JP2004206003A - Driving method of field sequential liquid crystal display device - Google Patents

Abstract

An object of the present invention is to provide a field sequential driving type liquid crystal display device having high display efficiency and high energy efficiency.
In a liquid crystal display element of a field sequential drive system, image data is written to each row of a scan line almost every other row. That is, in the matrix of M columns and N rows, first, odd-numbered rows are written in the order of the first row, the third row, the (N / 2) th row,..., The (N-1) th row, and then in the reverse direction. , The remaining even-numbered rows, ie, the Nth row, the (N−2) th row,... The backlight is turned on at the end of each field. As a result, high-quality display with reduced luminance unevenness and the like can be performed with high energy efficiency without constantly turning on the backlight light source.
[Selection diagram] FIG.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for driving a field sequential liquid crystal display device.
[0002]
[Prior art]
2. Description of the Related Art In recent years, a liquid crystal display device using a field sequential method has attracted attention. The field sequential method is a color display method using color mixture by “time division”. That is, when the light of two or more colors is continuously switched to emit light, and the switching speed is set to a speed exceeding the temporal resolution of the human eye, the human can change the two or more colors described above. This is a method that applies recognition by mixing colors.
[0003]
In the field sequential type full color LCD, one of the luminescent colors is turned on for each field obtained by dividing (time-sharing) each frame in the moving image display by the number of luminescent colors. Is three colors of R, G, and B, the backlight emits one of the three colors of R, G, and B sequentially, and the switching speed is sufficiently increased. Realizes any color light.
[0004]
That is, in the field sequential type full-color LCD, for example, each frame of color is divided into an R field, a G field, and a B field in advance, respectively. The above-described RGB fields are sequentially displayed with a time difference on the LCD.
[0005]
Specifically, when displaying the R field, the backlight emission is set to red (R), when displaying the B field, the backlight emission is set to blue (B), and the G field is set. When displaying, the light emission of the backlight is green (G). In the LCD, a color moving image is displayed by continuously displaying each color frame composed of the three color fields time-divided as described above while switching the three emission colors.
[0006]
According to the field sequential method, since it is not necessary to provide a color filter in the liquid crystal display device, light is not absorbed by the color filter, and high light use efficiency and low power consumption are realized. Further, since white color display can be performed by one pixel, high-resolution display can be performed with a smaller number of pixels as compared with the color filter method.
[0007]
[Problems to be solved by the invention]
While the field sequential system has the above advantages, it has the following problems. First, the liquid crystal is affected by the display in the immediately preceding field, does not reach the desired luminance in the response speed in one field period, the luminance becomes non-uniform, and unevenness easily occurs. As shown in FIG. 8, the response of the liquid crystal in the second field is affected by the display in the immediately preceding first field, has a different luminance from the display, and causes unevenness.
[0008]
Second, in the matrix of M rows and N columns, the transfer of the image signal is performed sequentially from the first row to the Nth row. It may be uneven. For example, as shown in FIG. 9, the unevenness is visually recognized as gradually decreasing from the pixel (1, 1) toward (M, N).
[0009]
In order to solve the above first and second problems, a color display signal and a signal that hardly contributes to display (for example, a black display signal) are transferred for each field in a period shorter than 1/2 of the field period. In addition, a method has been developed in which a light source of a corresponding color is turned on for almost a field period (see Patent Document 1).
[0010]
[Patent Document 1]
JP 2001-281623 A
The first problem is solved by writing a reset pulse to the pixel at the end of each field and immediately before transmitting the image signal of the next field (see FIG. 10).
[0012]
In addition, a field-sequential liquid crystal display device capable of displaying a uniform color image with high color purity even in a bright environment by preventing a decrease in color purity of a display image due to the influence of external light has been developed. (See Patent Document 2). This liquid crystal display device is arranged between the liquid crystal display element and the backlight light source, and is controlled so as to absorb incident light during the writing period of the unit color image data to the pixels of each row of the liquid crystal display element. And an optical shutter element controlled to transmit incident light after the writing period. The backlight light source is lit during the field period.
[0013]
[Patent Document 2]
JP-A-2002-221700
According to the liquid crystal display device having the above method, the unevenness can be eliminated. However, in the above-described liquid crystal display devices, the backlight is turned on even when all of them make a response that does not contribute to the display, and the energy efficiency is low. As described above, in the conventional field-sequential drive type liquid crystal display device, it has been difficult to realize high quality display with high energy efficiency and reduced luminance unevenness.
[0015]
In view of the above circumstances, an object of the present invention is to provide a field sequential driving type liquid crystal display device with high energy efficiency and high display quality.
[0016]
[Means for Solving the Problems]
In order to solve the above object, a method for driving a field sequential liquid crystal display device according to the present invention includes:
A first scanning step of scanning a plurality of scanning electrodes arranged in parallel in one direction at a predetermined number of lines;
A second scanning step of scanning the scanning electrodes in the other direction other than those scanned in the first scanning step;
Is provided.
[0017]
In the above method, in the first scanning step, for example, an odd-numbered scan electrode is scanned from the scan electrode to be scanned first,
In the second scanning step, for example, the even-numbered scanning electrodes are scanned.
[0018]
At least one reset signal may be applied to the scan electrode before the scan of the scan electrode.
[0019]
Further, the application of the reset signal is performed, for example, collectively to a plurality of the scanning electrodes.
[0020]
According to the method for driving a field sequential liquid crystal display device of the present invention, high-quality display with high energy efficiency and reduced luminance unevenness can be performed without constantly turning on a backlight light source.
[0021]
In addition, pixels with high luminance and pixels with low luminance are arranged with high uniformity, and display with high uniformity is possible.
[0022]
Further, by applying at least one reset signal to the scan electrode before the scan of the scan electrode, high-quality image display with reduced unevenness can be performed.
[0023]
The application of the reset signal is performed collectively to the plurality of scanning electrodes, so that high-quality image display with high uniformity and reduced unevenness can be performed.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a liquid crystal display device according to an embodiment of the present invention will be described with reference to the drawings.
[0025]
FIG. 1 shows a configuration of a liquid crystal display device according to the present embodiment. FIG. 2 shows a cross-sectional configuration of the liquid crystal display device shown in FIG.
[0026]
As shown in FIG. 1, the liquid crystal display device includes a liquid crystal display panel 10, a signal driver 20, a scan driver 30, an RGB decoder 40, an inverting amplifier 50, an LCD controller 60, a common signal driving amplifier 70, A backlight 80 and a backlight control circuit 90 are provided. The backlight 80 is provided on the back of the liquid crystal display panel 10.
[0027]
Referring to FIG. 2, a liquid crystal display panel 10 has a transparent upper substrate 11 and a lower substrate 12 provided to face each other, and a spacer 13 is provided between the upper substrate 11 and the lower substrate 12. The liquid crystal 14 is filled in the formed space.
[0028]
The liquid crystal 14 is composed of a ferroelectric or antiferroelectric liquid crystal display device made of a ferroelectric or antiferroelectric liquid crystal, or a liquid crystal display device in which a nematic liquid crystal is homogeneously aligned. The liquid crystal 14 is covered with an alignment film (not shown) and is aligned in a predetermined alignment state.
[0029]
The liquid crystal display panel 10 has an active matrix configuration, and a plurality of pixel electrodes 15 arranged in a matrix in a row direction and a column direction are provided on a surface facing the lower substrate 12. A common electrode 16 facing the pixel electrode 15 is provided on the opposing surface 11. Polarizing plates 17 and 18 are provided on the outer surfaces of the upper substrate 11 and the lower substrate 12, respectively.
[0030]
On the opposing surface of the lower substrate 12, a plurality of TFTs (not shown in FIG. 2) having sources connected to the plurality of pixel electrodes 15 are provided.
As shown in FIG. 1, the liquid crystal display panel 10 includes a plurality of scanning lines SL and a signal line (data line) DL orthogonal to each other. The TFT has a gate connected to the scanning line SL and a drain connected to the signal line. It is connected to the line DL.
[0031]
Each signal line DL is connected to the signal driver 20, stores predetermined image data in units of one row based on a horizontal control signal, and sequentially supplies a corresponding video display signal to each signal line DL.
[0032]
Each scanning line SL is connected to the scanning driver 30, and based on a vertical control signal, a scanning signal is sequentially applied to the scanning line SL to be in a selected state, and the pixel electrode 15 provided at a position crossing the signal line DL is selected. Then, the voltage of the video display signal supplied to the signal line DL is applied.
[0033]
The RGB decoder 40 and the inverting amplifier 50 extract the vertical (V) and horizontal (H) clock signals and the synchronizing signal (CSY) from the video signal and supply them to the LCD controller 60 described later. Based on the output field / line inversion signal FRP, red (R), green (G), and blue (B) color signals (RGB signals) included in the video signal are extracted, for example, each having an 8-bit width. , And supplies an inverted RGB signal to the signal driver 20.
[0034]
The LCD controller 60 generates the field / line inversion signal FRP based on the horizontal clock signal (H), the vertical clock signal (V), and the synchronization signal (CSY) supplied from the RGB decoder 40, and And a horizontal control signal and a vertical control signal are generated and supplied to the signal driver 20 and the scanning driver 30, so that a signal voltage is applied to the pixel electrode 15 at a predetermined timing, and the liquid crystal display panel 10 Control to write display data.
[0035]
The common signal drive amplifier 70 generates a common signal Vcom for driving a common potential applied to the common electrode 16 of the liquid crystal display panel 10 based on the field / line inversion signal FRP output from the LCD controller 60 described above. ,Output.
[0036]
The backlight 80 includes a light guide plate 81 and a light emitting member 82 as shown in FIG.
[0037]
The light guide plate 81 is formed of a transparent plate having substantially the same area as the liquid crystal display panel 10, for example, an acrylic resin plate. The light guide plate 81 is formed so that the upper surface is formed flat, and the lower surface is inclined from one end to the other end and becomes thin. The upper surface of the light guide plate 81 has substantially the same area as the liquid crystal display panel 10. One wide end surface of the light guide plate 81 constitutes an incident surface of emission light described later, and the entire upper surface constitutes an emission surface.
[0038]
On the lower surface of the light guide plate 81, a reflective film 83 made of a vapor-deposited or plated film of aluminum or the like is provided.
[0039]
The light emitting member 82 is arranged to face one wide side surface of the light guide plate 81. The light emitting member 82 includes a plurality of light emitting elements respectively emitting a plurality of unit color lights, for example, a red LED (light emitting diode) emitting a red unit color light, a green LED emitting a green unit color light, and a blue emitting a blue unit color light. An LED.
[0040]
A plurality of light emitting members 82 are arranged, for example, at predetermined intervals along the length direction of the incident end face of the light guide plate 81 so that the unit color light is made to enter the light guide plate 81 from almost the entire side surface thereof. ing.
[0041]
The light emitting member 82 is driven by a backlight control circuit 90 described later so as to sequentially emit a plurality of unit color lights. The unit color light emitted from the light emitting member 82 and incident on the side surface of the light guide plate 81 is subjected to total reflection at the interface between the upper surface of the light guide plate 81 and the outside air (air) and reflection at the reflection film 83 on the lower surface of the light guide plate 81. The light is guided to the entire light guide plate 81 by repetition, and is emitted from the entire upper surface of the light guide plate 81 toward the liquid crystal display panel 10 thereabove. Note that a diffusion layer 84 is provided on the upper surface of the light guide plate 81, and light emitted from the upper surface of the light guide plate 81 is diffused by the diffusion layer 84 and emitted as light having a substantially uniform luminance distribution.
[0042]
The backlight control circuit 90 controls the operation of the inverter circuit based on the backlight control signal generated and output by the LCD controller 50, and controls the lighting of the backlight 80. Here, the backlight control signal output from the LCD controller 60 is generated as a signal synchronized with the display data writing operation by the signal driver 20 and the scanning driver 30 described above, and is supplied to the backlight control circuit 90.
[0043]
The liquid crystal display device having the above configuration is driven by a so-called field sequential method. That is, in the field sequential method, one frame among a plurality of unit colors is divided into three fields obtained by dividing one frame for displaying one color image by the number of unit colors (R, G, B). The color image data is written to each pixel. In each field, a unit color light corresponding to the written image data is emitted from the backlight 80.
[0044]
In this manner, by sequentially writing image data for each time-divided field, and by switching each unit color light at high speed to emit light in accordance therewith, an arbitrary color can be obtained for each frame, and a color filter or the like can be obtained. A color image can be displayed without the need.
[0045]
More specifically, the LCD controller 50 supplies a gate signal to the TFTs in each row via the scanning line SL, and displays a plurality of TFTs in each column via the signal line DL for displaying an arbitrary color in a mixed color. Supplies a unit color image data signal corresponding to one of the unit colors.
[0046]
Thereby, a voltage corresponding to the unit color image data signal is applied between the electrodes of the pixels in each row, and the image data of one unit color of the plurality of unit colors is written to the pixels in each row for each field, The light transmission of each pixel is controlled by the degree of response of the liquid crystal 14 to this.
[0047]
For example, in a display device having a matrix of M columns and N rows (N: even number) that emits light in the order of R, G, and B, an orange color (R = 100%, G = 50%, B = 0%) is displayed. In the case of display, data is written into the pixel (1, 1) as shown in FIG. 3, and the liquid crystal 14 is driven in accordance with this, and the transmittance in each pixel region is controlled. Lighting of the unit color light (R, G, B) is performed for each unit color field, and a desired color (orange) is obtained for each frame.
[0048]
In the present embodiment, the writing of image data to each row as described above is performed as shown in the timing chart of FIG. That is, the LCD controller 60 sequentially applies the scanning signal to every other line (excluding the folded portion) on the scanning line SL to set it in the selected state. The LCD controller 60 supplies a video display signal to each signal line DL. Thus, the display signal is transmitted almost every other row of the pixel.
[0049]
In the example shown in FIG. 4, the display signal is first written in the odd-numbered rows, that is, the first row, the third row, the fifth row,..., The (N-1) th row. Next, for the remaining even-numbered rows, the Nth row, the (N−2) th row,...
[0050]
According to such a display signal transmission method, the following advantages can be obtained.
In the field sequential system, since image data is sequentially written for each row in each field, a time lag occurs between the pixel written at the beginning and the pixel written at the end in response of the liquid crystal 14. Lighting is performed near the end of each field, but this time lag causes a difference in the response of the liquid crystal 14, resulting in different arrival luminance levels. This causes color unevenness and luminance unevenness on the screen.
[0051]
However, in the above method, the pixels of the second row, which are written last and have insufficient response of the liquid crystal 14, are sandwiched between the first and third rows which are written first and have sufficient response of the liquid crystal 14. . As a result, the unevenness on the screen is averaged and hardly visually recognized.
[0052]
Further, pixels written relatively quickly and having a relatively high luminance and pixels written relatively slowly and having a relatively high luminance are uniformly arranged as a whole. As a result, for example, pixels near the end (M, N) have an intermediate transmission timing of the display signal, so that unevenness is less likely to be visually recognized, and display quality is improved.
[0053]
FIG. 5 schematically shows driving of the liquid crystal 14 in response to a display signal. In this figure, the upper diagram shows the application timing of the display signal to the scanning signal line in one frame, and the lower diagram shows the driving state of the liquid crystal (data write amount) and the lighting period of the backlight by the application timing.
[0054]
In the scanning signal line in the upper figure, the data write timing is divided into an odd-numbered row and an even-numbered row, and (1, 1) to (M, N-1) in the odd-numbered row are from the upper side to the lower side in the figure. Data is written sequentially.
[0055]
On the other hand, data is sequentially written in the even-numbered rows (1, 2) to (M, N) of the scanning signal lines from the bottom to the top in the drawing. Then, data is written to the even-numbered rows of the scanning signal lines after the writing timing of the odd-numbered rows ends.
[0056]
As the timing of the liquid crystal switching shown in the figure below, the maximum difference between the display areas occurs in the odd rows (1, 1) and the even rows (1, 2). After the period in which the maximum difference occurs ends, a period in which the backlight is turned on comes.
[0057]
This relationship is similarly performed in each of the field (R), the field (G), and the field (B), as shown in FIG. 5, and lighting of red light, lighting of green light, and lighting of blue light are performed. .
[0058]
As described above, display signals are transmitted in the order of odd rows (1, 1) to (M, N-1) and then even rows (M, N) to (1, 2), and the liquid crystal 14 is driven. Based on the order of writing, a time lag occurs in the response of the liquid crystal 14, and the difference gradually increases and becomes the maximum between (1,1) and (1,2). However, a decrease in luminance due to an insufficient response of the liquid crystal 14 near (1, 2) becomes difficult to be visually recognized due to a high luminance based on sufficient response near (1, 1).
[0059]
In the present embodiment in which the display signal is transmitted every other line by being turned upside down, it is possible to make the luminance unevenness based on the transmission order of the transmission signal less visible and to improve the display quality.
[0060]
FIG. 6 shows an example of a timing chart in one field when the method of the present embodiment is applied to a display operation of a liquid crystal display panel of 220 rows.
[0061]
In FIG. 6, the number of the scanning signal lines is 220, and the writing order of each of the scanning signal lines 1 to 110 is odd-numbered from the top, and the writing of the even-numbered scanning signal lines 111 to 220 is performed from the top. Writing is performed in order from the bottom.
[0062]
The frequency used is 60 Hz. In this case, one frame is about 16.6 seconds. Since one frame is composed of three color (R, G, B) fields, each field is about one-third of about 5.5 milliseconds.
[0063]
Referring to the figure, first, a reset signal having a width of 20 microseconds is written twice at 500 microsecond intervals. At this point, one millisecond elapses. The reset signal is applied to make the influence of the immediately preceding field uniform, thereby alleviating unevenness.
[0064]
Next, a write signal having a width of 10 microseconds is sequentially written to the odd rows 1, 3,..., 217, and 219 as shown in the write order. Writing takes 1.1 milliseconds, at which point 2.1 milliseconds elapse.
[0065]
Thereafter, signals of the same write width are sequentially written to the even-numbered rows 220, 218,... Writing takes 1.1 milliseconds, at which point 3.2 milliseconds elapse.
[0066]
After the writing, no operation is performed for 350 microseconds, and the response time of the liquid crystal 14 is used. At this point, 3.55 milliseconds have elapsed.
The backlight is turned on for the remaining 2 ms of the field. As described above, 5.55 ms of one field elapses.
[0067]
In the above embodiment, only 0.35 milliseconds is secured from the time when the write signal is sent to the second row where the last write is completed to the time when the light is turned on. Therefore, the response of the liquid crystal 14 is insufficient for the row where writing is slow.
[0068]
However, this inadequate response is sandwiched between the first and third rows on both sides where the writing is the fastest and the response time is sufficiently ensured, and the unevenness is difficult to be visually recognized. Also, the other rows where writing is relatively slow and the response time is not sufficiently ensured are arranged between the rows where writing is relatively fast, and the unevenness is hard to be visually recognized.
[0069]
The present invention is not limited to the above embodiment, and various modifications and applications are possible. Hereinafter, modifications of the above embodiment to which the present invention is applicable will be described.
[0070]
In the above example, the reset signal is transmitted twice at the head of each field. However, the signal may be transmitted once or may be driven without transmitting the reset signal.
[0071]
In the above-described embodiment, writing is performed every other line except for the folded portion. However, for example, writing may be performed every other row. For example, as shown in FIG. 7, writing may be performed every two rows. Such changes can be made in various ways depending on the size of the liquid crystal panel, the number of scanning signal lines, and the like, and may be every five rows or every ten rows.
[0072]
In the above embodiment, a TFT is used as a switching element. However, if a desired driving capability and driving timing can be realized, for example, an active matrix substrate using an MIM element may be used, or a simple matrix substrate may be used. Is also good.
[0073]
In the above-described embodiment, the backlight 80 has a configuration including the light-emitting elements (LEDs) that emit a plurality of unit color lights. However, the light source such as a backlight is not limited to this, and for example, may be configured to include a surface light source in which a plurality of light emitting elements that emit light of a plurality of unit colors are arranged in a row direction and a column direction.
[0074]
【The invention's effect】
According to the method for driving a field sequential liquid crystal display device of the present invention, it is possible to perform field sequential driving with high display quality.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a liquid crystal display device according to an embodiment of the present invention.
FIG. 2 is a diagram showing a cross-sectional configuration of the liquid crystal display device shown in FIG.
FIG. 3 is a diagram showing a timing chart of a display signal and a response of a liquid crystal.
FIG. 4 is a diagram showing a timing chart according to the embodiment of the present invention.
FIG. 5 is a diagram showing a timing chart of a display signal and a response of a liquid crystal according to the embodiment of the present invention.
FIG. 6 is a diagram showing a timing chart of a display signal according to the example.
FIG. 7 is a diagram showing a timing chart according to a modified example of the embodiment of the present invention.
FIG. 8 is a diagram showing a timing chart of a display signal and a response of a liquid crystal in a conventional field sequential liquid crystal display device.
FIG. 9 is a diagram showing a timing chart of a display signal and a response of a liquid crystal in a conventional field sequential liquid crystal display device.
FIG. 10 is a diagram showing a timing chart of a display signal of a method of applying a reset pulse and a response of a liquid crystal.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 10 ... Liquid crystal display panel, 20 ... Signal driver, 30 ... Scan driver, 40 ... RGB decoder, 50 ... Inverting amplifier, 60 ... LCD controller , 70: common signal drive amplifier, 80: backlight, 90: backlight control circuit

Claims (4)

A first scanning step of scanning a plurality of scanning electrodes arranged in parallel in one direction at a predetermined number of lines;
A second scanning step of scanning the scanning electrodes in the other direction other than those scanned in the first scanning step;
A method for driving a field sequential liquid crystal display device, comprising: In the first scanning step, an odd-numbered scan electrode is scanned from the scan electrode to be scanned first,
2. The method according to claim 1, wherein, in the second scanning step, an even-numbered scanning electrode is scanned. 3. The method according to claim 1, wherein at least one reset signal is applied to the scan electrodes before scanning of the scan electrodes. 4. The method according to claim 3, wherein the reset signal is applied to a plurality of the scan electrodes at a time.

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