Projection display device using two liquid crystal display panels

Abstract: A projection display device adopting two digital display panels, by which the maximum brightness, which is the same as that in a exemplary case of adopting three digital display panels, is obtained by using only two digital display panels, is provided. Accordingly, R'/G'/B'/W data obtained by converting R/G/B data using a predetermined algorithm for a four-color sequence system is displayed via an optical engine having two digital display panels, with the same brightness as that when data is displayed using three digital display panels. Hence, the structure of the optical engine can be simplified, and a convergence adjusting point can be reduced.

Description: The present invention relates to a display device comprising a source of white light for providing a beam of white light, a polarizing beam splitter for splitting the beam of white light from the source of white light into first and second orthogonally polarized beams, colour switch means for switching the colour of the polarized beams, first and second LCD panels for modulating the first and second polarized beams (P, S) respectively, beam combining means for combining the modulated beams from the LCD panels and a controller for generating control signals for the LCD panels in dependence on an input RGB signal. Existing types of display devices that are driven in a digital system include plasma display panels (PDP), liquid crystal display (LCD) panels and ferroelectric liquid crystal (FLC) panels. FLC panels have a structure in which ferroelectric liquid crystal is sandwiched between an optical planar mirror formed on a silicon substrate and glass, and have a wide viewing angle and a fast response speed compared to existing panels. A exemplary display device using three LCD panels is made up of R, G and B controllers, an optical engine and a screen. The optical engine is made up of R, G and B LCD panels and an optical system which includes an optical source, a collimating lens, a polarized beam splitter, a reflective mirror and a projection lens. The R, G and B controllers receive R, G and B signals, respectively, and control the offset, contrast and brightness of the received signals, perform signal processing such as gamma compensation, and generate R, G and B data on a field-by-field basis in synchronization with a vertical synchronization signal, respectively, to display the R, G and B data on the R, G and B LCD panels, respectively. Also, the R, G and B controllers each receive a vertical synchronization signal and a horizontal synchronization signal, and generate clock and panel control signals for controlling the R, G and B LCD panels, respectively. In the optical engine, light emitted from the optical source is split into R, G and B light beams by the polarized light beam splitter, and the R, G and B light beams are projected to the R, G and B LCD panels, respectively, by the reflective mirror. Then, the R, G and B LCD panels transmit or reflect incident light beams corresponding to data values R, G and B applied by the R, G and B controllers to cells each formed as a matrix, under the control of the clock and panel control signal, and then display the light beams on the screen via the projection lens. In a exemplary display device using three LCD panels, the use of three LCD panels increases the manufacturing costs and complicates the structure of an optical system. Also, the convergence of each of the R, G and B light must be adjusted, so that the number of process steps increases. The reader is directed to US-A-6132047 which describes a three panel projector, US-A-5706063 which describes a two panel projector, US-A-5833338 which describes single panel and double panel projectors and the use of a colour wheel for sequentially separating the R, G and B spectral components of a light beam from a light source, US-A-5784038 which describes the use of two colour wheels and two liquid crystal display panels in developing a projection image, and US-A-5929843 wherein the white component data is extracted from input R, G, B colour data and use to generate R'/G'/B'/W data for displaying a full colour image on a liquid crystal display panel. Other references of interest, relating to projection display devices, are the JP-A-11-6980, JP-A-08-8168039, JP-9-90402, JP-A-10-123477, JP-A-10-23445, JP-A-08-294138 and JP-A-10-148885. To solve the above problems, an objective of the present invention is to provide a display device adopting two digital display panels, by which the same maximum brightness as that in the case of adopting three digital display panels is obtained using only two digital display panels. A display device according to the present invention is characterised in that the colour switch means is configured to switch the colours of the polarized beams between red, green, blue and white and the controller is configured to generate red, green, blue and white data signals for controlling the LCD panels from the input RGB signal, using a predetermined arithmetic algorithm and in synchronism with the changing beam colours. The above objective and advantage of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: Fig. 1 is a block diagram illustrating the structure of a exemplary display device using three liquid crystal display (LCD) panels; Fig. 2 is a block diagram illustrating the structure of a display device using two digital display panels according to the present invention; Fig. 3 shows the quantity of light, the time and the luminance in a three-color sequence system applied to a exemplary display device using three LCD panels; Fig. 4 shows the quantity of light, the time and the luminance in a four-color sequence system applied to a display device using two digital display panels according to the present invention; Fig. 5 is a detailed configuration view of a first embodiment of the optical engine of Fig. 2; Fig. 6 is a detailed configuration view of a second embodiment of the optical engine of Fig. 2; Fig. 7 is a detailed configuration view of a third embodiment of the optical engine of Fig. 2. Fig. 8 is a flowchart illustrating an algorithm for converting three colors into four colors, which is applied to the present invention; and Fig. 9 shows a color vector diagram for explaining a four-color conversion algorithm according to the present invention. As shown in Fig. 1, a exemplary display device using 3 LCD panels is made up of R, G and B controllers 101, 102 and 103, an optical engine 104 and a screen 105. Here, the optical engine 104 is made up of R, G and B LCD panels 106, 107 and 108 and an optical system 109 which includes (but does not show) an optical source, a collimating lens, a polarized beam splitter, a reflective mirror and a projection lens. The R, G and B controllers 101, 102 and 103 receive R, G and B signals, respectively, and control the offset, contrast and brightness of the received signals, perform signal processing such as gamma compensation, and generate R, G and B data on a field-by-field basis in synchronization with a vertical synchronization signal, respectively, to display the R, G and B data on the R, G and B LCD panels, 106, 107 and 108, respectively. Also, the R, G and B controllers 101, 102 and 103 each receive a vertical synchronization signal and a horizontal synchronization signal, and generate clock and panel control signals for controlling the R, G and B LCD panels, 106, 107 and 108, respectively. In the optical engine 104, light emitted from the optical source (not shown) is split into R, G and B light beams by the polarized light beam splitter (not shown), and the R, G and B light beams are projected to the R, G and B LCD panels, 106, 107 and 108, respectively, by the reflective mirror (not shown). Then, the R, G and B LCD panels, 106, 107 and 108, transmit or reflect incident light beams corresponding to data values R, G and B applied by the R, G and B controllers 101, 102 and 103 to cells (not shown) each formed as a matrix, under the control of the clock and panel control signal, and then display the light beams on the screen 105 via the projection lens. As shown in Fig. 2, a display device using two digital display panels according to the present invention includes a controller 201, an optical engine 202 and a screen 203. The controller 201 receives R, G and B signals, and vertical and horizontal synchronization signals, controls the offset, the contrast and the brightness, performs signal processing such as gamma correction to first generate Ri/Gi/Bi data according to a 3-color sequence system, converts the Ri/Gi/Bi data into R'/G'/B'/W data using a 4-color conversion algorithm, and outputs the R'/G'/B'/W data. Also, the controller 201 generates a control signal for controlling LCD panels 204 and 205 in the optical engine 202, and a color switching control signal for controlling a color switching means 206. Here, the optical engine 202 is made up of first and second LCD panels 204 and 205 and an optical system 207. As shown in Fig. 3, the maximum luminance (Ymax1) in an image displaying method based on an R/G/B three-color sequence algorithm using three LCD panels is the sum of the products of the quantity of light by the time for R, G and B, so that it is calculated as in Equation 1: Y max1 = (1/3 × 1) + (1/3 × 1) + (1/3 × 1) = 1 As shown in Fig. 4, the maximum luminance (Ymax2) in an image displaying method based on the R/G/B/W four-color sequence algorithm using two LCD panels according to the present invention is the sum of the products of the quantity of light by the time for R, G, B and W, so that it can be calculated as in Equation 2: Y max2 = (2/3 × 1/4) + (2/3 × 1/4) + (2/3 × 1/4) + (2 × 1/4) = 1 Accordingly, the luminance value in a method of displaying via two LCD panels using the R/G/B/W four-color sequence system according to the present invention is equal to that in a method of displaying via three LCD panels using the exemplary R/G/B three-color sequence system. Simple addition of only the achromatic color W to Ri/Gi/Bi in the 3-color sequence system improves the brightness of the luminance, but the color is transited to the achromatic color, degrading the saturation of the color. The transition of an output color in the vector direction of the achromatic color due to the addition of the achromatic color W is prevented by the following R/G/B/W four-color sequence conversion algorithm which is applied to the present invention will be described with respect to Fig. 8. In the first step 801, Ri, Gi and Bi signals are received, then in step 802 an IncY value for determining an increment of the luminance is determined as shown in Equation 3 or 4: IncY = MIN ( Ri , Gi , Bi ) IncY = MEAN ( Ri , Gi , Bi ) That is, the IncY value can be determined as the minimum value selected among the values Ri, Gi and Bi or as the average of Ri, Gi and Bi. In step 803, the values of vector_R, vector_G, and vector_B are calculated as shown in Equations 5, 6 and 7: vector_R = IncY * sel * (Ri / Ri * Ri + Gi * Gi + Bi * Bi ) vector_G = IncY * sel * ( Gi / Ri * Ri + Gi * Gi + Bi* Bi ) vector_B = IncY* sel* ( Bi / Ri* Ri + Gi * Gi + Bi * Bi ) wherein sel denotes a scale constant, which can be obtained experimentally and depends on the characteristics of a system. When sel is too large, it may be impossible that the system expresses the values vector_R, vector_G, and vector_B, and when sel is too small, the effect of an improvement in luminance may be reduced due to small brightness compensation. Thus, it is experimentally effective to optimally determine the value of sel within 1 ≤ sel ≤ 3 . In step 804, the minimum value among the values vector_R, vector_G and vector_B is selected as the value of the achromatic white color W to be used in the four-color sequence display system, as shown in Equation 8. W = min(vector_R , vector_G and vector_B) In this way, the achromatic color W, which is added in order to improve the luminance, is obtained. In step 805, a transition of an input color in the achromatic color vector direction due to the addition of the achromatic white color W is compensated for by the operations shown in Equations 9, 10 and 11: Rv = Ri + vector_R Gv = Gi + vector_G Bv = Bi + vector_B In step 806, R', G' and B', which have been compensated for in the transition in the achromatic color vector direction, are determined as shown in Equations 12, 13 and 14, and output: R' = Rv - W G' = Gv - W B' = Bv - W According to the above algorithms, the luminance is increased due to the addition of the achromatic color W, and due to the addition of vector_R, vector_G, and vector_B to the signals Ri, Gi and Bi, respectively, as shown in Equations 9, 10 and 11. Also, the transition of color in the achromatic color vector direction is compensated for by subtracting the value of an added achromatic color W from each of the values Rv, Gv and Bv as in Equations 12, 13 and 14. Then the R'/G'/B'/W data is output in step 807 as the data obtained in the four-color sequence system. As shown in Fig. 9, the Ro/Go/Bo/W four-color conversion algorithm will now be described in consideration of only the R and G vectors, excluding the B vector, for convenience of explanation. First, when the vector of an input color signal C1 is slanted in the R vector direction with respect to an achromatic color, an addition of a calculated achromatic color W to the C1 vector may cause a transition of the input color signal C1 toward the achromatic color. However, when a vector is calculated by subtracting W, which is the same as the R vector and the G vector, from the vector of the input color signal C1 multiplied by a scaling constant or the like, the input color signal C1 may be shifted in the R vector direction, indicated by arrow 91. Thus, a final output synthesized vector has almost the same phase as that of the original C1 vector. Even when an input color signal C2 is calculated using an algorithm according to the present invention by the above-described method, it is shifted in the G vector direction, indicated by arrow 92. Thus, if a final synthesized vector including W is drawn, it has almost the same phase as that of the C2 vector. The operation of displaying the R'/G'/B'/W data of the controller 201, which is output in step 807 as the data obtained in the four-color sequence system, on the screen 203 via the optical engine 202 having two LCD panels 204 and 205, will now be described. A first embodiment of the optical engine 202 is shown in Fig. 5, and includes an optical source 501, a collimating lens 502, a color switcning means 503, first and second polarized light beam splitters 504 and 505, first and second LCD panels 506 and 507, first and second reflective mirrors 508 and 509, and a projection lens 510. The optical source 501 is made up of a lamp for producing light, and a reflective mirror for reflecting light emitted from the lamp to guide the light, and radiates light. The collimating lens 502 converts incident light output from the optical source 501 into parallel light or focusing light. The color switching means 503 is formed of an LCD shutter or a color wheel, and receives a white color light from the collimating lens 502 and sequentially switches and outputs four colors R, G, B and W during one vertical period under the control of a color switching control signal received from the controller 201. That is, during a first 1/4 vertical period, only the wavelength of the color R among the received light is transmitted, while the remaining wavelengths are blocked. During the next 1/4 vertical period, only the wavelength of the color G among the received light is transmitted, while the remaining wavelengths are blocked. Then, the wavelengths of the colors B and W are sequentially switched and transmitted during the remaining two 1/4 vertical periods. The first polarized light beam splitter 504 transmits, for example, a P wave among light received from the color switching unit 503, and reflects an S wave so that the direction in which light travels is changed by 90 degrees. The first reflective mirror 508 reflects light transmitted by the first polarized light beam splitter 504, and guides the reflected light to the first LCD panel 506. The second reflective mirror 509 reflects light reflected by the first polarized light beam splitter 504, and guides the reflected light to the second LCD panel 507. The first LCD panel 506 is installed on the light path of light reflected by the first reflective mirror 508, and transmits the incident light corresponding to the R'/G'/B'/W data values applied from the controller 201 to the data lines of each cell formed of a matrix, under the control of a clock and panel control signal. That is, the incident light of each color is transmitted during the time corresponding to the value of each of the R/G/B/W data, within a 1/4 vertical period. The second LCD panel 507 is installed on the path of incident light reflected by the second reflective mirror 509, and transmits the incident light corresponding to the R'/G'/B'/W data values applied to the data lines of each cell formed of a matrix, under the control of the clock and panel control signal, likewise for the first LCD panel 506. The second polarized beam splitter 505 transmits P wave light among light received from the first and second LCD panels 506 and 507 and reflects S wave light, so that the travel path of the S wave light from the first LCD panel 506 is consistent with the travel path of the P wave light from the second LCD panel 507. The projection lens 510 magnifies the light received from the second polarized beam splitter 505 and projects it toward the screen 511. In this way, the R'/G'/B'/W data converted by the four-color sequence system are displayed on a screen via an optical engine having two LCD panels. A second embodiment of the optical engine 202 is shown in Fig. 6, and includes an optical source 601, first and second polarized beam splitters 602 and 611, first and second reflective mirrors 603 and 610, first and second collimating lenses 604 and 605, first and second color switching means 606 and 607, first and second LCD panels 608 and 609, a projection lens 612 and a screen 613. The optical source 601 is made up of a lamp for producing light, and a reflective mirror for reflecting light emitted from the lamp to guide the light, and radiates light. The first polarized beam splitter 602 transmits, for example, a P wave among light received from the light source 601 and reflects an S wave so that the direction of travel of light is changed by 90 degrees. The first reflective mirror 603 reflects light reflected by and received from the first polarized beam splitter 602, and guides the reflected light to the second collimating lense 605. The first collimating lens 604 focuses light transmitted by the first polarized beam splitter 602 into a parallel beam or focusing beam, and the second collimating lens 605 focuses light reflected by the first reflective mirror 603 into a parallel beam or focusing beam. The first color switching means 606 receives light via the first collimating lense 604, and sequentially switches and outputs the R, G, B and W signals at intervals of 1/4 vertical periods during one vertical period under the control of a color switching control signal received from the controller 201. The second color switching means 607 receives light via the second collimating lense 605, and sequentially switches and outputs the R, G, B and W signals at intervals of 1/4 vertical periods during one vertical period under the control of the color switching control signal received from the controller 201. The second reflective mirror 610 reflects light output from the first color switching unit 606, and guides the reflected light toward the second LCD panel 609. The first and second LCD panels 608 and 609 are installed on the paths of light beams output from the second color switching unit 607 and the second reflective mirror 610, respectively, and transmit the incident light beams corresponding to the R'/G'/B'/W data values applied by the controller 201 to the data lines of each cell formed as a matrix, under the control of the clock and panel control signal. That is, the incident R, G, B and W light is transmitted corresponding to the data values R', G', B' and W at intervals of 1/4 vertical periods during one vertical period. The second polarized beam splitter 611 transmits P wave light among light received from the second LCD panel 609, and reflects S wave light among light received from the first LCD panel 608 so that the travel path of the P wave light is consistent with that of the S wave light received from the second LCD panel 609. The projection lens 612 magnifies the light received from the second polarized beam splitter 611 and projects it toward the screen 613. The operation of a third embodiment of the optical engine 202 will now be described with reference to Fig. 7. The first and second embodiments of the optical engines 202 use transmissive LCD panels, but the third embodiment uses reflective ferroelectric liquid crystal (FLC) panels. A transmissive LCD panel displays an image by transmitting incident light corresponding to a data value input to the data line of the transmissive LCD panel, and a reflective FLC panel displays an image by reflecting incident light corresponding to a data value input to the data line of the reflective FLC panel. The optical engine 202 according to the third embodiment includes an optical source 701, a collimating lense 702, a color switching unit 703, a polarized beam splitter 704, first and second FLC panels 705 and 706, a projection lens 707 and a screen 708. The optical source 701 is made up of a lamp for producing light and a reflective mirror for reflecting light emitted from the lamp to guide the light, and radiates light. The collimating lens 702 focuses light irradiated from the optical source 701 into parallel light or focusing light. The color switching unit 703 is an LCD shutter or a color wheel, and receives white color light from the collimating lense 702 and sequentially switches and outputs the R, G, B and W signals during one vertical period under the control of a color switching control signal received from the controller 201. That is, during a first 1/4 vertical period, only the wavelength of the color R among the received light is transmitted, while the remaining wavelengths are blocked. During the next 1/4 vertical period, only the wavelength of the color G among the received light is transmitted, while the remaining wavelengths are blocked. Then, the wavelengths of the colors B and W are sequentially switched and transmitted during the remaining two 1/4 vertical periods. The polarized beam splitter 704 transmits, for example, P wave light among light received from the color switching unit 703 and guides the P wave light toward the second FLC panel 706, and reflects an S wave light to change the direction of travel of light by 90 degrees and guides the reflected S wave light toward the first FLC panel 705. The first and second FLC panels 705 and 706 reflect the incident light beams corresponding to the R'/G'/B'/W data values applied by the controller 201 to the data lines of each cell formed as a matrix, under the control of the clock and panel control signal, thereby displaying the image of each pixel. Then, the polarized beam splitter 704 transmits P wave light among light reflected by the first FLC panel 705, and reflects S wave light among light reflected by the second FLC panel 706 so that the travel path of the S wave light is consistent with that of the P wave light received from the first FLC panel 705. The projection lens 707 magnifies the light received from the polarized beam splitter 704 and projects it toward the screen 708. In this way, the R'/G'/B'/W data converted by the four-color sequence system are displayed on a screen via an optical engine having two LCD or FLC panels. Therefore, the maximum brightness when three LCD panels are adopted can also be obtained by using two LCD or FLC panels. The above-described optical engines have been simplified for convenience of explanation. However, it is apparent to one of ordinary skill in the optical engine designing techniques that the optical engines can further include a glass polarizer, various shutters, cubes, and the like in order to improve the quality of image such as contrast, and that the location of collimating lenses can be changed. According to the present invention as described above, R'/G'/B'/W data converted by the four-color sequence system is displayed via an optical engine having two digital display panels, with the same brightness as that when three digital display panels are used. Hence, the structure of the optical engine can be simplified, and a convergence adjusting point can be reduced.

Claims: A display device composting: a source (501, 601, 701) of white light for providing a beam of white light, a polarizing beam splitter (504; 604, 704) for splitting the beam of white light from the source (501, 601, 701) of white light into first and second orthogonally polarized beams (P, S); colour switch means (503; 606, 607; 703) for switching the colour of the polarized beams (P, S); first and second LCD panels (506, 507; 605, 606; 705, 706) for modulating the first and second polarized beams (P, S) respectively; beam combining means (505; 605; 705) for combining the modulated beams from the LCD panels (506, 507; 608, 609; 705, 706); and a controller (201) for generating control signals for the LCD panels in dependence on an input RGB signal, characterised in that the colour switch means (503; 606, 607; 703) is configured to switch the colours of the polarized beams (P, S) between red, green, blue and white and the controller is configured to generate red, green, blue and white data signals for controlling the LCD panels (506, 507; 608, 609; 705, 706) from the input RGB signal, using a predetermined arithmetic algorithm and in synchronism with the changing beam colours. A display device according to claim 1, wherein the LCD panels (506, 507; 608, 609) are transmissive. A display device according to claim 1, wherein the LCD panels (705, 706) are reflective. A display device according to claim 3, wherein the LCD panels (705, 706) are ferroelectric LCD panels. A display device according to claim 1 or 2, including: a lens (502) for collimating or focusing the beam of white light from the light source (501); a first mirror (508) for reflecting the first polarized beam (P) to the first LCD panel (506); a second mirror (509) for reflecting the second polarized beam (S) to the second LCD panel (507); and a lens for producing a magnified image from light output from beam combining means (505) for display on said screen, wherein the colour switching means (503) is positioned between the collimating lens (502) and the beam splitter (504). A display device according to claim 1 or 2, including: a first lens (605) for collimating or focusing the first polarized beam (P); a first mirror (603) for directing the first polarized beam (P) to the first lens (605); a second lens (604) for collimating or focusing the second polarized beam (S); a second mirror (610) for changing the direction of the second polarized beam (S); and a lens for producing a magnified image from light output from beam combining means (612) for display on said screen, wherein the colour switching means (606, 607) comprises a first colour switch (607) between the first lens (605) and the first LCD panel (608) and a second colour switch (606) between the second lens (604) and the second mirror (610). The display device according to claim 3 or 4, including a lens (702) for collimating or focusing the beam of white light from the source of white light (701) and a lens for producing a magnified image from light output from beam combining means (704) for display on said screen, wherein the beam splitter (704) and the beam combiner (704) are the same device (704). A display device according to any preceding claim, wherein the red, green, blue and white data signals are sequentially generated in respective time periods corresponding to predetermined portions of a vertical period. A display device according to claim 8, wherein said time periods are one quarter of a vertical period. A display device according to any preceding claim, wherein said controller (201) is configured to receive horizontal and vertical synchronization signals and generate clock and panel control signals therefrom.

Inventors: KIM YOUNG-SUN, KIM, YOUNG-SUN
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 2000
Main classification: H04N9
IPC codes: H04N5, G02F1, H04N9, G09G3