a suppresses the phenomenon of a drop in the potential output from the liquid crystal display device 100, thereby stabilizing the operation of the liquid crystal display device 100. It is also possible to configure the device without using 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 switching circuit 112. The arithmetic circuit 114 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 connected to the power supply 112 via the open / close circuit 112 in accordance with the potential of the wiring connected to the power supply 112. , and the supply of power to the second DC-DC converter 118b can be controlled.

[0046] The first switch 190a, the first switch 190b, and the second switch 190c provided in the backup circuit The switch 193a, the second switch 193b, the third switch 194a, and the third switch 19 4b synchronizes the timing of connection and disconnection with 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 the disconnected state. When the switching circuit 112 is in a disconnected state, the first switch 190a, the first switch 190b, the second switch 190c, 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 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 extracts the data from the storage device 140. 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 readable image signal data and outputs it. In synchronization with 4, the control signals (start pulse SP and clock signal CK) are 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 inverted appropriately by a method such as frame inversion driving. If the image signal is analog, it can be converted to digital via an A / D converter. The signal may be converted into a digital signal and supplied to the liquid crystal display device 100.

[0050] The arithmetic circuit 114 also uses the switching circuit 112 to connect the first DC-DC converter to the power supply unit 150. and controls the supply of power to the first DC-DC converter 118a and the second DC-DC converter 118b. Furthermore, the arithmetic circuit 114 includes a first backup circuit 119a and a second backup circuit 119b. The charge state of the capacitor provided in the circuit 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 then 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 still image from the image signal Data containing the still image. , a control signal indicating a still image, a signal generating circuit 115a, and a liquid crystal driving circuit The arithmetic circuit 114 can output a moving image signal from the image signal Data including the moving image to the arithmetic circuit 115b. It detects the motion picture and sends consecutive frames to the LCD panel along with a control signal indicating that it is a moving image. It can output to 120.

[0052] The arithmetic circuit 114 outputs different signals to the liquid crystal display device 100 of this embodiment in accordance with the input electronic data. In this embodiment, the arithmetic circuit 114 determines that the image is a still image. The operation is performed in the still image display mode, and the arithmetic circuit 114 determines that the image is 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] 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. The user of the device selects the operation mode of the liquid crystal display device manually or using an externally connected device, This function switches between video display mode and still image display mode.

[0054] The above-described functions are examples of the functions possessed by the arithmetic circuit 114, and various functions may be employed 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 (for example, to detect the difference between the image signals). Since this is easy, when the input image signal (image signal data) is an analog signal, Alternatively, an A / D converter or the like can 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.

[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 generator, 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 referred to as 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 exemplified 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 line side driving circuit 121B. It extends from the source line side driving circuit 121B.

[0061] The pixel 123 has a transistor 214 as a switching element, and the transistor 214 is connected to The display device 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 drain electrodes is connected to one of the plurality of 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] The transistor 214 is preferably a transistor with reduced off-state current. 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. The written state can be maintained for a long period of time, 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 the 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 that applies an electric field 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) When using a pixel electrode, the pixel electrode and the 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 liquid crystal Examples include polymer liquid crystals and banana-shaped liquid crystals.

[0067] The LCD driving mode is Twisted Nematic (TN) 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 (FFS) mode mode, MVA (Multi-domain Vertical Alignment) mode mode, PVA (Patterned Vertical Alignment) mode, ASM(Axially Symmetric aligned Micro-cell ) mode can be used as appropriate. Of course, in this embodiment, 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 pixel electrode provided on a second substrate. The vertical electric field generated between the pixel electrodes on the substrate and the opposing common electrode causes the alignment of the liquid crystal. The direction is controlled, but the pixel electrode is changed appropriately depending on the liquid crystal material or the liquid crystal driving mode. It is also possible to configure the liquid crystal to have its orientation 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 from the display control circuit 113. potential Vss, start pulse SP, clock signal CK, and image signal Data, etc.), and This is an input terminal for supplying a common potential Vcom or the like to the pixel drive circuit unit 121.

[0070] The pixel driving circuit unit 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 have a plurality of pixels. The shift register circuit (shift register) is a driving circuit for driving the pixel unit 122. It has a function (also called a "function").

[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 121 is supplied with 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, and the display control circuit 113 outputs 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 the terminal portion 126 and the other end is connected to the common electrode 128. The 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-state current, as described in the third embodiment. By using a transistor, the potential applied to both terminals of the liquid crystal element 215 decreases over time. It can suppress the bottom.

[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 line at the common connection portion.

[0076] A specific example of the common connection part is a conductive particle in which an insulating sphere is coated with a metal thin film. By doing so, it is possible to electrically connect the common electrode 128 to the common potential line. The common connection section 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 determined that the backlight 132 is turned on, the display control circuit 113 increases the light intensity of the backlight 132. This ensures good visibility of the display screen, and on the other hand, the LCD display is extremely bright. 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 backlight 132 to reduce the light intensity, and reduces the amount of light consumed by the backlight 132. In this way, the display control circuit operates in response to the signal input from the photometry circuit. 113 can control the driving method of light sources such as backlights and sidelights.

[0078] The backlight unit 130 includes a backlight control circuit 131 and a backlight 132. The backlight 132 may be selected and combined depending on the intended use of the liquid crystal display device 100. For example, a light emitting diode (LED) or the like can be used as the backlight 132. For example, a white light emitting element (e.g., an LED) can be disposed. 1 receives a backlight signal for controlling the backlight from the display control circuit 113 and a power supply voltage. Of course, the backlight unit 130 is not used, and the display is visible in external light. A liquid crystal display panel of this type is preferable because it consumes less power.

[0079] The backlight unit 130 and the pixel electrodes of the liquid crystal display panel 120 are provided with areas that transmit 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 seen 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 depending on the application 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 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 light 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, 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 low. The DC-DC converter does not consume power during the image retention period of the LCD panel, A display device can be provided that consumes less power during an image retention period.

[0082] 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 connected to the DC-DC Because the capacitor is connected to the DC-DC converter, the capacitor that is not filled with charge Even when connected to a power adapter, this eliminates problems caused by sudden charging of the capacitor.

[0083] Note that this embodiment mode can be appropriately combined with other embodiment modes shown 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. I will explain.

[0085] A method for driving the liquid crystal display device 100 shown in FIG. 1 will be described with reference to FIGS. 3 to 6. The method of driving the liquid crystal display device described in this embodiment is as follows: Change the refresh frequency (or frequency) of the display panel to reduce the load during write operations. uses a DC-DC converter to supply a fixed potential and charge a capacitor, and the load When the image retention period becomes shorter, the priority is given to the capacitor without using a DC-DC converter. This is a display method in which a fixed potential is supplied automatically.

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

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

[0088] The LCD display unit 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. Specifically, the image changes more than 60 times (60 frames) per second. By doing so, the human eye perceives the image as a moving image with less flicker. Unlike moving images and partial moving images, the time-divided images are switched at high speed over multiple frame periods. Even if the operation is switched between consecutive frames, for example, the nth frame and the (n+1)th frame, 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 the 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 LCD 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 calculation circuit 114 distinguishes between moving images and still images and performs A case where a process for outputting different signals 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 extracted and output to the signal generating circuit 115a together with a control signal indicating that it is a still image. When the electronic data changes from a still image to a moving image, the LCD driver 115b outputs the The image signal including the moving image is input to the signal generating circuit 11 together with the control signal indicating that the image is a moving image. 5a and the liquid crystal drive circuit 115b.

[0092] Next, the state of signals supplied to pixels will be explained 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] 4, the clock signal GC supplied from the display control circuit 113 to the gate line side driving circuit 121A is K, and a start pulse GSP. The display control circuit 113 also includes a source line side drive circuit 121B and the start pulse SSP. To explain the timing of the clock signal output, the waveform of the clock signal is shown in Figure 4 as a simple square wave. It is shown as a waveform.

[0094] FIG. 4 also shows the potential of the data line, pixel electrode, and common electrode. In addition, when the switching element 127 is provided, the potential of the source line 125, the potential of the pixel electrode, The potential of terminal 126A, the potential of terminal 126B, and the potential of the common electrode are shown.

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

[0096] The period 1402 corresponds to a period during which a still image is displayed (also called an image retention 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. During the period 1402 shown in FIG. The configuration for supplying each signal to stop the operation of the period 1402 and The refresh rate prevents image 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 in which the 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 synchronization frequency is supplied as a 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 pixel electrode is supplied with the potential of the source line 125.

[0099] In addition, the display control circuit 113 connects the terminal 126A of the switching element 127 to the switching element 127 is supplied with a potential that makes it 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 pulse During the period 1402, the source pulse SSP supplied to the source line 125 is stopped. The image signal Data that was being transmitted stops. 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 protection is achieved by supplying a fixed potential preferentially from the capacitor without using a C converter. This reduces the amount of electricity consumed during the storage period.

[0102] In addition, when the liquid crystal display panel includes a switching element 127, the display control circuit 113 A terminal 126A of the switching element 127 is connected to a voltage that causes the switching element 127 to be in a non-conductive state. 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 the period 1402, the power supply potential generating circuit 117 supplies the common potential Vcom to the common electrode 128. Therefore, 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 reduces power consumption.

[0104] In addition, the clocks supplied to the gate line side driving circuit 121A and the source line side driving 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 included in the second backup circuit 119b, 17 to output a fixed potential to the liquid crystal display panel 120. 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 that the voltage applied to both terminals of the liquid crystal element 215 decreases over time when a capacitor is used. This is preferable because it can suppress the above.

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

[0107] The operation of the display control circuit during the period 1403 when switching from a moving image 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 reaches 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). The arithmetic circuit 114 controls the power supply potential generating circuit 117 to generate a common The generation of the potential Vcom can be stopped.

[0109] By 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 the noise is retained as a still image, the display control circuit is equipped with less malfunctions. The liquid crystal display device can display still images with little image degradation.

[0110] Next, display of the period 1404 during which a still image is switched to a video or a still image is rewritten. The operation of the control circuit is shown in FIG. In this case, the display control circuit controls the potential of the terminal 126A so that the switching element 127 is in a conducting state. The potential is set to a value that puts the electrode into a negative state (S1 in FIG. 5(B), the first step).

[0111] Next, regardless of whether the switching element 127 is present or not, the power supply potential is changed from the low power supply potential Vss to The high power supply potential Vdd is applied (S2 in FIG. 5B, second step). Then, the clock signal GCK is a pulse signal longer than the normal clock signal GCK, which is then given as a high potential. After providing the clock signal GCK, a plurality of clock signals GCK are supplied (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 section 121 can be resumed. As a result, the pixel driving circuit unit 121 can be driven without malfunction.

[0113] 6, a period 601 in which a moving image is displayed or a period 602 in which a still image is displayed is shown. , which shows the frequency of writing image signals for each frame period. "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 also represent another period. may be.

[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 other periods are held.

[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 depending on the characteristics of the image to be displayed. In addition to changing the rewrite frequency (or frequency), In addition, a DC-DC converter is used to supply a fixed potential and charge the capacitor, and when the load is small, During the image retention period, the fixed voltage is 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 150 is supplied to the DC-DC converter A fixed potential is supplied to the liquid crystal display panel 120 via the power supply potential generating circuit 117. The first backup circuit 119a and the second backup circuit 119b have the following characteristics: The DC-DC converter is connected to the LCD panel. When a load that writes an image to 120 and a load that charges a capacitor are connected, It is only necessary to select and use one that shows a high conversion efficiency.

[0117] The first backup circuit 119a and the second backup circuit 119b include: If the capacitor charge level 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 has 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 above will be described with reference to the flowchart 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 counter operation, the arithmetic circuit 1 14 reads the electronic data from the memory device 140 and stops the counter operation.

[0121] Next, the calculation 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 the 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 the 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] Next, 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 of, for example, several seconds to several tens of minutes. A value of 600 seconds or less is preferable, and a value of 10 seconds or more will significantly reduce power consumption. By setting the time to 600 seconds or less, it is possible to prevent the quality of the stored image from deteriorating.

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

[0125] The monitoring operation of the arithmetic circuit 114 will be described with reference to the flowchart shown in FIG. During the time counting 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 using the 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 set potential can be determined by referring to the potential of the wiring electrically connecting the The absolute value of the set potential should be 5V or more. The off-state current of the pixel transistor is sufficiently low, and the transistor is not affected by noise or the like. It is sufficient to prevent the transistor from being turned on by mistake. A conductor layer is used in the channel formation region, and a normally-off n-type transistor with a threshold voltage Vth of approximately 0 V is formed. When using a transistor as a pixel transistor, the gate potential should be kept below -5V. .

[0127] The first DC-DC converter 118a and the second DC-DC converter 118b are supplied with power. When the power supply is not supplied, the first backup circuit 119a or the second backup The output potential of the capacitor included in the circuit 119b is equal to 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 that constitutes the liquid crystal display device 100. The output potential decreases.

[0128] Therefore, the first backup circuit 119a or the second backup circuit 119b is provided The charge of the capacitor is insufficient, and the absolute value of the gate potential of the pixel transistor falls below the set potential. If the voltage is lower than the first DC-DC converter, the calculation circuit 114 uses the switching circuit 112 to switch the power supply unit 150 to the first DC-DC converter. 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 do so.

[0129] The arithmetic circuit 114 also periodically checks the first backup circuit 119a and the second backup circuit 119b. The potential of the capacitor provided in the trip circuit 119b is referenced, and when it exceeds a set potential, the switching circuit The first DC-DC converter 118a and the 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 118b is connected to the capacitor. By setting the potential to about 98% of the output potential of the converter 118b, the load of the converter can be realized. It is possible to reduce power consumption while setting it within a range that does not cause problems 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 low. The DC-DC converter does not consume power during the image retention period of the LCD panel, A liquid crystal display device can be provided in which the power consumption during the image retention period is reduced.

[0132] 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 connected to the DC-DC Because the capacitor is connected to the DC-DC converter, the capacitor that is not filled with charge Even when connected to a power adapter, this eliminates problems caused by sudden charging of the capacitor.

[0133] In particular, in the liquid crystal display device of this embodiment, a transistor with reduced off-state current is used in each pixel, By applying this to the switching element of the common electrode, it is expected that the potential can be maintained by the storage capacitor. As a result, the frequency of writing image signals can be dramatically reduced. 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 shown in this specification. .

[0135] (Embodiment 3) In this embodiment, the 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 FIGS. 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. This is an inverted staggered transistor with a bottom gate structure that can be used in the present embodiment. The transistor having the oxide semiconductor layer shown in FIG. 1 in a channel formation region has a source The current flowing through the electrodes and drain current is extremely small, so the pixel transistors of the LCD 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] 9A to 9E, a process of manufacturing a transistor 510 on a substrate 505 will be described. Explain.

[0138] First, a conductive film is formed on a substrate 505 having an insulating surface, and then a first photolithography is performed. A gate electrode layer 511 is formed by a process. If the resist mask is formed by the inkjet method, a photomask can be used. Therefore, manufacturing costs can be reduced.

[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. , which has the function of preventing the diffusion of impurity elements from the substrate 505, and The insulating layer is made of one or more films selected from a silicon film, a silicon nitride oxide film, and a silicon oxynitride film. The insulating film can be formed by a laminated structure.

[0141] The material of the gate electrode layer 511 is molybdenum, titanium, tantalum, tungsten, or aluminum. Metallic materials such as aluminum, copper, neodymium, scandium, etc., or alloy materials containing these as the main components The insulating film can be formed as a single layer or a laminate 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 , an aluminum oxynitride layer, an aluminum nitride oxide layer, or a hafnium oxide layer may be formed as a single layer or can be formed by laminating.

[0143] The oxide semiconductor of this embodiment is an oxide semiconductor obtained by removing impurities and becoming i-type or substantially i-type. Such highly purified oxide semiconductors have low resistance to interface states and interface charges. Since the interface between the oxide semiconductor layer and the gate insulating 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., frequency 2.45 GHz) 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 film formation methods such as the plasma CVD method and the like can also 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, it is important that the film quality as a gate insulating layer is good, and that the oxidation Any material may be used as long as it can reduce the interface state density with the compound 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 pretreatment before the formation of the oxide semiconductor film 530. 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 and exhaust the impurities. A pump is preferable. However, 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 process may be carried out on 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 silicon dioxide into the gate insulating layer 507 to generate plasma. It is preferable to remove the powdery material (also called particles or dust) that is sputtered. In an argon atmosphere, a voltage is applied to the substrate using an RF power supply to form plasma near the substrate. It is also possible to use nitrogen, helium, oxygen, etc. 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 contain indium. (In), gallium (Ga), and zinc (Zn), The stoichiometric ratio is not particularly important. In addition, elements other than In, Ga, and Zn may be contained. In this embodiment, an In—Ga—Zn—O-based oxide target is used as the oxide semiconductor film 530. The cross section at this stage is shown in FIG. 9(A).

[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 ratio of [0.01 to 0.01] may also 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 The body membrane can be a dense membrane.

[0152] The oxide semiconductor film 530 is formed using a sputtering gas containing 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. The concentration of impurities contained in the sputtered oxide semiconductor film can be reduced. Damage caused by coating is reduced. The removed sputtering gas is introduced, and an oxide semiconductor is deposited on the substrate 505 using the target. To remove residual moisture in the deposition chamber, an adsorption 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 added. The deposition chamber evacuated using a cryopump may contain, 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 silicon.

[0155] As an example of the film formation conditions, the distance between the substrate and the target is 100 mm, and the pressure is 0.6 Pa. The conditions were: DC power 0.5kW, oxygen (oxygen flow rate 100%) atmosphere. In addition, when a pulsed DC power supply is used, powdery substances (particles, etc.) generated during film formation are This is preferable because it can reduce the thickness (also called "slippage") 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 film. In addition, a resist mask for forming an island-shaped oxide semiconductor layer is applied to the substrate. If the resist mask is formed by the ink jet 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 film 530 .

[0158] The etching of the oxide semiconductor film 530 here can be performed by dry etching or wet etching. For example, wet etching of the oxide semiconductor film 530 may be used. 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 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 facilities, and the oxide semiconductor layer was heated 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 without being exposed to the air. The recontamination of elements is prevented, and 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 heat source such as a resistance heating element. A device that heats the object to be treated by radiation may be used. For example, a GRTA (Gas Reactor Tank Apparatus) apid Thermal Anneal) equipment, LRTA (Lamp Rapid T RTA (Rapid Thermal Anneal) equipment, etc. The LRTA device can be used with halogen lamps, metal halide lamps, etc. lamp, xenon arc lamp, carbon arc lamp, high-pressure sodium lamp, high-pressure mercury lamp It is a device that heats the object to be treated by radiating light (electromagnetic waves) emitted from a lamp or other lamp. 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 material to be treated by heat treatment An active gas is used.

[0161] For example, as the first heat treatment, a base is placed 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 several minutes, and then the substrate is moved and placed in an inert gas atmosphere heated to a high temperature. You may also perform a GRTA.

[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 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 SiO 2 gas, and Introduce high-temperature N2O gas or ultra-dry air (dew point below -40°C, preferably below -60°C). 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. or 7N or more (i.e., the impurity concentration in oxygen gas or N2O gas is 1 ppm or less, preferably It is preferable to set the concentration of the oxygen gas or N2O gas to 0.1 ppm or less. The oxidation process, which is simultaneously reduced by the removal of impurities through dehydration or dehydrogenation treatment, By supplying oxygen, which is the main component material of the oxide semiconductor, the oxide semiconductor layer can be enhanced. Purify and make it 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 can also be subjected to the first heat treatment. In that case, after the first heat treatment, The substrate is removed and subjected to a photolithography process.

[0165] In addition to the above, the first heat treatment may be performed after the oxide semiconductor layer is formed. After stacking the source electrode layer and the drain electrode layer on the insulating layer, or This may be done either after forming an insulating layer on the drain electrode layer or after forming an insulating layer on the drain electrode layer.

[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 first heat treatment of film 530.

[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 whose 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; 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 the surface. Then, a second oxide semiconductor film that is thicker than the first oxide semiconductor film is formed. a second film is formed at 450°C or higher and 850°C or lower, preferably 600°C or higher and 700°C or lower. 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, resulting in an oxide semiconductor film having a thick crystalline region. A compound 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 layer and the drain electrode layer may be, for example, Al, Cr, Cu, Ta, or T. Metal film containing an element selected from I, Mo, and W, or metal nitride containing the above elements as components Films such as titanium nitride, molybdenum nitride, and tungsten nitride can be used. 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, In particular, a titanium 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, The mask is removed (see FIG. 9(C)).

[0170] The third photolithography process involves exposure to ultraviolet light or KrF laser light when forming a resist mask. The source electrodes adjacent to each other on the oxide semiconductor layer 531 may be formed by using 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 transistor to be formed later. The channel length L is determined. When performing exposure with a channel length L of less than 25 nm, Extreme ultraviolet rays have extremely short wavelengths ranging from a few nm to a few 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 addition, in order to reduce the number of photomasks and steps used in the photolithography process, The resist mask is formed by a multi-tone mask, which is an exposure mask that allows the incident light to have 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. Therefore, it can be used in multiple etching processes to process 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. However, it is desirable to optimize the etching conditions so that the conductive film alone does not It is difficult to achieve a condition in which the oxide semiconductor layer 531 is etched while the oxide semiconductor layer 532 is not etched at all. When the conductive film is etched, only a part of the oxide semiconductor layer 531 is etched, and the groove 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 (ammonia hydrogen peroxide) was used as an etchant. A mixture of water and hydrogen peroxide is used.

[0174] Next, plasma treatment is performed using gases such as N2O, N2, or Ar to remove the exposed The plasma treatment may be performed to remove adsorbed water or the like attached to the surface of the oxide semiconductor layer. In this case, the insulating layer 5, which serves as a protective insulating film in contact with a part of the oxide semiconductor layer, is formed without being exposed to the air. Form 16.

[0175] The insulating layer 516 has a thickness of at least 1 nm, and is formed by a method such as sputtering. The insulating layer 516 can be formed by appropriately 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 oxide semiconductor layer is deformed by the hydrogen. The 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 this embodiment, the temperature is set to 100° C. The silicon oxide film is formed by sputtering using a rare gas (typically In an atmosphere of oxygen, or a mixture of rare gases 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 sputtering. 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] As in the case of forming the oxide semiconductor film 530, residual moisture in the deposition chamber for the insulating layer 516 is removed. To achieve this, 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 opto-pump 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 with 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 2 For example, the temperature is increased by heating in a nitrogen atmosphere. The second heat treatment is carried out at 250°C for 1 hour under atmospheric pressure. A part of the body layer (channel forming region) is heated while being 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 and Impurities such as moisture, a hydroxyl group, or hydrides (also called hydrogen compounds) 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. Purify and make it Type I (authentic).

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

[0182] Furthermore, when a silicon oxide layer containing many defects is used as the insulating layer 516, after the silicon oxide layer is formed, 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. It is heated to a temperature of 100℃ to 400℃ and then heated with a sputter containing high-purity nitrogen from which hydrogen and moisture have been removed. 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 remaining moisture in the film forming 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 carried out by maintaining a constant heating temperature. Alternatively, the temperature may be increased from room temperature to a heating temperature of 100°C or more and 200°C or less, and then reduced from the heating temperature to room temperature. The temperature drop at this temperature may be repeated several times.

[0186] The transistor described as an example in this embodiment has a source electrode and a drain electrode in an off state. Because the current flowing through it is extremely small, when applied to pixel transistors in liquid crystal display panels, This can prevent the deterioration of image information written to pixels during the image retention period. The retention period can be extended and the frequency of writing images can be reduced. 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. This not only stops the DC-DC converter but also prevents the transistors exemplified in this embodiment from The charge stored in the capacitor does not leak through the capacitor, further reducing power consumption. It can be reduced.

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

[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 backup DC-DC converter that outputs +14V to the power generation circuit via a backup circuit, It has a DC-DC converter that outputs -14V to the power supply generation circuit via a step-up circuit. The power generation circuit supplies power to the signal generation circuit, and the power is supplied to the liquid crystal display panel via the conversion board. Supply.

[0191] The microprocessor reads the image data from the flash memory and 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, The lithium ion capacitor supplies power to the drive circuit, which is then connected to the LCD panel 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 rectifying element; The DC-DC converter is connected to the power supply circuit via a limiter circuit and two rectifier elements. A capacitor is connected between the two rectifying elements of the second circuit. The microprocessor monitors the potential of the

[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 its initial value of 4V to 3.5V is measured using the The time it took for the display device to operate was measured, and the potential of the capacitor was monitored every 2 seconds.

[0194] The lithium ion capacitor is capable of driving the liquid crystal display device for the image writing interval. The plot of the time required for image writing is shown by the solid line in Fig. 12. If the time is extended to 00 seconds, the time that 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 is strongly dependent on the interval between images written. The DC-DC converter stops 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. We investigated the operating time using the lithium ion capacitor explained in the example. Two converters are connected so that the potential is directly output to the synthesis circuit, and the output potential of the converters is I set it to +13V and -13V.

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

[0197] Compared with 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 LCD 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 LCD display panel 121 Pixel driving circuit unit 121A Gate line side drive circuit 121B Source line side drive circuit 122 pixel section 123 pixels 124 gate lines 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 Capacitor element 214 transistor 215 Liquid crystal element 505 board 506 Protective insulation layer 507 Gate insulating 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

1. A display panel and a secondary battery are included. the display panel includes a pixel section and a gate line side driving circuit; the pixel portion includes a pixel having a transistor, A signal is input to the gate of the transistor from the gate line side driving circuit, One of the source and the drain of the transistor is connected to a pixel electrode of a liquid crystal element, A pixel signal is input to the other of the source and the drain of the transistor, the transistor includes an oxide semiconductor in a channel formation region, a function of changing a power supply potential supplied to the gate line side driver circuit from a high power supply potential to a low power supply potential after stopping the supply of a plurality of clock signals to the gate line side driver circuit while maintaining the display of an image in the pixel unit; and a function of changing the power supply potential supplied to the gate line side driver circuit from a low power supply potential to a high power supply potential while maintaining the display of an image in the pixel portion, and then resuming the supply of the plurality of clock signals to the gate line side driver circuit.

2. a display panel and a lithium ion capacitor; the display panel includes a pixel section and a gate line side driving circuit; the pixel portion includes a pixel having a transistor, A signal is input to the gate of the transistor from the gate line side driving circuit, One of the source and the drain of the transistor is connected to a pixel electrode of a liquid crystal element, A pixel signal is input to the other of the source and the drain of the transistor, the transistor includes an oxide semiconductor in a channel formation region, a function of changing a power supply potential supplied to the gate line side driver circuit from a high power supply potential to a low power supply potential after stopping the supply of a plurality of clock signals to the gate line side driver circuit while maintaining the display of an image in the pixel unit; and a function of changing the power supply potential supplied to the gate line side driver circuit from a low power supply potential to a high power supply potential while maintaining the display of an image in the pixel portion, and then resuming the supply of the plurality of clock signals to the gate line side driver circuit.

3. In claim 1 or claim 2, The electronic device, wherein the oxide semiconductor is an In—O-based oxide semiconductor.

Images