JP7730741B2 - Liquid crystal device and method for driving liquid crystal device - Google Patents

Description

This disclosure relates to a liquid crystal device and a method for driving a liquid crystal device.

Static drive is known as one method of driving liquid crystal devices. In static drive, individual wiring is provided for each segment electrode, and a drive voltage is applied to each segment electrode individually from a driver. This prevents crosstalk, as occurs when duty drive (time-division drive) is used. This makes it possible to apply a higher drive voltage to each segment electrode, improving response speed and transmittance. On the other hand, static drive has the disadvantage of requiring a large number of wires. However, in recent years, improvements in packaging technologies such as COG (chip-on-glass) technology and the adoption of multi-layer wiring have made the increased number of wires less of a problem. A prior example of a liquid crystal device using static drive is described, for example, in JP 2021-9200 A (Patent Document 1).

When a higher drive voltage is applied to a liquid crystal device using static drive, temporary differences in transmittance may occur depending on the position of each segment electrode when the drive voltage is applied. Such differences in transmittance become more pronounced the greater the difference in wiring length from the driver to each segment electrode.

Japanese Patent Application Laid-Open No. 2021-9200

One of the objectives of a specific aspect of the present disclosure is to suppress temporary differences in transmittance when a voltage is applied to a liquid crystal device that uses static driving.

[1] A liquid crystal device according to one aspect of the present disclosure,
A pair of electrodes arranged opposite to each other;
a liquid crystal layer disposed between the pair of electrodes;
a driver that applies a drive voltage to the liquid crystal layer via the pair of electrodes;
Including,
the driver, when applying a driving voltage of a predetermined value higher than at least a threshold value of the liquid crystal layer to the pair of electrodes, provides a period in which the driving voltage is gradually increased over time,
the driver provides a period in which the drive voltage is gradually increased over time from 0 volts to a first value that is 10% or more of the predetermined value, and then immediately increases the drive voltage to the predetermined value;
It is a liquid crystal device.
[2] A method for driving a liquid crystal device according to one aspect of the present disclosure includes:
A method for driving a liquid crystal device having a liquid crystal layer disposed between a pair of electrodes, comprising:
a period in which the driving voltage is gradually increased over time when a driving voltage having a predetermined value higher than at least a threshold value of the liquid crystal layer is applied to the pair of electrodes by a static driving method ;
A method for driving a liquid crystal device.

The above configuration makes it possible to suppress temporary differences in transmittance when voltage is applied in a liquid crystal device that uses static driving.

Fig. 1A is a schematic diagram showing the configuration of a liquid crystal device, and Fig. 1B is a schematic plan view showing the configuration of the liquid crystal device. FIG. 2 is a waveform diagram for explaining the drive signal supplied by the driver. 3A to 3E are diagrams showing examples of waveforms when the effective voltage is gradually increased. 4A to 4E are diagrams for explaining how the voltage changes when the effective voltage is gradually increased over time. FIG. 5 is a diagram for explaining the method of applying the effective voltage (grayscale pattern) considered in this embodiment. FIG. 6A is a diagram showing the rise characteristics (change in transmittance over time) when a driving voltage is applied according to the gradation pattern 1 shown in FIG. 5, and FIG. 6B is an enlarged view of a portion of FIG. 6A. 7A is a diagram showing the rise characteristics (change in transmittance over time) when a drive voltage is applied according to the gradation pattern 2 shown in FIG. 5, and FIG. 7B is an enlarged view of a portion of FIG. 7A. 8A is a diagram showing the rise characteristics (change in transmittance over time) when a drive voltage is applied according to the gradation pattern 3 shown in FIG. 5, and FIG. 8B is an enlarged view of a portion of FIG. 8A. 9A is a diagram showing the rise characteristics (change in transmittance over time) when a drive voltage is applied according to the gradation pattern 4 shown in FIG. 5, and FIG. 9B is an enlarged view of a portion of FIG. 9A. 10A is a diagram showing the rise characteristics (change in transmittance over time) when a driving voltage is applied according to the gradation pattern 5 shown in FIG. 5, and FIG. 10B is an enlarged view of a portion of FIG. 10A. 11A is a diagram showing the rise characteristics (change in transmittance over time) when a driving voltage is applied according to the gradation pattern 6 shown in FIG. 5, and FIG. 11B is an enlarged view of a portion of FIG. 11A. 12A is a diagram showing the rise characteristics (change in transmittance over time) when a driving voltage is applied according to the gradation pattern 7 shown in FIG. 5, and FIG. 12B is an enlarged view of a portion of FIG. 12A. FIG. 13A is a diagram showing the rise characteristics (change in transmittance over time) when a driving voltage is applied according to the gradation pattern 8 shown in FIG. 5, and FIG. 13B is an enlarged view of a portion of FIG. 13A. 14A is a diagram showing the rise characteristics (change in transmittance over time) when a driving voltage is applied according to the gradation pattern 9 shown in FIG. 5, and FIG. 14B is an enlarged view of a portion of FIG. 14A. 15A is a diagram showing the rise characteristics (change in transmittance over time) when a driving voltage is applied using the gradation pattern 10 shown in FIG. 5, and FIG. 15B is an enlarged view of a portion of FIG. 15A. FIG. 16 is a diagram showing the rise characteristics (change in transmittance over time) when a drive voltage is applied in the liquid crystal device used for the verification.

The inventors of this application conducted theoretical and experimental investigations into the causes of temporary differences in transmittance when voltage is applied to statically driven liquid crystal devices. As a result, they discovered that differences in the wiring length from the driver that supplies the drive voltage to the pixel (pixel electrode) cause differences in the transient response characteristics immediately after the drive voltage is applied, which in turn causes temporary differences in transmittance. This is explained in detail below.

Figure 16 shows the rise characteristics (change in transmittance over time) of the liquid crystal device used in the verification when a drive voltage is applied. For verification purposes, the sheet resistance of the transparent conductive film used for the wiring was set relatively high at 30 Ω/sq. to more significantly enhance the difference due to wiring length. The rise characteristics were measured in both Region A, close to the driver 22, and Region B, far from the driver 22, as shown in Figure 1B (described later). The basic configuration of the liquid crystal device was the same as that of the embodiment described later, and it had a liquid crystal layer with approximately vertical alignment. As shown in the figure, the change in transmittance was greater in Region A, close to the driver 22, than in Region B. Specifically, the transmittance in Region A rose significantly to over 20% at the very beginning (up to 20 ms), then dropped to just under 15%, and then rose again while maintaining a lower transmittance than Region B. On the other hand, the transmittance in Region B rose to just under 15% at the very beginning, then dropped to just under 10%, and then rose again while maintaining a higher transmittance than Region A. After approximately 800 ms has passed since the application of the driving voltage, there is almost no difference in the transmittance between regions A and B.

This difference in transmittance change is presumably due to differences in the alignment changes in the liquid crystal layer immediately after voltage application. Specifically, in Region B, the resistance is large and the time constant is high, mainly due to differences in wiring length, so it takes slightly longer for the drive voltage to rise to a constant value compared to Region A. As a result, the drive voltage rises in a relatively short time in Region A compared to Region B, resulting in a more rapid change in the alignment of the liquid crystal molecules. For example, if the liquid crystal layer is vertically aligned, as the liquid crystal molecules tilt toward the substrate surface, they tilt more than their steady state. They then bounce back vertically to correct this, and then tilt again toward their steady state. In other words, the liquid crystal molecules vibrate more strongly. The difference in the degree of vibration of the liquid crystal molecules between Regions A and B is presumably responsible for the temporary difference in transmittance during the rise characteristics.

Recently, in liquid crystal devices used in automotive applications, for example, there has been a trend to set the Ni point (isotropic-nematic phase transition point) of the liquid crystal material higher to expand the operating temperature range, which results in higher threshold voltages and saturation voltages. Furthermore, when a chiral agent is added to the liquid crystal material to suppress color change at high transmittance, the saturation voltage tends to become higher, and therefore the drive voltage also tends to become higher. This makes the above-mentioned inconveniences more pronounced.

Based on the above results, the inventors of the present application came up with the idea that by gradually (for example, in stages) increasing the drive voltage rather than immediately increasing it significantly, it is possible to suppress differences in drive voltage (differences in the rate of increase) during the transitional period, and thereby suppress temporary differences in transmittance due to vibration of liquid crystal molecules. Below, we will explain in detail an embodiment of a liquid crystal device based on this idea.

Figure 1(A) is a schematic diagram showing the configuration of a liquid crystal device. Figure 1(B) is a schematic plan view showing the configuration of a liquid crystal device. The liquid crystal device of this embodiment is composed of a first substrate 11, a second substrate 12, pixel electrodes (individual electrodes) 13, a common electrode (opposing electrode) 14, alignment films 15 and 16, a liquid crystal layer 17, polarizers 19 and 20, a controller 21, and a driver 22. In this liquid crystal device, a pixel is formed in each region (partial region) where each pixel electrode 13 and common electrode 14 face each other with the liquid crystal layer 19 in between.

The first substrate 11 and the second substrate 12 are each, for example, rectangular substrates in a plan view, and are arranged with their respective sides (hereinafter referred to as "first sides") closest to the liquid crystal layer 19 facing each other. Each substrate may be a light-transmitting substrate such as a glass substrate or a plastic substrate. Spherical spacers (not shown) made of, for example, a resin film are dispersed between the first substrate 11 and the second substrate 12, and these spherical spacers maintain the gap between the substrates at the desired size (for example, approximately several μm). Instead of spherical spacers, pillars made of resin or the like may be provided on the first substrate 11 side or the second substrate 12 side and used as spacers.

Each pixel electrode 13 is provided on one side of the first substrate 11. Each pixel electrode 13 is formed by appropriately patterning a transparent conductive film such as indium tin oxide (ITO).

The common electrode 14 is provided on one side of the second substrate 12. This common electrode 14 is provided integrally with each pixel electrode 13 so as to face the pixel electrodes 13. The common electrode 14 is formed by appropriately patterning a transparent conductive film made of, for example, indium tin oxide (ITO).

The alignment film 15 is provided on one side of the first substrate 11, covering each pixel electrode 13. The alignment film 16 is provided on one side of the second substrate 12, covering the common electrode 14. Each alignment film 15, 16 determines the alignment state of the liquid crystal layer 17 in its initial state (when no voltage is applied). Each alignment film 15, 16 has been subjected to a uniaxial alignment process, such as rubbing, and has a uniaxial alignment force that determines the alignment of the liquid crystal molecules in the liquid crystal layer 17 along that direction. The direction in which the uniaxial alignment force is exerted is called the easy axis of alignment. The alignment process on each alignment film 15, 16 is set, for example, to alternate (anti-parallel). Horizontal alignment films or vertical alignment films are used as the alignment films 15, 16, depending on the operating mode of the liquid crystal layer 17. For example, in this embodiment, vertical alignment films are used as the alignment films 15 and 16, which regulate the pretilt angle of the liquid crystal molecules near the interface between each film and the liquid crystal layer 17 to a vertical direction close to 90° (for example, 80° to 89.9°).

The liquid crystal layer 17 is provided between the first substrate 11 and the second substrate 12. The liquid crystal layer 17 is made of, for example, a nematic liquid crystal material with fluidity. In this embodiment, the liquid crystal layer 17 is made of a liquid crystal material with negative dielectric anisotropy to which a chiral agent has been added. The thickness of the liquid crystal layer 17 can be, for example, several μm. Note that, depending on the operating mode of the liquid crystal layer 17, a liquid crystal material with positive dielectric anisotropy may also be used. As an example, in this embodiment, the dielectric anisotropy Δε is -3.4, the refractive index anisotropy Δn is 0.102, the viscosity (viscosity) is 54.1 mPa·s, and the thickness of the liquid crystal layer 17 is 4 μm.

Polarizing plate 19 is disposed on the other side of first substrate 11 (the side not facing liquid crystal layer 17). Similarly, polarizing plate 20 is disposed on the other side of second substrate 12 (the side not facing liquid crystal layer 17). These polarizing plates 19, 20 are disposed, for example, so that their absorption axes are substantially perpendicular to each other. In this embodiment, polarizing plates 19, 20 are disposed so that a normally black mode is achieved, in which the transmittance of transmitted light is extremely low when no voltage is applied to liquid crystal layer 17.

The controller 21 is connected to the driver 22 and generates control signals including image data corresponding to the image to be displayed and supplies them to the driver 22.

The driver 22 is connected to the controller 21 and each pixel electrode 13 and common electrode 14, and supplies voltage to each pixel electrode 13 and common electrode 14 based on a control signal from the controller 21. The voltage generated between each pixel electrode 13 and common electrode 14 and applied to the liquid crystal layer 17 corresponds to the drive voltage.

As shown in FIG. 1(B), the driver 22 is disposed, for example, on one side of the first substrate 11, and is connected to the wiring connected to each pixel electrode 13 and common electrode 14 using COG technology. Control signals are supplied from the controller 21 to the driver 22 using, for example, a flexible wiring substrate 23 as shown. Furthermore, each pixel corresponding to each pixel electrode 13 is provided in the effective display area 24. For example, the wiring lengths from the driver 22 to the pixel electrodes 13 in areas A and B shown in the figure are different, which can cause the temporary transmittance difference described above.

Figure 2 is a waveform diagram explaining the drive signals supplied by the driver. Starting from the top, the waveform labeled COM indicates the voltage applied to the common electrode 14, and the waveforms labeled SEG0 to SEG4 each indicate an example of the voltage applied to the pixel electrodes 13.

The voltage COM applied to the common electrode 14 alternates between the reference potential VSS and a relatively higher potential VR every half period within one period T. Similarly, the voltages SEG0 to SEG4 applied to each pixel electrode 13 alternate between the potential VR and the reference potential VSS.

Here, using the period of the voltage COM of the common electrode 14 as a reference, voltage SEG0 is out of phase with voltage COM by 1/2 period, voltage SEG1 is out of phase with voltage COM by 1/8 period, voltage SEG2 is out of phase with voltage COM by 1/4 period, voltage SEG3 is out of phase with voltage COM by 3/8 period, and voltage SEG4 is in phase with voltage COM. In practice, the period of voltage SEG can be shifted in even more stages (for example, 512 stages).

The waveform labeled St-A shows the drive voltage generated between the pixel electrode 13 and common electrode 14 when voltage SEG0 is applied. As shown in the figure, potentials of +VR and -VR alternate every half period within period T, and a drive voltage is applied to the liquid crystal layer 17 for the entire period T.

The waveform labeled St-B shows the drive voltage generated between the pixel electrode 13 and common electrode 14 when voltage SEG1 is applied. As shown in the figure, potentials of +VR and -VR alternate every half period within the period T, and the drive voltage is applied to the liquid crystal layer 17 for 3/4 of the period T.

The waveform labeled St-C shows the drive voltage generated between the pixel electrode 13 and common electrode 14 when voltage SEG2 is applied. As shown in the figure, potentials of +VR and -VR alternate every half period within the period T, and the drive voltage is applied to the liquid crystal layer 17 for half of the period T.

The waveform labeled St-D shows the drive voltage generated between the pixel electrode 13 and common electrode 14 when voltage SEG3 is applied. As shown in the figure, potentials of +VR and -VR alternate every half period within the period T, and the drive voltage is applied to the liquid crystal layer 17 for 1/4 of the period T.

The waveform labeled St-E shows the drive voltage generated between the pixel electrode 13 and common electrode 14 when voltage SEG4 is applied. As shown in the figure, potential VSS is always present during period T, and no voltage is applied to the liquid crystal layer 17 for the entire period T.

In this way, by setting the length of the period (pulse width) during which voltage is applied to the pixel electrodes 13 in multiple stages within the cycle T, it is possible to variably set the effective value (hereinafter referred to as "effective voltage") of the drive voltage applied to the liquid crystal layer 17 between the pixel electrodes 13 and the common electrode 14, thereby achieving gradation control. In other words, gradation control can be achieved through pulse width modulation. Based on this principle, in this embodiment, the driver 22 controls the magnitude of the effective voltage applied to the liquid crystal layer 17 between each pixel electrode 13 and the common electrode 14. Furthermore, by gradually increasing this pulse width over time, it is possible to gradually increase the effective voltage over time.

Figures 3(A) to 3(E) are diagrams showing examples of waveforms when the effective voltage is gradually increased. Figure 3(A) shows a waveform when the pulse width is very short and therefore the effective voltage is small. As time passes, the pulse width is gradually increased as shown in Figures 3(B), 3(C), and 3(D), respectively, thereby gradually increasing the effective voltage. Figure 3(E) shows a waveform when the pulse width is at its maximum and therefore the effective voltage is at its maximum. In this way, the effective voltage can be gradually increased over time using the pulse width.

Figures 4(A) through 4(E) are diagrams illustrating voltage changes as the effective voltage gradually increases over time. Four representative examples are shown here. Specifically, the example shown in Figure 4(A) shows an effective voltage controlled to immediately reach its maximum value at a certain time t0. Note that, as used herein, "maximum value" refers to the maximum value within the rated range that can be set as a driving voltage (the same applies below). This "maximum value" is an example of a predetermined value higher than the threshold value of the liquid crystal layer 17, and refers to the maximum value within the rated range that can be set as a driving voltage. The waveforms shown in Figures 4(A) through 4(E) all show the waveforms of the effective voltage when the device is ultimately driven at a constant predetermined value higher than the threshold value of the liquid crystal layer 17. Of these, the waveform shown in Figure 4(A) shows the case where the effective voltage immediately reaches the predetermined value from time t0. The waveforms shown in Figures 4(B) through 4(E) show the waveforms of the effective voltage when the effective voltage gradually reaches the predetermined value over a certain period of time from time t0. Furthermore, the waveforms shown in Figures 4(B) to 4(E) each include a period during which the effective voltage does not exceed the predetermined value from time t0 until it reaches the predetermined value, but gradually rises toward the predetermined value within a range smaller than the predetermined value.

The example shown in Figure 4(B) shows an example in which the effective voltage, which was 0 volts, gradually increases from time t0 before reaching its maximum value. As shown by the dotted line, the time it takes for the effective voltage to reach its maximum value can be increased or decreased as desired. Note that, although the effective voltage actually increases in a step-like manner when viewed microscopically, for ease of understanding, the effective voltage is shown here as increasing linearly (the same applies to Figures 4(C) to 4(E)).

The example shown in Figure 4(C) shows an example in which the effective voltage, which was 0 volts, immediately increases at time t0 to a predetermined value less than the maximum value (approximately half the maximum value in the illustrated example), and then gradually increases over time to reach the maximum value, similar to Figure 4(B) described above. As shown by the dotted line, the time required for the effective voltage to reach the maximum value can be increased or decreased as desired.

The example shown in Figure 4(D) shows an example in which the effective voltage, which is 0 volts, gradually increases from time t0 to a predetermined value, and then immediately reaches its maximum value at a certain time. As shown by the dotted line, the time required for the effective voltage to reach the predetermined value can be increased or decreased as desired.

The example shown in Figure 4(E) shows the effective voltage, which, like Figure 4(B) above, gradually increases over time from time t0 and is then controlled to a predetermined value smaller than the maximum value (approximately 1/3 of the maximum value in the example shown). As shown by the dotted line, the time required for the effective voltage to reach the predetermined value can be increased or decreased as desired.

In this embodiment, an effective voltage controlled to have one of the waveforms shown in Figures 4(A) to 4(E) is applied as a drive voltage to the liquid crystal layer 17 between the pixel electrode 13 and the common electrode 14.

Figure 5 is a diagram illustrating the method of applying the effective voltage (gradation pattern) considered in this embodiment. This diagram shows the pulse width for each gradation pattern over time after the application of the effective voltage begins. As described above, the drive voltage is controlled by the pulse width, so the magnitude of the pulse width indirectly indicates the magnitude of the drive voltage. Note that each value shown in Figure 5 indicates the magnitude of the effective voltage applied over time from the start of application of the effective voltage, and represents the magnitude of the effective voltage expressed as a ratio (% value) of the above-mentioned predetermined value (the above-mentioned maximum value, as an example) to this.

Figure 6(A) shows the rise characteristics (change in transmittance over time) when a drive voltage is applied using gradation pattern 1 shown in Figure 5, and Figure 6(B) is a partially enlarged view of Figure 6(A). Each figure was obtained by measuring the transmittance of pixels in regions A and B shown in Figure 1(B) above. Gradation pattern 1 is a comparative example in which the pulse width is immediately set to 100% from time t0, the start of application, thereby immediately increasing the effective voltage to its maximum value (see Figure 4(A)).

As shown in Figure 6 (A), there is almost no difference in transmittance between the pixels in regions A and B overall, but as shown in Figure 6 (B), during the transitional period immediately after voltage application, when the transmittance reaches its highest point of around 30%, there is a difference of just over 1% in the transmittance between the pixels in regions A and B. This difference in transmittance is difficult to detect with the human eye when the pixel width or length is small, but it can be perceived as uneven transmittance when, for example, one side of a pixel is 5 mm or longer. It can also be seen that oscillations and overshoots in transmittance occur immediately after voltage application.

Figure 7(A) shows the rise characteristics (change in transmittance over time) when a drive voltage is applied using gradation pattern 2 shown in Figure 5, and Figure 7(B) is a partially enlarged view of Figure 7(A). Each figure was obtained by measuring the transmittance at pixels in regions A and B shown in Figure 1(B) above. Gradation pattern 2 gradually increases the pulse width over time from time t0, the application start time, so that the effective voltage gradually increases and then reaches its maximum value (see Figure 4(B)). This pattern takes a relatively long time for the effective voltage to reach its maximum value. More specifically, gradation pattern 2 gradually increases the effective voltage over a time approximately twice as long (1.7 seconds in this example) as the time required for the transmittance oscillation to converge when gradation pattern 1 is used. Note that the "time required for transmittance oscillations to converge when gradation pattern 1 is used" here refers to the time required for the transmittance oscillations that occur when the drive voltage is set to a predetermined value (for example, the maximum value) immediately from time t0 using gradation pattern 1, which is a comparative example, to converge sufficiently and reach a steady state; in the example shown in Figure 6(A), this is 0.85 seconds. The same applies to gradation patterns 3 to 10, which will be described below.

As shown in Figure 7(A), there is almost no difference in transmittance between the pixels in regions A and B overall, and as shown in Figure 7(B), there is no difference in transmittance between the pixels in regions A and B even during the transition period immediately after voltage application. No overshoot occurs. However, the response time, which is the time it takes to reach the specified transmittance (approximately 21% in this example), is long at approximately 1.7 seconds.

Figure 8(A) shows the rise characteristics (change in transmittance over time) when a drive voltage is applied using gradation pattern 3 shown in Figure 5, and Figure 8(B) is a partially enlarged view of Figure 8(A). Each figure was obtained by measuring the transmittance of pixels in regions A and B shown in Figure 1(B) above. Gradation pattern 3 is a pattern in which the pulse width is gradually increased over time from time t0, the application start time, so that the effective voltage gradually increases before reaching its maximum value (see Figure 4(B)). Gradation pattern 3 is a pattern in which the time required for the effective voltage to reach its maximum value is shorter than that of gradation pattern 2. More specifically, gradation pattern 3 is a pattern in which the effective voltage is gradually increased over the same time (approximately 0.85 seconds in this example) as the time required for the transmittance oscillation to converge when gradation pattern 1 is used.

As shown in Figure 8(A), there is almost no difference in transmittance between the pixels in regions A and B overall, and as shown in Figure 8(B), there is no difference in transmittance between the pixels in regions A and B even during the transition period immediately after voltage application. No overshoot occurs. However, the response time is relatively long at approximately 0.85 seconds, although it is shorter than that for gradation pattern 2.

Figure 9(A) shows the rise characteristics (change in transmittance over time) when a drive voltage is applied according to gradation pattern 4 shown in Figure 5, and Figure 9(B) is a partially enlarged view of Figure 9(A). Each figure was obtained by measuring the transmittance of pixels in regions A and B shown in Figure 1(B) above. Gradation pattern 4 sets the pulse width to approximately 50% immediately after time t0, which is the start time of application, and then gradually increases the pulse width over time, causing the effective voltage to rapidly increase to approximately 50% of its maximum value and then gradually increase to its maximum value (see Figure 4(C)). More specifically, gradation pattern 4 immediately increases the effective voltage to a predetermined value smaller than the maximum value, and then gradually increases the effective voltage over the same time (0.85 seconds in this example) as the time required for the transmittance oscillation to converge when gradation pattern 1 is used.

As shown in Figure 9 (A), there is almost no difference in transmittance between the pixels in regions A and B overall, and as shown in Figure 9 (B), there is no difference in transmittance between the pixels in regions A and B even during the transition period immediately after voltage application. The response time is also very short, at approximately 0.05 seconds. Note that an overshoot phenomenon is observed during the transition period. Based on the results of gradation pattern 4, it can be said that it is more effective to immediately increase the effective voltage to a predetermined value less than the maximum value (for example, 50% or less), and then gradually increase it to the maximum value. Furthermore, this gradation pattern is particularly suitable for applications where the occurrence of overshoot is not a particular problem.

Figure 10(A) shows the rise characteristics (change in transmittance over time) when a drive voltage is applied according to gradation pattern 5 shown in Figure 5, and Figure 10(B) is a partially enlarged view of Figure 10(A). Each figure was obtained by measuring the transmittance of pixels in regions A and B shown in Figure 1(B) above. Gradation pattern 5 is a pattern in which the pulse width is gradually increased over time from time t0, the application start time, so that the effective voltage gradually increases and then reaches its maximum value (see Figure 4(B)). Gradation pattern 5 is a pattern in which the time required for the effective voltage to reach its maximum value is even shorter than that of gradation pattern 3. More specifically, gradation pattern 5 is a pattern in which the effective voltage is gradually increased to its maximum value over approximately half the time required for the transmittance oscillation to converge when gradation pattern 1 is used (approximately 0.42 seconds in this example).

As shown in Figure 10 (A), there is almost no difference in transmittance between the pixels in regions A and B overall, and as shown in Figure 10 (B), there is no difference in transmittance between the pixels in regions A and B even during the transition period immediately after voltage application. The response time is also relatively short, at approximately 0.4 seconds. No overshoot occurs.

Figure 11(A) shows the rise characteristics (change in transmittance over time) when a drive voltage is applied according to gradation pattern 6 shown in Figure 5, and Figure 11(B) is a partially enlarged view of Figure 11(A). Each figure was obtained by measuring the transmittance of pixels in regions A and B shown in Figure 1(B) above. Gradation pattern 6 gradually increases the pulse width over a certain period of time starting from time t0, and then maximizes the pulse width at a certain time, causing the effective voltage to gradually increase and then immediately reach its maximum value at a certain time (see Figure 4(D)). More specifically, gradation pattern 6 gradually increases the effective voltage to a predetermined value (50% of the maximum value) over the same time (approximately 0.85 seconds in this example) as the time required for the transmittance oscillation to converge when gradation pattern 1 is used, and then the effective voltage reaches its maximum value.

As shown in Figure 11(A), there is almost no difference in transmittance between the pixels in regions A and B overall, and as shown in Figure 11(B), there is no difference in transmittance between the pixels in regions A and B even during the transition period immediately after voltage application. The response time is approximately 0.87 seconds, which is relatively long. No overshoot occurs.

12(A) shows the rise characteristics (change in transmittance over time) when a drive voltage is applied according to gradation pattern 7 shown in FIG. 5, and FIG. 12(B) is a partially enlarged view of FIG. 12(A). Each figure was obtained by measuring the transmittance of pixels in regions A and B shown in FIG. 1(B). Gradation pattern 7 gradually increases the pulse width over a fixed period starting from time t0, then maximizes the pulse width at a certain time. This causes the effective voltage to gradually increase and then immediately reach its maximum value at a certain time (see FIG. 4(D)). Gradation pattern 7 has a shorter period of time during which the effective voltage is gradually increased than gradation pattern 6. More specifically, gradation pattern 7 gradually increases the effective voltage to a predetermined value (25% of the maximum value) over approximately half the time required for the transmittance oscillation to converge when gradation pattern 1 is used (approximately 0.42 seconds in this example), and then maximizes the effective voltage.

As shown in Figure 12 (A), there is almost no difference in transmittance between the pixels in regions A and B overall, and as shown in Figure 12 (B), there is no difference in transmittance between the pixels in regions A and B even during the transition period immediately after voltage application. The response time is also relatively short, at approximately 0.47 seconds. No overshoot occurs.

Figure 13(A) shows the rise characteristics (change in transmittance over time) when a drive voltage is applied according to gradation pattern 8 shown in Figure 5, and Figure 13(B) is a partially enlarged view of Figure 13(A). Each figure was obtained by measuring the transmittance of pixels in regions A and B shown in Figure 1(B) above. Gradation pattern 8 gradually increases the pulse width over a certain period of time from time t0, and then maximizes the pulse width at a certain time. This causes the effective voltage to gradually increase and then immediately reach its maximum value at a certain time (see Figure 4(D)). Gradation pattern 8 is a pattern in which the length of the period during which the effective voltage is gradually increased is even shorter than that of gradation pattern 7. More specifically, gradation pattern 8 gradually increases the effective voltage to a predetermined value (12% of the maximum value) over approximately one-quarter of the time required for the transmittance oscillation to converge when gradation pattern 1 is used (approximately 0.22 seconds in this example), and then maximizes the effective voltage.

As shown in Figure 13(A), there is almost no difference in transmittance between the pixels in regions A and B overall, and as shown in Figure 13(B), there is no difference in transmittance between the pixels in regions A and B even during the transition period immediately after voltage application. The response time is also relatively short at approximately 0.33 seconds. Note that an overshoot phenomenon is observed during the transition period, but whether this will be a problem or not depends on the application and cannot be generalized. Based on the results of gradation pattern 8, it can be said that it is more effective to gradually increase the effective voltage to a predetermined value smaller than the maximum value (for example, 10% or more) and then increase it to the maximum value.

Figure 14(A) shows the rise characteristics (change in transmittance over time) when a drive voltage is applied according to gradation pattern 9 shown in Figure 5, and Figure 14(B) is a partially enlarged view of Figure 14(A). Each figure was obtained by measuring the transmittance of pixels in regions A and B shown in Figure 1(B) above. Gradation pattern 9 gradually increases the pulse width over a certain period of time from time t0, and then reduces the pulse width to approximately 25% at a certain time. This causes the effective voltage to gradually increase and then immediately reach approximately one-quarter of its maximum value at a certain time (see Figure 4(E)). More specifically, gradation pattern 9 gradually increases the effective voltage to a predetermined value (25% of the maximum value) over approximately one-quarter of the time required for the transmittance oscillation to converge when gradation pattern 1 is used (approximately 0.22 seconds in this example), and then maintains the effective voltage at that predetermined value.

As shown in Figure 14 (A), there is almost no difference in transmittance between the pixels in regions A and B overall, and as shown in Figure 14 (B), there is no difference in transmittance between the pixels in regions A and B even during the transition period immediately after voltage application. The response time is also relatively short at approximately 0.24 seconds. No overshoot occurs. The results of gradation pattern 9 show that gradually increasing the effective voltage is effective even when changing the transmittance to intermediate tones.

15(A) shows the rise characteristics (change in transmittance over time) when a drive voltage is applied according to the gradation pattern 10 shown in FIG. 5, and FIG. 15(B) is a partially enlarged view of FIG. 15(A). Each figure was obtained by measuring the transmittance of pixels in regions A and B shown in FIG. 1(B). Gradation pattern 10 gradually increases the pulse width over a fixed period starting from time t0, then maximizes the pulse width at a certain time, causing the effective voltage to gradually increase and then immediately reach its maximum value at a certain time (see FIG. 4(D)). Gradation pattern 10 has an even shorter period of time during which the effective voltage is gradually increased than gradation pattern 8. More specifically, gradation pattern 10 gradually increases the effective voltage to a predetermined value (25% of the maximum value) over approximately 1/8 of the time required for the transmittance oscillation to converge when gradation pattern 1 is used (approximately 0.11 seconds in this example), and then increases the effective voltage to its maximum value.

As shown in Figure 15(A), there is almost no difference in transmittance between the pixels in regions A and B overall, and as shown in Figure 15(B), there is no difference in transmittance between the pixels in regions A and B even during the transition period immediately after voltage application. The response time is also very short at approximately 0.15 seconds. No overshoot occurs.

According to the above-described embodiment, it is possible to suppress temporary differences in transmittance when a voltage is applied to a liquid crystal device using static drive. In particular, by setting the period during which the drive voltage is gradually increased over time to be between 1/8 and 2 times the length of the time required for the transmittance oscillations that occur when the drive voltage is set to the predetermined value immediately after the start of application (gradation pattern 1) to converge, it is possible to suppress temporary differences in transmittance when a voltage is applied to a liquid crystal device using static drive.

Note that the present disclosure is not limited to the content of the above-described embodiment, and various modifications can be made within the scope of the gist of the present disclosure. For example, in the above-described embodiment, the magnitude of the effective voltage was controlled using pulse width modulation, but the magnitude of the effective voltage may also be controlled by increasing or decreasing the potential itself applied to each pixel electrode 13 by the driver 22.

Furthermore, although the above embodiment does not provide a detailed description of the configuration of the wiring connecting each pixel electrode 13, common electrode 14, and driver 22, various known configurations can be used for this wiring. For example, wiring may be arranged in areas where no pixel electrodes 13 are provided (e.g., inter-electrode areas) on one surface of the first substrate 11 where the driver 22 is arranged, or wiring may be arranged on one surface of the first substrate 11 below each pixel electrode 13 with an insulating film interposed therebetween. In the latter case, each wiring may be connected to each pixel electrode 13 via a through-hole appropriately provided in the insulating film.

Furthermore, in the above embodiment, image display use was given as an example of the use of the liquid crystal device, but the use of the liquid crystal device is not limited to this.

11: First substrate, 12: Second substrate, 13: Pixel electrode, 14: Common electrode, 15, 16: Alignment film, 17: Liquid crystal layer, 19, 20: Polarizer, 21: Controller, 22: Driver, 23: Flexible wiring board, 24: Effective display area

Claims (7)

A pair of electrodes arranged opposite to each other;
a liquid crystal layer disposed between the pair of electrodes;
a driver that applies a drive voltage to the liquid crystal layer via the pair of electrodes;
Including,
the driver, when applying a driving voltage of a predetermined value higher than at least a threshold value of the liquid crystal layer to the pair of electrodes, provides a period in which the driving voltage is gradually increased over time,
the driver provides a period in which the drive voltage is gradually increased over time from 0 volts to a first value that is 10% or more of the predetermined value, and then immediately increases the drive voltage to the predetermined value;
Liquid crystal device. A pair of electrodes arranged opposite to each other;
a liquid crystal layer disposed between the pair of electrodes;
a driver that applies a drive voltage to the liquid crystal layer via the pair of electrodes;
Including,
the driver, when applying a driving voltage of a predetermined value higher than at least a threshold value of the liquid crystal layer to the pair of electrodes, provides a period in which the driving voltage is gradually increased over time,
the driver immediately increases the driving voltage to a second value that is 50% or less of the predetermined value, and then provides a period in which the driving voltage is gradually increased over time to the predetermined value.
Liquid crystal device. A pair of electrodes arranged opposite to each other;
a liquid crystal layer disposed between the pair of electrodes;
a driver that applies a drive voltage to the liquid crystal layer via the pair of electrodes;
Including,
the driver, when applying a driving voltage of a predetermined value higher than at least a threshold value of the liquid crystal layer to the pair of electrodes, provides a period in which the driving voltage is gradually increased over time,
the driver supplies the driving voltage to the pair of electrodes by a static driving method;
Liquid crystal device. the driver variably sets the magnitude of the drive voltage by pulse width modulation;
The liquid crystal device according to any one of claims 1 to 3. the predetermined value is a maximum value within a rated range that can be set as the drive voltage;
The liquid crystal device according to any one of claims 1 to 4 . the driver sets the period during which the drive voltage is gradually increased over time to be between 1/8 and 2 times longer than the time required for the oscillation of transmittance to converge when the drive voltage is immediately set to the predetermined value after the start of application.
The liquid crystal device according to any one of claims 1 to 5 . A method for driving a liquid crystal device having a liquid crystal layer disposed between a pair of electrodes, comprising:
a period in which the driving voltage is gradually increased over time when a driving voltage having a predetermined value higher than at least a threshold value of the liquid crystal layer is applied to the pair of electrodes by a static driving method ;
A method for driving a liquid crystal device.