JPH07121138A - Time division color liquid crystal display device and driving method thereof - Google Patents

Abstract

(57) [Abstract] [Purpose] Realization of a time-division color liquid crystal display screen with excellent reproducibility of display colors including halftones. [Configuration] The scanning timing of the time division three primary color light emitting device is
It is delayed by the optical response speed of the liquid crystal. In addition, a non-light emitting period corresponding to the optical response time of the liquid crystal is provided. on the other hand,
The amplitude of the image signal is increased as compared with the case of statically writing the same signal to compensate for the insufficient writing in the halftone. Furthermore, optimum γ correction is performed by comparing with the previously written data. These provide excellent color reproducibility.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time division color liquid crystal display device in which a time division three primary color light emitting device and a liquid crystal display device are combined and a driving method thereof.

[0002]

2. Description of the Related Art Examples of conventional time-division color liquid crystal display devices are Japanese Patent Laid-Open Nos. 58-186791 and 62-75.
There are 514 and the like. FIG. 5 is a diagram showing the structure. The time division color liquid crystal display device comprises a time division three primary color light emitting device 59 and a monochrome display liquid crystal display device 58. The time-divisional three-primary-color light emitting device is a light source that emits light of three primary colors R (red), G (green), and B (blue) independently. This light source is displayed in a single color, and the colors are sequentially scanned from the top to the bottom of the screen. In synchronization with this scanning, the liquid crystal display device also sequentially writes images corresponding to that color. This figure shows the state when the screen is rewritten from R to G. The green image signal holding area 53 is an area where the image signal is newly rewritten, and the red image signal holding area 54 is an area where the previously written image signal is still held. Liquid crystal display device 53
The boundary between the red light emitting region 52 and the green light emitting region 51 of the time-divisional three primary color light emitting device 59 moves downward in synchronization with the image signal being rewritten to green for each scanning line. For example, a NTSC video signal is sent as a 1-field color signal at 60 Hz, so if you write an R, G, B screen at 180 Hz, which is three times as high, it will look the same as if you displayed a 1-field color image. . This method has a feature that the number of pixels of the liquid crystal display device is one-third as compared with the case where a color filter is used and the pixel pitch is increased, so that the aperture ratio can be increased.

[0003]

However, the conventional time-division color liquid crystal display device has a problem that the color reproducibility is not so good because the response speed of the liquid crystal is slow. This will be described with reference to FIG. It takes time for the liquid crystal of the corresponding liquid crystal display device 58 to respond after a part of the time-divisional three-primary-color light emitting device 59 changes from red light emission to green light emission. For example, it is difficult to obtain a response speed of 1 msec or less even in an active matrix type liquid crystal display device using a fast response liquid crystal. Since the vertical scanning period when rewriting the screen of each color at 180 Hz is only about 5.6 msec, it is a time that cannot be ignored with respect to the lighting time. Moreover, its response speed varies depending on the drive voltage. Therefore,
Even if a pixel which is also a pixel on the same scanning line is displayed for a green image signal, a certain pixel still has a display for a red image signal. For this reason, the image data of each of the three primary colors is not displayed with the original brightness, and differs from the actual color.

The time-division color liquid crystal display device and the driving method thereof according to the present invention solve such problems, and an object thereof is to realize excellent color reproducibility.

[0005]

In the time-division color liquid crystal display device and its driving method of the present invention, the scanning timing of the time-division three-primary-color light-emitting device is equivalent to the response speed of the liquid crystal as compared with the switching of the screen of the liquid crystal display device. Delay by the time you do. Alternatively, the time during which the liquid crystal responds is set to a non-lighting period to prevent color bleeding. Further, the input image signal is amplified so as to compensate for the insufficient applied voltage due to the slow response speed of the liquid crystal. Further, it has a function of adjusting this amplification amount by comparing with the previously written signal and always applying an optimum image signal.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS This embodiment will be described below with reference to the drawings. FIG. 1 is a diagram showing the structure of a time division color liquid crystal display device.
The time division color liquid crystal display device comprises a time division three primary color light emitting device 9 and a liquid crystal display device 8 for monochrome display. The time-divisional three-primary-color light emitting device is a light source that emits light of three primary colors R (red), G (green), and B (blue) independently. This light source is displayed in a single color, and the colors are sequentially scanned from the top to the bottom of the screen.
In synchronization with this scanning, the liquid crystal display device also sequentially writes images corresponding to that color. This figure shows the state when the screen is rewritten from R to G. The green image signal holding area 3 is an area where the image signal is newly rewritten, and the red image signal holding area 4 is an area where the previously written image signal is still held. The boundary between the red light emitting region 2 and the green light emitting region 1 of the time division three primary color light emitting device 9 moves downward in synchronization with the image signal being rewritten to green for each scanning line of the liquid crystal display device 8. For example, the NTSC video signal is sent as a 1-field color signal at 60 Hz, so if you write the R, G, and B screen at 180 Hz, which is tripled, it will look the same as displaying a 1-field color image. . This method has a feature that the number of pixels of the liquid crystal display device is one-third as compared with the case where a color filter is used and the pixel pitch is increased, so that the aperture ratio can be increased. In this embodiment,
The scanning timing of the time-divisional three-primary-color light-emitting device 9 is delayed with respect to the scanning timing of the liquid crystal display device 8 by the time required for the optical response of the liquid crystal.

Generally, the response speed of a liquid crystal display device using a field effect liquid crystal is represented as shown in FIG. That is, when a voltage is applied, the response is relatively fast, but when there is no voltage or the voltage is reduced, the response speed becomes slow. Here, since the normally white mode is taken as an example, the fall time T1 is shorter than the rise time T2. In normally black mode the opposite is true. In addition, the response time is further delayed when the amplitude is reduced in the halftone, which also changes depending on the voltage condition. Therefore, in the present embodiment, the fall time T1 and the rise time T2 of the actually used drive voltage are measured, and then the scanning timing of the time-divisional three-primary-color light-emitting device is delayed by a certain time between T1 and T2.
This makes it possible to minimize the color shift.

Next, the circuit configuration of this embodiment will be described. FIG. 2 is an example of a circuit block diagram of a time division color liquid crystal display device. The timing controller 21 controls all timings of the time division color liquid crystal display device. First, the image signal is sampled by the sampling circuit 22 and stored in the field memory 23 for each of R, G and B. Next, the accumulated image signals are sent to the signal selection circuit 24 one by one. Since image signals of three colors are sent one by one in the period of one field, a speed about three times as fast as sampling is required. The sent image signal is amplified by the signal amplification circuit 25 according to the optical characteristics of the liquid crystal display device. The amplified signal is sent to the data driver 26 to drive the liquid crystal display device. Although an active matrix type liquid crystal display device 28 having a relatively high response speed is used here,
Other liquid crystal display devices may be used as long as the response speed is fast.
The active matrix type liquid crystal display device is sequentially selected line by line by the scan driver 27, and the image signal is written by the data driver in synchronization with the selection pulse. On the other hand, the time-divisional three-primary-color light emitting device 29 is also controlled by the timing controller, and sequentially changes the emission color in synchronization with the data driver 26 and the scanning driver 27. However, as described above, in this embodiment, the time-divisional three-primary-color light emitting device 9 is scanned with a delay of a certain time from the scanning timing of the active matrix type liquid crystal display device 8.

When the time-divisional three-primary-color light emitting device is divided into a plurality of blocks and one block simultaneously emits light corresponding to several scanning lines of the liquid crystal display device, that is, the number of light emitting blocks is the number of scanning lines. When there is only a fraction of the number, it is desirable to satisfy the following conditions. That is, the time from the start of the selection time of the liquid crystal display device corresponding to each light emitting block to the light emission is longer than the smaller one of T1 and T2, and light is emitted from the end of the selection time of the liquid crystal display device corresponding to each light emission block. Time to T1 and T2
Is smaller than the larger one.

Next, a second embodiment will be described. In the above-mentioned time-division color liquid crystal display device, no gap was provided between the light emitting regions of each color in order to maximize the light utilization efficiency, but in order to realize more accurate color reproduction, the optical response of the liquid crystal was started. Ideally, no light is emitted during the period from the end to the end. Therefore, as shown in FIG. 4, the green light emitting region 41 and the red light emitting region 42 of the time division three primary color light emitting device 49 are shown.
A non-light emitting region 45 is provided between the and. On the other hand, the liquid crystal display device 48 is sequentially scanned from the top of the screen, and the green signal holding area 4
A newly rewritten image signal is held in the reference numeral 3, and a red image signal holding area 44 holds the previously written image signal. Since the non-light emitting area 45 corresponds to the portion of the green signal holding area 43 immediately after scanning, light is not transmitted until the liquid crystal responds and the desired transmittance is obtained. Specifically, non-light emission may be performed during a period where the fall time T1 and the rise time T2 in FIG.

When the time-divisional three-primary-color light emitting device is divided into a plurality of blocks and one block simultaneously emits light corresponding to several scanning lines of the liquid crystal display device, that is, the number of light emitting blocks is the scanning line. When there is only a fraction of the number, it is desirable to satisfy the following conditions. That is, immediately after the start of the selection time of the liquid crystal display device corresponding to each light emitting block, T1 and T2 are set in the selection period of the block.
The non-emission period may be set to a time longer than the larger one.

This embodiment can be realized by inserting a desired blanking period between the light emitting periods of the respective colors of the time division three primary color light emitting device. Further, when switching the three primary colors using a rotating color filter or the like, it suffices to insert a black light shielding region between the color filters of the respective colors. Of course, an area corresponding to the non-selection period is required.

In the third embodiment, a method of correcting the signal applied to the liquid crystal to improve the color reproducibility will be described. In general,
When the liquid crystal display device is driven at about 180 Hz,
Shows a V-T curve, that is, the applied voltage dependence of the transmittance. 61 is V-T in the case of static drive
It is a curve. In this case, the optical response of the liquid crystal does not have to be taken into consideration because the driving is always performed with the same voltage amplitude. However, if the previously written signal is at white level, 62,
In the case of the black level, a VT curve as shown by 63 is drawn. This is because the transitional state during the period in which the liquid crystal is responding also affects the average transmittance, and the larger the voltage difference from the previously written signal, the V of static drive.
-It deviates from the T curve. Therefore, in the present embodiment, in order to reduce this shift amount as much as possible, the image signal amplitude is modulated using a VT curve as shown by 64 as a model. This considers the response of the liquid crystal at an average signal amplitude, and extends the signals on the white side and the black side from the static drive.

In general, since the γ characteristic of liquid crystal is different from that of the CRT, a dedicated γ correction circuit is often provided. For example, in FIG. 2, the signal amplification circuit 25 may have a γ correction function. FIG. 7 shows an example of input / output characteristics of the γ correction circuit. In the case of the normally white mode, the signal level is inverted and then converted into an AC signal for input / output conversion as shown in this figure. As a result, even a liquid crystal display device can perform halftone display like a CRT. In this embodiment, this input / output characteristic may be changed. FIG. 8 shows an example of input / output characteristics of the γ correction circuit in this embodiment. Since the characteristic of FIG. 7 corresponds to the case of static driving, the signals on the white side and the black side are expanded from that. With this decompressed signal, you can get the true transmittance just when there is an average signal change,
The color reproducibility in the halftone will be improved.

In the fourth embodiment, a method of correcting the signal applied to the liquid crystal according to the amount of change of the signal to realize accurate color reproducibility will be described. In FIG. 6, when the previously written signal is white, the lower side of the VT curve shifts to the high voltage side, and when the previously written signal is black, the upper side of the VT curve shifts to the low voltage side. is doing. Therefore, when the previously written signal is white, the voltage should be extended as the original signal approaches black. Similarly, when the previously written signal is black, the voltage should be compressed as the original signal approaches white. When the previously written signal is halftone, it is possible to obtain the same transmittance as that in the static drive for all signals by expanding or compressing according to the voltage. That is, very accurate color reproducibility can be realized.

FIG. 9 shows an example of input / output characteristics of the γ correction circuit in this embodiment. Reference numeral 81 indicates the case where the previously written signal is white, and the signal on the black level side is expanded. Reference numeral 82 indicates a case where the previously written signal is black, and the signal on the white level side is compressed. If the previously written signal is halftone, a similar curve is set between these two curves to expand or compress the signal by the required amount.

Next, the circuit configuration of this embodiment will be described. FIG. 10 is an example of a circuit block diagram of a time division color liquid crystal display device. The timing controller 91 controls all timings of the time division color liquid crystal display device. First, the image signal is sampled by the sampling circuit 92 and stored in the field memory 93 for each of R, G and B. Next, the stored image signals are sent to the signal selection circuit 94 one by one. For example, with an NTSC video signal, it is necessary to write one screen every 1/60 second, so an image signal for one color is sent every 1/180 second. On the other hand, the same signal is also sent to the signal comparison circuit 100. In the signal comparison circuit, the sent image signal is compared with the previously written signal for each pixel, that is, the signal of 1/180 second before. For example, in the case of rewriting from red to green, the voltages of the red and green signals of the same pixel are compared, the optimum correction amount is selected from the γ correction table 101 and sent to the signal amplification circuit 95. In the signal amplification circuit 95, the image signal sent from the signal selection circuit 94 is subjected to γ correction based on the data sent from the γ correction table 101 and sent to the data driver 96. The active matrix type liquid crystal display device 98 is sequentially selected line by line by the scan driver 97, and the image signal is written by the data driver in synchronization with the selection pulse. On the other hand, the time-divisional three-primary-color light emitting device 99 is also controlled by the timing controller, and sequentially changes the emission color in synchronization with the data driver 96 and the scanning driver 97. This method can be used not only for video display but also for various data displays.

Examples of the time-divisional three-primary-color light-emitting device used in the time-divisional color liquid crystal display device include a fluorescent display tube in which anode electrodes coated with phosphors of three primary colors are arranged in strips, and a disc-shaped color filter. Something that rotates on a white light source,
There are various methods such as a method in which light of a white light source is separated into three primary colors and optically scanned, and a method in which a high-speed response liquid crystal shutter such as a π cell and a color polarizing plate are combined. It can be applied to a time-division color liquid crystal display device using a divided three-primary-color light emitting device.

[0019]

As described above, in the time-division color liquid crystal display device and the driving method thereof according to the present invention, the timing of switching the emission color of the time-division three primary color light-emitting device is delayed by the time of the optical response of the liquid crystal. The deviation can be minimized. In addition, accurate color reproduction can be always realized by setting the non-light emission only during the optical response time of the liquid crystal. On the other hand, by correcting the signal applied to the liquid crystal by a certain amount, the color reproducibility can be improved without changing the circuit configuration. Since these devices have almost no change in structure from the conventional one, it is possible to realize a high-quality liquid crystal display device at low cost. Furthermore, accurate color reproducibility can be realized by performing optimum correction according to the amount of signal change.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a time division color liquid crystal display device.

FIG. 2 is a circuit block diagram of a time division color liquid crystal display device.

FIG. 3 is a diagram showing an optical response of liquid crystal.

FIG. 4 is a diagram showing a structure of a time division color liquid crystal display device.

FIG. 5 is a diagram showing a structure of a conventional time-division color liquid crystal display device.

FIG. 6 is a diagram showing applied voltage dependency of transmittance of a liquid crystal display device.

FIG. 7 is a diagram showing input / output characteristics of a conventional γ correction circuit.

FIG. 8 is a diagram showing input / output characteristics of a γ correction circuit.

FIG. 9 is a diagram showing input / output characteristics of a γ correction circuit.

FIG. 10 is a circuit block diagram of a time division color liquid crystal display device.

[Explanation of symbols]

 1, 41, 51 Green light emitting area 2, 42, 52 Red light emitting area 3, 43, 53 Green image signal holding area 4, 44, 54 Red image signal holding area 8, 48, 58 Liquid crystal display device 9, 29, 49, 59, 99 Time division three primary color light emitting device 45 Non-light emitting area 21, 91 Timing controller 22, 92 Sampling circuit 23, 93 Field memory 24, 94 Signal selection circuit 25, 95 Signal amplification circuit 26, 96 Data driver 27, 97 Scan driver 28, 98 Active matrix type liquid crystal display device 100 Signal comparison circuit 101 γ correction table

Claims (24)

[Claims] 1. A time-division color liquid crystal display device combining a time-division three-primary-color light-emitting device and a liquid crystal display device, wherein a timing controller delays the scanning timing of the time-division three-primary-color light-emitting device by a predetermined time from the scanning timing of the liquid-crystal display device. The time-division color liquid crystal display device, wherein the fixed time is set to a value between the rise time and the fall time of the optical response of the liquid crystal. 2. The light-emitting surface of the time-divisional three-primary-color light-emitting device is divided into N in the vertical scanning direction, and the timing controller scans the N-divided light-emitting surface in synchronization with scanning of the liquid crystal display device. And a function of turning on the light emitting surface after a fixed time has elapsed after the start of the selection period of the pixel array group of the liquid crystal display device corresponding to each of the N-divided light emitting surfaces. 2. The time-division color liquid crystal display device according to claim 1, wherein the rising time and the falling time are set to be larger than the shorter time. 3. The time from the end of the selection period of the pixel array group of the liquid crystal display device corresponding to each of the N-divided light emitting surfaces to the lighting of the light emitting surfaces is the rise time and fall time of the optical response of the liquid crystal. 3. The method according to claim 1, wherein the time is set to be smaller than the longer time.
The time-division color liquid crystal display device described. 4. The time-division color liquid crystal display device according to claim 1, wherein the liquid crystal display device is a monochrome display active matrix type. 5. A method of driving a time-divisional color liquid crystal display device, which is a combination of a time-divisional three-primary-color light emitting device and a liquid crystal display device, wherein the time-divisional three-primary-color light-emitting device has a light-emitting region in the same direction as the scanning direction of the liquid crystal display device. The scanning is performed by delaying the scanning timing of the time-divisional three-primary-color light-emitting device by a certain time from the scanning timing of the liquid crystal display device, and the certain time is set to a value between the rising time and the falling time of the optical response of the liquid crystal. A method for driving a time-division color liquid crystal display device characterized. 6. The light emitting surface of the time-divisional three-primary-color light-emitting device is set to N.
The light emitting surface is divided and sequentially scanned, and the light emitting surface is turned on after a certain period of time from the start of the selection period of the pixel array group of the liquid crystal display device corresponding to each of the N divided light emitting surfaces. The method for driving a time-division color liquid crystal display device according to claim 5, wherein the rising time and the falling time are set to be larger than the shorter time. 7. The time from the end of the selection period of the pixel array group of the liquid crystal display device corresponding to each of the N-divided light emitting surfaces until the light emitting surface is turned on is the rise time and fall time of the optical response of the liquid crystal. 7. The method for driving a time-division color liquid crystal display device according to claim 5, wherein the time is set smaller than the longer time. 8. A time division color liquid crystal display device in which a time division three primary color light emitting device and a liquid crystal display device are combined with each other, and no light is emitted between the light emission region of each color and the light emission region of another color of the time division three primary color light emission device. And a timing controller for delaying the scanning timing of the time-divisional three-primary-color light emitting device by a certain time from the scanning timing of the liquid crystal display device, the certain time having a large rise time and fall time of the optical response of the liquid crystal. A time-division color liquid crystal display device characterized by being set to a value greater than or equal to one of the values. 9. The light emitting surface of the time-divisional three-primary-color light-emitting device is divided into N in the vertical scanning direction, and the timing controller scans the N-divided light-emitting surface in synchronization with scanning of the liquid crystal display device. And a function of turning on the light emitting surface after a fixed time after the end of the selection period of the pixel array group of the liquid crystal display device corresponding to each of the N divided light emitting surfaces, and the optical response of the liquid crystal during the fixed time. 9. The time division color liquid crystal display device according to claim 8, wherein the rising time and the falling time are set to be longer than the longer time. 10. The non-light emitting period of each of the N-divided light emitting surfaces is set to be larger than the difference between the rise time and the fall time of the optical response of the liquid crystal. Time-sharing color liquid crystal display device. 11. The time-division color liquid crystal display device according to claim 8, wherein the liquid crystal display device is a monochrome display active matrix type. 12. A method of driving a time-divisional color liquid crystal display device in which a time-divisional three-primary-color light-emitting device and a liquid crystal display device are combined, wherein the time-divisional three-primary-color light-emitting device has a light-emitting region in the same direction as the scanning direction of the liquid crystal display device. A non-light emission period is provided before scanning and the emission period ends and emission of another color is started, and the scanning timing of the time-divisional three-primary-color light-emitting device is delayed from the scanning timing of the liquid crystal display device by a certain period of time so as to be constant. A method for driving a time-division color liquid crystal display device, wherein the time is set longer than the larger value of the rise time and the fall time of the optical response of the liquid crystal. 13. A light emitting surface of the time-divisional three-primary-color light-emitting device is divided into N areas and sequentially scanned, and a predetermined time period for starting a selection period of a pixel array group of the liquid crystal display device corresponding to each of the N-divided light emitting surfaces. 13. The time-division color liquid crystal display device according to claim 12, wherein the light emitting surface is turned on later, and the certain time is set to be longer than the longer one of the rising time and the falling time of the optical response of the liquid crystal. Driving method. 14. The time division according to claim 12, wherein the non-emission period of each of the N-divided light emitting surfaces is larger than the difference between the rise time and the fall time of the optical response of the liquid crystal. Driving method for color liquid crystal display device. 15. A time-division color liquid crystal display device in which a time-division three-primary-color light emitting device and a liquid crystal display device are combined with each other, comprising a signal amplification circuit for amplifying a video signal input to the liquid crystal display device, and the amplified video image. A time-division color liquid crystal display device, wherein a signal amplitude is larger than a signal amplitude required when the liquid crystal display device is continuously driven with the same signal amplitude. 16. The time-division color liquid crystal according to claim 15, wherein the signal amplification circuit has a γ correction function for further expanding the signals on the white level side and the black level side as compared with the halftone level. Display device. 17. The signal amplified by the signal amplifying circuit is between a voltage required for black level writing at all times and a voltage required for rewriting from a white level to a black level, and a white level 17. The time-division color liquid crystal display device according to claim 15 or 16, wherein the voltage is between a voltage required for always writing the white level and a voltage required for rewriting from the black level to the white level. 18. A method for driving a time-division color liquid crystal display device, which is a combination of a time-division three-primary-color light emitting device and a liquid crystal display device, wherein a video signal input to the liquid crystal display device is amplified, and the amplified video signal amplitude is adjusted. A method for driving a time-division color liquid crystal display device, wherein the signal amplitude is made larger than that required when the liquid crystal display device is continuously driven with the same signal amplitude. 19. The time-division color liquid crystal according to claim 18, wherein the amplified video signal further expands the signal on the white level side and the signal on the black level side to perform γ correction compared to the halftone level. Driving method of display device. 20. The signal amplified by the signal amplifying circuit is between the voltage required for writing the black level and the voltage required for rewriting from the white level to the black level, and the white level 20. The time-division color liquid crystal display device according to claim 18, wherein the voltage is between a voltage required for always writing the white level and a voltage required for rewriting from the black level to the white level. Driving method. 21. In a time division color liquid crystal display device in which a time division three primary color light emitting device and a liquid crystal display device are combined, a signal amplification circuit for amplifying a video signal input to the liquid crystal display device and a video signal of each pixel are previously set. A time-division color liquid crystal display device comprising a signal comparison circuit for comparing with a written video signal and a γ correction table for performing different γ correction based on the comparison result. 22. The time according to claim 21, wherein the γ correction table is set so that the signal amplification amount increases as the change in the video signal compared to the previously written signal increases. Split color liquid crystal display device. 23. A method for driving a time-division color liquid crystal display device, which is a combination of a time-division three-primary-color light-emitting device and a liquid crystal display device, according to a change amount when a video signal of each pixel is compared with a previously written video signal. A method for driving a time-division color liquid crystal display device, characterized in that the amplification amount of a video signal amplitude is also changed. 24. The method of driving a time-division color liquid crystal display device according to claim 23, wherein the signal amplification amount is increased as the change of the video signal is larger than that of the previously written signal.