JP4869525B2 - Passive matrix type liquid crystal display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor display device (hereinafter referred to as a display device). In particular, the present invention relates to a passive matrix display device.
[0002]
[Prior art]
In recent years, display devices using liquid crystal elements are used in various applications ranging from small to large. In particular, passive matrix liquid crystal display devices are often used in small display devices such as mobile phones because they have advantages such as low cost and low power consumption.
[0003]
Here, in this specification, a liquid crystal element refers to an element having a structure in which a liquid crystal material is sandwiched between two electrodes via an alignment film. As a liquid crystal material, a material having a known structure can be used freely.
[0004]
FIG. 5 shows an example of a passive matrix liquid crystal display device.
[0005]
In the passive matrix liquid crystal display device, the substrate 1301 in which the signal lines 1302 are arranged in stripes and the counter substrate 1304 in which the scanning lines 1303 are arranged in stripes are bonded to each other so that the signal lines 1302 and the scanning lines 1303 are orthogonal to each other. A liquid crystal is filled between the substrate 1301 and the counter substrate 1304. The signal lines 1302 and the scanning lines 1303 are driven by a driving LSI provided outside the substrate.
[0006]
FIG. 3 shows a conventional signal waveform applied to the signal line 1302, the scanning line 1303, and the pixel (between the electrodes of the liquid crystal element of the pixel) of the display device shown in FIG. A signal having a voltage different from that in the non-selection period is applied to the scan line only in the period in which the scan line is selected. Further, the polarity of the voltage is reversed every frame period. A rectangular wave pulse having a constant period is applied to the signal line during a period in which black display is not performed.
[0007]
On the other hand, in a portion where black is displayed on the screen, a pulse having a voltage (indicated by Vop and -Vop in FIG. 3) higher than the rectangular wave pulse during a period when black display is not performed is applied to the signal line. In the pixel, a difference voltage between the potential of the signal line and the potential of the scanning line is applied.
[0008]
Here, if an electric field in a certain direction is continuously applied between the two electrodes of the liquid crystal element, there is a problem that ions in the liquid crystal material are biased and the deterioration of the liquid crystal element is promoted. Therefore, in a display device using a general liquid crystal element, the polarity of the voltage applied to the liquid crystal element is changed at regular intervals, and the direction of the electric field applied between the two electrodes of the liquid crystal element is changed. A driving method is used.
[0009]
FIG. 2 schematically shows the polarity of the voltage applied to each pixel of the liquid crystal display device. Here, in FIG. 2 (1), FIG. 2 (2), and FIG. 2 (3), the state of the pixel portion of the nth frame and the state of the pixel portion of the (n + 1) th frame are shown. In FIG. 2, a pixel of 4 rows and 4 columns is shown as a representative pixel portion. In the figure, the polarity of the voltage applied to the liquid crystal element differs between the pixel represented by + and the pixel represented by −.
[0010]
For example, FIG. 2A shows a driving method called gate line inversion, in which the polarities of signal voltages applied to liquid crystal elements are made different between adjacent scanning lines. Further, FIG. 2B shows a driving method called source line inversion in which the polarities of signals applied to the liquid crystal elements are made different between adjacent signal lines. Lastly, FIG. 2C illustrates a driving method called frame inversion, in which the polarity of a signal applied to the liquid crystal element is inverted every time an image is displayed (hereinafter referred to as one frame period). Note that the driving method is not limited to the driving method shown in FIG.
[0011]
[Problems to be solved by the invention]
As described above, when the signal voltage applied to the liquid crystal element is inverted by alternating current every frame period, the signal amplitude is doubled, so that the power supply voltage of the driver needs to be 20V or more. Therefore, the power consumption of the driver could not be reduced.
[0012]
Therefore, an object of the present invention is to provide a passive matrix liquid crystal display device that can operate at a low voltage and consumes less power.
[0013]
[Means for Solving the Problems]
The present invention proposes a display device that performs display by inverting the signal voltage applied to the liquid crystal element with a very long period, or a liquid crystal display device that does not reverse the polarity.
[0014]
As a result, a liquid crystal display device is provided in which the power supply voltage of the driver is reduced and power consumption is kept low.
[0015]
The configuration of the liquid crystal display device of the present invention will be described below.
[0016]
According to the present invention,
A plurality of signal lines and a plurality of scanning lines are arranged in a matrix on the first substrate, a counter electrode is arranged on the second substrate, and a liquid crystal with the liquid crystal sandwiched between the first and second substrates In the display device,
There is provided a liquid crystal display device characterized in that polarity inversion of a signal for driving a liquid crystal is performed in synchronization with power-on or power-off.
[0017]
According to the present invention,
A plurality of signal lines and a plurality of scanning lines are arranged in a matrix on the first substrate, a counter electrode is arranged on the second substrate, and a liquid crystal with the liquid crystal sandwiched between the first and second substrates In the display device,
There is provided a liquid crystal display device characterized in that the polarity of a signal for driving a liquid crystal is inverted at a timing when the entire liquid crystal screen is rewritten.
[0018]
According to the present invention,
A plurality of signal lines and a plurality of scanning lines are arranged in a matrix on the first substrate, a counter electrode is arranged on the second substrate, and a liquid crystal with the liquid crystal sandwiched between the first and second substrates In the display device,
A liquid crystal display device is provided in which the polarity of a signal for driving a liquid crystal is inverted at a specific time determined by a user.
[0019]
According to the present invention,
A plurality of signal lines and a plurality of scanning lines are arranged in a matrix on the first substrate, a counter electrode is arranged on the second substrate, and a liquid crystal with the liquid crystal sandwiched between the first and second substrates In the display device,
The liquid crystal display device has a backlight, and the liquid crystal display device is characterized in that the polarity of the signal for driving the liquid crystal is reversed during the period when the backlight is turned off.
[0020]
The liquid crystal display device may be characterized in that the polarity inversion period is one hour or longer.
[0021]
According to the present invention,
A plurality of signal lines and a plurality of scanning lines are arranged in a matrix on the first substrate, a counter electrode is arranged on the second substrate, and a liquid crystal with the liquid crystal sandwiched between the first and second substrates In the display device,
A liquid crystal display device is provided in which the polarity of the voltage between the pixel electrode and the counter electrode is not reversed.
[0022]
A liquid crystal display device having a function of performing display by correcting deterioration of the liquid crystal may also be used.
[0023]
Liquid crystal deterioration correction may be a liquid crystal display device that stores and corrects the accumulated time of voltage application for each pixel.
[0024]
A television, a personal computer, a portable terminal, a video camera, or a head mounted display using a liquid crystal display device may be used.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
The configuration of the liquid crystal display device of the present invention will be described below.
[0026]
First, as a first embodiment, a case where AC inversion (inversion of the polarity of a voltage applied to a liquid crystal element) is performed with a very long cycle (for example, once every hour) will be described.
[0027]
In the conventional liquid crystal display device, AC inversion is performed at a frequency of 60 to 100 Hz, that is, a cycle of 10 to 16.6 ms. If the cycle is longer than this, it will be perceived as flicker by human eyes.
[0028]
The liquid crystal material of the 1980s has a problem that the liquid crystal element deteriorates in a relatively short time, for example, 10 hours, unless frequent AC inversion is performed. However, the degree of deterioration is decreasing in recent liquid crystal materials.
[0029]
The present inventor pays attention to this point and performs polarity reversal at a very long period to solve the above-described problems of the prior art.
[0030]
If polarity inversion is performed in a very long cycle, flicker is not considered. This is because flicker is felt by moving images with different brightness in a cycle that can be visually perceived.
[0031]
FIG. 1 shows driving waveforms of signal line potential, scanning line potential, and potential between electrodes of a liquid crystal element of a pixel when a liquid crystal display device to which the present invention is applied is driven. With the driving method of FIG. 1, it is possible to suppress the signal amplitude smaller than that of the conventional driving method shown in FIG. 1 that are the same as those in FIG. 3 are denoted by the same reference numerals.
[0032]
A problem in the case of the driving method as shown in FIG. 1 is that, when inversion occurs once in a long cycle, an action such as a momentary disturbance of the image occurs.
[0033]
The following are countermeasures against momentary image disturbance.
[0034]
1) Reverse the polarity while the user is not using it.
For example, the polarity is reversed when the power of the liquid crystal display device is turned on or off, or the polarity is reversed at a specific time specified by the user (such as a time not normally used such as midnight).
2) The polarity is reversed when the entire screen of the liquid crystal display device changes to another screen.
[0035]
By taking such measures, the problem of instantaneous disturbance of the image can be solved.
[0036]
Thereby, in the present invention, the driver can be driven with a voltage of about 10V.
[0037]
Details of the driving method will be described in the embodiments.
[0038]
Next, as a second embodiment, an example in which polarity inversion is not performed will be considered.
[0039]
Even though the liquid crystal element has hardly deteriorated in recent years, when a DC voltage for a long time is applied, the VT curve (transmittance-applied voltage curve) of the liquid crystal element changes, and the display characteristics change. FIG. 4 is a schematic diagram of a VT curve of the liquid crystal element. The curve shifts to the left with time with respect to the initial value (indicated as initial in FIG. 4) (indicated as after time in FIG. 4). Therefore, when the liquid crystal element deteriorates in this way, some correction is necessary. In the liquid crystal display device, various images are displayed on the screen. That is, since various video signal voltages are applied to individual pixels, the method of applying the signal voltage and the history differ from pixel to pixel. Therefore, when the liquid crystal display device is driven without reversing the polarity, the degree of deterioration differs for each pixel.
[0040]
Therefore, in the case of performing correction corresponding to the deterioration of the liquid crystal element, it is necessary to configure a circuit for performing correction according to the history for each pixel. FIG. 8 is a block diagram showing the configuration of a display system that performs correction. This system has a block with the following functions. First, data in the memory circuit is 0 in the initial stage. In this case, when a digital video signal is input to the cumulative luminance addition circuit, an output corresponding to 0 is input to the video correction circuit. In this case, no correction is performed, and the digital video signal is input to an LCD (Liquid Crystal Display) as it is.
[0041]
The output of the cumulative luminance adding circuit is also input to the memory circuit and stored therein.
[0042]
Next, when a digital video signal is input, new digital video signal data is added to the stored contents of the memory circuit. Using this data, the video correction circuit corrects the digital video signal. Further, the addition data is input to the memory circuit, and the stored data in the memory is rewritten. By repeating this, the accumulated luminance of each pixel is obtained. Using these data, the deterioration of the liquid crystal is predicted and corrected for each pixel.
[0043]
When the power of the liquid crystal display device is turned off, the data in the memory circuit is transferred to the nonvolatile memory so that the stored contents are not lost. When the power of the liquid crystal display device is turned on, data is transferred from the nonvolatile memory to the memory circuit and used. The reason why the non-volatile memory is not directly used is that the non-volatile memory has a slow response and the number of possible rewrites is small.
[0044]
In this way, the voltage applied to each pixel is stored, and it can be determined how much load has been applied to which pixel. If the correction amount is determined and corrected according to the applied load, the deterioration of the liquid crystal can be corrected. That is, the liquid crystal can be driven without polarity inversion, and the power supply voltage of the display device can be lowered. Specifically, it becomes possible to drive with a voltage of around 10V.
[0045]
【Example】
Examples of the present invention will be described below.
[0046]
[Example 1]
FIG. 6 shows an example in which polarity inversion is performed in synchronization with power-off of the liquid crystal display device. First, at t1, the backlight is turned off. Thereby, even if the display image is disturbed after that, the user does not see it. Next, at t2, the polarity is inverted and a signal is written. It is better to write several times. Next, at t3, the power of the liquid crystal display device is turned off.
[0047]
By forming such a sequential, the user does not need to see the deterioration of image quality due to polarity inversion. The polarity inversion has already been completed when the liquid crystal display device is turned on. Therefore, the image display may be started as it is.
[0048]
Although not shown, the same method can be used when polarity inversion is performed when the liquid crystal display device is turned on. After turning on the power supply of the display device, the polarity is reversed, and after writing several times, the backlight is turned on. In this method as well, as in the method shown in FIG. 6, the user does not need to see the image quality degradation at the time of polarity reversal.
[0049]
[Example 2]
FIG. 7 is a block diagram showing a system for setting the time of polarity reversal according to the user's wishes. The user sets a desired time in the polarity inversion time setting timer circuit via the user interface. For example, the time is set at 3 am. The polarity reversing time setting timer circuit gives a signal to the CPU to switch the polarity at the set time. In response to this, the CPU outputs a signal to the LCD controller, operates a driving circuit of a liquid crystal display device (LCD), and performs polarity inversion. When the polarity inversion is finished, the CPU stops the operation of the liquid crystal display (LCD).
[0050]
By having a function as shown in FIG. 7, in this case, the polarity is reversed during a time period when the user does not normally use the display device, and the user does not see a decrease in image quality when the polarity is switched. At this time, the backlight need not naturally be lit.
[0051]
[Example 3]
In the present embodiment, an example in which polarity inversion is performed by detecting a case in which the screen image is switched from the entire screen but not from a part is shown.
[0052]
For example, when the display device is a television, the image content changes greatly when the channel is switched. In such a case, even if there is a discontinuity between the previous video and the subsequent video, the original video signal is also discontinuous, so the user does not feel uncomfortable.
[0053]
It is also possible to reverse the polarity when switching the entire screen, and to avoid visually recognizing a decrease in image quality when switching the polarity.
[0054]
[Example 4]
In this example, an example in which a passive matrix liquid crystal display device of the present invention is manufactured is shown.
[0055]
FIG. 9 is a cross-sectional view of the passive matrix liquid crystal display device of the present invention.
[0056]
A striped signal line electrode 5102 is formed over a glass substrate 5101. This electrode is obtained by depositing ITO or the like and patterning it. Next, an alignment film 5103 is formed by printing.
[0057]
Similarly, stripe-shaped scanning line electrodes 5107 to 5110 are formed over the counter substrate 5106. This electrode is obtained by depositing ITO and patterning it. Next, an alignment film 5111 is formed by printing.
[0058]
These two substrates are bonded to each other so that the signal lines 5102 and the scanning lines 5107 to 5110 are orthogonal to each other, sealed with a sealant 5105, and liquid crystal 5104 is injected. A passive matrix liquid crystal display device is completed through the above steps.
[0059]
FIG. 10 shows a cross-sectional view of the passive matrix liquid crystal display device obtained as described above, which is different from FIG. In FIG. 10, the same portions as those in FIG. 9 are denoted by the same reference numerals, and description thereof is omitted.
[0060]
Note that the substrate 5101 and the counter substrate 5106 are not limited to glass substrates, and a substrate other than a glass substrate such as a plastic substrate can also be used.
[0061]
The present invention can be implemented by freely combining with the first to third embodiments.
[0062]
[Example 5]
The liquid crystal display device of the present invention has various uses. In this embodiment, a semiconductor device incorporating the liquid crystal display device of the present invention will be described.
[0063]
Examples of semiconductor devices incorporating a liquid crystal display device include portable information terminals (electronic notebooks, mobile computers, mobile phones, and the like), video cameras, digital cameras, personal computers, televisions, and the like. Examples of these are shown in FIGS.
[0064]
FIG. 11A illustrates a mobile phone, which includes a main body 2601, an audio output portion 2602, an audio input portion 2603, a display portion 2604, operation switches 2605, and an antenna 2606. The present invention can be applied to the display portion 2604.
[0065]
FIG. 11B illustrates a video camera, which includes a main body 2611, a display portion 2612, an audio input portion 2613, an operation switch 2614, a battery 2615, and an image receiving portion 2616. The present invention can be applied to the display portion 2612.
[0066]
FIG. 11C illustrates a mobile computer or a portable information terminal, which includes a main body 2621, a camera portion 2622, an image receiving portion 2623, operation switches 2624, and a display portion 2625. The present invention can be applied to the display portion 2625.
[0067]
FIG. 11D illustrates a head mounted display which includes a main body 2631, a display portion 2632, and an arm portion 2633. The present invention can be applied to the display portion 2632.
[0068]
FIG. 11E illustrates a television set including a main body 2641, a speaker 2642, a display portion 2643, a receiving device 2644, an amplifying device 2645, and the like. The present invention can be applied to the display portion 2643.
[0069]
FIG. 11F illustrates a portable book, which includes a main body 2651, a display portion 2652, a storage medium 2653, an operation switch 2654, and an antenna 2655, and is stored in a mini disc (MD) or a DVD (Digital Versatile Disc). Data and data received by the antenna are displayed. The present invention can be applied to the display portion 2652.
[0070]
FIG. 12A illustrates a personal computer, which includes a main body 2701, an image input portion 2702, a display portion 2703, and a keyboard 2704. The present invention can be applied to the display portion 2703.
[0071]
FIG. 12B shows a player that uses a recording medium in which a program is recorded, and includes a main body 2711, a display portion 2712, a speaker portion 2713, a recording medium 2714, and an operation switch 2715. This apparatus uses a DVD (Digital Versatile Disc), CD, or the like as a recording medium, and can perform music appreciation, movie appreciation, games, and the Internet. The present invention can be applied to the display portion 2712.
[0072]
FIG. 12C illustrates a digital camera which includes a main body 2721, a display portion 2722, an eyepiece portion 2723, an operation switch 2724, and an image receiving portion (not shown). The present invention can be applied to the display portion 2722.
[0073]
FIG. 12D illustrates a one-eye head-mounted display which includes a display portion 2731 and a band portion 2732. The present invention can be applied to the display portion 2731.
[0074]
【Effect of the invention】
In a conventional liquid crystal display device, polarity inversion is required once in one frame period, and in order to perform inversion once in one frame period and to ensure good display, the power supply voltage of the driver is 20V. I had to set it above. Therefore, the power consumption of the liquid crystal display device has been increased.
[0075]
In the liquid crystal display device of the present invention, the driving voltage of the driver can be lowered without deteriorating the image quality by performing polarity inversion with a long period as described above. Thus, low power consumption of the liquid crystal display device can be achieved.
[0076]
[Brief description of the drawings]
FIG. 1 is a diagram showing a waveform of a pixel potential of a liquid crystal display device of the present invention.
FIG. 2 is a diagram showing a pixel inversion method.
FIG. 3 is a diagram showing a waveform of a pixel potential of a conventional liquid crystal display device.
FIG. 4 is a diagram showing a VT curve of liquid crystal.
FIG. 5 illustrates a structure of a liquid crystal display device.
FIG. 6 is a diagram showing a first embodiment of the present invention.
FIG. 7 is a diagram showing a second embodiment of the present invention.
FIG. 8 is a system block diagram of the present invention.
FIG. 9 is a cross-sectional view of a liquid crystal display device of the present invention.
FIG. 10 is a cross-sectional view of a liquid crystal display device of the present invention.
FIG. 11 is a diagram showing an applied device of the liquid crystal display device of the present invention.
FIG. 12 is a diagram showing an applied device of the liquid crystal display device of the present invention.

Claims (4)

A plurality of signal lines provided on the first substrate;
A plurality of scanning lines provided on the second substrate so as to be orthogonal to the plurality of signal lines;
A liquid crystal sandwiched between the first substrate and the second substrate;
A backlight, and
The backlight turns off,
After the backlight is turned off, the signal for driving the liquid crystal is inverted in polarity,
After the signal for driving the liquid crystal has a polarity inversion, Ri power Do off,
The passive matrix liquid crystal display device according to claim 1, wherein the polarity of the signal for driving the liquid crystal is inverted only after the backlight is turned off until the power is turned off. In claim 1 ,
Between by the signal for driving the liquid crystal is polarity inversion between said power supply is turned off, a passive matrix liquid crystal display device in which the write of the signal for driving the liquid crystal is characterized by being performed a plurality of times . A plurality of signal lines provided on the first substrate;
A plurality of scanning lines provided on the second substrate so as to be orthogonal to the plurality of signal lines;
A liquid crystal sandwiched between the first substrate and the second substrate;
A backlight, and
The power is turned on
After the power is turned on, the signal for driving the liquid crystal is inverted in polarity,
After the signal for driving the liquid crystal has a polarity inversion, the backlight is lit,
The passive matrix liquid crystal display device according to claim 1, wherein the polarity of the signal for driving the liquid crystal is inverted only after the power is turned on until the backlight is turned on. In claim 3 ,
During a period from the signal for driving the liquid crystal is a polarity inversion until the backlight is turned on, a passive matrix liquid crystal display device, characterized in that writing of the signal for driving the liquid crystal is performed a plurality of times.

Images