JP3569846B2 - Active matrix type liquid crystal display - Google Patents

Description

[Industrial applications]
[0001]
The present invention relates to a liquid crystal display device, and more particularly to an active matrix type liquid crystal display device suitable for driving pixels arranged in a matrix.
[Prior art]
[0002]
As a conventional active matrix liquid crystal display device, a device employing a twisted nematic display system is known. This liquid crystal display device has a configuration in which two transparent electrodes are used as electrodes for driving a liquid crystal layer, and the transparent electrodes are arranged on a substrate interface so as to face each other. According to this device, the direction of the electric field applied to the liquid crystal is substantially perpendicular to the substrate interface.Direction andLiquid crystal alignmentCan control.
[0003]
As a method of setting the direction of the electric field applied to the liquid crystal to a direction substantially parallel to the substrate interface, for example, there is a method using a comb-shaped electrode pair as described in JP-A-1-120528. .
[Problems to be solved by the invention]
[0004]
However, in a conventional liquid crystal display device employing a twisted nematic display method, a transparent electrode for generating an electric field must be provided in a light propagation path in order to rotate the liquid crystal in a direction substantially perpendicular to the substrate interface. For this reason, in a conventional apparatus, a transparent electrode represented by ITO is formed.for,It is necessary to use vacuum-type manufacturing equipment such as sputtering, which requires a lot of cost for equipment.It costs.The use of vacuum manufacturing equipment reduces throughput, which significantly increases manufacturing costs.Pull up.The transparent electrode generally has irregularities of about several tens of nm on its surface, and it is difficult to process a fine active element such as a thin film transistor together with the transparent electrode. The protruding portion formed on the transparent electrode is easily separated, and if the protruding portion is mixed with another portion such as an electrode, a point-like or linear display defect occurs and the yield is significantly reduced. For this reason, it is difficult for a conventional display device to stably provide a low-cost display device that meets market needs.
[0005]
The otherIn the prior art, the liquid crystal is oriented almost perpendicular to the substrate interface.To rotate,The transmittance changes depending on the rotation angle of the liquid crystal, and the transmittance changes depending on the viewing angle. For this reason, the luminance changes significantly when the viewing angle direction is changed, and it is difficult to display halftones. In the conventional configuration, a common electrode is required, and the formation of the common electrode may lower the yield or the throughput.
[0006]
An object of the present invention is to adjust the orientation of liquid crystal without providing a transparent electrode in a light propagation path.Can controlProviding an active matrix type liquid crystal display deviceIt is.
[Means for Solving the Problems]
[0007]
The present inventionIn order to achieve the object, a liquid crystal layer is provided between a pair of substrates, and one of the substrates has a plurality of scanning wirings and signal wirings arranged in a matrix.ArrangementThe area on the substrate is divided into multiple pixel areas by each scanning wiring and each signal wiring.Divided, each scanning wiringAre connected to the scanning wiring driving means, and each signal wiring is connected to the signal wiring driving means in an active matrix type liquid crystal display device,In each pixel region, a plurality of active elements and a plurality of capacitive elements are arranged in a state where they are connected to each other in a liquid crystal in a liquid crystal composition in an equivalent circuit,One active element is connected in series with one capacitance element and connected to one signal wiring and one scanning wiring, and the other active element is connected in series to the other capacitance element and connected to the other signal wiring and one scanning wiring. Connected to the scanning wiring,Each of the pixel regions has at least an opaque first source electrode and an opaque second source electrode,The first source electrode is connected to the one active element, the second source electrode is connected to the other active element, and the signal line driving means is connected to signal lines belonging to each pixel region. Signals having different potentials are applied according to image information, and each liquid crystal molecule in the liquid crystal composition is caused by an electric field generated by a potential difference between the first source electrode and the second source electrode.ControlledActive matrix type liquid crystal displaySuggest.
[0008]
When constructing an active matrix liquid crystal display device, the following elementsCan be added.
[0009]
(1) Electrodes are respectively connected to a pair of signal lines in each pixel region, and each electrode is connected in parallel with each signal line.ArrangementParallel electrode is formed, and a comb-shaped electrode piece protruding from each parallel electrode is connected to each parallel electrode, and a part of each electrode piece is opposed to and parallel to the parallel electrode.ArrangementHave been.
[0010]
(2) Electrodes are connected to a pair of signal lines in each pixel region, respectively, and each electrode is connected in parallel with each signal line.ArrangementThe parallel electrodes are formed, and each parallel electrode is connected to an electrode piece protruding from each parallel electrode in a direction crossing each parallel electrode, and each electrode piece faces each other.ArrangementHave been.
[0011]
(3) The signal line driving means includes: a video data output means for sequentially outputting data relating to a video signal of each pixel in accordance with video information; a complement conversion means for converting output data of the video data output means into complement data of the video signal. Data selection means for selecting one of the specified data from the output data of the video data output means and the output data of the complement conversion means, and latch data obtained based on the data selected by the data selection means and the initialization data. An addition means for sequentially accumulating the data, an initialization means for alternately generating positive-polarity initialization data and negative-polarity initialization data for each predetermined period in which the number of times of generation of the scanning signal reaches a predetermined number, Latch means for adding and latching the added value of (i) and the initialization data from the initialization means and sequentially outputting this data as latch data to the addition means; A video signal output means for outputting a video signal of a voltage level according to the calculated value to each video signal wiring, and a data selection means for changing a data selection destination when an addition value of the addition means exceeds a set value. It is composed of change command means for commanding.
[0012]
(4) The initialization data generation timing of the initialization means is set to one horizontal period or a plurality of horizontal periods of the scanning signal.
[0013]
(5) The voltage level of the bias signal generated from the bias signal generating means is set to a voltage level between a voltage level for displaying an image in white and a voltage level for displaying an image in black.
[0014]
According to the above-described means, when a signal is applied to each scanning wiring and each signal wiring according to video information, each time a scanning signal is applied to each scanning wiring, a pair of signal wirings belonging to each pixel region are Signals having different potential differences are applied. When a signal having a different potential difference is applied to each signal wiring, an electric field according to the potential difference acts on the liquid crystal in each pixel region, and the liquid crystal molecules rotate parallel to the transparent substrate surface. This allows the alignment of the liquid crystal in each pixel areaCan control.Therefore, the alignment of the liquid crystal can be controlled without providing a transparent electrode in the light propagation path.
BEST MODE FOR CARRYING OUT THE INVENTION
[0015]
Next, an embodiment of an active matrix type liquid crystal display device according to the present invention will be described with reference to the drawings.FIG. 1 is a diagram for explaining the operation of liquid crystal in a liquid crystal panel used in a liquid crystal display device, and FIG.Do not apply voltageFIG. 1B is a cross-sectional view when voltage is applied, and FIG. 1C is a cross-sectional view when voltage is applied.Do not apply voltageFIG. 1D shows a surface view when a voltage is applied. In FIG. 1, the active elements are omitted, and only the configuration for one pixel is shown.
[0016]
In FIG. 1, a pair of transparent substrates 203 are bonded inside a pair of polarizing plates 206, and an alignment control film 204 is laminated inside each transparent substrate 203. A liquid crystal composition is mounted between the alignment control films 24, and a pair of electrodes 201 and 202 are mounted in one alignment control film 204 so as to face each other. Each of the electrodes 201 and 202 is connected to a signal wiring, and a signal having a different potential difference is applied to each of the electrodes 201 and 202.Applied.Rod-like liquid crystal molecules 205 are inserted in the liquid crystal composition, and each liquid crystal molecule 205 is rotatably arranged in parallel to the interface of the substrate 203 by an electric field generated from the electrodes 201 and 202. When no voltage is applied to the electrodes 201 and 202, the liquid crystal molecules 205 have a slight angle with respect to the longitudinal direction of the electrodes 201 and 202, that is, 45 ° ≦ | Angle) | <90 °To keepOriented.
[0017]
On the other hand, when a voltage is applied to the electrodes 201 and 202, an electric field 207 is formed between the electrodes 201 and 202, and the position of the liquid crystal molecules 205 is controlled along the direction of the electric field 207. At this time, when light enters the liquid crystal molecules 205, the light passes through the liquid crystal molecules 205. In this case, when the polarization transmission axis of the polarizing plate 206 is set to a predetermined angle 209, the light transmittance of the liquid crystal molecules 205 can be changed by applying the electric field 207.
[0018]
Next, when imparting contrast to the liquid crystal panel, a mode using a state in which the orientations of the liquid crystal molecules 205 on the upper and lower substrates 203 are substantially parallel (a birefringent mode using an interference color due to a birefringent phase difference), Among the modes using the state where the orientation directions of the liquid crystal molecules 205 on the 203 intersect and the molecular arrangement in the cell is twisted (the optical rotation mode using the optical rotation in which the polarization plane rotates in the liquid crystal composition layer). Either mode can be used. When the birefringence mode is used, the direction of the liquid crystal molecules is changed in the plane by applying a voltage while the direction of the molecular long axis (optical axis) is substantially parallel to the substrate interface, and the axis of the polarizing plate 206 set at a predetermined angle 209 is adjusted. The light transmittance can be changed by changing the angle formed by the light. By using the optical rotation mode, it is possible to change only the azimuth in the direction of the molecular long axis by applying a voltage, and to change the optical rotation caused by unwinding the helix.Available.
[0019]
Using the above display mode, the major axis of the liquid crystal molecules is always almost parallel to the substrate 203 and does not rise, so that the change in brightness when the viewing angle direction is changed is small, and there is no visual dependency. Visual characteristics can be greatly enhanced.
[0020]
Next, a specific configuration of the active matrix type liquid crystal display device will be described with reference to FIGS.
[0021]
In FIG. 2, the active matrix liquid crystal display device includes a liquid crystal display panel 60, a thin film transistor substrate 61, a counter substrate 62, a scanning wiring driving circuit 63, a signal wiring driving circuit 64, and a control circuit 65. In the liquid crystal display panel 60, a thin film transistor substrate 61 and a counter substrate 62 are arranged to face each other, and a nematic liquid crystal composition is mounted between these substrates. On the thin film transistor substrate 61, m + 1 signal lines and n scanning lines are arranged in a matrix, and the display area of the thin film transistor substrate 61 is divided into m × n pixel regions by each signal line and each scanning line. Have been. In each pixel region, thin film transistor elements 5a and 5b, capacitance elements 6a and 6b, and liquid crystal 9 are provided. The gate electrodes of the thin film transistors 5a and 5b are connected to one scanning line 3. The drain electrode of the thin film transistor element 5a is connected to one signal line 1, and the source electrode is connected to the liquid crystal 9 and the capacitor 6a. The other end of the capacitive element 6a is connected to the other scanning line 4. On the other hand, the thin film transistor element 5b has a drain electrode connected to the other signal line 2, and a source electrode connected to the liquid crystal 9 and the capacitor 6b. The other end of the capacitive element 6b is connected to the other scanning line 4.
[0022]
The thin film transistor elements 5a and 5b are formed on a thin film transistor substrate 61, and a gate oxide film 11 and a protective film 12 are laminated on the thin film transistor elements 5a and 5b. The scanning lines 3 and 4 are stacked above the gate insulating film 11, and the signal lines 1 and 2 and the source electrodes 7 a and 7 b are inserted into the protective film 12. A pair of alignment control films 16 are stacked on the protective film 12, and the liquid crystal layer 9 is formed in each alignment control film 16. A transparent resin layer 14 for flattening the surface is laminated on the upper alignment control film 16. Above the transparent resin layer 14, striped R, G, and B color filters 13 are provided. It is installed. A light-shielding film 15 made of an organic polymer is formed in a region of the color filter 13 except for a light propagation path. A transparent substrate is bonded on the color filter 13, and polarizing plates are provided on both sides of the transparent substrate and the thin film transistor substrate 61.Be attached.
[0023]
Each substrate is formed using a glass substrate having a thickness of 1.1 mm and a polished surface. The liquid crystal layer 9 sandwiched between the substrates has a positive dielectric anisotropy Δε of 4.5 and a value of 4.5. And a nematic liquid crystal composition having a birefringence Δn of 0.072 (589 nm, 20 ° C.). Note that, instead of using a crystal having a positive dielectric anisotropy Δε, it is also possible to use a negative crystal.
[0024]
The polyimide type alignment control film 16 applied to each substrate is subjected to a rubbing treatment, and the pretilt angle is set to 3.5 °. The rubbing directions on the upper and lower interfaces are parallel to each other, and the angle between the rubbing directions and the direction of the applied electric field is set to 85 °. The gap between the upper and lower substrates has spherical polymer beads dispersed and sandwiched between the substrates, and is 4.5 μm in a liquid crystal sealed state. Therefore, Δn · d is 0.324 μm. When the substrate thus constructed sandwiches the substrate between two polarizing plates, the polarization transmission axis of one of the polarizing plates is set to approximately 85 ° in the rubbing direction, and the polarization transmission axis of the other polarizing plate is set to the rubbing direction. As shown in FIG. 9, the liquid crystal display panel having normally closed characteristics is substantially rectangular (−5 °).Can be configured.
[0025]
Here, if m = 120 and n = 30, the number of pixels of the liquid crystal display panel 60 is 40 (× 3) × 30 = 3600. At this time, the pixel pitch per pixel is 80 μm in the horizontal direction and 240 μm in the vertical direction, as shown in FIG. FIG. 3 shows an area of one pixel surrounded by the signal wiring 1 in the g-th column, the signal wiring 2 in the (j + 1) -th column, the scanning wiring 4 in the (j-1) -th row, and the scanning wiring 3 in the j-th row. Is shown. In each pixel, as shown in FIG. 5, thin film transistor elements 5a and 5b using semiconductor active layers (amorphous silicon) 8a and 8b having an inverted stagger structure are formed.
[0026]
As the thin film transistor elements 5a and 5b, a two-terminal element such as a polysilicon thin film transistor, a silicon wafer MOS transistor, or a MIM (Metal-Intrinsic-Metal) diode can be used.
[0027]
As shown in FIG. 7, the source electrodes 7a and 7b of the thin film transistor elements 5a and 5b (they may function as drains in an actual driving state, but in the present embodiment, the electrode connected to the signal wiring is referred to as the drain electrode). The electrodes 6a and 6b are formed using the gate insulating film 11 and a part of the scanning line 4 on the previous line. The capacitive elements 6a and 6b are provided to hold the potentials of the source electrodes 7a and 7b at a constant potential and to absorb noise due to signals. The two thin film transistors 5a and 5b provided in one pixel are connected to the source electrodes 7a and 7b, respectively, and as shown in FIG. 6, the direction E of the electric field between the source electrode 7a and the source electrode 7b. Is mainly the component parallel or horizontal to the board surface.Have.It is also possible to provide a redundant configuration by providing three or more thin film transistors in one pixel and connecting the transistors in parallel. Similarly, by using three or more capacitance elements 6a and 6b, and connecting the respective capacitance elements in parallel,Can be redundantly configured.The source electrodes 7a and 7b are used as pixel electrodes, and the alignment of the liquid crystal molecules of the liquid crystal layer 9 is determined by the potential difference between the source electrodes 7a and 7b.Controlled.The distance between the source electrodes 7a and 7b is 48 μm according to the wiring rule. Light is transmitted between the source electrodes 7a and 7b, enters the liquid crystal layer 9, and is modulated. Therefore, it is not necessary to provide a translucent pixel electrode, for example, a transparent electrode such as ITO in order to control the alignment of the liquid crystal molecules. Electrode layerCan be reduced. By forming in the same layer as the video signal wiring, the process can be greatlyCan be shortened.
[0028]
Generally, the alignment accuracy of a photomask is significantly higher than the alignment accuracy between two opposing glass substrates. Therefore, these components can be arranged separately on the substrates on both sides, but it is desirable to form them on one substrate. In this embodiment, the alignment between the source electrode 7a and the source electrode 7b is performed only with a photomask.To be done,Of the electric field E applied to the liquid crystal layer 9Variation can be reduced.Each source electrode 7a, 7b isCan be formedTherefore, the distance d between the source electrodes 7a and 7bVariationLess than 5%Can be suppressed.The scanning signal lines 3 and 4 are formed of a tantalum thin film so that they can also serve as gate electrodes. The video signal lines 1 and 2 are formed of a titanium thin film at the same time as the source electrodes 7a and 7b so that they can also serve as drain electrodes.
[0029]
On the other hand, the scanning wirings 3 and 4 and the signal wirings 1 and 2 are not particularly limited in material, and chromium, aluminum, or the like can be used. Considering the corrosion of metals, metals having high corrosion resistance are desirable. Since the scanning wirings 3 and 4 are preferably made of a metal having a low electric resistance, the scanning wirings 3 and 4 may be composed of two or more metal layers.
[0030]
Epoxy resin is used as the material of the transparent resin 14. On the transparent resin 14 and the substrate 61 having the thin film transistor elements 5a and 5b, a polyimide type alignment control film 16 is applied. In this case, it is also possible to directly rub the surface of the transparent resin 14 without forming another film as the orientation control film 16 on the flattened transparent resin 14. In this case, the epoxy resin has both functions of flattening and controlling the alignment of liquid crystal molecules. This eliminates the step of applying the alignment film, making the manufacturing easier and shorter. In general, in the conventional TN type, there are various characteristics required for the alignment control film 16, and it is necessary to satisfy all of them. Therefore, it is limited to some materials such as polyimide. A particularly important characteristic is the tilt angle. However, in the display mode of the present embodiment, a large inclination angle is not required, and the selection range of the material is significantly improved. Similarly, the protective film 12 for protecting the thin film transistors 5a and 5b may be made of epoxy resin and subjected to a rubbing process. The light-shielding film 15 is formed on a glass plate using chromium in order to eliminate a decrease in contrast due to the influence of the misalignment region. This light-shielding film 15 is preferably formed of an organic polymer. That is, if the light-shielding film 15 is formed of an organic polymer, no conductive substance is present on the counter substrate 62 at all.
[0031]
In this case, in the configuration of the present embodiment, even if conductive foreign matter is mixed during the manufacturing process, there is no possibility that the electrodes are in contact with each other via the counter substrate 62 because the organic polymer is an insulator. Reduce the failure rate due to contact between electrodes to 0Can be suppressed.
[0032]
Therefore, the degree of cleanliness of the formation of the alignment film 16, rubbing, liquid crystal encapsulation and the like is increased, and the manufacturing processCan be simplified.When the light-shielding film 15 is formed of an organic polymer containing a black dye, the reflectance of the organic polymer is low.Can be prevented.The light shielding film 15 is laid out in a stripe shapeif,The printing processCan be used.As a result, the manufacturing processSimplify and reduce costs.
[0033]
Next, a driving method of the liquid crystal display panel 60 will be described with reference to FIG.
[0034]
When the liquid crystal display panel 60 is driven by a signal from the signal wiring driving circuit 64 and a scanning signal from the scanning wiring driving circuit 63, line sequential driving in which signals are sequentially written for each row of the scanning wiring of the liquid crystal display panel 60 is performed.Done.When a scanning signal is sequentially applied to the scanning wiring and a gate voltage 71 is sequentially applied as a selection pulse to the gate electrodes of the thin film transistors 5a and 5b, the thin film transistors 5a and 5b are turned on, and the respective signal wirings 1 and 2 are connected. The applied voltage is written to the capacitance elements 6a and 6b as drain voltages 72 and 73, respectively. When the writing period (1H) of this row ends, the gate voltage 71 falls to the off level, and the thin film transistors 5a and 5b are turned off. As a result, the voltage written in each of the capacitance elements 6a and 6b is held, but actually, when the gate voltage 71 falls to the off level, the voltage shift is caused by the coupling noise due to the parasitic capacitance of the thin film transistors 5a and 5b. 76 and 77 occur and are held at that voltage. Here, the voltage applied to the liquid crystal in the liquid crystal layer 9 is the voltage 78 between the source voltages 74 and 75 of the thin film transistor elements 5a and 5b. The brightness (transmittance) of the pixel is determined by the voltage 78. As described above, the brightness is determined by the difference between the signal voltages to be written, so that this driving method is hereinafter referred to as a differential driving method. Therefore, in the present embodiment, the differential drive signal sent from the image source having the differential drive signal is supplied to the signal lines 1 and 2 via the signal line drive circuit 64.
[0035]
As described above, in the present embodiment, since there is no transparent electrode for controlling the alignment of the liquid crystal, the manufacturing process is simplified and the yield is improved.Increase,Manufacturing costsCan be reduced.In particular, equipment and steps for forming a transparent electrode are not required, and the cost of manufacturing equipment can be significantly reduced and the number of steps can be reduced, thereby reducing costs. Since the common electrode is not required by adopting the differential drive method, the process of forming the common electrodeCan be reduced,It is no longer necessary to provide any electrodes on the opposing substrate. Therefore, the contact failure with the common electrode due to this becomes zero, and the yield is reduced.Is improved, and costs can be reduced.
[0036]
In the present embodiment, characteristics as shown in FIG. 9 were obtained as electro-optical characteristics indicating the relationship between the voltage applied to the liquid crystal and the brightness. From FIG. 9, the contrast ratio becomes 150 or more at the time of 7 V driving, and the difference in the curve when the visual sense is changed to left, right, up and down is extremely smaller than that of the conventional system, and the display characteristics hardly change even when the visual sense is changed. . The liquid crystal alignment was also good, and no alignment failure domain was generated.
[0037]
In the conventional driving method, when the thin film transistor element is switched from the on state to the off state, a voltage shift occurs via the parasitic capacitance of the thin film transistor element, and this voltage shift generates a DC component as a liquid crystal application voltage. However, in the present embodiment, when the thin film transistor elements 5a and 5b are switched from the on state to the off state, the DC component of the liquid crystal voltage generated by the voltage shifts 76 and 77 received through the parasitic capacitance of the thin film transistor elements 5a and 5b is different from that of each thin film transistor. Since the elements 5a and 5b cancel each other, it was confirmed that no occurrence occurred. Therefore, in the present embodiment, there is no need to correct the DC component, and the liquid crystal is converted to an AC having no DC component.Drive,FlickerCan be suppressed.Similarly, no afterimage due to the DC component was observed, and the luminance gradient was not conspicuous. When using a two-terminal element such as an MIM diode, the color position of the elementVariationThe image quality defect such as the uneven brightness due to the above is also canceled by the two two-terminal elements, so that the uneven brightness is eliminated.
[0038]
Here, the electro-optical characteristics of a liquid crystal display device using a twisted nematic (TN) type, which is a conventional method, are shown in FIG. The nematic liquid crystal composition used in this device has the same dielectric anisotropy Δε as in the above embodiment, a positive value of 4.5, a refractive index anisotropy Δn of 0.072 (589 nm, 20 nm). ° C), the gap is 7.3 µm, and the twist angle is 90 °. Therefore, Δn · d is 0.526 μm.
[0039]
It is understood from FIG. 10 that the curve changes sharply in the visual direction. In the vicinity of the step structure of the adjacent portion of the thin film transistor, an alignment defect domain in which the alignment direction of the liquid crystal molecules is different from that of the peripheral portion occurs. In the common electrode, the DC componentCan't cancel,It was confirmed that flicker, afterimage and luminance gradient occurred.
[0040]
(2nd Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS.
[0041]
In this embodiment, a single thin film transistor element 5c and a single capacitance element 6c are provided for each pixel, the gate electrode of the thin film transistor element 5c is connected to one scanning wiring 4, and the drain electrode is connected to one signal wiring 1. The source electrode is connected to the liquid crystal 9 and the capacitor 6c, the other end of the capacitor 6c is connected to the other signal line 2, and the other end of the liquid crystal 9 is connected to the other signal line 2. And the electrodes of each pixel are configured as shown in FIG. Also in the present embodiment, the alignment of the liquid crystal is controlled by the potential difference between the source electrode 7c and the signal wiring 2.Control.That is, similarly to the first embodiment, when a scanning signal is sequentially applied to each of the scanning lines 3 and 4, a potential difference between the signal lines 1 and 2 according to the video information is generated.Occurs.Note that the capacitor 6c is formed between the signal wiring 2 and the source electrode 7c. The capacitive element 6c was formed with the gate insulating film 11 interposed between the electrode 20 and the signal wiring formed at the same time when the scanning wiring was formed. As shown in FIG. 13, since the source electrode 7c and the electrode 20 have different layers, a hole is formed in the gate insulating film 11 to make contact between the source electrode 7c and the electrode 20.
[0042]
In the above configuration, when driving the thin film transistor element 5c in each pixel, when the scanning wiring 4 is scanned by the scanning signal, the thin film transistor element 5c is turned on, and the potential difference generated between the signal wirings 1 and 2 is a capacitance. The element 6c is charged, and the charged voltage is held by the capacitor 6c. Next, after the scanning wiring 3 is scanned and the thin film transistor element 5c is turned off, the potential of the signal wiring 2 fluctuates, but the potential of the source electrode 7c also fluctuates similarly by the capacitor 6c. No matter how the potential changes, the potential difference between the source electrode 7c and the signal wiring 2 is kept constant. Therefore, in this embodiment, the liquid crystal is driven by the same driving method as in the above embodiment.Can be driven.
[0043]
As described above, in the present embodiment, the liquid crystal 9 is provided by providing one thin film transistor element and one capacitor element for each pixel.Can be drivenThe planar structure of each pixel is simplified, and the yield isIs improved.Since the number of transistor elements provided in each pixel is reduced, the area of an effective portion (opening) that transmits light can be increased, and the transmittance can be improved.Can contributeWith the display panelCan be bright.
[0044]
(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIG.
[0045]
In the present embodiment, the source electrodes 7a and 7b are formed in a comb shape, and the respective electrodes are arranged so as to mesh with each other. Other configurations are the same as those of the first embodiment. Therefore, only the configuration of the electrodes will be described. That is, parallel electrodes 7c and 7d parallel to the signal lines 1 and 2 are formed on the source electrodes 7a and 7b of each pixel region, and the parallel electrodes 7c and 7d form a comb-shaped portion at the center of each pixel region. Are connected to the electrode pieces 7e and 7f protruding therefrom. The parallel electrodes 7c and 7d and the electrode pieces 7e and 7f are arranged parallel to each other and opposed to each other.
[0046]
When an electric field E is generated between the source electrodes 7a and 7b, the electric field E is expressed as E = V / d. If the distance d between the two electrodes to which the electric field E is applied is long, the electric field is effectively applied to the liquid crystal. Not the liquid crystalThresholdVoltage rises. However, when the source electrodes 7a and 7b are comb-shaped and the source electrodes 7a and 7b are provided with the parallel electrodes 7c and 7d and the electrode pieces 7e and 7f, the distance between the parallel electrodes 7c and 7d and the electrode pieces 7e and 7f is 48 μm. To 16μm and about 1/3Can be reduced.As a result, the electric field applied to the liquid crystal becomes about three times, and as a result, both the threshold voltage and the response time (the time during which the liquid crystal moves) are different from those of the first embodiment.Can be shortened.
[0047]
When a voltage at which the brightness changes by 10% of the total change amount (defined as V10) is defined as a threshold voltage, in the first embodiment, the threshold voltage is 9.5V. According to the present embodiment, the threshold voltage is 5.8V. As for the response time, the on / off switching is performed between a voltage of 0 V and a voltage (defined as V90) at which the brightness changes by 90% of the total change amount, and the response time (tON + tOFF) at that time is measured. What was 650 ms in the embodiment was reduced to 140 ms in the embodiment. Here, tON and tOFF both represent the time required to change by 90% with respect to the total amount of dynamic luminance change.
[0048]
As described above, in the present embodiment, in addition to the effects of the above-described embodiments, the threshold voltage is higher than that of the first embodiment.Can be loweredTogether with the response timeCan be shortened.In the present embodiment, not only the method using the differential driving method but also other display modes can be used.
[0049]
(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described with reference to FIG.
[0050]
In the present embodiment, the source electrodes 7a and 7b are formed in a comb shape like the above-described embodiment, and the electrodes are arranged so as to mesh with each other. The other configuration is the same as that of the first embodiment. Only the configuration will be described.
[0051]
In the present embodiment, parallel electrodes 7c and 7d parallel to the signal wirings 1 and 2 are connected to the source electrodes 7a and 7b, respectively, and are perpendicular to the parallel electrodes 7c and 7d from the parallel electrodes 7c and 7d, respectively. The electrode pieces 7e, 7f, 7g extending in the directions are connected. The electrode pieces 7e, 7f, 7g are arranged to face each other, an electric field E is applied between the electrode piece 7e and the electrode piece 7f, and an electric field E is applied between the electrode piece 7f and the electrode piece 7g.Applied.
[0052]
As described above, in the present embodiment, the direction of the electric field applied to the liquid crystal is shifted by 90 ° from that of the above-described embodiment, so that the electric field between the signal lines 1 and 2 fluctuates due to the voltage fluctuation of the signal lines 1 and 2. Even if the liquid crystal isCan be controlled stablyAt the same time, the crosstalk with the signal lines 1 and 2Can be resolved.
[0053]
(Fifth embodiment)
Next, a fifth embodiment of the present invention will be described with reference to FIGS.
[0054]
In this embodiment, a plurality of thin film transistors 5a, 5b and capacitors 6a, 6b are provided for each pixel, the gate electrode of the thin film transistor 5a is connected to one scanning wiring 4, and the drain electrode is connected to one signal wiring 1. The source electrode is connected to the capacitor 6a and the liquid crystal 9, the other end of the capacitor 6a is connected to the other scanning line 3, the gate electrode of the thin film transistor 5b is connected to the other scanning line 3, and the drain electrode is connected. It is connected to the other signal line 2, the source electrode is connected to the liquid crystal 9 and the capacitor 6b, and the other end of the capacitor 6b is connected to one scanning line 4.
[0055]
In this embodiment, since the gate electrodes of the thin film transistors 5a and 5b are connected to different scanning lines 3 and 4, the difference signal of the even lines of the signal lines is delayed by one horizontal period from the difference signal of the odd lines. A delay circuit is provided on the output side of the signal line driving circuit 64. That is, in the pixel configuration of the present embodiment, the row for supplying the signal for differential drive is shifted by one row. Conversely, it is also possible to delay the odd-numbered difference driving signals from the even-numbered difference signals.
[0056]
Next, a driving method having the above configuration will be described.
[0057]
In driving each of the thin film transistors 5a and 5b, a method is adopted in which a scanning signal is applied to one scanning wiring and a bias voltage is applied to the other scanning wiring. That is, when the selection pulse 151 is applied to the gate electrode of the thin film transistor element 5a in order to drive the thin film transistor element 5a, the bias voltage Vb is applied to the ground level of the capacitive element 6a to which the source electrode 7a of the thin film transistor element 5a is connected. (+) 160 is applied. For this reason, when the thin film transistor element 5a is turned on, the voltage Vc1 written to the capacitor element 6a is, assuming that the potential of the signal wiring 1 at that time is Vd1,
Vc1 = Vd1-Vb (+)
It becomes.
[0058]
On the other hand, the voltage Vc2 written to the capacitor 6b is written when the selection pulse 152 is applied to the scanning wiring 3, and the bias voltage Vb2 is applied to the ground level of the capacitor 6b to which the source electrode 7b of the thin film transistor 5b is connected. (−) 161 is applied. Therefore, assuming that the potential of the signal wiring 2 at this time is Vd2,
Vc2 = Vd2 + Vb (−)
It becomes.
[0059]
Therefore, the voltage Vlc159 applied to the liquid crystal is
Vlc = | Vc1-Vc2 | = | Vd1-Vb (+)-(Vd2 + Vb (-)) |
And Vb (+) = − Vb (−) = Vb,
Vlc = | Vd1-Vd2-2Vb | = | Vd2-Vd1 + 2Vb |
Here, Vd2−Vd1 is positive.
[0060]
Therefore, if Vb is set to 1 V and the voltage Vlc = Vw = 7 V for displaying white, Vd2−Vd1 is 5 V at the maximum, and therefore, as described in the first embodiment, the maximum amplitude of the signal line driving circuit 64 is set. Becomes 2 × 5V of 10V, which can be reduced from 14V amplitude to 10V amplitude. As a result, the power consumption of the signal line driving circuit 64 is reduced to about half.Can be reduced.
[0061]
As described above, in the present embodiment, in addition to the effects of the first embodiment, the voltage of the signal line driving circuit 64 can be reduced, and the power consumption can be reduced.Can be reduced.
[0062]
In the embodiment, the bias voltage Vb is
Vb = (Vw +Vblk) / 2
ToCan be set.Here, Vw indicates a voltage for displaying white, and Vblk indicates a voltage for displaying black.
[0063]
Assuming that Vw = 7V, Vblk = 3V, and Vb = 5V, the maximum amplitude of the signal line drive circuit 64 is 2 × 2V, that is, 4V, and an LSI (5V withstand voltage LSI) by a normal process of forming the signal line drive circuit 64 ToCan be used.Therefore, when the signal line drive circuit 64 is configured by an LSI, it is possible to significantly reduce the cost.
[0064]
Next, a specific configuration of a conversion circuit that converts a video signal into a differential drive signal will be described with reference to FIGS.
[0065]
The video signal conversion circuit 100 according to the present embodiment includes a latch 101, a complement converter 102, a selector 103, an adder 104, a comparator 105, a latch 106, a buffer 107, and an initialization circuit 110. The dot clock 108 is input to 106 and the adder 104, and the data related to the video signal is input to the latch 101. The latch 101 sequentially inputs video signal data according to the dot clock 108, latches the input data, and sequentially transfers the latched data to the selector 103 and the complement converter 102.Transfer toThe complement converter 102 converts the data transferred from the latch 101 into complement data, and converts the converted data to a selector 103.Transfer toThe selector 103 selects one of the data from the latch 101 or the complement converter 102 in accordance with a command from the comparator 105 and adds the selected data to the adder 104.Transfer toThe adder 104 sequentially accumulates the data from the selector 103 and the data from the latch 106 according to the dot clock 108, and transfers the added data to the comparator 105, the latch 106, and the buffer 107. The adder 104 adds the display data before being latched by the latch 106 to the data from the latch 101 or, when the complement converter 102 is selected, the display data from the latch 106 and the data from the selector 103. Is subtracted, and the calculated value is passed through the buffer 107.Output.The signal output from the buffer 107 is applied to the signal wiring. Since the difference signal output from the buffer 107 only needs to have the absolute value of the voltage difference between adjacent signal wirings, it is also possible to create a difference drive signal by subtraction.
[0066]
Here, only addition or subtraction is performed by the adder 104.ButWhen repeated, the absolute value of the signal generated by the addition or subtraction becomes a very large value. Therefore, when the output of the adder 104 exceeds the reference value 109 or falls below the reference value, the comparator 105 Is inverted, and the selector 103 selects the addition or the subtraction.Command.FIG. 20 shows the relationship between the output data and the output of the comparator 105 at this time.
[0067]
As described above, in the present embodiment, when the data from the latch 101 is selected by the selector 103 and the added value of the selected data exceeds the reference value 109, the complement value by the complement converter 102 Is selected by the selector 103. When the data output from the complement converter 102 is selected by the selector 103, the data is subtracted by the adder 104, and the added value of the adder 104 is inverted. On the other hand, when the added value of the adder 104 falls below the negative reference value 109, the data from the latch 101 is selected by the selector 103 according to a command from the comparator 105. Therefore, the amplitude of the voltage output from the signal line driving circuit 64 is (the voltage Vw required for displaying white) × 2 at the maximum.GoodWill be.
[0068]
In principle, the liquid crystal needs to be driven by AC, and in the present embodiment, the polarity of the differential drive signal is inverted every vertical period (one frame) using the vertical synchronization signal Vsync. For this reason, in the present embodiment, each time the vertical synchronization signal Vsync is input to the initialization circuit 110, the initialization circuit 110 alternately outputs the initialization data of the positive polarity and the initialization data of the negative polarity so that the latch 106 Is to clear the data. When the positive polarity initialization data and the negative polarity initialization data are set in the latch 106 for each frame, the polarity of the differential drive signal can be inverted for each frame. This is equivalent to alternately adding positive polarity initialization data or negative polarity initialization data to the head of the video signal data every vertical period. Although two data of the positive polarity and the data of the negative polarity are used as the initialization data, it is also possible to use three or more data as the initialization data.
[0069]
As described above, according to the present embodiment, the liquid crystal is applied with the voltage of the inverted polarity every vertical period, so that the liquid crystal is subjected to AC.Can be driven.
[0070]
In this embodiment, the voltage is applied to the liquid crystal.When no voltage is appliedA mode in which black is displayed and white is displayed when a voltage is applied, that is, a normally closed mode is used.
[0071]
In the above embodiment,AccumulationAlthough the adder 104 and the latch 106 are used as the arithmetic unit for adding,AccumulationOther arithmetic units can be used as long as they perform the addition.
[0072]
By having the conversion circuit 100 in the present embodiment inside a liquid crystal display device, it can be used as an image source, for example, a personal computer, a workstation, or the like.Can respond.
[0073]
In the above embodiment, the polarity of the differential drive signal can be inverted every horizontal period (1H) using a vertical synchronization signal. That is, the latch 106 is cleared every horizontal period using the positive polarity initialization data and the negative polarity initialization data, and the positive polarity initialization data or the negative polarity initialization data are alternately latched in the latch 106. Let it. Based on such latched data, data isAccumulationWhen added, the video signal data is converted into the differential drive signal 111. It is also possible to use the vertical synchronization signal to polarize the inversion of the differential drive signal for each of a plurality of horizontal periods.
[0074]
As described above, when the polarity of the differential drive signal is inverted every one horizontal period or a plurality of horizontal periods using the vertical synchronizing signal, the polarities of the flicker generated for each line are canceled each other, and the flicker is generated.Can be reducedIn addition, the phenomenon of vertical stripes when displaying wind patterns etc., so-called vertical smear,Can be reduced.
【The invention's effect】
[0075]
According to the present invention,The orientation of the liquid crystal can be adjusted without providing a transparent electrode in the light propagation path in the pixel area.Since control can be performed, the yield can be increased and the number of manufacturing steps can be reduced.Visual characteristicsHas been improved,Multi-tone display becomes easy. Image defects such as brightness gradient, afterimage, flickerAnd reduce the voltagepower consumptionCan be reduced.
[Brief description of the drawings]
[0076]
FIG. 1 is a diagram illustrating an operation of a liquid crystal in a liquid crystal display panel of a liquid crystal display device according to the present invention.
FIG. 2 is an overall configuration diagram of a liquid crystal display device.
FIG. 3 is a diagram illustrating a configuration of one pixel region of the liquid crystal display panel according to the first embodiment of the present invention.
FIG. 4 is a diagram illustrating an equivalent circuit of a pixel according to the first embodiment of the present invention.
FIG. 5 is a sectional view taken along line A in FIG. 3;
FIG. 6 is a sectional view taken along line B in FIG. 3;
FIG. 7 is a sectional view taken along line C in FIG. 3;
FIG. 8 is a diagram showing a voltage waveform applied to each electrode of the first embodiment.
FIG. 9 is a diagram showing electro-optical characteristics of the first embodiment.
FIG. 10 is a diagram showing electro-optical characteristics of a conventional liquid crystal display device.
FIG. 11 is a front view illustrating a configuration of a pixel region according to a second embodiment of the present invention.
FIG. 12 is a diagram illustrating an equivalent circuit of a pixel according to a second embodiment of the present invention.
FIG. 13 is a sectional view taken along line D in FIG. 10;
FIG. 14 is a diagram illustrating a pixel configuration according to a third embodiment of the present invention.
FIG. 15 is a diagram illustrating a pixel configuration according to a fourth embodiment of the present invention.
FIG. 16 is a diagram illustrating a pixel configuration according to a fifth embodiment of the present invention.
FIG. 17 is a diagram illustrating an equivalent circuit of a pixel according to a fifth embodiment.
FIG. 18 is a diagram showing a voltage waveform applied to each electrode of the fifth embodiment.
FIG. 19 is a configuration diagram of a conversion circuit that converts a video signal into a difference signal.
20 is a waveform chart for explaining the operation of the conversion circuit shown in FIG.
[Explanation of symbols]
[0077]
1,2 signal wiring
3,4 scanning wiring
5a, 5b thin film transistor element
6a, 6b capacitive element
7a, 7b Source electrode
9 Liquid crystal layer
11 Gate insulating film
12 Protective film
13 Color filter
15 Light shielding film
16 Alignment film

Claims (1)

A liquid crystal layer is interposed between a pair of substrates. A plurality of scanning lines and signal lines are arranged in a matrix on one substrate, and a region on the substrate is divided into a plurality of pixel regions by each scanning line and each signal line. In the active matrix type liquid crystal display device , each scanning line is connected to the scanning line driving unit, and each signal line is connected to the signal line driving unit.
In each pixel region, a plurality of active elements and a plurality of capacitive elements are arranged in a state where they are connected to each other in a liquid crystal in a liquid crystal composition in an equivalent circuit,
One active element is connected in series with one capacitance element and connected to one signal wiring and one scanning wiring,
The other active element is connected in series with the other capacitive element and connected to the other signal wiring and one scanning wiring,
Each of the pixel regions has at least an opaque first source electrode and an opaque second source electrode,
The first source electrode is connected to the one active element, the second source electrode is connected to the other active element,
The signal line driving means applies signals having different potentials to signal lines belonging to each pixel region in accordance with video information, and each liquid crystal molecule in the liquid crystal composition has the first source electrode and the second source electrode. An active matrix liquid crystal display device which is controlled by an electric field generated by a potential difference between source electrodes.

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