JP2012093770A - Liquid crystal display device and common voltage adjustment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of automatically adjusting a common voltage in a short time.SOLUTION: The liquid crystal display device includes liquid crystal panels 7 to 9 irradiated with light at different wavelength regions to generate image light according to the video data supplied by a frame unit, wherein a sensor unit 12 detecting the luminance of image light with combined colors by each color of R, G, B is disposed between a color combining prism 10 combining colors of image light in the wavelength regions generated by the respective liquid crystal panels and a projection lens 11 projecting the image light with colors combined by the color combining prism 10. A counter electrode voltage generating circuit 5 supplies a given common voltage to a common electrode to which a plurality of liquid crystal cells constituting a liquid crystal panel 108 are commonly connected. A control unit 6 adjusts a common voltage generated by the counter electrode voltage generating circuit 5 based on the output of the sensor unit 12 so as to minimize flicker which is a difference in the luminance in image light between continuous frames.

Description

  The present invention relates to a liquid crystal display device using a liquid crystal panel typified by a liquid crystal projector and the like, and in particular, an AC drive type liquid crystal display device in which a common voltage is supplied to a common electrode to which a plurality of liquid crystal cells are connected in common. About.

  In the liquid crystal display device, as a countermeasure against deterioration of the liquid crystal, AC driving is performed in which the polarity of the voltage applied to the liquid crystal is inverted at a predetermined cycle. The AC drive includes dot inversion drive, line inversion drive, frame inversion drive, and the like. In the liquid crystal display device, the liquid crystal panel is driven by one or a combination of these.

  FIG. 7 shows the waveform of video data for line inversion driving. In the video data shown in FIG. 7, positive-polarity video data and polarity-negative video data whose polarity is inverted with reference to the reference voltage Vref are alternately switched every horizontal scanning period. In the line inversion drive, as shown in FIG. 7, the polarity of the video signal is inverted every horizontal scanning period. The positive video data and the negative video data are vertically symmetrical about the reference voltage Vref. In this line inversion drive, if the brightness of the image displayed by the positive polarity video data is different from the brightness of the image displayed by the negative polarity video data, the difference in brightness is indicated as flicker (brightness flicker). Visible. Also, the video data is inverted between frames, resulting in a difference in brightness in the displayed image, and this difference in brightness is visually recognized as flicker. The common voltage Vcom is a voltage applied to the common electrode of each liquid crystal cell, and is adjusted so that the flicker generated when the video data is inverted is minimized.

  In a projector that employs an AC drive method, usually, the amount of flicker in a projected image is measured at the time of factory shipment, and the common voltage is adjusted so that the measured value of flicker is minimized. The adjustment of the common voltage balances the potential applied to the liquid crystal cell when the positive video data and the negative video data are applied, thereby reducing the difference in brightness of the display image between frames. FIG. 8 shows a schematic configuration of a system capable of performing such common voltage adjustment.

  Referring to FIG. 8, a projector 100 is a three-plate projector including three liquid crystal panels 107 to 109 that form images of respective colors of R (red), G (green), and B (blue). A color composition prism 110 that synthesizes image light (R image light, G image light, and B image light) from the liquid crystal panels 107 to 109, and a projection that projects RGB image light synthesized by the color composition prism 110 onto an external screen. A lens 111. Projector 100 also includes a processing circuit for forming images (RGB) based on video signals supplied from an external video signal source such as a personal computer on liquid crystal panels 107-109. This processing circuit is provided in each of the liquid crystal panels 107 to 109. FIG. 8 shows only a processing circuit related to the liquid crystal panel 108, which includes the video processing circuit 101, the scaler circuit 102, the liquid crystal driving circuit 103, the reference voltage generation circuit 104, and the counter electrode voltage generation circuit 101.

  The video processing circuit 101 performs processing necessary for displaying on the liquid crystal panel 108 video (G) based on a video signal supplied from an external video signal source such as a personal computer. The video signal (G) output from the video processing circuit 101 is subjected to pixel conversion to an appropriate size by the scaler circuit 102 and then supplied to the liquid crystal driving circuit 103. The liquid crystal drive circuit 103 drives the liquid crystal panel 108 based on the video signal (G) supplied from the scaler circuit 102. In driving the liquid crystal panel 108, the liquid crystal driving circuit 103 inverts the polarity of the video signal (G) every horizontal scanning period with reference to the reference voltage from the reference voltage generating circuit 104.

  The counter electrode voltage generation circuit 105 is a common voltage generation circuit that supplies a constant common voltage to a common electrode to which a plurality of liquid crystal cells constituting the liquid crystal panel 108 are connected in common. The control unit 105 can be connected to the external control device 200 via an interface (not shown). Based on the output of the sensor unit 201 supplied via the external control device 200, the counter electrode voltage generation circuit The magnitude of the common voltage generated at 105 is controlled. The sensor unit 201 includes a luminance sensor that detects the luminance of an image projected by the projector 100.

  In the system shown in FIG. 8, at the time of shipment, the projector 100 is connected to the external control device 200, and the common voltage Vcom is adjusted so that the flicker is minimized. Thus, the projector 100 in which the common voltage Vcom is adjusted is shipped.

  In addition to the above-described system, a projector in which a luminance sensor is provided in the projector and the common voltage Vcom can be adjusted has been proposed (see Patent Document 1). In this projector, the luminance sensor is disposed between a cross dichroic prism that synthesizes image light (RGB) from each liquid crystal panel and an optical system that projects the synthesized light from the cross dichroic prism. Based on the output of the brightness sensor, the common voltage in each liquid crystal panel is adjusted separately. Specifically, when adjusting the common voltage for the R liquid crystal panel, the image light from the other G and B liquid crystal panels is shielded.

Japanese Patent Laid-Open No. 2005-22169

  However, the system shown in FIG. 8 has the following problems.

  The common voltage varies depending on the environmental temperature of the projector and usage conditions. For this reason, the common voltage adjusted at the time of shipment may not be an optimum value depending on the environmental temperature and the usage situation of the place where the projector is actually installed. In such a case, flicker occurs and the image quality of the displayed video is deteriorated. Further, displaying an image in a state where flicker occurs shortens the life of the liquid crystal panel.

  In the projector described in Patent Document 1, since the projector automatically adjusts the common voltage using a brightness sensor provided therein, the common voltage is set regardless of the environmental temperature and the use situation. An optimal value can be set. However, in this projector, the luminance sensor is common to the R, G, and B liquid crystal panels, and the common voltage is adjusted based on the output of the luminance sensor by sequentially driving the liquid crystal panels. Therefore, it takes time to adjust the common voltage.

  An object of the present invention is to provide a liquid crystal display device capable of solving the above-described problems and automatically adjusting a common voltage in a short time.

  In order to achieve the above object, the present invention is generated by a plurality of liquid crystal panels that are respectively illuminated with light having different wavelength ranges and that generate image lights having different wavelength ranges based on video data, and the plurality of liquid crystal panels. A color synthesis prism that color-synthesizes the image light for each wavelength range, a luminance sensor unit disposed on an emission side of the color synthesis prism, and a plurality of liquid crystal panels that are connected to the plurality of liquid crystal panels, respectively. A plurality of counter electrode voltage generation circuits for supplying a constant common voltage to a common electrode to which liquid crystal cells are connected in common, and a common electrode generated by each counter electrode voltage generation circuit for the plurality of counter electrode voltage generation circuits A control unit that controls the magnitude of the voltage, and the luminance sensor unit includes a plurality of luminance sensors that detect luminance of the color-synthesized image light, and the plurality of luminances A sensor is provided on a surface including a panel effective pixel area when the direction in which the color-combined image light is emitted from the color-combining prism side, and the control unit is configured to output the plurality of luminance sensors. Based on the above, the magnitude of the common voltage is adjusted so as to suppress flicker, which is the luminance difference of the image light between successive frames, for each of the image light for each wavelength region.

  According to the present invention, the common voltage of the R, G, and B liquid crystal panels can be adjusted at the same time, so that the common voltage can be adjusted in a shorter time than a conventional liquid crystal display device. There is an effect that can be done.

1 is a block diagram illustrating a schematic configuration of a liquid crystal display device according to a first embodiment of the present invention. It is a schematic diagram which shows the structure of the sensor unit shown in FIG. 3 is a flowchart showing a procedure of optimum common voltage determination processing performed in the liquid crystal display device shown in FIG. 1. It is a schematic diagram which shows the other example of the sensor unit shown in FIG. It is a schematic diagram which shows the structure of the sensor unit used for the liquid crystal display device which is the 2nd Embodiment of this invention. It is a schematic diagram which shows the structure of the sensor unit used for the liquid crystal display device which is the 3rd Embodiment of this invention. It is a wave form diagram of video data of line inversion drive. It is a block diagram which shows the general structure of the system which can perform adjustment of a common voltage.

  Next, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram showing a schematic configuration of a liquid crystal display device according to a first embodiment of the present invention. The liquid crystal display device of the present embodiment drives a liquid crystal panel by one or a combination of dot inversion driving, line inversion driving, and frame inversion driving. Here, a line inversion driving method is adopted. Assume.

  Referring to FIG. 1, the liquid crystal display device is a three-plate projector including three liquid crystal panels 7 to 9 that form images of respective colors of R (red), G (green), and B (blue). The color synthesis prism 10 that synthesizes the image light from the liquid crystal panels 7 to 9 and the projection lens 11 that projects the RGB image light synthesized by the color synthesis prism 10 onto an external screen. The liquid crystal panels 7 to 9 are each illuminated with light having different wavelength ranges, and generate image light based on video data supplied in units of frames. The color synthesis prism 10 is, for example, a cross dichroic prism.

  In addition, the liquid crystal display device includes a processing circuit for forming images on the liquid crystal panels 7 to 9 based on video signals supplied in units of frames from an external video signal source such as a personal computer. This processing circuit is provided in each of the liquid crystal panels 7 to 9. FIG. 1 shows only a processing circuit related to the liquid crystal panel 8 including the video processing circuit 1, the scaler circuit 2, the liquid crystal driving circuit 3, the reference voltage generation circuit 4, and the counter electrode voltage generation circuit 5.

  The image processing circuit 1, the scaler circuit 2, the liquid crystal drive circuit 3, the reference voltage generation circuit 4, the counter electrode voltage generation circuit 5, the liquid crystal panels 7 to 9, the color synthesis prism 10, and the projection lens 11 are the projectors shown in FIG. The processing circuit is basically the same. A movable sensor unit 12 is inserted between the color synthesis prism 10 and the projection lens 11, and the control unit 6 controls the counter electrode voltage generation circuit 6 based on the output of the sensor unit 12 in FIG. Different from the projector shown.

  FIG. 2 shows the configuration of the sensor unit 12. The sensor unit 12 includes a sensor part 121 in which a plurality of RGB luminance sensor parts 120 are arranged, a support part 122 that supports the sensor part 121, and one end of the support part 122 attached to the output shaft of the motor. And a motor part 123 that moves the sensor part 121 between the first and second positions. In the first position, the sensor part 121 is inserted into the optical path of the combined light emitted from the color combining prism 10. By moving the sensor part 121 to the second position, the sensor part 121 can be retracted from the optical path of the combined light. The movement of the sensor part 121 by the motor unit 123 is controlled by the control unit 6.

  One RGB luminance sensor unit 120 is provided at the center, and eight are provided at regular intervals around it. Each of the RGB luminance sensor units 120 includes an R filter that transmits light in a wavelength range corresponding to the wavelength of R light, an R luminance sensor that detects the luminance of light transmitted through the filter, and the wavelength of G light. A G filter for transmitting light in a wavelength region corresponding to the G, a G luminance sensor for detecting the luminance of light transmitted through the filter, and a B filter for transmitting light in a wavelength region corresponding to the wavelength of B light And a B luminance sensor for detecting the luminance of light transmitted through the filter. Outputs of the R, G, and B luminance sensors of the RGB luminance sensor unit 120 are supplied to the control unit 6. The transmission wavelength range of each of the luminance sensors for R, G, and B does not need to be completely matched with the wavelength range of the light that illuminates the liquid crystal panels 7 to 9, and the image light of each color of R, G, and B It suffices that the wavelength range is set so that the brightness of each can be detected.

  The control unit 6 controls the operation of the entire liquid crystal display device, and also performs control such as mode switching and common voltage adjustment. Specifically, the control unit 6 immediately before the display of an image based on the video signal supplied from the video signal source is started or when a specific key prepared on the apparatus main body or the remote controller is pressed. Switch the operation mode to the common voltage adjustment mode. In the common voltage adjustment mode, the control unit 6 supplies flicker detection video data stored in a memory (not shown) to the processing circuits provided in the liquid crystal panels 7 to 9, respectively. Then, R, G, and B video signals are generated. Then, the control unit 6 adjusts the common voltage so that the flicker is minimized for the image displayed based on the R, G, and B video signals.

  In the common voltage adjustment, the control unit 6 moves each of the R, G, and B luminance sensors supplied from each of the RGB luminance sensor units 120 with the sensor part 121 moved to the first position. Based on the output, a flicker value is calculated. Here, the flicker value is given by the difference in brightness of the display image between consecutive frames, and is calculated for each image for R, G, and B. Further, the control unit 6 changes the value of the common voltage generated by the counter electrode voltage generation circuit 6 stepwise in a predetermined voltage range, and is calculated based on the output of the RGB luminance sensor unit 120. The common voltage value at which the flicker value of each of the images for G, G and B is minimized is acquired. And the control part 6 controls the counter electrode voltage generation circuit 6 regarding the liquid crystal panels 7-9 so that it may become the acquired common voltage value.

  Next, the operation of the liquid crystal display device of this embodiment will be specifically described. Since the operation in the normal mode is the same as that in the existing mode, the optimum common voltage determination process in the common voltage adjustment mode as a feature will be described in detail here.

  FIG. 3 shows a procedure for determining the optimum common voltage. When the operation mode is switched to the common voltage adjustment mode, the control unit 6 moves the sensor part 121 to the first position (step S100), and supplies the flicker detection video data to each processing circuit of the liquid crystal panels 7-9. Supply (step S101). As a result, R, G, and B images based on the flicker detection video data are formed on the liquid crystal panels 7 to 9 in units of frames. Then, the R image light, G image light, and B image light emitted from the liquid crystal panels 7, 8, and 9 are color-synthesized by the color synthesis prism 10, and the color synthesis image light is converted into each RGB luminance of the sensor part 121. The light enters the sensor unit 120.

  Next, the control unit 6 sets the value of the common voltage generated by the counter electrode voltage generation circuit 6 to a preset value (step S102), and the R and G components constituting the RGB luminance sensor unit 120 are set. The flicker value is calculated based on the output of each of the luminance sensors for B and B (step S103). The flicker value is calculated for each of the R, G, and B images.

  Specifically, when calculating the flicker value of the R image, each of the R luminance sensors of the eight RGB luminance sensor units 120 provided in the sensor part 120 is supplied from the R luminance sensor for each frame. Sampling and integrating the luminance values. Next, a difference between the integrated values is obtained between consecutive frames, and the obtained difference is integrated over a plurality of frames to obtain a flicker value. Thus, the flicker value is calculated for each R luminance sensor. Then, the flicker value obtained from one R luminance sensor arranged in the center is compared with the flicker value obtained from each of the eight R luminance sensors arranged in the vicinity thereof, and the difference of the difference is obtained. The average value is calculated. The average value of the calculated flicker value differences is stored in a memory (not shown). For each of the G image and the B image, the average value of the flicker value difference is calculated and stored in a memory (not shown) in the same procedure as the R image.

  When the average value of the difference in flicker values is calculated for each of the R, G, and B images, the control unit 6 then proceeds to determine all the common voltages to be measured that are set in a predetermined voltage range. In step S104, it is determined whether or not flicker has been measured. For example, when the mon voltage value is increased step by step for each unit voltage in a predetermined voltage range, it is determined in step S104 whether or not the set value of the common voltage has reached the maximum common voltage value in the predetermined voltage range. To do.

  If the determination in step S104 is “No”, the control unit 6 returns to step 101 and increases the set value of the common voltage by the unit voltage. Thereafter, the processes of steps S102 to S104 are performed.

  If the determination in step S104 is “Yes”, the control unit 6 sets the flicker value stored in the memory (not shown) for each set value of the common voltage for each of the R, G, and B images. The average value of the differences is examined, and the common voltage value at which the average value is minimized is determined as the optimum common voltage (step S105). Based on the optimum common voltage values of the R, G, and B images obtained in this way, the control unit 6 controls each counter electrode voltage generation circuit that supplies a common voltage to the liquid crystal panels 7 to 9. .

  According to the liquid crystal display device of the present embodiment described above, the RGB luminance sensor unit 120 is composed of the luminance sensors for R, G, and B, so that the liquid crystal panels 7 to 9 are used for R and G. , B images can be formed simultaneously, and the common voltage can be adjusted for each image. The time required for the adjustment of the common voltage in this case is much greater than the adjustment time of the common voltage in the projector described in Patent Document 1 in which the luminance sensor is common to each of the R, G, and B liquid crystal panels. Shorter.

  Further, the optimum value of the common voltage is different between the central portion and the peripheral portion of the panel effective pixel region. In such a case, if the common voltage is adjusted only in the central part, the adjustment value of the common voltage may deviate from the actual optimum value of the common voltage in the peripheral part, and flicker may occur in the peripheral part. . On the other hand, if the common voltage is adjusted only at the peripheral portion, the adjustment value of the common voltage may deviate significantly from the actual optimum value of the common voltage at the central portion, and flicker may occur at the central portion. In the present embodiment, at the first position, one RGB luminance sensor unit 120 is arranged at the center of the panel effective pixel region and eight at the periphery thereof, and the flicker value between the center and the periphery is set. Since the adjustment of the common voltage is performed based on the average value of the differences, the adjustment value of the common voltage does not greatly deviate from the actual optimum value of the common voltage in the central portion and the peripheral portion. Therefore, the occurrence of flicker can be effectively suppressed in the central portion and the peripheral portion. Here, the panel effective pixel area corresponds to the effective image area in each liquid crystal panel set based on the effective projection area of the projection lens.

  The liquid crystal display device of the present embodiment described above is an example of the present invention, and the configuration and operation thereof can be changed as appropriate. For example, the number and arrangement of the RGB luminance sensor units 120 provided in the sensor unit 12 are not limited to the example illustrated in FIG. 2, and the adjustment value of the common voltage corresponds to the adjustment of the common voltage in the center and the peripheral part. The value can be changed as appropriate under the condition that the value does not greatly deviate from the actual optimum value. For example, as shown in FIG. 4, one RGB luminance sensor unit 120 may be arranged at the center of the panel effective pixel region 11 a and one at the top, bottom, left, and right. The sensor part 121 has a circular shape, and when the incident surface direction of the projection lens 11 is viewed from the color synthesizing prism 10 side, the outer edge of the sensor part 121 is exactly the panel effective pixel region 11a at the first position. It is inscribed on all four sides.

  The flicker detection video data may be any video data as long as flicker can be detected. Preferred flicker detection video data includes 100% white video with the entire display screen displaying white, 50% white video with 50% white display area on the display screen, and white display on the display screen. There are video data such as 10% white video with an area ratio of 10%, black video with the entire display screen displayed in black, and checkered pattern video.

(Second Embodiment)
FIG. 5 is a schematic diagram showing a configuration of a sensor unit used in the liquid crystal display device according to the second embodiment of the present invention.

  The liquid crystal display device of the present embodiment is basically the same as the configuration shown in FIG. 1 except for the sensor unit. The sensor unit shown in FIG. 5 is a fixed type, and includes four RGB luminance sensor units 120 disposed between the color synthesis prism 10 and the projection lens 11. The RGB luminance sensor unit 120 has the same configuration as that of the RGB luminance sensor unit 120 shown in FIG. 1, and includes R, G, and B luminance sensors. The RGB luminance sensor units 120 are provided on the upper, lower, left, and right sides of the panel effective pixel region 11a when the incident surface direction of the projection lens 11 is viewed from the color synthesis prism 10 side.

  In the liquid crystal display device of the first embodiment, the RGB luminance sensor unit 120 is arranged in the panel effective pixel region 11a, and adjusts the common voltage using dedicated flicker detection video data. An image cannot be displayed based on a normal video signal supplied from a video signal source. On the other hand, according to the liquid crystal display device of the present embodiment, the RGB luminance sensor unit 120 is disposed outside the panel effective pixel region 11a, and a normal voltage supplied from an external video signal source is used to adjust the common voltage. It is possible to use a video signal. Although it is desirable to use dedicated video data for flicker detection, it is possible to detect flicker with a certain degree of accuracy even with normal video data supplied from an external video signal source. Further, in the liquid crystal display device according to the first embodiment in which the luminance sensor is arranged in the panel effective pixel area 11a, flicker relating to an actually displayed image is measured. The liquid crystal display device of the first embodiment is higher than the liquid crystal display device.

  In the present embodiment, the control unit 6 displays an image based on a normal video signal supplied from an external video signal source on the liquid crystal panels 7 to 9 and receives an input indicating that the operation mode is shifted to the common voltage adjustment mode. If it has been done, the common voltage is adjusted based on the images displayed on the liquid crystal panels 7 to 9 so that the flicker is minimized. The common voltage adjustment procedure will be described below.

  The control unit 6 sets the value of the common voltage generated by the counter electrode voltage generation circuit 6 to a preset value, and each luminance for R, G, and B constituting the RGB luminance sensor unit 120 The flicker value is calculated based on the sensor output. This flicker value is calculated for each of the R, G, and B images.

  Specifically, when calculating the flicker value of the R image, the luminance value supplied from the R luminance sensor is sampled for each frame for each of the R luminance sensors of the four RGB luminance sensor units 120. To accumulate. Next, a difference between the integrated values is obtained between successive frames, and the obtained difference is integrated over a predetermined number of frames to obtain a flicker value. Thus, the flicker value is calculated for each R luminance sensor. Next, an average value of the flicker values calculated for the four R luminance sensors is calculated. The calculated average flicker value is stored in a memory (not shown). For each of the G image and the B image, an average flicker value is calculated and stored in a memory (not shown) in the same procedure as the R image.

  When the average value of the flicker values is calculated for each of the R, G, and B images, the control unit 6 subsequently measures flicker for all the common voltages to be measured in a predetermined voltage range. It is determined whether or not.

  When determining that there is still a common voltage to be measured, the control unit 6 increases the set value of the common voltage by a unit voltage and averages the flicker values for the R, G, and B images. Calculate the value.

  When it is determined that there is no more common voltage to be measured, the control unit 6 sets the flicker value stored in a memory (not shown) for each set value of the common voltage for each of the R, G, and B images. The average value is examined, and the common voltage value at which the average value is minimized is determined as the optimum common voltage. Based on the optimum common voltage values of the R, G, and B images obtained in this way, the control unit 6 controls each counter electrode voltage generation circuit that supplies a common voltage to the liquid crystal panels 7 to 9. .

  Also in the liquid crystal display device according to the present embodiment, the RGB luminance sensor unit 120 is composed of R, G, and B luminance sensors, so that the liquid crystal panels 7 to 9 have R, G, and B use. These images can be formed simultaneously, and the common voltage can be adjusted for each image.

  In the liquid crystal display device of the first embodiment, since a movable sensor unit is used, drive control of the sensor unit by the control unit is necessary. However, in the liquid crystal display device of the present embodiment, the sensor unit is a fixed type. There is no need for such control. Therefore, the load of processing in the configuration of the apparatus and the control unit is reduced by the amount that does not require drive control of the sensor unit.

  The liquid crystal display device of the present embodiment described above is an example of the present invention, and the configuration and operation thereof can be changed as appropriate. For example, the number and arrangement of the RGB luminance sensor units 120 are not limited to the example shown in FIG. It is sufficient that at least one RGB luminance sensor unit 120 is disposed outside the panel effective pixel region 11a.

(Third embodiment)
FIG. 6 is a schematic diagram showing a configuration of a sensor unit used in the liquid crystal display device according to the third embodiment of the present invention.

  The liquid crystal display device of the present embodiment is basically the same as the configuration shown in FIG. 1 except for the sensor unit. The sensor unit shown in FIG. 6 is a fixed type, and includes three luminance sensor units 120 a to 120 c arranged on the upper surface side of the color synthesis prism 10. FIG. 6 shows an arrangement state of the sensor unit when viewed from the upper surface side of the color synthesis prism 10.

  When the R image light from the liquid crystal panel 7 passes through the color synthesis prism 10, a part of the R image light leaks out of the prism from the upper and lower surfaces of the color synthesis prism 10 due to refraction and reflection at the reflection surface. Similarly, when the G image light from the liquid crystal panel 8 and the B image light from the liquid crystal panel 9 pass through the color synthesis prism 10, a part of each image light is caused by refraction or reflection on the reflection surface. The color composition prism 10 leaks out of the prism from the upper and lower surfaces. The luminance sensor unit 120 a detects the luminance of the R image light that leaks to the upper surface side of the color synthesis prism 10. The luminance sensor unit 120 b detects the luminance of the G image light that leaks to the upper surface side of the color synthesis prism 10. The luminance sensor unit 120 c detects the luminance of the B image light that leaks to the upper surface side of the color synthesis prism 10.

  The luminance sensor unit 120a is disposed on a region on the first incident surface side where the R image light from the liquid crystal panel 7 is incident on the upper surface of the color synthesis prism 10. More desirably, the luminance sensor unit 120a includes a first incident surface on the upper surface of the color combining prism 10, a reflective surface 10a that reflects the R image light from the liquid crystal panel 7 toward the projection lens 11, and the liquid crystal panel 9. Are arranged in a region partitioned by the reflection surface 10 b that reflects the B image light from the projection lens 11. In this region, most of the light leaking to the upper surface of the color combining prism 10 is the leaked light of the R image light from the liquid crystal panel 7. Therefore, the brightness sensor unit 120a efficiently detects the brightness of the leaked light of the R image light. Is possible.

  The luminance sensor unit 120b is disposed in a region on the second incident surface side where the G image light from the liquid crystal panel 8 is incident on the upper surface of the color synthesis prism 10. More preferably, the luminance sensor unit 120b is disposed in an area defined by the second incident surface and the reflecting surfaces 10a and 10b on the upper surface of the color combining prism 10. In this region, most of the light leaking to the upper surface of the color synthesis prism 10 is the leakage light of the G image light from the liquid crystal panel 8, so the luminance sensor unit 120b efficiently detects the luminance of the leakage light of the G image light. Is possible.

  The luminance sensor unit 120c is disposed in a region on the third incident surface side on which the B image light from the liquid crystal panel 9 is incident on the upper surface of the color combining prism 10. More desirably, the luminance sensor unit 120c is disposed in a region defined by the third incident surface and the reflecting surfaces 10a and 10b on the upper surface of the color combining prism 10. In this region, most of the light leaking to the upper surface of the color synthesis prism 10 is the leakage light of the B image light from the liquid crystal panel 9, so that the brightness sensor unit 120c efficiently detects the brightness of the leakage light of the B image light. Is possible.

  In the liquid crystal display device of the first embodiment, the RGB luminance sensor unit 120 is arranged in the panel effective pixel region 11a, and adjusts the common voltage using dedicated flicker detection video data. An image cannot be displayed based on a normal video signal supplied from a video signal source. On the other hand, according to the liquid crystal display device of this embodiment, the luminance sensor units 120a to 120c are arranged on the upper surface of the color synthesis prism 10, and are supplied from an external video signal source for common voltage adjustment. It is possible to use a normal video signal. Although it is desirable to use dedicated video data for flicker detection, it is possible to detect flicker with a certain degree of accuracy even with normal video data supplied from an external video signal source.

  In the present embodiment, the control unit 6 displays an image based on a normal video signal supplied from an external video signal source on the liquid crystal panels 7 to 9 and receives an input indicating that the operation mode is shifted to the common voltage adjustment mode. If it has been done, the common voltage is adjusted based on the images displayed on the liquid crystal panels 7 to 9 so that the flicker is minimized. The common voltage adjustment procedure will be described below.

  The control unit 6 sets the value of the common voltage generated by the counter electrode voltage generation circuit 6 to a preset value, and calculates the flicker value based on the outputs of the luminance sensor units 120a to 120c. This flicker value is calculated for each of the R, G, and B images.

  Specifically, when calculating the flicker value of the R image, the luminance value supplied from the luminance sensor unit 120a is sampled and integrated for each frame. Next, a difference between the integrated values is obtained between successive frames, and the obtained difference is integrated over a predetermined number of frames to obtain a flicker value. In this way, the flicker value of the R image is calculated. The calculated flicker value is stored in a memory (not shown). For each of the G image and the B image, flicker values are calculated and stored in a memory (not shown) in the same procedure as the R image.

  When the flicker value is calculated for each of the R, G, and B images, the control unit 6 subsequently performs flicker measurement for all the common voltages to be measured in a predetermined voltage range. Judge whether or not.

  If it is determined that there is still a common voltage to be measured, the control unit 6 increases the set value of the common voltage by a unit voltage and calculates a flicker value for each of the R, G, and B images. To do.

  When it is determined that there is no more common voltage to be measured, the control unit 6 uses the flicker value stored in a memory (not shown) for each set value of the common voltage for each image for R, G, and B. The common voltage value having the smallest flicker value is determined as the optimum common voltage. Based on the optimum common voltage values of the R, G, and B images obtained in this way, the control unit 6 controls each counter electrode voltage generation circuit that supplies a common voltage to the liquid crystal panels 7 to 9. .

  Also in the liquid crystal display device of this embodiment, the R, G, and B images can be simultaneously formed on the liquid crystal panels 7 to 9, and the common voltage can be adjusted for each image.

  In the liquid crystal display device of the first embodiment, since a movable sensor unit is used, drive control of the sensor unit by the control unit is necessary. However, in the liquid crystal display device of the present embodiment, the sensor unit is a fixed type. There is no need for such control. Therefore, the load of processing in the configuration of the apparatus and the control unit is reduced by the amount that does not require drive control of the sensor unit.

  In addition, since it is not necessary to provide R, G, and B filters in the luminance sensors 120a to 120c, the apparatus cost can be reduced accordingly.

  In the liquid crystal display device according to the second embodiment, when a part of the projection lens 11 is shifted in the direction perpendicular to the optical axis to adjust the display position of the image on the screen, the panel effective pixel considering the lens shift. It is necessary to arrange the RGB luminance sensor unit outside the area. In this case, the arrangement of the RGB luminance sensor units is further restricted, and the degree of freedom in design is reduced. According to the liquid crystal display device of the present embodiment, since the luminance sensor unit can be arranged regardless of the panel effective pixel region, the arrangement of the luminance sensor unit is not limited when the lens shift is taken into consideration.

  The liquid crystal display device of the present embodiment described above is an example of the present invention, and the configuration and operation thereof can be changed as appropriate. For example, the number and arrangement of the luminance sensor units are not limited to the example shown in FIG. The luminance sensor units 120a to 120c may be disposed on the lower surface of the color synthesis prism. In addition, the luminance sensor units 120a to 120c may be disposed on each of the upper surface and the lower surface of the color synthesis prism. In this case, each of the luminance sensor units 120a calculates the flicker value of the R image light, and stores the average value in the memory for each common voltage. Similarly, the average values of the luminance sensor units 120b and 120c are stored in the memory for each common voltage. Then, for each of the R, G, and B images, the common voltage having the lowest average value is determined as the optimum common voltage.

  In the configuration shown in FIG. 6, leakage light of other image light may be incident on each of the luminance sensor units 120a to 120c. In order to prevent the leakage of other image light, the luminance sensor unit 120a includes an R filter that transmits light in a wavelength region corresponding to the wavelength of the R light, and the luminance of the light transmitted through the filter is reduced. The luminance sensor for R which comprises the luminance sensor for R to detect, and the luminance sensor unit 120b includes a G filter that transmits light in a wavelength region corresponding to the wavelength of the G light, and detects the luminance of the light transmitted through the filter. The brightness sensor unit 120c includes a B filter that transmits light in a wavelength region corresponding to the wavelength of the B light, and includes a B brightness sensor that detects the brightness of the light transmitted through the filter. Also good.

  Further, in order to shield the leakage light of other image light, a shielding plate may be provided at the position of the reflective surfaces 10a and 10b that divide the region in the region where the luminance sensor unit 120a is disposed. Similarly, a shielding plate may be provided at the positions of the reflecting surfaces 10a and 10b that divide the areas of the areas where the luminance sensor units 120b and 120c are arranged.

  In the configuration shown in FIG. 6, instead of the luminance sensor units 120 a to 120 c, at least one RGB luminance sensor composed of R, G, and B luminance sensors is connected to the upper or lower surface of the color combining prism 10. Or you may arrange | position to the area | region of the output surface side from which the color-combined image light is radiate | emitted on the upper and lower surfaces. More preferably, the RGB luminance sensor is arranged in an area defined by the emission surface and the reflection surfaces 10a and 10b on the upper surface, the lower surface, or the upper and lower surfaces of the color synthesis prism 10. In this region, most of the light leaking from the color synthesizing prism 10 is the leaked light of the color-combined image light. Can be detected efficiently.

  In addition, each of the luminance sensor units 120a to 120c may directly detect a part of the RGB image light from the liquid crystal panels 7 to 9 instead of the leakage light from the color synthesis prism 10.

  In each of the embodiments described above, the adjustment of the common voltage is executed when the common voltage adjustment mode is selected. However, the adjustment of the common voltage may be executed periodically. For example, when a counter that counts the driving time of the liquid crystal panel (or the operating time of the projector) is provided, and the driving time reaches each set time of 100h, 200h,..., 1000h based on the count value in the counter In addition, the common voltage may be adjusted. Here, “h” indicates time.

  Further, the flicker values calculated when the power of the projector is turned on / off may be compared, and it may be determined whether or not to adjust the common voltage based on the comparison result. In particular. When an input to turn off the power of the projector is made, the flicker values in the R, G, and B images are calculated. Thereafter, when an input to turn on the power is made, the flicker value in each of the R, G, and B images is calculated, and the flicker value calculated when the power is turned off and the flicker value of the corresponding image are calculated. Are compared. The common voltage is adjusted only when the flicker value at power-on does not match the flicker value at power-off (or when the difference between the two flicker values exceeds a predetermined range). The adjustment of the common voltage in this case is executed based on the flicker value when the power is turned on.

  In each embodiment, an example in which a video signal is supplied in units of frames has been described. However, the present invention is not limited to this, and a video signal is supplied in units of fields. May be. When a video signal is supplied in units of fields, the operation can be explained by replacing “frame” with “field”.

DESCRIPTION OF SYMBOLS 1 Image processing circuit 2 Scaler circuit 3 Liquid crystal drive circuit 4 Reference voltage generation circuit 5 Counter electrode voltage generation circuit 6 Control part 7-9 Liquid crystal panel 10 Color composition prism 11 Projection lens 12 Sensor unit

Claims (6)

A plurality of liquid crystal panels that are respectively illuminated with light having different wavelength ranges and generate image lights having different wavelength ranges based on video data;
A color synthesizing prism that color-synthesizes image light for each wavelength range generated by the plurality of liquid crystal panels;
A luminance sensor unit disposed on an emission side of the color synthesis prism;
A plurality of counter electrode voltage generation circuits that are respectively connected to the plurality of liquid crystal panels, and that supply a constant common voltage to a common electrode to which a plurality of liquid crystal cells constituting the liquid crystal panel are connected in common;
A control unit for controlling the magnitude of the common voltage generated in each counter electrode voltage generation circuit for the plurality of counter electrode voltage generation circuits,
The brightness sensor unit includes a plurality of brightness sensors that detect brightness of the color-synthesized image light,
The plurality of luminance sensors are provided on a surface including a panel effective pixel region when viewing a direction in which the color-combined image light is emitted from the color-combining prism side,
The control unit, based on the outputs of the plurality of luminance sensors, for each of the image light for each wavelength range, to suppress the flicker that is the luminance difference of the image light between successive frames, A liquid crystal display device that adjusts the size.   The luminance sensor unit includes a first position where the plurality of luminance sensors are arranged in an optical path of the color-combined image light emitted from the color synthesis prism, and the plurality of luminance sensors are arranged outside the optical path. The liquid crystal display device according to claim 1, wherein the liquid crystal display device moves between the second position and the second position.   3. The liquid crystal display according to claim 2, wherein the plurality of luminance sensors are arranged in an effective display area corresponding to each effective pixel area of the plurality of liquid crystal panels in the optical path at the first position. apparatus.   The plurality of luminance sensors include a first luminance sensor disposed in a central portion of the effective display area, and a plurality of second luminance sensors disposed around the first luminance sensor. Item 4. A liquid crystal display device according to item 3.   The plurality of luminance sensors are arranged outside an effective display area corresponding to each effective pixel area of the plurality of liquid crystal panels in the optical path of the color-combined image light emitted from the color combining prism. The liquid crystal display device according to claim 1. A plurality of liquid crystal panels that are illuminated with light of different wavelength ranges and generate image light based on video data; a color synthesis prism that color-synthesizes the image light for each wavelength range generated by the plurality of liquid crystal panels; and A plurality of luminance sensors arranged on the emission side of the color synthesis prism and detecting the luminance of the color synthesized image light; and the plurality of luminance sensors receive the color synthesized image light from the color synthesis prism side. A method for adjusting a common voltage of a liquid crystal display device having a luminance sensor portion provided on a surface including a panel effective pixel region when viewing the emitted direction,
For each of the plurality of liquid crystal panels, a constant common voltage is supplied to a common electrode to which a plurality of liquid crystal cells constituting the liquid crystal panel are connected in common,
Based on the outputs of the plurality of luminance sensors, the image light for each wavelength range is supplied to the plurality of liquid crystal panels so as to suppress flicker, which is the luminance difference of the image light between successive frames. A common voltage adjustment method for adjusting the magnitude of the common voltage.

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