JPH09159999A - Liquid crystal display device and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent picture quality deterioration such as crosstalk. SOLUTION: A display area is divided into (n) subfields for displaying one frame image in order along the time base, and the said subfields consist basically of A÷×m pixels or scanning lines [where A is a positive integer, (n) is a positive integer between 3 and A, and (m) is a positive integer less than (n)]. This driving method of the liquid crystal display device drives a selected scanning line with the same polarity with a pixel group arranged on the same scanning line, inverts the said polarity to compensate a flicker, and selects the said pixel or scanning line in the subfield at a, specific interval.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device in which a switching element for selection is arranged for each pixel or each scanning line, and a driving method thereof.

[0002]

2. Description of the Related Art A liquid crystal display device is thin and lightweight, and can be driven at a low voltage. Therefore, it is widely used in wristwatches, calculators, word processors, personal computers, small game machines and the like. Recently, the demand for pen-input electronic notebooks has increased, and along with this, portable terminals (PDs)
The demand for A) is expanding.

When driving a liquid crystal display device, there is a driving method for inverting the polarity within the same screen. In this driving method, the signal line inversion for inverting the polarity for each signal line and the polarity for each scanning line are performed. Examples include horizontal polarity inversion (hereinafter referred to as H inversion) and dot inversion in which polarities are inverted between adjacent pixels. These driving methods can compensate for a flicker component (for example, surface flicker) due to polarity inversion. In particular, the H inversion has been widely used due to the one-sided arrangement of the signal line driver accompanying the narrowing of the frame and the demand for a low breakdown voltage driver for lower power consumption.

[0004]

In a large-screen, high-definition LCD, the number of signal lines increases and the capacitance component between the common electrode and the signal lines increases. Further, the sheet resistance of the common electrode causes the resistance component to largely change according to the distance from the feeding point. Therefore, when the polarity of the common electrode is reversed, as shown in FIG. 19, since the time constant of the common electrode is different in the screen, the voltage value of the common electrode varies (waveform becomes dull). Since this depends on the signal voltage, when the window is displayed, the image quality is well known as crosstalk. As a method for solving this, it is usually considered to reduce the sheet resistance of the common electrode, but this method has a limit and is not sufficient.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a liquid crystal display device and a driving method thereof which can prevent deterioration of image quality such as crosstalk.

[0006]

According to the present invention, a pair of substrates having A pixels or scanning lines and a switching element for selecting the pixels or scanning lines on at least one substrate, and the pair of substrates. The liquid crystal material sandwiched between them, the driving means for driving the selected scanning line with the same polarity for the pixel groups arranged on the same scanning line, and the polarity reversing means for reversing the polarity and compensating for flicker. And a display area is divided into n subfields that sequentially display one frame image along the time axis,
The subfield is basically composed of A / n × m (where A is a positive integer, n is a positive integer of 3 to A, and m is a positive integer of n or less) pixels or scanning lines. Therefore, the liquid crystal display device is characterized in that the pixels or the scanning lines are selected at predetermined intervals in the subfield.

Further, according to the present invention, at least one substrate is sandwiched between a pair of substrates having A pixels or scanning lines and a switching element for selecting the pixels or scanning lines, and the pair of substrates. The display area is divided into n sub-fields that sequentially display one frame image along the time axis, and the sub-fields are A / n × m (where A is Positive integer, n
Is a positive integer of 3 to A, m is a positive integer of n or less), which is a driving method of a liquid crystal display device basically composed of pixels or scanning lines, and is the same for selected scanning lines. Drive with the same polarity with respect to the pixel group arranged in the scanning line of
A method for driving a liquid crystal display device is provided, in which the polarity is inverted to compensate for flicker and the pixels or scanning lines are selected at predetermined intervals in the subfield.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In a liquid crystal display device and a driving method according to the present invention, when an image is displayed by A pixels or scanning lines each provided with a switching element for selection, one frame is used. The image is divided into n sub-fields that are sequentially displayed along the time axis, and the sub-fields are divided by A / n of the plurality of pixels or scanning lines.
Basically, it is composed of × m (where A is a positive integer, n is a positive integer not less than 3 and not more than A, and m is a positive integer not more than n) pixels or scanning lines.

In this structure, in order to improve the image quality, the scanning lines to be written and the scanning lines in the vicinity thereof have polarities different from each other as much as possible, and the number of adjacent scanning lines having the same polarity is minimized. .

Further, when displaying an image by scanning lines, the image signal of one frame image is interlaced to n: m, and the switching element is selected and driven according to the processed image signal. According to this driving method and the multi-field driving method, since the number of scanning line selections is reduced, low power consumption is realized, and the flicker component (for example, surface flicker) due to the inversion of each polarity is compensated by the selection method. can do.

According to the present invention having the above-mentioned structure, that is, adopting the H inversion and the multi-field driving at the same time, according to the present invention, when the execution voltage to the pixel is different depending on the image signal due to the rising rise of the voltage of the common electrode, the scanning line is changed. By reversing the polarity of the common electrode before the selection period of, the writing operation is performed with the voltage of the common electrode completely rising, so the voltage distribution of the common electrode in the screen that depends on the image signal is always The image quality can be made uniform, and the image quality deterioration due to crosstalk can be significantly reduced. Further, since the ON time of the gate line can be lengthened and the writing time to the pixel electrode can be lengthened in synchronization with the polarity inversion cycle, the writing characteristic to the pixel electrode can be improved.

When the H inversion and the multi-field driving are used at the same time, the polarity inversion period and the scanning line selection period are synchronized with each other, so that a plurality of scanning lines are displayed adjacent to each other with the same polarity. , Horizontal stripes may appear in the display. This adjacent scan line group of the same polarity changes its position along the time axis, so it moves rather than stands still, and when it enters the region visually recognized by the spatiotemporal frequency characteristics of vision, it greatly increases. However, the image quality will deteriorate.

Further, in a high-definition image having no correlation between images, the flicker component is not compensated, and aliasing distortion may occur due to the difference in the flicker component. This aliasing distortion also moves rather than being stationary, so that when it enters the region visually recognized by the spatiotemporal frequency characteristics, the image quality is greatly deteriorated.

In multi-field driving,
Since the holding period is significantly increased, the flicker component for each scanning line is increased. Therefore, the line interference generated in each subfield is visually recognized, which causes a problem that the image quality of a still image is deteriorated.

In order to prevent deterioration of image quality due to line interference, horizontal stripe interference, and aliasing distortion caused by such line interference, the following means is provided to make the region invisible to the visual spatiotemporal frequency characteristic.

As a first means, the intervals of pixels or scanning lines selected in a subfield are made the same in each subfield, and the polarity is set with respect to the cycle of selecting or deselecting each pixel or scanning line. The inversion cycles are not matched.

As a second means, in the first means, the polarity inversion periods are made different (not the same) between the subfields.

As a third means, the intervals of the pixels or the scanning lines selected in the subfield are changed according to the polarity inversion cycle, and the display is performed, that is, each pixel or the scanning line is changed with respect to the polarity inversion cycle. The periods for selecting or deselecting are set to be inconsistent. Note that the pixels or scanning lines selected in each subfield may have the same interval between the subfields.

As a fourth means, the intervals of pixels or scanning lines selected in the subfields do not coincide with the polarity inversion cycle, and the intervals of pixels or scanning lines selected in each subfield differ. To do so. The polarity inversion period may be the same in each subfield in each subfield.

According to the first means, even if the scanning order is likely to cause image quality deterioration due to the polarity reversal period for compensating for flicker, the polarity reversal period can be selectively changed, thereby deteriorating the image quality. It can be greatly improved.

According to the first and third means, scanning line groups which are spatially adjacent to each other and have the same polarity are not generated, or the scanning lines are not applied to the visible region due to visual characteristics, or are hardly visible. In the first and third means, for example, in order to display an image with a scanning line, the image signal is set to n: m.
When the interlace processing is performed, the number of adjacent scanning lines having the same polarity in one frame can be reduced to n or less. Therefore, the flicker (luminance difference) associated with the writing polarity does not have spatial periodicity in the panel plane, or the spatial frequency in the panel plane becomes high. Therefore, for example, the same polarity group (horizontal stripes) resulting from the synchronization of the polarity inversion period and the selection period of the multi-field driving switching element does not apply to the region visually recognized by the visual characteristics, or becomes difficult to be visually recognized, Image quality deterioration can be greatly improved.

Further, in a high-definition image having no correlation between the images, when a flicker associated with the writing polarity is generated as a new carrier on the spatial frequency axis, which causes aliasing distortion, this aliasing distortion also Since there is no spatial periodicity or the spatial frequency in the panel surface is high, it does not fit in the visible area due to visual characteristics, or it becomes difficult to be visible, and the deterioration of image quality can be greatly improved. .

According to the third means, depending on the scanning line selection or non-selection cycle, even if the polarity inversion cycle is likely to cause image quality deterioration, the selection order of the scanning lines can be selectively changed. , The image quality deterioration can be greatly improved.

According to the second and fourth means, when the flicker cannot be compensated by one method, the polarity inversion period and the scanning line selection or non-selection period are set over a plurality of subfields. By changing it, it can be made difficult to be visually recognized. Also, this one method and the second and fourth means can be used at the same time. Further, in the case of compensating the flicker caused by the polarity reversal, it can be performed by the common voltage. However, even if the flicker compensation is performed more effectively by changing the common voltage according to the polarity reversal period. Good.

According to the second and fourth means, the scanning order or the polarity inversion period is made different for each subfield group, and the flicker and the horizontal stripe flow which may occur by a certain method are visually recognized by visual characteristics. Not done,
Or it can be made difficult to be visually recognized.

In the liquid crystal display device of the present invention, the type of substrate material and liquid crystal material is not particularly limited.

Embodiments of the present invention will be described below in detail with reference to the drawings.

(Embodiment 1) In each of the following embodiments, a multi-field driving method for lowering the driving frequency by applying one frame (one frame image) to a plurality of sub-fields is applied. The multi-field driving method is disclosed in Japanese Patent Laid-Open No. 3-271795, and therefore detailed description thereof will be omitted.

In the first embodiment, the intervals of pixels or scanning lines selected in a subfield are the same in each subfield, and the polarity inversion cycle does not match the selection or non-selection cycle of pixels or scanning lines. The case will be described.

FIG. 1 is a schematic view showing the structure of the main part of the liquid crystal display device of the present invention. Further, FIG. 2 shows multi-field driving, n = 3, m = 1 (the number of subfields is 3/1 = 3).
FIG. 7 is a diagram showing an input image signal and a polarity inversion signal when H and H inversion are used. The liquid crystal display device of the present invention includes a polarity inversion signal generation unit 10, a common voltage output unit 11, a liquid crystal display panel 12, a gate line drive circuit 13, an n: m interlace processing circuit 14, and an n counter circuit 15. ,
It is mainly composed of a signal line driver 16 and a scanning line selection signal generation circuit 18. The liquid crystal display panel 12
Is a pixel or scan line on at least one substrate,
And a pair of substrates having switching elements for selecting pixels or scanning lines, and a liquid crystal material sandwiched between the pair of substrates.

In the liquid crystal display device having the above-mentioned structure, FIG.
As shown in, in one subfield, every third scanning line is selected by every three scanning lines by the scanning line selection signal S1, and in the next subfield, the scanning line immediately below the selected scanning line is selected. Similarly, it is sequentially selected. Note that FIG.
In the figure, the portions with diagonal lines show the scanning lines selected in each subfield. Here, the polarities of the non-selected scanning lines not marked with diagonal lines are maintained at the polarities when the respective scanning lines were last selected. Further, the shaded area indicates + polarity, and the plain area indicates −polarity.

In the driving method of the present invention, since the polarity inversion cycle is changed according to the scanning line selection order, the scanning line selection signal generating circuit 18 outputs the scanning line selection signal S1 to the polarity inversion signal generator 10 and the gate line. It is input to the drive circuit 13. At this time, the n counter circuit 15 outputs a start pulse to the gate line driver for each field, and the count signal S2 from the n counter circuit 15 is input to the gate line drive circuit 13. The gate line of the scanning line of the switching element is driven by the scanning line selection signal S1 and the count signal S2.

On the other hand, the polarity inversion signal generator 10 inputs an inversion signal P1 indicating the polarity inversion period to the n: m interlace processing circuit 14 and the common voltage output unit 11. The polarity inversion signal P1 is used to compensate for flicker.
The polarity is inverted for each scanning line and each field. The input inversion signal P1 is processed in the n: m interlace processing circuit 14, the signal is input to the signal line driver 16, and the polarity of the signal line of the liquid crystal display panel 12 is inverted based on the signal. Further, the input inversion signal P1 inverts the polarity of the common voltage of the liquid crystal display panel 12 via the common voltage output unit 11.

With such a driving method, the following effects can be obtained.

(1) In H reversal driving, it is usually necessary to perform reversal operation for each scanning line at a high frequency. Therefore, it is necessary to design the driver so that sufficient current flows at the moment of reversal. Conventionally, a driver having a large current gain in one direction, for example, a driver in which a current easily flows from the + side to the − side, is used to drive once after shifting to a high potential during inversion. By combining the H inversion drive and the multi-field drive, this operation becomes unnecessary, or it becomes unnecessary to flow a large current at the time of inversion. For this reason, the timing of writing can be delayed, so that a driver capable of high-speed operation becomes unnecessary.

(2) In H inversion driving, the polarity of the driver is the same for all signal lines. Therefore, since the signal (correction signal) given from D0 has the same polarity at that time, the effect is increased to some polarity (+ or −). For example, −write is normally poorly held as compared to + write. Therefore, by setting the correction signal to the − side, it is possible to favorably hold the − write. In this case, the retention of + writing may be deteriorated, but the image quality can be improved by making the retention characteristics of both polarities equal.

(3) One of the causes of image quality deterioration is the phenomenon of punch-through. This is due to the TFT (ThinFilm Transisto)
The pixel voltage fluctuates due to the coupling due to the parasitic capacitance due to the reduction of the gate voltage when the switching is turned off in r).

The amount of fluctuation varies depending on the left and right of the screen because the gate signal is dull depending on the left and right of the screen (sharp near the gate driver, but becomes dull as it goes away (goes to the right of the waveform)). Therefore, in order to improve this, the size of D0 can be given with an inclination on the left and right of the screen.

(4) The switching characteristics of the TFT are determined by the ON voltage and the OFF voltage of the gate voltage. In the signal line inversion drive, since the polarities of the adjacent pixels are different, the ON voltage and the OFF voltage cannot be determined according to the respective polarities. In the case of H inversion drive, this is possible, but since the inversion drive cycle is usually short, if the voltage is shifted each time, power will be consumed.

By combining the H inversion drive and the multi-field drive, the inversion drive cycle becomes four times that of the H inversion drive, so that the ON voltage and the OFF voltage can be satisfactorily determined according to the respective polarities. Can improve the image quality.

In the case of performing scanning line selection and inversion as shown in FIG. 2, over three subfields,
Since the scanning is performed line-sequentially, the previous scanning line and the next scanning line have the same polarity. Therefore, when one field is composed of three subfields SF11 to SF13, the image quality may be deteriorated as a so-called horizontal stripe flow in which three scanning line groups having the same polarity and adjacent to each other move.

Therefore, the case where the polarity inversion signal P1 is changed according to the scanning line selection signal for display will be described.

In this embodiment, the polarity reversal signal P1 is generated by the polarity reversal signal generator by the signal S1 received from the scanning line selection signal generator 18, and the polarity reversal signal P1 is generated in the n: m interlace processing circuit 14 according to S1. The output control of the selected image information and the unselected image information is performed, and the conversion of the image information is performed by P1. In addition,
The content of processing performed by the n: m interlace processing circuit 14 is not particularly limited, but the content of processing is for improving deterioration of a display image.

Further, the conversion of image information is not particularly limited, but, for example, in the case where the signal voltage is determined in accordance with the inversion of the common voltage, even at the same gradation, +
The conversion is performed so that the writing and the −writing have different signal levels. For example, when a liquid crystal cell showing a voltage-transmittance curve as shown in FIG.
The T1 transmittance is shown for the signal voltage of 2, and the T1 transmittance is shown for the V1 signal voltage in the negative writing.

In this embodiment, the image signal is a digital signal, and digital-analog conversion (hereinafter referred to as D / A) is performed in the signal line driver 16, and V1 and V1
The two image signals (denoted by DV1 and DV2, respectively) are given by the following equation, and the input image signal and the inverted signal of the polarity are output in a 1: 1 correspondence.

[0046]

[Equation 1]

In this case, it is necessary to change the polarity inversion method and also to convert the input image signal (in this case, negate). For example, the polarity inversion signal (P0) and the polarity inversion signal (P0) that has been subjected to processing for improving the deterioration of the display image.
An exclusive OR is performed with 1), the image signal is negated in one state, and output to the signal line driver 16.
FIG. 4A shows the contents of processing performed in the n: m interlace processing circuit 14, and FIG. 4B shows the signal waveform of each part. Although the processing content in FIG. 4A is not particularly limited, for example, it has a selector 31 and a selector 32, and the selector 31 selects the image signal D1 or D0 by the scanning line selection signal, and the selector 32 selects P.
The image signal inversion output is selected by the exclusive OR of 0 and P1.

Here, D0 is a signal which is not actually written, but is a signal necessary for applying a certain voltage to the signal line to an unselected engine for correction. In this case, D0 may be any value, but it is preferable to improve the image quality through coupling (capacitance) between the signal line and the pixel. Therefore, D0 can be the same signal as D1.

In the above description, the case where the writing polarity and the inversion of the image signal are the same has been described. However, in the voltage-transmittance characteristic, by providing a reference section for comparing each signal voltage value with the image signal information. You may convert into an appropriate image signal for every polarity.

In the present invention, by combining the two methods of the polarity reversal method and the scanning line selection method, the scanning line groups having the same polarity can be minimized or the scanning line groups having the same polarity can be minimized. The flowing horizontal stripes can be made less visible.

FIG. 5 shows signals related to the driving method of the present invention,
An image displayed on the liquid crystal display panel by the signal is shown. In FIG. 5, the shaded area indicates + polarity, the plain area indicates −polarity, and the diagonally shaded area indicates the scanning line selected in each subfield. Here, the polarities of the non-selected scanning lines not marked with diagonal lines are maintained at the polarities when the respective scanning lines were last selected.

Here, in multi-field driving, n = 4 and m = 1 (the number of subfields is 4/1 = 4).
This is a case where the drive frequency is used, and the drive frequency can be reduced, and the power consumption in the signal line driver 16, the gate line drive circuit 13, the liquid crystal display panel 12, and the common voltage generation unit 11 can be reduced. In addition, the polarity inversion period is set every 4 scanning lines, and the scanning line immediately below which is selected in the next field is such that the scanning line group adjacent to the scanning line having the same polarity is minimized, Writing is performed so as to have the opposite polarity to. By doing so, even when multi-field driving is adopted, it is possible to reduce the number of adjacent scanning lines having the same polarity to two or less, and further increase the spatial frequency.

Here, when the multi-field driving method is used, since it is necessary to perform compensation between scanning lines, the bias of polarities among a plurality of lines is important. For example, in the present embodiment, the compensation relationship for every four lines becomes a problem, and in FIG. 5, there is a scanning line group in which the polarities are biased at a ratio of 3: 1. However, since this scanning line group moves by three pixels in the next field, the horizontal stripe flow has a triple flow velocity, making it difficult to be visually recognized. This driving method is 2n: 1 (n
≧ 2) Particularly effective in multi-field driving, but is not limited to the above embodiment.

FIG. 6 shows a modification example of the polarity inversion cycle of FIG. 5, and shows a signal according to the driving method of the present invention and an image displayed on the liquid crystal display panel by the signal, similarly to FIG. Here, the polarities of the scanning lines are unified in the sub-fields, and the period is reversed only in each sub-field. In addition, in FIG. 6, the shaded portion indicates + polarity, and the uncoated portion indicates −.
The polarity is shown, and the portion with a diagonal line shows the scanning line selected in each subfield. Here, the polarities of the non-selected scanning lines not marked with diagonal lines are maintained at the polarities when the respective scanning lines were last selected.

Here, in multi-field driving, n = 5 and m = 1 (however, the number of subfields is 5).
Similarly, in this case as well, the drive frequency can be reduced, and the power consumption in the signal line driver 16, the gate line drive circuit 13, the liquid crystal display panel 12, and the common voltage generation unit 11 can be reduced. be able to.
Further, since the common voltage is maintained at a constant voltage (+ polarity or −polarity) in the subfield, the signal line driver 16, the liquid crystal display panel 12, and the common voltage generator 11 consume less power. The reduction effect becomes large. However, in this method, since + writing and −writing are performed on the entire screen, surface flicker may occur.

Therefore, as shown in FIGS. 7A and 7B, the input image information is double-speed processed, the data group of the next subfield is recorded in the memory, and the data group of the other subfield is written. Perform in SF1. For example, the writing at this time is performed with + polarity. Continue to SF2
The writing of the data group recorded in the memory during the period is reversed in polarity with respect to the subfield and is written with a negative polarity. Since this sub-field period is performed by a half period of the normal multi-field driving, the surface flicker enters the high frequency region and is not visually recognized. In this case, the power consumption in the clock section of the gate line drive circuit 13 increases, but the power consumption in the common voltage generation section 11 is significantly reduced, and the power consumption as a whole is low.

The above processing may be performed by using a memory provided in the n: m interlace processing circuit 14 shown in FIG. Here, for the sake of brief explanation,
Although no particular reference has been made to the deviation of the signal timing due to the buffer in the n: m interlace processing circuit 14 and the buffer in the signal line driver, the timing with respect to the scanning line is actually selected so as to obtain a desired image. Are matched.

Further, although it is expected that the number of ICs and power consumption will increase due to having a memory, as shown in FIG. 8, by controlling the signal output from the computer side which outputs the signal, the inside of the module is controlled. It is possible to adopt a configuration having no memory. Normally, in the information terminal body,
The video RAM 21 and the control circuit 22 control the signal output to the module. In the present embodiment, since the input image is converted in accordance with the processing means of n: m interlace, the scanning line selection signal S1 of the module circuit is input to the control circuit 22 from the scanning line selection signal generation circuit 28. Then, the control circuit 22
Will change the address designation and the image output timing with the video RAM 21. In FIG. 8, reference numerals 23 to 27 denote a liquid crystal display panel, an n: m interlace processing circuit, a signal line driver, and
An n counter circuit and a gate line drive circuit are shown, and their functions are the same as those shown in FIG.

Further, in the present embodiment, since the reversal period of the common voltage can be significantly reduced, the rise of the common voltage at the time of reversing the polarity can be prevented from becoming a problem. That is, since the polarity of the common voltage may be inverted during the blanking period, the time constant of the common voltage during writing becomes relatively long. Therefore, the sheet resistance of the counter electrode can be increased.
Alternatively, the number of power feeding points can be reduced.

The above driving method is 2n + 1: 1 (n ≧ 1)
This is particularly effective when multi-speed driving is performed at double speed, but the present invention is not limited to the above embodiment.

(Second Embodiment) In the second embodiment, the intervals of pixels or scanning lines selected in a subfield are set to be the same in each subfield, and the polarity is selected with respect to the selection or non-selection period of pixels or scanning lines. And the polarity inversion periods are not the same between fields.

FIG. 9 shows a signal according to another driving method of the present invention and an image displayed on the liquid crystal display panel by the signal. In FIG. 9, the shaded area indicates + polarity, the uncoated area indicates −polarity, and the diagonally shaded area indicates the scanning line selected in each subfield. Here, the polarities of the non-selected scanning lines not marked with diagonal lines are maintained at the polarities when the respective scanning lines were last selected.

Here, in multi-field driving, n = 5 and m = 2 (the number of subfields is 2.5, but the display image is composed of three subfields) is used. Therefore, the drive frequency can be reduced, and the power consumption in the signal line driver 16, the gate line drive circuit 13, the liquid crystal display panel 12, and the common voltage generation unit 11 can be reduced. In this case, the polarity inversion method is performed by alternately inverting every three scanning lines and every two scanning lines, and the scanning line immediately below which is selected in the next field has the same polarity adjacently. Writing is performed so that the scanning line group has the minimum polarity and the reverse polarity to the upper scanning lines. By doing this,
Even when the multi-field driving method is adopted, the number of adjacent scanning lines having the same polarity can be reduced to two or less, and the spatial frequency can be further increased.

However, in this method, since + writing and −writing are biasedly present in the screen at a ratio of 3: 2, it is expected that a direct current component is applied to the liquid crystal material and the alignment film. Therefore, the ratio of the number of scanning lines for + writing and −writing is switched for every several subfields.
In this case, it is considered that the surface flicker at the time of switching may be visually recognized, but by lowering the switching frequency (for example, 1 [Hz]) or less, which is not visually recognized by the visual characteristics, it is possible to reduce image quality deterioration. Also, the common voltage generating unit 11 may output the optimum common voltage according to the bias of the polarities.

FIG. 10 shows a modified example of the scanning line selection method of FIG. 9, and shows a signal related to the driving method of the present invention and an image displayed on the liquid crystal display panel by the signal similarly to FIG. In the driving method shown in FIG. 10, two scanning lines are not continuously driven in the subfield. Note that, in FIG. 10, the shaded portion indicates + polarity, the uncoated portion indicates −polarity, and the diagonally shaded portion indicates the scanning line selected in each subfield. Here, the polarities of the non-selected scanning lines not marked with diagonal lines are maintained at the polarities when the respective scanning lines were last selected.

Here again, in the case of using n = 5 and m = 2 (the number of sub-fields is 2.5, the display image is composed of three sub-fields) in multi-field driving. Therefore, the drive frequency can be reduced, and the power consumption in the signal line driver 16, the gate line drive circuit 13, the liquid crystal display panel 12, and the common voltage generation unit 11 can be reduced. Also in this case, the polarity inversion method is performed by alternately inverting every three scan lines and every two scan lines, and the scan line immediately below which is selected in the next field has the same polarity adjacently. The writing is performed so that the scanning line group has a minimum polarity and the scanning line group has a polarity opposite to that of the upper scanning line.

By doing so, even when the multi-field driving method is adopted, the number of adjacent scanning lines having the same polarity can be reduced to two or less, and the spatial frequency can be further increased. Further, in this method, + writing and −writing exist unevenly at a ratio of 3: 2 for each scanning line, but they are averaged in the screen, and compared with the case of FIG. It is considered that the DC component is not applied to.

Also in this case, as in the case shown in FIG. 9, the ratio of the number of scanning lines for + writing and −writing may be switched every several subfields. This driving method is 2n + 1: 2
(N ≧ 1) Particularly effective in multi-field driving, but is not limited to the above embodiment.

(Third Embodiment) In the third embodiment, the interval between pixels or scanning lines selected in a subfield is changed with respect to the polarity inversion period.

FIG. 11 shows a signal according to another driving method of the present invention and an image displayed on the liquid crystal display panel by the signal. In FIG. 11, the shaded area indicates + polarity, and the solid area indicates −.
The polarity is shown, and the portion with a diagonal line shows the scanning line selected in each subfield. Here, the polarities of the non-selected scanning lines not marked with diagonal lines are maintained at the polarities when the respective scanning lines were last selected.

Here, in the multi-field drive, n = 6 and m = 2 (the number of subfields is 3) are used, and the drive frequency can be reduced, and the signal line driver 16 and the gate line drive circuit can be reduced. Power consumption in the liquid crystal display panel 12, the common voltage generator 11, and the liquid crystal display panel 12 can be reduced.

When this driving method is used, there is a portion adjacent to which the number of scanning lines having the same polarity does not become n or less. However, as shown in FIG. 11, since the interval between the horizontal stripes changes and the horizontal stripe flow also disappears, the spatial spectrum of the horizontal stripes is dispersed and becomes difficult to be visually recognized, and at the same time, it is effective for the aliasing distortion.

(Fourth Embodiment) In the fourth embodiment, the intervals of pixels or scanning lines selected in the subfields are changed with respect to the polarity inversion period, and the subfields are not the same.

FIG. 12 shows a signal according to another driving method of the present invention and an image displayed on the liquid crystal display panel by the signal. In FIG. 12, the shaded area indicates + polarity, and the solid area indicates −.
The polarity is shown, and the portion with a diagonal line shows the scanning line selected in each subfield. Here, the polarities of the non-selected scanning lines not marked with diagonal lines are maintained at the polarities when the respective scanning lines were last selected.

Here, in the multi-field drive, n = 3 and m = 1 (the number of subfields is 3) are used, and the drive frequency can be reduced, and the signal line driver 16 and the gate line drive circuit can be reduced. Power consumption in the liquid crystal display panel 12, the common voltage generator 11, and the liquid crystal display panel 12 can be reduced.

In this driving method, SF1 to SF6
The scanning lines are selected in the same order, and the + and − polarities are inverted between the subfields. In the subsequent SF7 to SF12, the selection order different from the above is set, and the polarities are inverted between the subfields. In the same manner, SF13 to SF18 are also performed, and a portion in which the selection order of the scanning lines is not the same is included. By doing so, it is possible to make it difficult to visually recognize a horizontal stripe or a horizontal stripe flow that occurs when driving in a certain selection order.

(Embodiment 5) Embodiment 5 is an application example in which the image quality is improved by changing the polarity inversion method during the holding period in each of the above embodiments.

In the multi-field driving, since the writing operation is not performed during the period when the scanning line is not selected, the pixel electrode is theoretically in the floating state even if the signal line voltage and the common electrode voltage are changed. The electric field applied to the liquid crystal layer is kept constant. However,
In reality, a leak current is generated and the pixel electrode potential changes due to the switching characteristics of the TFT, which is a switching element, and the characteristics of the liquid crystal material. In this case, by controlling the polarity reversal during the holding period, it is possible to improve the pixel potential variation and the luminance variation due to the leak.

Here, in multi-field driving, n = 4 and m = 1 (the number of subfields is 4/1 = 4).
In general, the holding characteristic at the time of −writing (−) has a larger leak current than the holding characteristic at the time of + writing (+). Therefore, regarding the polarity during the holding period, for example, as shown in FIG. , − The voltage during writing is applied to the signal line. In this figure, the voltage values applied to the signal lines Xn and Xn + 1 are shown with respect to the common potential (Vcom) for the sake of clarity. The voltage value V0 in this case is not particularly limited, but it is preferable that the holding characteristics at the time of + writing and the holding characteristics at −writing are equal.

In this case, the processing is carried out by inputting the scanning line selection signal S1 to the signal line driver 16 and outputting V0 created in the signal line driver 16 to the signal line during the non-selection period. Note that V0 may be given based on D0. Not limited to this example, in order to improve the switching characteristics during the holding period, the polarity inversion period during the holding period can be variously changed.

Further, regarding the polarity of the common voltage, in order to improve the blunting of the waveform at the time of rising due to the high resistance of the common electrode and the long time constant, as shown in FIG. By reversing the polarity at the time of writing, the waveform of the common voltage can be made to completely rise at the time of writing.
For example, when a window is displayed as shown in FIG. 15 (A), as shown in FIG. 15 (B), portions having different contrasts are generated on the left and right sides of the window, and the image quality is deteriorated due to crosstalk.

For example, when black is displayed in the window and halftones are displayed outside the window, the left and right halftones of the window are brighter than the outside portion. This is shown in FIG.
This is because, as shown in FIG. 9, the rising of the waveform of the common voltage is different between the scanning line selection period without a window and the scanning line selection period with a window due to capacitive coupling between the signal line and the common electrode. Therefore, it is considered that a difference occurs in the effective voltage applied to the pixel electrode during writing and crosstalk appears. According to the present embodiment, as shown in FIG. 16, the polarity of the common voltage is reversed much faster than usual, so that the rising of the waveform of the common voltage is not affected. Therefore, crosstalk can be eliminated and the image quality can be significantly improved.

The present embodiment is not limited to 4: 1 multi-field driving, but can be applied to all n: m multi-field driving. Here, the case where the driving method of the present embodiment is applied to the second embodiment in which the 2LINE write operation is continuously performed will be described.

When the writing operation is continuously performed, it is considered that there is no period in which the reversal is performed in advance with respect to the common electrode in the writing period of the next scanning line (FIG. 17).
(A)). Even in this case, the scanning line selection timing can be set as shown in FIG. 17B. In this case, the gate line driving circuit has a function of changing the timing of the shift register. In FIG. 17B, the timing is changed by the clock. After the scanning line before being continuously selected is selected, the clock is stopped, the polarity is inverted, and then the common voltage is sufficiently raised. , Reactivate the clock and shift the signal. Along with this, the scanning line selection signal is turned on to select the scanning lines that are successively selected. After that, a shift operation is normally performed by a higher speed clock signal to match the selection operation of the next scanning line.

Further, the writing period can be extended in synchronization with the polarity inversion period. For example, FIG. 18 (B)
As shown in, the writing characteristic can be improved and the image quality can be significantly improved by making the selection period of the scanning line longer than usual. In this case, the processing in the scanning line selection signal generating circuit 18 and the gate line driving circuit 13 is assumed to be as shown in FIG. 18A, for example.

Here, the 4: 1 multi-field driving method is described. That is, from the scanning line selection signal, four scanning line selection signals S10, S11, S12, S
13 are output, and the scanning lines G4n and G4 are output respectively.
The output control of n + 1, G4n + 2, and G4n + 3 is performed. In this case, the signal from S2 is output as a signal having a scanning line selection period that is four times as long as the signal obtained by simply combining multi-field driving and H inversion.
Here, it is assumed that a signal for displaying a desired image is output from the signal line driver 16 to the signal line.

The present invention is not limited to the above-described embodiments, but can be implemented with various modifications without departing from the scope of the invention.

[0088]

According to the liquid crystal display device of the present invention, a pair of substrates having A pixels or scanning lines and a switching element for selecting the pixels or scanning lines on at least one substrate, and the pair of substrates. The liquid crystal material sandwiched between them, the driving means for driving the selected scanning line with the same polarity for the pixel groups arranged on the same scanning line, and the polarity reversing means for reversing the polarity and compensating for flicker. And a display area is divided into n subfields that sequentially display one frame image along the time axis,
The subfield is basically composed of A / n × m (where A is a positive integer, n is a positive integer of 3 to A, and m is a positive integer of n or less) pixels or scanning lines. Since the pixels or the scanning lines are selected at a predetermined interval in the subfield, it is possible to prevent image deterioration such as crosstalk.

Further, according to the present invention, the number of pixels or scanning lines having the same polarity adjacent to each other can be reduced by not synchronizing the period of selecting or deselecting pixels or scanning lines and the period of polarity inversion. Therefore, it is possible to make it difficult for the horizontal stripe interference caused by the interference to be visually recognized. Furthermore, since horizontal stripes do not flow along the time axis, the image quality can be significantly improved over the visual characteristics.

Further, according to the present invention, the writing operation is performed at a normal speed and the polarity is inverted for each subfield, so that the power consumption at the common electrode is significantly reduced without degrading the image quality. You can

Further, according to the present invention, by changing the polarity inversion period during the holding period, the leak current due to the TFT and the liquid crystal layer is controlled, and the holding characteristics in + writing and −writing are made equal, and the image quality is improved. Can be greatly improved. Further, in the common electrode, by reversing the polarity during the next writing during the holding period, the writing operation can be performed with the common electrode rising to the desired voltage, so the writing characteristics can be optimized. Can be greatly improved.

Further, according to the present invention, by lengthening the writing period in accordance with the polarity inversion period, the writing characteristic to the pixel electrode can be improved and the image quality can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a main part of a liquid crystal display device of the present invention.

FIG. 2 is a diagram showing a signal waveform and a polarity distribution when the driving method of the present invention is used.

FIG. 3 is a diagram showing a voltage-transmittance curve of liquid crystal.

FIG. 4A is a diagram for explaining processing contents of an n: m interlace processing circuit, and FIG. 4B is a diagram showing signal waveforms of respective parts.

FIG. 5 is a diagram showing a signal waveform diagram of 4: 1 multi-field driving and a polarity distribution when the driving method of the present invention is used in Example 1.

FIG. 6 is a diagram showing a signal waveform diagram of 5: 1 multi-field driving and a polarity distribution when the driving method of the present invention is used in Example 1.

7A and 7B are block diagrams showing processing contents of a circuit in double-speed writing driving of 5: 1 multi-field driving.

FIG. 8 is a block diagram showing a configuration of image signal conversion processing in the liquid crystal display device of the present invention.

FIG. 9 is a diagram showing a signal waveform diagram of 5: 2 multi-field driving and a polarity distribution when the driving method of the present invention is used in Example 2.

FIG. 10 is a diagram showing a signal waveform as a modification of the second embodiment and a polarity distribution when the driving method of the present invention is used.

FIG. 11 is a signal waveform diagram of the third embodiment and a diagram showing a polarity distribution when the driving method of the present invention is used.

FIG. 12 is a signal waveform diagram of the fourth embodiment and a diagram showing a polarity distribution when the driving method of the present invention is used.

FIG. 13 is a diagram showing a signal waveform according to the fifth embodiment.

FIG. 14 is a signal waveform diagram for compensating for leak characteristics as a modification of the fifth embodiment.

15A and 15B are display image diagrams showing crosstalk by window display.

FIG. 16 is a signal waveform diagram of each part when a window is displayed when the driving method of the present invention is performed.

17A and 17B are signal waveform diagrams showing a scanning line selection method and a polarity inversion method according to a modification of the fifth embodiment.

18A is a diagram showing a processing configuration according to a modification of the fifth embodiment, and FIG. 18B is a signal waveform diagram showing scanning lines and a polarity inversion period according to the modification of the fifth embodiment.

FIG. 19 is a signal waveform diagram of each part when a window is displayed when a conventional driving method is performed.

[Explanation of symbols]

10 ... Polarity inversion signal generator, 11 ... Common voltage output,
12, 23 ... Liquid crystal display panel, 13, 27 ... Gate line drive circuit, 14, 24 ... n: m interlace processing circuit,
15, 26 ... N counter circuit, 16, 25 ... Signal line driver, 18, 28 ... Scan line selection signal generating circuit, 21 ...
Video RAM, 22 ... Control circuit, 31, 32 ...
Selector.

Claims (10)

[Claims] 1. A pair of substrates having A pixels or scanning lines and a switching element for selecting the pixels or the scanning lines on at least one substrate, and a liquid crystal material sandwiched between the pair of substrates. A display area including driving means for driving the selected scan lines with the same polarity for the pixel groups arranged on the same scan line, and polarity inversion means for inverting the polarity and compensating for flicker, Is divided into n subfields that sequentially display one frame image along the time axis, and the subfields are A / n × m (where A is a positive integer and n is 3).
To A are positive integers, m is a positive integer not more than n), or pixels, or scanning lines, and the pixels or scanning lines are selected at predetermined intervals in the subfield. Liquid crystal display device. 2. The intervals of the pixels or scanning lines selected in the sub-field are made the same in each sub-field, and the polarities are inverted with respect to a cycle of selecting or non-selecting each pixel or scanning line. The liquid crystal display device according to claim 1, wherein the periods do not match. 3. The liquid crystal display device according to claim 2, wherein the polarity inversion period is different between the subfields. 4. The liquid crystal display device according to claim 1, wherein the liquid crystal display device displays by changing the intervals of the pixels or the scanning lines selected in the subfield in accordance with the polarity inversion cycle. 5. The intervals of the pixels or the scanning lines selected in the subfields do not match the cycle of the polarity inversion, and the intervals of the pixels or the scanning lines selected between the subfields are different. The liquid crystal display device according to claim 1. 6. A pair of substrates having A pixels or scanning lines and a switching element for selecting the pixels or the scanning lines on at least one substrate, and a liquid crystal material sandwiched between the pair of substrates. , And the display area is divided into n subfields that sequentially display one frame image along the time axis,
The subfield is basically composed of A / n × m (where A is a positive integer, n is a positive integer of 3 to A, and m is a positive integer of n or less) pixels or scanning lines. In the driving method of a liquid crystal display device, a selected scan line is driven with the same polarity with respect to pixel groups arranged on the same scan line, and the polarity is inverted to compensate for flicker, A method for driving a liquid crystal display device, characterized in that the pixels or the scanning lines are selected at predetermined intervals in a field. 7. The intervals of the pixels or scanning lines selected in the sub-field are made the same in each sub-field, and the polarities are inverted with respect to a cycle of selecting or non-selecting each pixel or scanning line. 7. The method for driving a liquid crystal display device according to claim 6, wherein the periods do not match. 8. The method of driving a liquid crystal display device according to claim 7, wherein the polarity inversion periods are different between the subfields. 9. The method for driving a liquid crystal display device according to claim 6, wherein the liquid crystal display device is displayed by changing the intervals of the pixels or scanning lines selected in the subfield in accordance with the polarity inversion cycle. 10. The intervals of the pixels or scanning lines selected in the subfields do not match the period of the polarity inversion, and the intervals of the pixels or scanning lines selected in each subfield are different. 7. The method for driving a liquid crystal display device according to claim 6.