JP3503303B2 - Display device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device for forming an image by a frame sequential method.

[0002]

When displaying a color image, a cathode ray tube (Cathode Ray Tube ... CRT) is provided with three electron beams corresponding to respective colors of R, G and B, and these electron beams are simultaneously emitted. Irradiate the R, G, B phosphors of
The one that directly displays an image by line scanning, the one that combines three small black-and-white liquid crystal panels and the dichroic mirror that separates the light flux emitted from the light source into the RGB three primary colors, synthesizes a color image, and projects it on a screen etc. It is becoming mainstream.

However, in any of the above-described image display devices, precise color registration adjustment is necessary to form an image of three primary colors, and there is a problem that the cost becomes high. Therefore, as another method, one field screen is made to correspond to R, G, and B colors, one frame is formed by these three field screens, and one frame is formed by the afterimage phenomenon obtained in each field screen. There is also known a so-called frame-sequential type which is adapted to represent a color image.

An example of the structure of a display device for obtaining field images of R, G, and B in a frame sequential manner is, for example, R,
Liquid crystal shutter that can be switched to pass only light of either G or B (Liquid Crystal Shutter
..LCS) optical system is known, and this liquid crystal shutter optical system is provided on the front surface of the display surface of the CRT, and only one of R, G, and B colors can be transmitted per field. If you perform sequential switching control so that
R, G, and B field images can be sequentially obtained. In this case, the CRT displays the field image based on the luminance signal corresponding to each of R, G, and B.

In the case of the frame-sequential type, a normal composite video signal, that is, a video signal A in which one frame is 1/60 second as shown in FIG. Is performed to generate R, G, and B primary color signals. When each of these primary color signals is written to and read from the memory means assigned to each, the RG is read at a speed three times as high as that at the time of writing, for example.
The B primary color signals are sequentially read out to generate a field sequential signal C in which fields of RGB primary color signals are sequentially formed in one frame as shown in FIG. 7B.

Next, referring to FIGS. 8A, 8B and 8C,
The color selection by the liquid crystal shutter optical system 20 will be described. 8A shows R light, FIG. 8B shows B light, and FIG. 8C.
Shows a state in which G light is selected, and FIG.
By sequentially repeating the switching states of the liquid crystal cells 22 and 24 shown in (c) to (c), it is possible to form a color image by RBG frame sequential.

Each of the liquid crystal cells 22 and 24 uses the birefringence of a liquid crystal (for example, nematic, smectic, FLC, etc.) or optical activity (optical rotation) to give a delay of 0 or half wavelength to a specific wavelength, that is, its Polarization plane is 9
When the light is polarized by 0 ° and the drive is turned off, a state is obtained in which the light of a color that has a specific polarization plane in advance by the color polarization plates 21 and 23 is polarized by 90 °.
On the other hand, when it is turned on, the incident light is transmitted as it is. Therefore, by changing the combination of the on / off states of the liquid crystal cells 22 and 24, the light passing through the last polarizing plate 25 has three primary colors R,
It is possible to switch so as to select and transmit only light of one of G and B colors.

In addition, in FIGS. 8A, 8B, and 8C, the color polarizing plates 21 and 23 and the polarizing plate 25 will be described as having the following characteristics as an example. Color polarizing plate 21 ... G light and R light are transmitted from the horizontal polarization axis, and R light and B light are transmitted from the vertical polarization axis. Color polarizing plate 23: R light is transmitted from the horizontal polarization axis, and G light and B light are transmitted from the vertical polarization axis. -Polarizing plate 25: Only the light of the vertically polarized component is transmitted.

For example, as shown in FIG.
For example, when the liquid crystal cell 22 is on and the liquid crystal cell 24 is off, R which has passed through the vertical polarization axis of the color polarizing plate 21.
The light, the B light, and the G light and the R light transmitted through the horizontal polarization axis pass through the liquid crystal cell 22 which is turned on as they are and reach the color polarizing plate 23. Then, in the color polarizing plate 23, only B light is emitted from the vertical polarization axis and R is emitted from the horizontal polarization axis.
Only light is transmitted and passes through the liquid crystal cell 24.
Here, since the liquid crystal cell 24 is turned off, the incident light is polarized by 90 °, and the R light that becomes a vertically polarized wave is the polarizing plate 2
5 will be transmitted.

Further, as shown in FIG. 8B, for example, when both the liquid crystal cell 22 and the liquid crystal cell 24 are turned on, the R light transmitted through the vertical polarization axis of the color polarizing plate 21,
The B light and the G light and R light transmitted through the horizontal polarization axis pass through the liquid crystal cell 22 as they are and reach the color polarizing plate 23.
Then, in the color polarizing plate 23, only the B light is transmitted from the vertical polarization axis and only the R light is transmitted from the horizontal polarization axis, and the B light and the R light are allowed to pass through the liquid crystal cell 24 which is turned on. Therefore, only the B light, which is the vertically polarized light component, is transmitted through the polarizing plate 25.

Further, as shown in FIG. 8C, for example, when the liquid crystal cell 22 is off and the liquid crystal cell 24 is on, R light transmitted through the vertical polarization axis of the color polarizing plate 21,
The B light and the G light and R light that have passed through the horizontal polarization axis pass through the liquid crystal cell 22 that is turned off, so that the polarization component is 90
The polarized wave is polarized and reaches the color polarizing plate 23. Then, in the color polarizing plate 23, only G light from the vertical polarization axis,
Further, only R light is transmitted from the horizontal polarization axis.
Further, the G light and the R light pass through the liquid crystal cell 24 which is turned on as they are, and only the G light which is a vertically polarized component passes through the polarizing plate 25.

That is, the order of the colors selected by the liquid crystal shutter optical system 20 in one frame by the driving pattern of the liquid crystal cells 22 and 24 is as shown in FIG. FIG. 9A shows a liquid crystal shutter optical system 20.
The order of colors selected by the liquid crystal cell 2 in FIG.
2 is ON / OFF, and FIG. 9C shows ON / OFF of the liquid crystal cell 24. That is, by controlling ON / OFF of the liquid crystal cells 22 and 24 as shown in FIG. 9C, n frames, n + 1 frames, and n + 2 frames are obtained as shown in FIG. 9A. It becomes possible to select the screen of each color of R, G, B within one frame. The liquid crystal shutter optical system 12
The number of liquid crystal cells used in the above is not limited to the above-mentioned two, and the color polarizing plates 21 and 23 can also be configured by combining other colors.

[0013]

By the way, the liquid crystal cell 2
The response speed of either ON or OFF of 2 and 24 is slow, and normally the response level at ON time can be ignored sufficiently fast as in the example shown in FIG. 9, but the response at OFF time is slow, so color shading Will occur. Although not shown, the same applies when the response speed at the time of turning on is slow.
Switching of each color of R, G, and B is performed during the vertical blanking period, but as shown in FIG.
If the response speed when 4 is turned off is slow, the colors do not switch completely during the vertical blanking period, and other colors are mixed at the beginning of the next field, that is, at the top of the screen, and appear on the screen as color shading. Will end up.

That is, in the example shown in FIG. 10, the liquid crystal cell 22 is turned on and the liquid crystal cell 24 is turned off in the R color field, but since both the liquid crystal cells 22 and 24 are turned on in the period SH3, the R color is turned on. B color is mixed in the field. Similarly, in the G color field, the liquid crystal cell 22 is turned off and the liquid crystal cell 24 is turned on during the period SH4.
Then, the liquid crystal cells 22 and 24 are both turned on, and the B color is mixed in the G color field. Therefore, due to such color shading, an image of a color different from that of the input composite video signal is output, and there is a problem that a good image cannot be obtained.

[0015]

SUMMARY OF THE INVENTION The present invention has been made to solve such problems, and includes two or more polarizing filters that transmit light polarized in a specific direction with respect to visible light. Two or more liquid crystal shutters that perform a switching operation of transmitting light of a specific plane of polarization by turning on / off a driving voltage, and on / off control of the liquid crystal shutters according to the timing of a field screen displayed in one frame And a liquid crystal shutter driving means capable of outputting a driving voltage for performing the above, and in a display device capable of displaying a color image by a frame sequential method, the on / off drive control of the two or more liquid crystal shutters has a slow response speed. The display device is configured so that the switching operation can be performed once and simultaneously in one frame to display a color image.
Further, the length of the blanking period between field screens is set according to the response speed of the switching operation.

According to the present invention, the color shading can be reduced or eliminated by setting the drive pattern of the liquid crystal cell for selecting the RGB color fields.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the display device of the present invention will be described below. FIG. 1 is a diagram showing an example of a circuit block of video signal processing for obtaining R, G, and B field images in a frame sequential system in the display device of the present embodiment. A normal composite video signal, that is, the video signal A shown in FIG. 7A is first input to the RGB separation circuit 1 to perform color signal separation processing.
The B primary color signal is generated. Then, after converting each primary color signal into a digital signal by the A / D converters 2a, 2b, 2c, the R memory 3 of the FiFo type memory unit 3 is once provided.
a, B memory 3b and G memory 3c are written respectively.

When reading from the memory unit 3,
For example, RGB primary color signals are sequentially read out at a speed three times as high as that at the time of writing, and are converted into analog signals by the D / A converter 4, so that RGB signals can be displayed in one frame shown in FIG. 7B.
The field sequential signal C in which the fields of the respective primary color signals are sequentially formed is generated. This frame sequential signal C is
By supplying the light to the RT 5 and letting it illuminate, the RBG color images are sequentially formed through the liquid crystal shutter optical system 6.

2 is equipped with a liquid crystal shutter optical system 6, and FIG.
The structural example of the display device which forms an image by the field sequential signal C shown in (b) is simply shown. CR in Figure 2
T5 is a high-intensity cathode ray tube which displays the frame sequential signal C with the brightness of each primary color signal shown in FIG. 7B.
The light emitted from is transmitted through the liquid crystal shutter optical system 6 arranged in front of it, so that a color image can be formed. The liquid crystal shutter optical system 6 is composed of a color filter that transmits light of a specific color, a polarizing plate and a liquid crystal shutter, as seen in, for example, US Pat. No. 4,758,818, US Pat. As described, the color polarizing plates 7 and 9, the polarizing plate 11 and the liquid crystal cells 8 and 1
It has 0.

For example, the liquid crystal cells 8 and 10 in this case respectively use the birefringence of the nematic liquid crystal to give a delay of 0 or half wavelength to a specific wavelength, that is, to polarize its polarization plane by 90 ° and drive it. When is turned off, the state where the light of the color having a specific polarization plane is polarized by 90 ° in advance by the color polarization plates 7 and 9 is obtained, while when turned on, Is designed to allow the incident light to pass therethrough. Therefore, by changing the combination of the on / off states of the liquid crystal cells 8 and 10, only the light of one of the three primary colors R, G and B is selected as the light passing through the last polarizing plate 11. It is possible to switch so as to make it transparent. The liquid crystal cells 8 and 10 of the present embodiment will be described assuming that the off-drive response speed is slow.

Further, the above-mentioned frame sequential signal C is the synchronizing circuit 1
2, and the field sync signal, the frame sync signal, etc. are extracted. The control circuit 13 is configured to be able to control various functional circuit parts of the display device, and in this case, for example, as shown in the figure, the frame synchronization signal supplied from the synchronization circuit 12, that is, the main deflection frequency synchronization signal. On the basis of the above, the LCS drive circuit 14 for generating a drive signal for performing on / off control of the liquid crystal cells 8 and 10 is provided inside. The structure of the liquid crystal shutter optical system 6 shown in this figure is an example, and is limited to this structure as long as it is configured to perform color selection based on a drive signal from the control circuit 13 side. No need.

The LCS drive circuit 14 generates a drive signal from the sync signal to control the on / off of the liquid crystal cells 8 and 10. That is, by performing the on / off control three times during one frame, it becomes possible to sequentially form each image of RGB.

Next, referring to FIGS. 3A, 3B and 3C,
The color selection by the liquid crystal shutter optical system 6 will be described. 3A shows R light, FIG. 3B shows B light, and FIG. 3C.
Shows a state in which G light is selected, and FIG.
By sequentially repeating the switching states of (c) to (c), it is possible to form a color image by frame sequential RBG. The horizontal and vertical polarization axes shown in FIG. 2 are not shown in the color polarizing plates 7 and 9 and the polarizing plate 11 in these figures.

Further, in FIGS. 3A, 3B and 3C, the color polarizing plates 7 and 9 and the polarizing plate 11 will be described as having the following characteristics as an example. Color polarizing plate 7 ... R light is transmitted from the horizontal polarization axis, and B light and G light are transmitted from the vertical polarization axis. Color polarizing plate 9: G light is transmitted from the horizontal polarization axis, and R light and B light are transmitted from the vertical polarization axis. -Polarizing plate 11 ... Only the light of the vertically polarized component is transmitted.

As shown in FIG. 3A, for example, when the liquid crystal cell 8 is off and the liquid crystal cell 10 is on,
The B light, the G light passing through the vertical polarization axis of the color polarization plate 7, and the R light passing through the horizontal polarization axis are polarized by 90 ° by passing through the liquid crystal cell 8 which is turned off. To reach. Then, in the color polarizing plate 9, only R light is transmitted from the vertical polarization axis and only G light is transmitted from the horizontal polarization axis, and passes through the liquid crystal cell 10. Here, since the liquid crystal cell 10 is turned on, the incident light passes through as it is, and the R light which is a vertically polarized wave passes through the polarizing plate 11.

Further, as shown in FIG. 3B, when both the liquid crystal cell 8 and the liquid crystal cell 10 are on, for example, B light and G light transmitted through the vertical polarization axis of the color polarizing plate 7 are used.
The light and the R light transmitted through the horizontal polarization axis pass through the liquid crystal cell 8 as they are and reach the color polarizing plate 9. In the color polarizing plate 9, only the B light is transmitted from the vertical polarization axis, and the B light is transmitted as it is through the liquid crystal cell 10 which is turned on. Therefore, only the B light, which is a vertically polarized component, is transmitted from the polarizing plate 11.

As shown in FIG. 3C, when both the liquid crystal cell 8 and the liquid crystal cell 10 are off, the B light and the G light transmitted through the vertical polarization axis of the color polarizing plate 7 are used.
The light and the R light transmitted through the horizontal polarization axis pass through the liquid crystal cell 8 which is turned off, and the polarization component is polarized by 90 ° and reaches the color polarization plate 9. In the color polarizing plate 9, only B light is emitted from the vertical polarization axis and G is emitted from the horizontal polarization axis.
Only the light is transmitted, and the G light and the R light are polarized by 90 ° by passing through the liquid crystal cell 10 which is turned off,
Only G light, which is a vertically polarized component, is transmitted through the polarizing plate 11.

That is, the order of colors selected by the liquid crystal shutter optical system 6 within one frame is as shown in FIG. 4A is a sequence of colors selected by the liquid crystal shutter optical system 6, FIG. 4B is color shading, FIG. 4C is on / off of the liquid crystal cell 8, and FIG.
(D) shows ON / OFF of the liquid crystal cell 10. That is, as shown in FIG. 4C, the liquid crystal cells 8, 1
By performing on / off control of 0, as shown in FIG. 4A, n frame, n + 1 frame, n +
2 frames ... R, B, etc. within 1 frame
It becomes possible to select the screen of each color of G.

The application pattern of the drive voltage to the liquid crystal cells 8 and 10 in the present invention is conditioned on the switching control of the slower response speed (on or off) being performed once within one frame and simultaneously. ing. Therefore, in the present embodiment, when switching from the B color field to the G color field as illustrated, the liquid crystal cells 8 and 1
By configuring a color selection pattern in which 0 is turned off at the same time, for example, B color is mixed only in the first period SH1 of the G color field. Therefore, it is possible to reduce the color shading that has conventionally occurred in two fields. In particular, since the B color is the most inconspicuous color as the color signal component, it is possible to make the color shading almost inconspicuous.

Next, a modification of the above embodiment will be described with reference to FIGS. Although the above embodiment has been described on the condition that the liquid crystal cells 8 and 10 are switched from ON to OFF once and simultaneously in one frame, in this modification, the response speed of the liquid crystal cells 8 and 10 is changed. The blanking period between fields in which the slower switching control is performed is set longer according to the response speed of the liquid crystal cells 8 and 10. That is, this is an example in which the blanking period includes the period SH1 in which the color shading described in FIG. 4 occurs. As a result, since the color shading period becomes blanking, it is possible to prevent the other color from being displayed in a mixed state in a certain color field.

First, the color selection by the liquid crystal shutter optical system 6 in the modified example will be described with reference to FIG. FIG. 5A shows a state in which R light is selected, FIG. 5B shows B light, and FIG. 5C shows a state in which G light is selected. In addition, FIG.
In (b) and (c), the color polarizing plates 7a and 9a and the polarizing plate 1 are used.
1 will be described as having the following characteristics as an example. Color polarizing plate 7a: B light is transmitted from the horizontal polarization axis, and G light and R light are transmitted from the vertical polarization axis. Color polarizing plate 9a: B light and R light are transmitted from the horizontal polarization axis, and G light and B light are transmitted from the vertical polarization axis. -Polarizing plate 11 ... Only the light of the vertically polarized component is transmitted.

For example, as shown in FIG.
For example, when both the liquid crystal cell 8 and the liquid crystal cell 10 are off, the G light transmitted through the vertical polarization axis of the color polarizing plate 7a,
The R light and the B light transmitted through the horizontal polarization axis are polarized by 90 ° in the liquid crystal cell 8 which is turned off and reach the color polarizing plate 9a. Then, in the color polarizing plate 9a, B light is transmitted from the vertical polarization axis and R light is transmitted from the horizontal polarization axis, and passes through the liquid crystal cell 10. Here, since the liquid crystal cell 10 is turned off, the incident light is polarized by 90 °, and the R light that has become a vertically polarized wave passes through the polarizing plate 11.

As shown in FIG. 5B, when the liquid crystal cell 8 is on and the liquid crystal cell 10 is off, for example, G light and R light transmitted through the vertical polarization axis of the color polarizing plate 7a.
The light and the B light transmitted through the horizontal polarization axis pass through the liquid crystal cell 8 as they are and reach the color polarizing plate 9a. Then, in the color polarizing plate 9a, only the G light is transmitted from the vertical polarization axis and only the B light is transmitted from the horizontal polarization axis, and the G light and the B light are polarized by 90 ° in the liquid crystal cell 10 which is turned off. Therefore, only the B light, which has become the vertically polarized component, is transmitted through the polarizing plate 11.

Further, as shown in FIG. 5C, when both the liquid crystal cell 8 and the liquid crystal cell 10 are on, for example, G light and R light transmitted through the vertical polarization axis of the color polarizing plate 7a.
The light and the B light transmitted through the horizontal polarization axis pass through the liquid crystal cell 8 which is turned on as they are and reach the color polarizing plate 9. In the color polarizing plate 9, only the G light is transmitted from the vertical polarization axis, only the B light is transmitted from the horizontal polarization axis, and the G light and the R light are turned on.
Will pass through as is. Then, only G light, which is a vertically polarized component, is transmitted through the polarizing plate 11.

The order of the colors selected by the liquid crystal shutter optical system 6 within one frame by the on / off control of the liquid crystal cells 8 and 10 is as shown in FIG. Further, in the modification, the length of the blanking period between the G-color field and the R-color field of the next frame in which the liquid crystal cells 8 and 10 are both turned off is turned off according to the response time of the liquid crystal cells 8 and 10. The period is set to be completely off after being controlled, or the period is equal to the length of each color field.

FIG. 6A shows the order of each color field selected by the liquid crystal shutter optical system 6 and the blanking period between the G color field and the R color field, and FIG.
Is color shading in each field, Fig. 6
FIG. 6C shows ON / OFF of the liquid crystal cell 8, and FIG. 6D shows ON / OFF of the liquid crystal cell 10.

As shown in the figure, for example, the blanking period when switching from the G color field to the R color field of the next field is almost complete depending on the response time when both the liquid crystal cells 8 and 10 are turned off. By setting the period Bln1 until it is turned off, the period SH1 (shown in FIG. 4) in which G color shading occurs in the R color field becomes the blanking period, and RB
G It becomes possible to eliminate color shading in each color field.

In this way, the period until the liquid crystal cells 8 and 10 are almost completely turned off is set to the period Bln2 equivalent to the length of each RBG color field, so that the composite video signal shown in FIG. 3 (R memory 3
It is possible to make the vertical deflection cycle constant when writing data in the a, B memory 3b, and G memory 3c).

In this case, in the embodiment of the present invention, a field (black) which is a blanking period is added to the conventional example of the three-primary-color display system. It is preferable to use the γ-corrected one. Also, the liquid crystal cells 8, 10
Even when the response speed of the ON drive is slow, color shading can be eliminated by setting the length of the blanking period according to the response speed. Further, the number of liquid crystal cells used in the liquid crystal shutter optical system 6 is not limited to the above-mentioned two in the above-described embodiment, and the color polarizing plates 7 and 9 and the color polarizing plates 7a and 9a may be different from each other. It is also possible to use a combination of colors.

[0040]

As described above, in the display device of the present invention, when a color image is displayed by the field sequential method of RGB color fields, on / off drive of two or more liquid crystal shutters for selecting RGB color fields. As for control, the switching operation with the slower response speed is set to 1 within one frame.
It is possible to reduce the color shading more than before by forming a drive pattern and displaying a color image under the condition that it is performed once and simultaneously. Furthermore, by setting the blanking period to be long according to the response speed of the liquid crystal shutter when the liquid crystal shutter is turned off (or turned on) under the above conditions, the color shading period can be set as the blanking period. So you can eliminate color shading.

[Brief description of drawings]

FIG. 1 is a diagram showing a partial circuit block of a video signal processing system of a display device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a liquid crystal shutter optical system shown in FIG.

3 is an RBG based on the liquid crystal shutter optical system shown in FIG.
It is a figure explaining selection of each color.

4A and 4B are diagrams illustrating ON / OFF driving of liquid crystal cells in one frame by the liquid crystal shutter optical system shown in FIG. 2, RBG color images selected in one frame, and color shading.

5 is another R by the liquid crystal shutter optical system shown in FIG.
It is a figure explaining the selection pattern of each color of BG.

6 is a diagram illustrating an example of setting a blanking period corresponding to a response time when the liquid crystal cell illustrated in FIG. 5 is driven off.

FIG. 7 is a diagram schematically showing a field image for each RBG in a frame sequential signal.

FIG. 8 is a diagram illustrating a selection pattern of each color of RBG by a conventional liquid crystal shutter optical system.

9 is a diagram showing on / off driving of a liquid crystal cell of the liquid crystal shutter optical system shown in FIG. 8 and an order of images of each color of RBG selected in one frame by the liquid crystal cell.

FIG. 10 is a diagram schematically showing color shading in a conventional frame sequential method.

[Explanation of symbols]

6 Liquid crystal shutter optical system 7, 9 color polarizer 8, 10 liquid crystal cell 11 Polarizer

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-60-194426 (JP, A) JP-A-60-233625 (JP, A) JP-A-6-324637 (JP, A) JP-A-8- 248381 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N 9/12 G02F 1/133 G09G 3/36

Claims (3)

(57) [Claims] 1. Two or more polarization filters that transmit light polarized in a specific direction with respect to visible light, and two or more that perform a switching operation that transmits light of a specific polarization plane by turning on / off a drive voltage. And a liquid crystal shutter drive means capable of outputting a drive voltage for performing on / off control of the liquid crystal shutter according to the timing of the field screen displayed in one frame. In a display device capable of displaying a color image, the on / off drive control of the two or more liquid crystal shutters is performed by performing a switching operation with a slower response speed once and simultaneously in one frame to display a color image. A display device characterized by being capable of performing. 2. The display device according to claim 1, wherein a blanking period length between field screens is set according to a response speed of the switching operation. 3. The display device according to claim 2, wherein the blanking period is the same period as the field screen.