Optical Modulation Device and Projection Display Device

Abstract

To provide a light modulator capable of detecting and correcting deviation in a common electrode voltage.SOLUTION: A reflection type sheet polarizer 13b transmits first polarized light out of modulated light emitted from a reflection type liquid crystal display element 12b, and reflects second polarized light. A transmission type sheet polarizer 15b transmits the second polarized light reflected on the reflection type sheet polarizer 13b, and reflects the first polarized light. An optical sensor 21b receives the first polarized light reflected on the transmission type sheet polarizer 15b, and outputs a detection signal. A detection circuit 23b generates a primary flag composed of first to third flags according to a difference between an absolute value of a positive polarity peak and an absolute value of a negative polarity peak. A selection circuit 24b replaces the second and third flags with the first flag unless two adjoining frames of an input image signal represent substantially identical images. When a secondary flag is the second flag, a correction circuit 25b performs correction to lower the common electrode voltage. When the secondary flag is the third flag, the correction circuit performs correction to heighten the common electrode voltage.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a light modulation device and a projection display device. [Background technology]

[0002] A projection display device projects an enlarged image onto a screen by modulating illumination light according to the image to be projected using a light modulation device. The light modulation device includes a liquid crystal display element as one of its components. The liquid crystal display element has pixel electrodes, a common electrode disposed opposite the pixel electrodes, and liquid crystal sandwiched between the pixel electrodes and the common electrode.

[0003] The optical modulator applies a common electrode voltage (Vcom), which is a DC voltage, to the common electrode of the liquid crystal display element. The optical modulator applies an AC voltage that inverts at a frame or line period between the pixel electrode and the common electrode to optically modulate the incident illumination light. In this case, asymmetry may occur between the positive and negative polarities of the AC voltage applied between the pixel electrode and the common electrode due to variations in the characteristics of the transistors that drive the pixel electrodes, variations in the electro-optical properties of the liquid crystal material, variations in the alignment conditions of the liquid crystal, impurities mixed into the liquid crystal, differences in the materials of the pixel electrode and the common electrode, and so on.

[0004] When asymmetry occurs between the positive and negative polarities of the AC voltage, Vcom shifts from the AC voltage inversion center voltage, and a DC voltage component is applied to the LCD display element, causing flicker in the projected image. When flicker occurs in the projected image, contrast decreases and the display gradation becomes narrower. In addition, because a DC voltage component is applied to the LCD display element, ionic substances in the liquid crystal are attracted to one of the electrodes, which can cause image burn-in and reduce the reliability of the LCD display element's operation.

[0005] Patent Documents 1 and 2 describe suppressing flicker by detecting flickering of light caused by flicker using an optical sensor and adjusting Vcom. [Prior art documents]

Patent Document

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] The configuration described in Patent Document 1 needs to project an image of a specific pattern in order to correct the deviation from the inversion center voltage of Vcom. The configuration described in Patent Document 1 cannot correct the deviation of Vcom in a state where a normal image based on an input image signal is projected. Although the configuration described in Patent Document 2 does not require projecting an image of a specific pattern, a double-speed conversion process is required to double the frame rate and read each frame continuously twice. The configuration described in Patent Document 2 detects and corrects the deviation of Vcom by setting the positive polarity for the first readout of each frame and the negative polarity for the second readout.

[0008] In recent years, projection display devices often aim to improve the resolution in the time direction by setting the frame rate of the input image signal to 120 Hz, which is twice the conventionally common 60 Hz. When trying to adopt the configuration described in Patent Document 2 when the frame rate of the input image signal is 120 Hz, it is necessary to set the frame rate to 240 Hz. Trying to operate the projection display device at a frame rate of 240 Hz causes a substantial increase in circuit scale and cost, so it is substantially difficult to adopt the configuration described in Patent Document 2.

[0009] An object of the present invention is to provide an optical modulation device and a projection display device that do not require projection of an image of a specific pattern and double-speed conversion processing of the frame rate of an input image signal to correct the deviation of the common electrode voltage, and can detect and correct the deviation of the common electrode voltage.

Means for Solving the Problems

[0010] The present invention has a pixel electrode, a common electrode to which a common electrode voltage is applied, and liquid crystal sandwiched between the pixel electrode and the common electrode. The liquid crystal display element modulates, based on an input image signal, a first polarized light that is linearly polarized light in one incident direction and emits the modulated light. Among the modulated light emitted from the liquid crystal display element, a reflective polarizing plate transmits the first polarized light and reflects a second polarized light that is linearly polarized light in one direction orthogonal to the first polarized light. A transmissive polarizing plate transmits the second polarized light reflected by the reflective polarizing plate and reflects the first polarized light. A photosensor receives the first polarized light reflected by the transmissive polarizing plate and outputs a detection signal. A liquid crystal drive circuit supplies the pixel electrode with the input image signal having its polarity inverted between positive and negative polarities every one vertical period with respect to the common electrode voltage. A detection circuit calculates a difference between an absolute value of a positive-polarity side peak absolute value, which is the absolute value of the peak of the detection signal output from the photosensor during a vertical period in which the liquid crystal drive circuit supplies the pixel electrode with the input image signal in a positive polarity, and an absolute value of a negative-polarity side peak absolute value, which is the absolute value of the peak of the detection signal output from the photosensor during a vertical period in which the liquid crystal drive circuit supplies the pixel electrode with the input image signal in a negative polarity. If the difference is 0, a first flag is generated as a primary flag. If the difference is positive, a second flag is generated as a primary flag. If the difference is negative, a third flag is generated as a primary flag. A selection circuit compares two adjacent frames in the input image signal to determine whether or not they are substantially the same image. If it is determined that they are substantially the same image, the primary flag is output as a secondary flag as it is. If it is determined that they are not substantially the same image, the second and third flags are replaced with the first flag and output as a secondary flag. A correction circuit corrects the common electrode voltage without correction if the secondary flag is the first flag, corrects the common electrode voltage to be lower if the secondary flag is the second flag, and corrects the common electrode voltage to be higher if the secondary flag is the third flag. Provided is an optical modulation device including these components.

[0011] The present invention provides a projection display device including: a dichroic mirror that splits a light beam of white light emitted from a light source into light beams of red light, green light, and blue light with random polarization; a polarization conversion element that aligns and emits each of the light beams of red light, green light, and blue light with random polarization into a first polarization that is linearly polarized in one direction; the above-described light modulation device provided in the optical paths of the light beams of red light, green light, and blue light aligned in the first polarization; a color synthesis prism that color-synthesizes each of the light beams of red light, green light, and blue light that have passed through the transmissive polarizing plate in the light modulation device and that are linearly polarized in a second polarization that is orthogonal to the first polarization; and a projection lens that magnifies and projects the synthesized light color-synthesized by the color synthesis prism.

Advantages of the Invention

[0012] According to the light modulation device and the projection display device of the present invention, it is not necessary to project an image of a specific pattern and perform double-speed conversion processing of the frame rate of the input image signal in order to correct the shift of the common electrode voltage, and the shift of the common electrode voltage can be detected and corrected.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10A

Figure 10B

Figure 10C

Embodiments for Carrying Out the Invention

[0014] Hereinafter, an optical modulation device and a projection display device according to an embodiment will be described with reference to the accompanying drawings. The projection display device 1 shown in FIG. 1 is configured as follows. In FIG. 1, a light source 2 having a xenon lamp 2a and a concave mirror 2b emits high-intensity white light. An infrared transmission filter 3 is disposed at an inclination of 45 degrees on the optical path of the white light. The infrared transmission filter 3 transmits infrared rays having a wavelength of around 700 nm or more and reflects light fluxes in other wavelength bands. Thereby, infrared rays having a wavelength of around 700 nm or more are removed.

[0015] The light flux in the wavelength band other than the infrared band is bent by 90 degrees in the optical path by the infrared transmission filter 3 and enters the ultraviolet reflection filter 4. The ultraviolet reflection filter 4 reflects ultraviolet rays having a wavelength of around 400 nm or less and transmits light fluxes in other wavelength bands. Thereby, ultraviolet rays having a wavelength of around 400 nm or less are removed. The white light from which infrared rays and ultraviolet rays have been removed enters a dichroic mirror 5 disposed at an inclination of 45 degrees with respect to the optical path. The dichroic mirror 5 splits the incident white light into B light and RG light by reflecting blue light (hereinafter, B light) and transmitting red and green light (hereinafter, RG light).

[0016] On the optical path of the B light reflected by the dichroic mirror 5, a reflection mirror 6, a first fly-eye lens 7b for B light, a second fly-eye lens 8b for B light, a polarization conversion element 9b, a condenser lens 10b, a field lens 11b, a reflective polarizing plate 13b, and a reflective liquid crystal display element 12b for B light are arranged in this order. The reflection mirror 6 is arranged at an angle of 45 degrees with respect to the optical path of the B light emitted from the dichroic mirror 5, and bends the optical path of the B light by 90 degrees. The reflective liquid crystal display element 12b and the reflective liquid crystal display elements 12r and 12g described later are examples of liquid crystal display elements.

[0017] Since the cross-section of the white light emitted from the concave mirror 2b of the light source 2 is circular, the cross-section of the light beam reflected by the reflection mirror 6 is circular. In order to efficiently irradiate the effective pixel region of the rectangular reflective liquid crystal display element 12b with the light beam having a circular cross-section reflected by the reflection mirror 6, it is necessary to convert the circular light beam into a rectangular light beam.

[0018] The first fly-eye lens 7b has a configuration in which small rectangular convex lenses are arranged in a matrix. The second fly-eye lens 8b also has a configuration in which small rectangular convex lenses are arranged in a matrix. Each convex lens of the second fly-eye lens 8b is arranged at the focal position of each convex lens of the first fly-eye lens 7b. The first fly-eye lens 7b and the second fly-eye lens 8b divide the incident light beam into a plurality of rectangular partial light beams in order to match the shape of the light beam of the B light with the shape of the reflective liquid crystal display element 12b and to equalize the illuminance distribution on the reflective liquid crystal display element 12b.

[0019] The B light, which is a partial light beam emitted from the second fly-eye lens 8b, is random polarization with non-uniform polarization states. The polarization conversion element 9b converts a plurality of partial light beams of random polarization into a plurality of partial light beams of linearly polarized light in one direction. The polarization conversion element 9b is configured as shown in FIG. 2.

[0020] As shown in FIG. 2, inside the flat polarizing beam splitter array 91, a polarization separation surface 92 indicated by a dashed line and a reflection surface 93 indicated by a solid line are alternately formed in a direction along the plane. The polarization separation surface 92 and the reflection surface 93 are formed to have an angle of 45 degrees with respect to the light incident surface of the polarization conversion element 9b. The polarization separation surface 92 transmits P-polarized light (first polarization) and reflects S-polarized light (second polarization). The S-polarized light has its traveling direction bent by 90° at the polarization separation surface 92 and heads toward the reflection surface 93. The reflection surface 93 reflects the incident S-polarized light and bends the traveling direction by 90°.

[0021] In the region sandwiched between the polarization separation surface 92 and the reflection surface 93 and emitting the S-polarized light reflected by the reflection surface 93, a birefringent half-wave plate 94 is attached. In the region sandwiched between the polarization separation surface 92 and the reflection surface 93 and transmitting the P-polarized light transmitted through the polarization separation surface 92, the half-wave plate 94 is not attached. The half-wave plate 94 rotates the polarization direction of the incident S-polarized light by 90° and emits P-polarized light. In this way, the polarization conversion element 9b emits the incident random polarization aligned as P-polarized light, which is linearly polarized light in one direction.

[0022] The polarization conversion element 9b and the polarization conversion element 9rg described later may emit the incident random polarization aligned as S-polarized light, which is linearly polarized light in one direction. When the polarization conversion element 9b and the polarization conversion element 9rg described later emit S-polarized light, the light modulation devices of various colors described later are configured to correspond to the incident S-polarized light. In this case, the first polarization is S-polarized light, and the second polarization is P-polarized light.

[0023] The condenser lens 10b synthesizes a plurality of partial light beams of linearly polarized light (P-polarized light) emitted from the polarization conversion element 9b and emits a light beam combined into one. The field lens 11b converts the incident light beam of linearly polarized light into telecentric illumination light of B light.

[0024] Figure 3 shows an enlarged view of the portion marked 50 enclosed by the dashed line in Figure 1. In Figure 1 or Figure 3, rectangular openings are formed on three side surfaces of the substantially triangular prism-shaped support 20b, and on the inner surface side of the three side surfaces, a reflective liquid crystal display element 12b, a reflective polarizing plate 13b, and a transmissive polarizing plate 15b are fixed so as to close each opening. The reflective polarizing plate 13b is fixed to the side surface facing the field lens 11b of the support 20b, and the B light emitted from the field lens 11b is incident thereon. The reflective polarizing plate 13b is inclined at an angle of 45 degrees with respect to the optical path of the B light. A heat sink 19b for heat dissipation is fixed to the outer surface of the side surface to which the reflective liquid crystal display element 12b is fixed.

[0025] As shown in Figure 4, a wire grid polarizer is used as the reflective polarizing plate 13b. The reflective polarizing plate 13b, which is a wire grid polarizer, has a reflective surface formed by regularly arranging metal wires 132 such as aluminum in a stripe pattern at a pitch of about 140 nm on a polarizer optical glass plate 131. The reflective polarizing plate 13b has the characteristic of transmitting, as it is, the polarization component (here, P polarization) perpendicular to the metal wires 132 formed in a stripe pattern among the incident light beams, and reflecting the polarization component parallel to the metal wires 132 (here, S polarization).

[0026] When a wire grid polarizer is used as the reflective polarizing plate 13b, the reflective polarizing plate 13b can be made lightweight. Since the wire grid polarizer is less likely to absorb the incident light, when a wire grid polarizer is used as the reflective polarizing plate 13b, it is possible to suppress a decrease in the quality of the projected image caused by the birefringence of the glass generated by heat generation.

[0027] Returning to FIG. 1 or FIG. 3, the reflective polarizing plate 13b transmits the B light emitted from the field lens 11b. The B light transmitted through the reflective polarizing plate 13b is incident on the reflective liquid crystal display element 12b. The reflective liquid crystal display element 12b optically modulates based on the B signal among the RGB signals constituting the input image signal, and reflects and emits the B light (S polarized light) whose polarization state has changed due to the optical modulation as modulated light. The reflective polarizing plate 13b reflects the B light reflected by the reflective liquid crystal display element 12b. The B light reflected by the reflective polarizing plate 13b passes through the transmissive polarizing plate 15b and is incident on the cross dichroic prism 16. The cross dichroic prism 16 is an example of a color synthesis prism.

[0028] The transmissive polarizing plate 15b and the transmissive polarizing plates 15g and 15r described later are provided to improve the degree of polarization of the S polarized light and thus the contrast by reflecting and removing the unnecessary polarization (P polarized light) contained in the incident B light.

[0029] In FIG. 1, on the optical path of the RG light transmitted through the dichroic mirror 5, a first fly-eye lens 7rg for RG light, a second fly-eye lens 8rg for RG light, a polarization conversion element 9rg, a condenser lens 10rg, and a dichroic mirror 14 are arranged in this order. The first fly-eye lens 7rg, the second fly-eye lens 8rg, the polarization conversion element 9rg, and the condenser lens 10rg each have the same configuration and function as the first fly-eye lens 7b, the second fly-eye lens 8b, the polarization conversion element 9b, and the condenser lens 10b.

[0030] The dichroic mirror 14 splits the incident RG light into R light and G light by reflecting the green light (hereinafter, G light) among the RG light and transmitting the red light (hereinafter, R light).

[0031] On the optical path of the R light transmitted through the dichroic mirror 14, a field lens 11r, a reflective polarizing plate 13r, and a reflective liquid crystal display element 12r for R light are arranged in this order. The field lens 11r converts the incident linearly polarized light beam into telecentric illumination light for R light.

[0032] Rectangular openings are formed in three side surfaces of the substantially triangular prism-shaped support 20r, and a reflective liquid crystal display element 12r, a reflective polarizing plate 13r, and a transmissive polarizing plate 15r are fixed to the inner surface sides of the three side surfaces so as to close the respective openings.

[0033] The reflective polarizing plate 13r is fixed to the side surface of the support 20r facing the field lens 11r, and the R light emitted from the field lens 11r is incident thereon. The reflective polarizing plate 13r is inclined at an angle of 45 degrees with respect to the optical path of the R light. A heat sink 19r for heat dissipation is fixed to the outer surface of the side surface to which the reflective liquid crystal display element 12r is fixed.

[0034] The reflective polarizing plate 13r transmits the R light emitted from the field lens 11r. The R light transmitted through the reflective polarizing plate 13r is incident on the reflective liquid crystal display element 12r. The reflective liquid crystal display element 12r optically modulates based on the R signal among the RGB signals constituting the input image signal, and reflects the R light (S polarized light) whose polarization state has been changed by the optical modulation and emits it as modulated light. The reflective polarizing plate 13r reflects the R light reflected by the reflective liquid crystal display element 12r. The R light reflected by the reflective polarizing plate 13r passes through the transmissive polarizing plate 15r and is incident on the cross dichroic prism 16.

[0035] On the optical path of the G light reflected by the dichroic mirror 14, a field lens 11g, a reflective polarizing plate 13g, and a reflective liquid crystal display element 12g for G light are arranged in this order. The field lens 11g converts the incident linearly polarized light beam into telecentric illumination light for G light.

[0036] Rectangular openings are formed in three side surfaces of the substantially triangular prism-shaped support 20g, and a reflective liquid crystal display element 12g, a reflective polarizing plate 13g, and a transmissive polarizing plate 15g are fixed to the inner surface sides of the three side surfaces so as to close the respective openings.

[0037] The reflective polarizing plate 13g is fixed to the side surface facing the field lens 11g of the support 20g, and the G light emitted from the field lens 11g is incident thereon. The reflective polarizing plate 13g is inclined at an angle of 45 degrees with respect to the optical path of the G light. A heat sink 19g for heat dissipation is fixed to the outer surface of the side surface to which the reflective liquid crystal display element 12g is fixed.

[0038] The reflective polarizing plate 13g transmits the G light emitted from the field lens 11g. The G light transmitted through the reflective polarizing plate 13g is incident on the reflective liquid crystal display element 12g. The reflective liquid crystal display element 12g optically modulates based on the G signal among the RGB signals constituting the input image signal, and reflects the G light (S polarized light) whose polarization state has changed due to the optical modulation and emits it as modulated light. The reflective polarizing plate 13g reflects the G light reflected by the reflective liquid crystal display element 12g. The G light reflected by the reflective liquid crystal display element 12g passes through the transmissive polarizing plate 15g and is incident on the cross dichroic prism 16.

[0039] The cross dichroic prism 16 color - synthesizes the R light, G light, and B light incident from three side surfaces, and emits the synthesized light from the emission surface 16a. The projection lens 17 magnifies and projects the synthesized light emitted from the emission surface 16a onto the screen 18.

[0040] As shown in FIG. 1, on the optical paths of the unnecessary polarized light reflected by the transmissive polarizing plates 15r, 15g, and 15b, optical sensors 21r, 21g, and 21b are respectively arranged outside the supports 20r, 20g, and 20b. The optical sensors 21r, 21g, and 21b convert the incident light into an electrical signal according to the amount of light. The optical sensors 21r, 21g, and 21b convert the amount of light into voltage, current, frequency, etc., and output it as a detection signal.

[0041] Using FIGS. 5 and 6, explain at what positions in the vicinity of the supports 20r, 20g, and 20b the optical sensors 21r, 21g, and 21b are respectively arranged. Here, representatively, the position of the optical sensor 21b with respect to the support 20b will be explained.

[0042] In FIG. 5, the light beam Ha of B light, which is P-polarized light emitted from the condenser lens 10b, is refracted by the field lens 11b according to the size of the display area (effective pixel area) of the reflective liquid crystal display element 12b and enters the reflective polarizing plate 13b. The light beam Hb of P-polarized light that has passed through the reflective polarizing plate 13b is optically modulated by the reflective liquid crystal display element 12b, and a part of it becomes S-polarized light and is reflected, and then re-enters the reflective polarizing plate 13b. The light beam Hb that has become S-polarized light is reflected by the reflective polarizing plate 13b and enters the transmissive polarizing plate 15b as the light beam Hc.

[0043] The transmissive polarizing plate 15b transmits S-polarized light and reflects unnecessary P-polarized light. The photosensor 21b is disposed on the light beam Hd, indicated by a broken line, of the P-polarized light reflected by the transmissive polarizing plate 15b.

[0044] As shown in FIG. 6, the reflective polarizing plate 13b does not transmit 100% of the incident light beam Ha of B light that is P-polarized light, but reflects a certain proportion of P-polarized light and also reflects the S-polarized light slightly contained in the incident light beam Ha. Therefore, a light beam He, indicated by a broken line and containing P-polarized light and S-polarized light, is emitted from the surface of the reflective polarizing plate 13b on the side of the field lens 11b toward the outside of the support 20b. Since this light beam He has not been optically modulated by the reflective liquid crystal display element 12b, it is not affected by the flicker caused by the reflective liquid crystal display element 12b. In addition, the light beam He has a larger light quantity compared to the light beam Hd that is reflected by the transmissive polarizing plate 15b and is affected by the flicker caused by the reflective liquid crystal display element 12b.

[0045] Therefore, the photosensor 21b needs to be disposed at a position on the light beam Hd reflected by the transmissive polarizing plate 15b, avoiding the light beam He reflected by the reflective polarizing plate 13b and not being affected by the light beam He.

[0046] In this way, the photosensors 21r, 21g, and 21b are disposed at positions on the light beams Hd reflected by the transmissive polarizing plates 15r, 15g, and 15b and not being affected by the light beams He reflected by the reflective polarizing plates 13r, 13g, and 13b.

[0047] In FIG. 1, only one light sensor is shown for each of the light sensors 21r, 21g, and 21b. However, a plurality of light sensors 21r, 21g, and 21b may be arranged so as to receive a light beam Hd including reflected light that has undergone modulation by a plurality of pixels in the effective pixel region of the reflective liquid crystal display elements 12r, 12g, and 12b. The plurality of light sensors 21r, 21g, and 21b are preferably arranged in two orthogonal directions so as to receive a light beam Hd including reflected light that has undergone modulation in a rectangular region composed of a plurality of pixels in the horizontal direction and a plurality of pixels in the vertical direction in the effective pixel region.

[0048] Each light sensor among the plurality of light sensors 21r, 21g, and 21b has a single light receiving portion. Each one of the light sensors 21r, 21g, and 21b having a plurality of light receiving portions may be used. The plurality of light receiving portions receive reflected light that has undergone modulation by a plurality of pixels in the reflective liquid crystal display elements 12r, 12g, and 12b.

[0049] Using FIGS. 7 to 9, the correction operation of the common electrode voltage (hereinafter, Vcom) will be described in detail. As shown in FIG. 7, the optical modulation device 60 for B light includes, in addition to the reflective liquid crystal display element 12b, the reflective polarizing plate 13b, and the transmissive polarizing plate 15b, a light sensor 21b, a liquid crystal drive circuit 22b, a detection circuit 23b, a selection circuit 24b, and a correction circuit 25b. The reflective liquid crystal display element 12b has a pixel electrode 121, a common electrode 122, and liquid crystal 123 encapsulated between the pixel electrode 121 and the common electrode 122.

[0050] The liquid crystal drive circuit 22b supplies the pixel electrode 121 by inverting the polarity of the input image signal (R signal) between positive and negative polarities every one vertical period with respect to Vcom. The detection circuit 23b detects the state of Vcom based on the detection signal from the light sensor 21b and various drive signals output from the liquid crystal drive circuit 22b. As will be described later, the detection circuit 23b generates a primary flag based on the detection result of the state of Vcom. As will be described later, the selection circuit 24b outputs a secondary flag. The correction circuit 25b corrects Vcom according to the secondary flag and supplies the corrected Vcom to the common electrode 122 of the reflective liquid crystal display element 12b.

[0051] For the reflective liquid crystal display element 12r for R light as well, an optical modulation device 60 for R light is provided, which includes a liquid crystal drive circuit 22r, a detection circuit 23r, a selection circuit 24r, and a correction circuit 25r, similar to the liquid crystal drive circuit 22b, the detection circuit 23b, the selection circuit 24b, and the correction circuit 25b. For the reflective liquid crystal display element 12g for G light as well, an optical modulation device 60 for G light is provided, which includes a liquid crystal drive circuit 22g, a detection circuit 23g, a selection circuit 24g, and a correction circuit 25g, similar to the liquid crystal drive circuit 22b, the detection circuit 23b, the selection circuit 24b, and the correction circuit 25b.

[0052] FIG. 8 shows a specific configuration example of the detection circuits 23r, 23g, 23b, the correction circuits 25r, 25g, 25b, and the selection circuits 24r, 24g, 24b. The detection circuits 23r, 23g, 23b include an AD converter 231, a timing generator 232, a positive-polarity side data hold circuit 233, a negative-polarity side data hold circuit 234, a subtractor 235, and a flag generator 236. The selection circuits 24r, 24g, 24b include a frame memory 241, a comparator 242, and a flag selector 243. The correction circuits 25r, 25g, 25b include a data hold circuit 251, an arithmetic unit 252, and a DA converter 253.

[0053] Referring to FIG. 8 and the flowchart shown in FIG. 9, the operations of the detection circuit 23b, the selection circuit 24b, and the correction circuit 25b will be described as a representative example. The operation of the detection circuit 23b is as follows. When the power of the projection display device 1 is turned on, the projection display device 1 starts the process shown in FIG. 9. The AD converter 231 AD-converts the detection signal output from the optical sensor 21b (step S1 in FIG. 9). The detection signal converted into a digital signal is supplied to the positive-polarity side data hold circuit 233 and the negative-polarity side data hold circuit 234.

[0054] The liquid crystal drive circuit 22b inverts the polarity of the input image signal based on the horizontal and vertical scanning signals synchronized with the input image signal and the polarity switching signal that repeats high and low every one vertical period. The liquid crystal drive circuit 22b supplies the polarity switching signal and the horizontal and vertical synchronization signals to the timing generator 232. The timing generator 232 supplies the positive polarity side trigger signal and the negative polarity side trigger signal to the positive polarity side data hold circuit 233 and the negative polarity side data hold circuit 234, respectively.

[0055] The positive polarity side data hold circuit 233 and the negative polarity side data hold circuit 234 each store the detection signal supplied from the AD converter 231. The positive polarity side data hold circuit 233 detects the positive polarity side peak from the stored detection signal during the vertical period when the liquid crystal drive circuit 22b supplies the input image signal to the pixel electrode 121 with positive polarity, and outputs the positive polarity side peak absolute value which is the absolute value of the peak (step S2 in FIG. 9). The negative polarity side data hold circuit 234 detects the positive polarity side peak from the stored detection signal during the vertical period when the liquid crystal drive circuit 22b supplies the input image signal to the pixel electrode 121 with negative polarity, and outputs the negative polarity side peak absolute value which is the absolute value of the peak (step S3 in FIG. 9).

[0056] The subtractor 235 calculates the difference between the positive polarity side peak absolute value and the negative polarity side peak absolute value (step S3). As an example, the subtractor 235 subtracts the negative polarity side peak absolute value from the positive polarity side peak absolute value. When Vcom is higher than the inversion center voltage, when displaying the projection image on the positive polarity side, the S polarization is less than the specified amount and the P polarization is more than the specified amount. Conversely, when displaying the projection image on the negative polarity side, the S polarization is more than the specified amount and the P polarization is less than the specified amount.

[0057] Since the optical sensor 21b detects the P polarization that is not used to form the projection image, a positive difference obtained by subtracting the negative polarity side peak absolute value from the positive polarity side peak absolute value means that Vcom is too high. Conversely, a negative difference means that Vcom is too low.

[0058] The flag generator 236 generates, for example, a 2-bit flag according to the difference which is the calculation result by the subtractor 235. The flag generator 236 is supplied with a 2-frame timing signal which goes high every two frames, and when the 2-frame timing signal goes high, it generates and outputs a flag.

[0059] If the difference output from the subtractor 235 is 0, the flag generator 236 generates the first flag "00" as the primary flag, if the difference is positive, it generates the second flag "11" as the primary flag, and if the difference is negative, it generates the third flag "01" as the primary flag (steps S4 to S8 in FIG. 9). The first to third flags "00", "11", "01" of the primary flag respectively represent "0", "3", "1" in decimal. The flag generator 236 outputs a primary flag which is any one of the first to third flags "00", "11", "01" every two frames.

[0060] The operation of the selection circuit 24b is as follows. An input image signal F(n) is input to the selection circuit 24b. The frames of the input image signal proceed as... F(n - 1), F(n), F(n + 1).... The input image signal F(n) may mean the general term of a series of frames.

[0061] The frame memory 241 delays the input image signal F(n) by one frame period and outputs the image signal F(n - 1) one frame before. The frames output from the frame memory 241 proceed as... F(n - 2), F(n - 1), F(n).... Similarly, the image signal F(n - 1) may mean the general term of a series of frames with a one-frame delay.

[0062] The comparator 242 compares the input image signal F(n) with the image signal F(n - 1), and if the pixel values at the same pixel positions match for a predetermined ratio or more of all the pixels in one frame, it outputs "1" indicating a match, and if not, it outputs "0" indicating a mismatch as the comparison result signal. The predetermined ratio may be set to an appropriate value such as 90% for example.

[0063] That the pixel values at the same pixel position match for a predetermined ratio or more of all the pixels in one frame means that two adjacent frames in the input image signal F(n) are substantially the same image. The comparator 242 determines whether two adjacent frames are substantially the same image (step S9 in FIG. 9). If the comparator 242 determines that two adjacent frames are substantially the same image, it outputs "1" as a comparison result signal, and if it determines that two adjacent frames are not substantially the same image, it outputs "0" as a comparison result signal.

[0064] The determination of match and mismatch by the comparator 242 may be used as determination accuracy according to the level of adjustment accuracy of Vcom. When it is not necessary to make the adjustment accuracy of Vcom very high, the determination of match and mismatch by the comparator 242 may be performed simply. For example, when each pixel data is 12 bits, it may be determined whether the pixel values at the same pixel position of the input image signal F(n) and the image signal F(n - 1) match in the upper 10 bits.

[0065] Also, the comparator 242 does not necessarily have to determine whether the pixel values match for all the pixels in one frame, and may determine whether the pixel values match for some of the pixels within the frame. The comparator 242 may determine whether the pixel values match for some of the pixels corresponding to the spatial range in which the optical sensor 21b detects the light beam Hd. The comparator 242 may determine match or mismatch so that the adjustment accuracy of Vcom is ensured to be a predetermined accuracy or more.

[0066] If the comparison result signal supplied from the comparator 242 is "1" indicating a match, the flag selector 243 outputs the primary flag output from the flag generator 236 as the secondary flag as it is (step S10 in FIG. 9). If the comparison result signal is "0" indicating a mismatch, the flag selector 243 varies the flag output as the secondary flag depending on which of the first to third flags the primary flag is.

[0067] If the primary flag is the first flag "00", the flag selector 243 outputs the first flag "00" as the secondary flag as it is. If the primary flag is the second flag "11" or the third flag "01", the flag selector 243 replaces the second flag "11" or the third flag "01" with the first flag "00" and outputs it as the secondary flag (step S11 in FIG. 9). That is, if the comparison result signal is "0" indicating a mismatch, regardless of the primary flag output from the flag generator 236, the flag selector 243 fixedly outputs the first flag "00" as the secondary flag.

[0068] The first flag "00" indicates that Vcom is the inversion center voltage and there is no need to correct Vcom. The second flag "11" indicates that Vcom is higher than the inversion center voltage and Vcom needs to be corrected lower. The third flag "01" indicates that Vcom is lower than the inversion center voltage and Vcom needs to be corrected higher. When two adjacent frames are different images, the determination result of whether Vcom is higher or lower than the inversion center voltage may be incorrect. Replacing the second flag "11" or the third flag "01" with the first flag "00" when the comparison result signal is a mismatch is to prevent Vcom from being corrected when the determination result may be incorrect.

[0069] The operation of the correction circuit 25b is as follows. The secondary flag output from the selection circuit 24b is input to the arithmetic unit 252. The data hold circuit 251 holds the Vcom initial value, which is a digital value corresponding to the inversion center voltage of Vcom. As described above, due to various conditions such as variations in the characteristics of the pixel electrode driving transistors, even if Vcom is set based on the Vcom initial value, asymmetry may occur between the positive polarity side and the negative polarity side of the AC voltage, and it may be necessary to correct Vcom. Note that it is not essential for the data hold circuit 251 to hold the Vcom initial value. Even if the data hold circuit 251 does not hold the Vcom initial value, the Vcom correction values held in the data hold circuit 251 are sequentially updated, and an optimal Vcom correction value can be obtained after a predetermined time.

[0070] When the two-frame timing signal goes high, the data hold circuit 251 reads out the stored value. The arithmetic unit 252 reads out the Vcom initial value from the data hold circuit 251. If the secondary flag is the first flag "00", it does not correct the Vcom initial value, stores it in the data hold circuit 251, and supplies it to the DA converter 253.

[0071] The arithmetic unit 252 reads out the Vcom initial value from the data hold circuit 251. If the secondary flag is the second flag "11", it stores in the data hold circuit 251 a Vcom correction value obtained by subtracting 1 bit from the Vcom initial value, and supplies it to the DA converter 253 (step S12 in FIG. 9). The arithmetic unit 252 reads out the Vcom initial value from the data hold circuit 251. If the secondary flag is the third flag "01", it stores in the data hold circuit 251 a Vcom correction value obtained by adding 1 bit to the Vcom initial value, and supplies it to the DA converter 253 (step S12 in FIG. 9).

[0072] Even after the Vcom correction value is stored in the data hold circuit 251, the arithmetic unit 252 reads out the Vcom correction value from the data hold circuit 251 in the same manner. If the secondary flag is the second flag "11", it stores in the data hold circuit 251 a new Vcom correction value obtained by subtracting 1 bit from the Vcom correction value, and supplies it to the DA converter 253 (step S12 in FIG. 9). The arithmetic unit 252 reads out the Vcom correction value from the data hold circuit 251. If the secondary flag is the third flag "01", it stores in the data hold circuit 251 a new Vcom correction value obtained by adding 1 bit to the Vcom correction value, and supplies it to the DA converter 253 (step S12 in FIG. 9).

[0073] In the DA converter 253, the data hold circuit 251 and the arithmetic unit 252 repeatedly perform an operation of updating the Vcom correction value, so that an optimal Vcom correction value is supplied. The DA converter 253 DA-converts the input Vcom correction value and applies the analog value of Vcom to the common electrode 122 (step S13 in FIG. 9).

[0074] In this way, when the secondary flag is the first flag "00", the correction circuit 25b does not correct Vcom; when the secondary flag is the second flag "11", the correction circuit 25b corrects Vcom to be lower; when the secondary flag is the third flag "01", the correction circuit 25b corrects Vcom to be higher. The correction circuit 25b can always apply Vcom that matches the inversion center voltage to the common electrode 122.

[0075] In step S14 of FIG. 9, when the power supply of the projection display device 1 is turned off, the projection display device 1 ends the process shown in FIG. 9. If the power supply of the projection display device 1 is not turned off, the projection display device 1 repeats the processes after step S1. The correction circuit 25b repeats the operation of correcting Vcom every two frames.

[0076] Incidentally, the number of bits for adding or subtracting the lower bits of the first flag "00", the second flag "11", and the third flag "01" to the Vcom correction value (or the Vcom initial value) is represented. The "1" of the upper bit means subtraction, and the "0" of the upper bit means addition. The arithmetic unit 252 can be configured with a digital circuit that defines the upper and lower bits of the secondary flag in this way. When the arithmetic unit 252 is configured with such a digital circuit, even if, by mistake, "10" indicating the decimal number "2" that is not defined is input, Vcom is not corrected, so malfunction can be avoided.

[0077] In FIG. 8, the timing generator 232 may generate positive and negative polarity trigger signals during the blanking period of the input image signal F(n) based on the horizontal and vertical synchronization signals and supply them to the positive polarity side data hold circuit 233 and the negative polarity side data hold circuit 234.

[0078] The optical sensor 21b is preferably disposed at a position where it receives the reflected light modulated by pixels at the position where the vertical scanning starts or ends in the reflective liquid crystal display elements 12r, 12g, and 12b. By doing so, it is possible to detect the deviation of Vcom at the end of the display of one frame in which all the pixels of one frame are displayed with the positive electrode or the negative electrode.

[0079] The operation of the projection display device 1 (optical modulation device 60) will be described using the timing charts shown in FIGS. 10A to 10C. In FIG. 10A, (a) conceptually shows the waveforms of the input image signals F(n), F(n + 1),...; (b) shows the input image signals F(n), F(n + 1),...; and (c) shows the image signals F(n - 1), F(n),... of the previous frame. Since the frame rate of the input image signals F(n), F(n + 1),... is 120 Hz, the period of one frame is 1 / 120 second.

[0080] (d) in FIG. 10A shows the comparison results C(n), C(n + 2),... for each pixel of two adjacent frames by the comparator 242. (e) in FIG. 10A shows the comparison result signals 242(n - 2), 242(n), 242(n + 2),... indicating whether the pixel values match for a predetermined ratio or more of all the pixels in one frame. Based on the comparison results C(n), C(n + 2),... obtained during the period of one frame, the comparator 242 outputs the comparison result signals 242(n), 242(n + 2),... which are "1" indicating match or "0" indicating mismatch during the period of the next two frames.

[0081] As shown in (f) of FIG. 10B, the liquid crystal drive circuits 22r, 22g, and 22b supply a polarity switching signal that alternates between high and low to the timing generator 232. The liquid crystal drive circuits 22r, 22g, and 22b invert the polarities of the input image signals F(n), F(n + 1),... between positive and negative polarities every one vertical period with respect to Vcom and supply them to the pixel electrodes 121. Therefore, as shown in (g) of FIG. 10B, the liquid crystal drive voltage alternates between positive and negative polarities. During the period when the polarity switching signal is high, the input image signals become +F(n), +F(n + 2),..., and during the period when the polarity switching signal is low, the input image signals become -F(n + 1), -F(n + 3),...

[0082] In FIG. 10B, (h) indicates the vertical synchronization signal, (i) indicates the positive-polarity side trigger signal that the timing generator 232 supplies to the positive-polarity side data hold circuit 233, and (j) indicates the negative-polarity side trigger signal that the timing generator 232 supplies to the negative-polarity side data hold circuit 234. The positive-polarity side and negative-polarity side trigger signals go high at the start of each frame every two frames.

[0083] As shown in (k) of FIG. 10C, the positive-polarity side data hold circuit 233 outputs positive-polarity side peak absolute values 233(n), 233(n + 2),... every two frames. As shown in (m) of FIG. 10C, the negative-polarity side data hold circuit 234 outputs negative-polarity side peak absolute values 234(n), 234(n + 2),... every two frames. The timing for outputting the negative-polarity side peak absolute values 234(n), 234(n + 2),... is delayed by one frame period from the timing for outputting the positive-polarity side peak absolute values 233(n), 233(n + 2),.... Note that in FIG. 10C, the same positive-polarity side and negative-polarity side trigger signals as (i) and (j) of FIG. 10B are shown.

[0084] As shown in (n) of FIG. 10C, the subtractor 235 outputs difference signals 235(n), 235(n + 2),... between the positive-polarity side peak absolute value and the negative-polarity side peak absolute value. As shown in (o) of FIG. 10C, the flag selector 243 outputs secondary flags 243(n), 243(n + 2),....

[0085] As shown in (q) of FIG. 10C, each time the two-frame timing signal shown in (p) goes high, the data hold circuit 251 outputs Vcom correction values 251(n - 2), 251(n), 251(n + 2).... As shown in (r) of FIG. 10C, each time the two-frame timing signal goes high, the arithmetic unit 252 outputs new Vcom correction values 252(n), 252(n + 2), 252(n + 4)....

[0086] The Vcom correction value 252(n) is Vcom correction value 251(n - 2)+secondary flag 243(n). The Vcom correction value 252(n + 2) is Vcom correction value 251(n)+secondary flag 243(n + 2). The Vcom correction value 252(n + 4) is Vcom correction value 251(n + 2)+secondary flag 243(n + 4). However, if the secondary flags 243(n), 243(n + 2).... are the first flag "00", the arithmetic unit 252 does not execute the addition / subtraction process. If they are the second flag "11", the arithmetic unit 252 executes the subtraction process. If they are the third flag "01", the arithmetic unit 252 executes the addition process.

[0087] As described above, the optical modulation device 60 and the projection display device 1 including the optical modulation device 60 do not need to project an image of a specific pattern to correct the deviation of Vcom, and can always correct the deviation of Vcom while projecting a normal image based on the input image signal. Thereby, flicker occurring in the projected image can be suppressed, and the change over time of the liquid crystal display elements (reflective liquid crystal display elements 12r, 12g, 12b) can be suppressed. Since the flicker occurring in the projected image is suppressed, the projection display device 1 can display a high-quality image. Since the change over time of the liquid crystal display elements is suppressed, the reliability of the projection display device 1 can be improved.

[0088] According to the optical modulation device 60 and the projection display device 1 including the optical modulation device 60, it is not necessary to perform double-speed conversion processing on the frame rate of the input image signal. Therefore, even if the frame rate of the input image signal is 120 Hz or higher, a significant increase in circuit scale and cost can be avoided, and the deviation of Vcom can be corrected.

[0089] Since the optical sensors 21r, 21g, and 21b are attached inside the projection display device 1, the projection display device 1 does not become large-sized. The presence of the optical sensors 21r, 21g, and 21b does not prevent the replacement of the projection lens 17. The shadows of the optical sensors 21r, 21g, and 21b do not appear on the projected image that the projection lens 17 enlarges and projects onto the screen 18.

[0090] In the projection display device 1 shown in FIG. 1, a light modulation device 60 having the configuration shown in FIG. 8 is provided in the optical path of each color, but the light modulation device 60 may be provided only in the optical paths of some colors. Among R light, G light, and B light, the light modulation device 60 may be provided only in the optical path of G light, which is the brightest and most likely to have noticeable flicker. The light modulation device 60 may be provided only in the optical path of B light, which has a short wavelength and is likely to affect the organic materials used for optical components.

[0091] A conventional configuration in which an optical sensor is disposed near the projected image displayed on the screen 18 or inside the projection lens 17 and the configuration of the present embodiment may be used in combination.

[0092] The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention. The detection circuits 23r, 23g, 23b, the selection circuits 24r, 24g, 24b, and the correction circuits 25r, 25g, 25b may be constituted by integrated circuits, or at least some of the circuits may be constituted by a microcomputer.

Description of Reference Numerals

[0093] 1 Projection display device 2 Light source 5, 14 Dichroic mirror 9r, 9g, 9b Polarization conversion element 16 Cross dichroic prism 17 Projection lens 12r, 12g, 12b Reflective liquid crystal display element 13r, 13g, 13b Reflective polarizing plate 15r, 15g, 15b transmissive polarizing plate 21r, 21g, 21b optical sensor 22r, 22g, 22b liquid crystal drive circuit 23r, 23g, 23b detection circuit 24r, 24g, 24b selection circuit 25r, 25g, 25b correction circuit

Claims

1. A liquid crystal display element having a pixel electrode, a common electrode to which a common electrode voltage is applied, and liquid crystal sandwiched between the pixel electrode and the common electrode, which optically modulates first polarized light that is linearly polarized light in one direction of incidence based on an input image signal and emits it as modulated light; A reflective polarizing plate that transmits the first polarized light among the modulated light emitted from the liquid crystal display element and reflects second polarized light that is linearly polarized light in one direction orthogonal to the first polarized light; A transmissive polarizing plate that transmits the second polarized light reflected by the reflective polarizing plate and reflects the first polarized light; An optical sensor that receives the first polarized light reflected by the transmissive polarizing plate and outputs a detection signal; A liquid crystal drive circuit that inverts the polarity of the input image signal between positive and negative polarities every one vertical period with respect to the common electrode voltage and supplies it to the pixel electrode; A detection circuit that calculates the difference between the absolute value of the peak of the detection signal output from the optical sensor in each vertical period when the liquid crystal drive circuit supplies the input image signal to the pixel electrode with a positive polarity, which is the absolute value of the positive-polarity side peak, and the absolute value of the peak of the detection signal output from the optical sensor in each vertical period when the liquid crystal drive circuit supplies the input image signal to the pixel electrode with a negative polarity, which is the absolute value of the negative-polarity side peak, and generates a first flag as a primary flag if the difference is 0, generates a second flag as a primary flag if the difference is positive, and generates a third flag as a primary flag if the difference is negative; A selection circuit that compares two adjacent frames in the input image signal to determine whether they are substantially the same image, and if it is determined that they are substantially the same image, outputs the primary flag as a secondary flag as it is, and if it is determined that they are not substantially the same image, replaces the second and third flags with the first flag and outputs it as a secondary flag; A correction circuit that does not correct the common electrode voltage if the secondary flag is the first flag, corrects the common electrode voltage to be lowered if the secondary flag is the second flag, and corrects the common electrode voltage to be raised if the secondary flag is the third flag; An optical modulation device comprising the above.

2. The optical modulation device according to claim 1, wherein the optical sensor is disposed at a position that receives reflected light modulated by pixels at a position where vertical scanning starts or ends in the liquid crystal display element.

3. One optical sensor that receives the first polarized light reflected by the transmissive polarizing plate with a plurality of light receiving portions and outputs a detection signal, or a plurality of optical sensors that receive the first polarized light reflected by the transmissive polarizing plate with a single light receiving portion and output a detection signal. The optical modulation device according to claim 1 or 2.

4. A dichroic mirror that splits a light beam of white light emitted from a light source into light beams of red light, green light, and blue light with random polarization, A polarization conversion element that aligns and emits each light beam of red light, green light, and blue light with random polarization into the first polarized light that is linearly polarized in one direction, The optical modulation device according to any one of claims 1 to 3 provided in the optical paths of the light beams of red light, green light, and blue light aligned with the first polarized light, A color synthesis prism that color-synthesizes each light beam of the second polarized light, which is linearly polarized in one direction orthogonal to the first polarized light, of red light, green light, and blue light that has passed through the transmissive polarizing plate in the optical modulation device, A projection lens that enlarges and projects the synthesized light color-synthesized by the color synthesis prism, A projection display device comprising.

Images