JP2023044893A - Light modulator and projection type display device - Google Patents

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

The present invention relates to an optical modulation device and a projection display device.

A projection display device modulates illumination light according to an image to be projected by a light modulation device, thereby projecting a desired image in an enlarged manner onto a screen. A light modulation device includes a liquid crystal display element as one component. A liquid crystal display element includes a pixel electrode, a common electrode arranged to face the pixel electrode, and liquid crystal sandwiched between the pixel electrode and the common electrode.

The light modulator applies a common electrode voltage (so-called Vcom), which is a DC voltage, to the common electrode of the liquid crystal display element. The light modulating device modulates incident illumination light by applying an AC voltage that is inverted at a frame period or a line period between a pixel electrode and a common electrode. At this time, it is caused by variations in the characteristics of the pixel electrode driving transistor, variations in the electro-optical characteristics of the liquid crystal material, variations in the orientation conditions of the liquid crystal, contamination of the liquid crystal with impurities, and differences in the materials of the pixel electrode and the common electrode. As a result, an asymmetry may occur between the positive polarity side and the negative polarity side of the AC voltage applied between the pixel electrode and the common electrode.

If asymmetry occurs between the positive side and the negative side of the AC voltage, Vcom will deviate from the inversion center voltage of the AC voltage, and a DC voltage component will be applied to the liquid crystal display element, resulting in flicker in the projected image. do. When flicker occurs in the projected image, the contrast is lowered and the display gradation is narrowed. In addition, since a DC voltage component is applied to the liquid crystal display element, ionic substances in the liquid crystal are attracted to one of the electrodes, causing burn-in to the liquid crystal display element and lowering the operational reliability of the liquid crystal display element. I have something to do.

Japanese Unexamined Patent Application Publication Nos. 2005-100001 and 2003-200001 describe suppressing flicker by detecting light flicker caused by flicker using an optical sensor and adjusting Vcom.

JP 2009-193044 A JP 2011-2745 A

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 Japanese Patent Laid-Open No. 2002-200010 cannot correct the deviation of Vcom while projecting a normal image based on an input image signal. The configuration described in Patent Document 2 does not need to project an image of a specific pattern, but requires double-speed conversion processing in which the frame rate is doubled and each frame is successively read out twice. The configuration described in Patent Document 2 detects and corrects the deviation of Vcom by setting positive polarity in the first readout of each frame and negative polarity in the second readout.

In recent projection display devices, the frame rate of an input image signal is often set to 120 Hz, which is twice the conventional general 60 Hz, for the purpose of improving the resolution in the time direction. When the frame rate of the input image signal is 120 Hz, the frame rate needs to be 240 Hz if the configuration described in Patent Document 2 is to be adopted. If the projection type display device is operated at a frame rate of 240 Hz, the circuit scale and cost will increase significantly, so it is practically difficult to adopt the configuration described in Patent Document 2.

The present invention detects and corrects common electrode voltage deviations without the need for projection of a specific pattern image and double-speed conversion processing of the frame rate of an input image signal in order to correct common electrode voltage deviations. It is an object of the present invention to provide a light modulation device and a projection display device capable of

The present invention has a pixel electrode, a common electrode to which a common electrode voltage is applied, and a liquid crystal sandwiched between the pixel electrode and the common electrode, and a first polarized light that is incident linearly polarized light in one direction. based on an input image signal, and emits modulated light; A reflective polarizing plate that reflects a second polarized light that is linearly polarized light in one orthogonal direction, and a transmissive polarized light that transmits the second polarized light reflected by the reflective polarizing plate and reflects the first polarized light. a plate, an optical sensor that receives the first polarized light reflected by the transmissive polarizing plate and outputs a detection signal, and a polarity of the input image signal that is positive for each vertical period with respect to the common electrode voltage. and a liquid crystal drive circuit for supplying the input image signal to the pixel electrode after inverting it with a negative polarity, and output from the photosensor during a vertical period in which the liquid crystal drive circuit supplies the input image signal to the pixel electrode with a positive polarity. The positive peak absolute value, which is the absolute value of the peak of the detection signal, and the output from the photosensor during the vertical period in which the liquid crystal drive circuit supplies the input image signal to the pixel electrode with negative polarity A difference from the absolute value of the peak of the detection signal, which is the negative peak absolute value, is calculated. If the difference is 0, a first flag is generated as a primary flag, and if the difference is positive, a primary flag is generated. a detection circuit for generating a second flag and generating a third flag as a primary flag if said difference is negative; and comparing two adjacent frames in said input image signal to determine if they are substantially the same image. If it is determined that both are substantially the same image, the primary flag is output as it is as a secondary flag, and if it is determined that both are not substantially the same image a selection circuit that replaces the second and third flags with the first flag and outputs a secondary flag; and if the secondary flag is the first flag, the common electrode voltage is not corrected. a correction circuit for correcting the common electrode voltage to be lower if the secondary flag is the second flag, and correcting the common electrode voltage to be higher if the secondary flag is the third flag; and an optical modulation device.

The present invention includes a dichroic mirror that splits a white light beam emitted from a light source into randomly polarized red light, green light, and blue light beams, and a dichroic mirror that splits a light beam of white light emitted from a light source into each of randomly polarized red light, green light, and blue light. A polarization conversion element that aligns a light flux into a first polarized light that is linearly polarized light in one direction and emits the light, and a light path of each light flux of red light, green light, and blue light aligned with the first polarized light. and the second polarized light, which is linearly polarized light in one direction orthogonal to the first polarized light, of the red light, the green light, and the blue light transmitted through the transmissive polarizing plate in the optical modulator. and a projection lens for enlarging and projecting the synthesized light color-synthesized by the color synthesis prism.

According to the light modulation device and the projection display device of the present invention, there is no need to project an image of a specific pattern and double-speed conversion processing of the frame rate of an input image signal in order to correct the deviation of the common electrode voltage. Electrode voltage deviations can be detected and corrected.

It is a figure which shows the structure of the projection-type display apparatus of one Embodiment. FIG. 4 is a partial side view of a polarization conversion element included in the projection display device of one embodiment; 2 is an enlarged view of a portion indicated by reference numeral 50 surrounded by a dashed line in FIG. 1. FIG. 1 is a conceptual perspective view showing a wire grid polarizer used as a reflective polarizing plate provided in a projection display device of one embodiment; FIG. FIG. 4 is a partially enlarged view showing a light beam incident on a photosensor included in the optical modulation device of one embodiment; 4 is a partially enlarged view showing that the optical sensor included in the optical modulation device of one embodiment is arranged at a position that is not affected by a light beam that should not be incident on the optical sensor; FIG. It is a figure which shows the schematic structure of the optical modulation apparatus of one Embodiment. 3 is a block diagram showing a detailed configuration example of a detection circuit, a selection circuit, and a correction circuit included in the optical modulation device of one embodiment; FIG. 4 is a flowchart showing processing executed by the optical modulation device of one embodiment; 4 is a timing chart showing the operation of the projection display device of one embodiment; 4 is a timing chart showing the operation of the projection display device of one embodiment; 4 is a timing chart showing the operation of the projection display device of one embodiment;

An optical modulation device and a projection display device according to one embodiment will be described below 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 white light with high brightness. An infrared transmission filter 3 is arranged at an angle of 45 degrees on the optical path of the white light. The infrared transmission filter 3 transmits infrared rays having a wavelength of about 700 nm or more, and reflects light beams in other wavelength bands. As a result, infrared rays having a wavelength of about 700 nm or more are removed.

A light beam in a wavelength band other than the infrared band has its optical path bent 90 degrees by the infrared transmission filter 3 and is incident on the ultraviolet reflection filter 4 . The ultraviolet reflection filter 4 reflects ultraviolet rays with a wavelength of about 400 nm or less, and transmits light beams in other wavelength bands. As a result, ultraviolet light having a wavelength of about 400 nm or less is removed. The white light from which infrared rays and ultraviolet rays have been removed enters a dichroic mirror 5 arranged at an angle of 45 degrees with respect to the optical path. The dichroic mirror 5 reflects blue light (hereinafter referred to as B light) and transmits reddish green light (hereinafter referred to as RG light), thereby splitting incident white light into B light and RG light.

On the optical path of the B light reflected by the dichroic mirror 5 are a reflecting 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, and 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 reflecting 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 reflective liquid crystal display elements 12r and 12g, which will be described later, are examples of liquid crystal display elements.

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 luminous flux reflected by the reflecting mirror 6 is also circular. In order to efficiently irradiate the effective pixel area of the rectangular reflective liquid crystal display element 12b with the luminous flux reflected by the reflecting mirror 6 and having a circular cross section, the circular luminous flux must be converted into a rectangular luminous flux.

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 match the shape of the B light flux to the shape of the reflective liquid crystal display element 12b, and uniform the illuminance distribution on the reflective liquid crystal display element 12b. For this purpose, the incident beam is split into a plurality of rectangular partial beams.

The B light, which is the partial light beam emitted from the second fly-eye lens 8b, is randomly polarized light having different polarization states. The polarization conversion element 9b converts a plurality of randomly polarized partial light beams into a plurality of linearly polarized partial light beams in one direction. The polarization conversion element 9b is constructed as shown in FIG.

As shown in FIG. 2, inside a planar polarization beam splitter array 91, polarization splitting surfaces 92 indicated by broken lines and reflecting surfaces 93 indicated by solid lines are alternately formed along the surface. 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 splitting surface 92 transmits P-polarized light (first polarized light) and reflects S-polarized light (second polarized light). The traveling direction of the S-polarized light is bent by 90° at the polarization splitting surface 92 and travels toward the reflecting surface 93 . The reflecting surface 93 reflects the incident S-polarized light and bends the direction of travel by 90°.

A half-wave plate 94 having birefringence is attached to a region sandwiched between the polarization splitting surface 92 and the reflecting surface 93 and emitting the S-polarized light reflected by the reflecting surface 93 . A half-wave plate 94 is not attached to a region sandwiched between the polarization splitting surface 92 and the reflecting surface 93 and emitting the P-polarized light transmitted through the polarization splitting surface 92 . The half-wave plate 94 rotates the polarization direction of the incident S-polarized light by 90° and emits P-polarized light. In this manner, the polarization conversion element 9b aligns incident random polarized light into P polarized light, which is linearly polarized light in one direction, and emits it.

The polarization conversion element 9b and the polarization conversion element 9rg, which will be described later, may align incoming random polarized light into S-polarized light, which is linearly polarized light in one direction, and emit it. When the polarization conversion element 9b and the polarization conversion element 9rg, which will be described later, emit S-polarized light, the light modulators for each color, which will be described later, are configured to correspond to the incident S-polarized light. In this case, the first polarization is S-polarization and the second polarization is P-polarization.

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

FIG. 3 shows an enlarged view of a portion 50 surrounded by a dashed line in FIG. In FIG. 1 or FIG. 3, rectangular openings are formed in three side surfaces of a substantially triangular prismatic support 20b, and a reflective liquid crystal display element is provided on the inner surface side of the three side surfaces so as to cover the respective openings. 12b, a reflective polarizing plate 13b, and a transmissive polarizing plate 15b are fixed. The reflective polarizing plate 13b is fixed to the side surface of the support 20b facing the field lens 11b, 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.

As shown in FIG. 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 in which metal wires 132 such as aluminum are formed on a polarizer optical glass plate 131 in regular stripes at a pitch of about 140 nm, for example. The reflective polarizing plate 13b transmits the polarized light component perpendicular to the metal wires 132 (here, P-polarized light) of the incident light flux as it is, and transmits the polarized light component parallel to the metal wires 132 (here, S-polarized light). ) is reflected.

If a wire grid polarizer is used as the reflective polarizer 13b, the weight of the reflective polarizer 13b can be reduced. Since a wire grid polarizer does not easily absorb incident light, the use of a wire grid polarizer as the reflective polarizing plate 13b can suppress deterioration in quality of a projected image due to birefringence of glass caused by heat generation. .

Returning to FIG. 1 or 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 enters the reflective liquid crystal display element 12b. The reflective liquid crystal display element 12b modulates light based on the B signal of the RGB signals constituting the input image signal, and reflects and emits the B light (S-polarized light) whose polarization state is changed by the light modulation as modulated light. do. 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 13 b passes through the transmissive polarizing plate 15 b and enters the cross dichroic prism 16 . Cross dichroic prism 16 is an example of a color combining prism.

The transmissive polarizing plate 15b and transmissive polarizing plates 15g and 15r, which will be described later, reflect and remove unnecessary polarized light (P polarized light) contained in the incident B light, thereby improving the degree of polarization of S polarized light. As a result, it is provided to improve the contrast.

In FIG. 1, on the optical path of the RG light transmitted through the dichroic mirror 5 are a first fly-eye lens 7rg for RG light, a second fly-eye lens 8rg for RG light, a polarization conversion element 9rg, and a condenser lens 10rg. , and the 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 are respectively the first fly-eye lens 7b, the second fly-eye lens 8b, the polarization conversion element 9b, and the condenser lens 10rg. It has the same configuration and function as the lens 10b.

The dichroic mirror 14 reflects green light (hereinafter referred to as G light) of the RG light and transmits red light (hereinafter referred to as R light), thereby splitting the incident RG light into R light and G light.

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 into telecentric illumination light of R light.

Rectangular openings are formed in three side surfaces of a substantially triangular prismatic support 20r, and a reflective liquid crystal display element 12r and a reflective polarizing plate 13r are provided on the inner surface side of the three side surfaces so as to close the respective openings. , a transmissive polarizing plate 15r is fixed.

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.

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 enters the reflective liquid crystal display element 12r. The reflective liquid crystal display element 12r modulates light based on the R signal of the RGB signals constituting the input image signal, reflects the R light (S polarized light) whose polarization state has been changed by the light modulation, and emits it as modulated light. do. 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 13 r passes through the transmissive polarizing plate 15 r and enters the cross dichroic prism 16 .

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 into telecentric illumination light of G light.

Rectangular openings are formed in three side surfaces of a substantially triangular prism support 20g, and a reflective liquid crystal display element 12g and a reflective polarizing plate 13g are provided on the inner surfaces of the three side surfaces so as to close the respective openings. , a transmissive polarizing plate 15g is fixed.

The reflective polarizing plate 13g is fixed to the side surface of the support 20g facing the field lens 11g, 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.

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 enters the reflective liquid crystal display element 12g. The reflective liquid crystal display element 12g modulates light based on the G signal among the RGB signals constituting the input image signal, reflects the G light (S-polarized light) whose polarization state is changed by the light modulation, and emits it as modulated light. do. 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 enters the cross dichroic prism 16. FIG.

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 exit surface 16a. The projection lens 17 enlarges and projects the combined light emitted from the exit surface 16 a onto the screen 18 .

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

5 and 6, the position of the optical sensors 21r, 21g and 21b near the supports 20r, 20g and 20b will be described. Here, as a representative, the position of the optical sensor 21b with respect to the support 20b will be described.

In FIG. 5, the luminous flux Ha of P-polarized B light emitted from the condenser lens 10b is refracted by the field lens 11b in accordance with the size of the display area (effective pixel area) of the reflective liquid crystal display element 12b. It is incident on the polarizing plate 13b. The P-polarized luminous flux Hb transmitted through the reflective polarizing plate 13b is optically modulated by the reflective liquid crystal display element 12b, part of which is reflected as S-polarized light, and reenters the reflective polarizing plate 13b. The S-polarized beam Hb is reflected by the reflective polarizing plate 13b and enters the transmissive polarizing plate 15b as the beam Hc.

The transmissive polarizing plate 15b transmits S-polarized light and reflects unnecessary P-polarized light. The optical sensor 21b is arranged on the P-polarized light flux Hd indicated by the dashed line reflected by the transmissive polarizing plate 15b.

As shown in FIG. 6, the reflective polarizing plate 13b does not transmit 100% of the incident P-polarized B light beam Ha, but reflects a small proportion of the P-polarized light beam Ha, thereby making the incident light beam Ha slightly The included S-polarized light is also reflected. Therefore, a light beam He including P-polarized light and S-polarized light indicated by the dashed line is emitted from the surface of the reflective polarizing plate 13b on the field lens 11b side toward the outside of the support 20b. Since this luminous flux He is not optically modulated by the reflective liquid crystal display element 12b, it is not affected by flicker caused by the reflective liquid crystal display element 12b. In addition, the luminous flux He is affected by flicker caused by the reflective liquid crystal display element 12b and has a larger amount of light than the luminous flux Hd reflected by the transmissive polarizing plate 15b.

Therefore, the optical sensor 21b must be placed on the luminous flux Hd reflected by the transmissive polarizing plate 15b, avoiding the luminous flux He reflected by the reflective polarizing plate 13b, and arranged at a position not affected by the luminous flux He. .

In this way, the optical sensors 21r, 21g, and 21b are on the luminous flux Hd reflected by the transmissive polarizing plates 15r, 15g, and 15b, and are affected by the luminous flux He reflected by the reflective polarizing plates 13r, 13g, and 13b. It is placed in a position where there is no

Although only one optical sensor 21r, 21g, 21b is shown in FIG. A plurality of photosensors 21r, 21g, and 21b may be arranged to receive . The plurality of photosensors 21r, 21g, and 21b are orthogonal to each other so as to receive a light beam Hd including reflected light modulated by a rectangular area composed of a plurality of pixels in the horizontal direction and a plurality of pixels in the vertical direction in the effective pixel area. They are preferably arranged in two directions.

Each photosensor in the plurality of photosensors 21r, 21g, and 21b has a single light receiving portion. Each one optical sensor 21r, 21g, 21b having a plurality of light receiving portions may be used. A plurality of light-receiving portions receive reflected light modulated by a plurality of pixels in the reflective liquid crystal display elements 12r, 12g, and 12b.

The correcting operation of the common electrode voltage (hereinafter referred to as Vcom) will be described in detail with reference to FIGS. 7 to 9. FIG. As shown in FIG. 7, the B light optical modulator 60 includes a reflective liquid crystal display element 12b, a reflective polarizing plate 13b, a transmissive polarizing plate 15b, an optical sensor 21b, a liquid crystal drive circuit 22b, and a detection circuit. 23b, a selection circuit 24b, and a correction circuit 25b. The reflective liquid crystal display element 12 b has a pixel electrode 121 , a common electrode 122 , and liquid crystal 123 sealed between the pixel electrode 121 and the common electrode 122 .

The liquid crystal drive circuit 22b inverts the polarity of the input image signal (R signal) between positive and negative polarities around Vcom every vertical period, and supplies the signal to the pixel electrodes 121 . The detection circuit 23b detects the state of Vcom based on the detection signal from the optical sensor 21b and various drive signals output from the liquid crystal drive circuit 22b. As will be described later, detection circuit 23b generates a primary flag based on the detection result of the state of Vcom. As will be described later, 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.

A liquid crystal drive circuit 22r, a detection circuit 23r, a selection circuit 24r, and a correction circuit similar to the liquid crystal drive circuit 22b, detection circuit 23b, selection circuit 24b, and correction circuit 25b are also provided for the reflective liquid crystal display element 12r for R light. A light modulator 60 for R light with 25r is provided. A liquid crystal drive circuit 22g, a detection circuit 23g, a selection circuit 24g, and a correction circuit similar to the liquid crystal drive circuit 22b, detection circuit 23b, selection circuit 24b, and correction circuit 25b are also provided for the reflective liquid crystal display element 12g for G light. A light modulation device 60 for G light having 25g is provided.

FIG. 8 shows specific configuration examples of the detection circuits 23r, 23g, and 23b, the correction circuits 25r, 25g, and 25b, and the selection circuits 24r, 24g, and 24b. The detection circuits 23r, 23g, and 23b have an AD converter 231, a timing generator 232, a positive data hold circuit 233, a negative data hold circuit 234, a subtractor 235, and a flag generator 236. The selection circuits 24r, 24g, and 24b have a frame memory 241, a comparator 242, and a flag selector 243. The correction circuits 25r, 25g, and 25b have a data hold circuit 251, a calculator 252, and a DA converter 253.

The operations of the detection circuit 23b, the selection circuit 24b, and the correction circuit 25b will be described representatively with reference to the flow charts shown in FIGS. 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 processing shown in FIG. 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 side data hold circuit 233 and the negative side data hold circuit 234 .

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 for each vertical period. The liquid crystal drive circuit 22b supplies the timing generator 232 with a polarity switching signal and horizontal and vertical synchronization signals. The timing generator 232 supplies the positive side and negative side trigger signals to the positive side data hold circuit 233 and the negative side data hold circuit 234, respectively.

The positive data hold circuit 233 and the negative 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 in which the liquid crystal drive circuit 22b supplies the input image signal to the pixel electrode 121 in positive polarity, and detects the peak. is output (step S2 in FIG. 9). The negative data hold circuit 234 detects a positive peak from the stored detection signal during a vertical period in which the liquid crystal drive circuit 22b supplies the input image signal to the pixel electrode 121 with a negative polarity, and detects the peak. is output (step S3 in FIG. 9).

The subtractor 235 calculates the difference between the positive peak absolute value and the negative peak absolute value (step S3). As an example, the subtractor 235 subtracts the negative peak absolute value from the positive peak absolute value. When Vcom is higher than the inversion center voltage, the amount of S-polarized light is less than the specified amount and the amount of P-polarized light is greater than the specified amount when displaying the positive polarity side projection image. Conversely, when displaying a projected image on the negative polarity side, the amount of S-polarized light is greater than the prescribed amount, and the amount of P-polarized light is smaller than the prescribed amount.

Since the optical sensor 21b detects P-polarized light that is not used to form a projected image, a positive difference obtained by subtracting the negative peak absolute value from the positive peak absolute value means that Vcom is high. means too much. Conversely, a negative difference means that Vcom is too low.

The flag generator 236 generates, for example, a 2-bit flag according to the difference calculated by the subtractor 235 . The flag generator 236 is supplied with a two-frame timing signal that goes high every two frames, and generates and outputs a flag when the two-frame timing signal goes high.

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

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 progress as . . . F(n-1), F(n), F(n+1) . The input image signal F(n) may refer to a series of frames collectively.

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 progress in the order of . . . F(n-2), F(n-1), F(n) . Similarly, the image signal F(n-1) may refer generically to a series of frames delayed by one frame.

The comparator 242 compares the input image signal F(n) and the image signal F(n−1), and if the pixel values at the same pixel position match for a predetermined ratio or more of all pixels in one frame, It outputs "1" indicating a match, and otherwise outputs "0" indicating a mismatch as a comparison result signal. The predetermined ratio may be set to an appropriate value such as 90%.

The fact that the pixel values at the same pixel position match for a predetermined ratio or more of all 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). The comparator 242 outputs "1" as the comparison result signal if it is determined that the two adjacent frames are substantially the same image, and if it is determined that the two adjacent frames are not substantially the same image. If so, it outputs "0" as the comparison result signal.

The determination of matching or non-matching by the comparator 242 may be made according to the level of the adjustment accuracy of Vcom. If the adjustment accuracy of Vcom does not need to be so high, the comparator 242 may simply determine match or mismatch. For example, when each pixel data is 12 bits, it is determined whether or not the pixel values of the same pixel positions of the input image signal F(n) and the image signal F(n−1) match with the upper 10 bits. good too.

Further, the comparator 242 may not determine whether the pixel values of all pixels in one frame match or not, and may determine whether the pixel values of some pixels in the frame match. good. The comparator 242 may determine whether the pixel values of some pixels corresponding to the spatial range in which the optical sensor 21b detects the light flux Hd match. The comparator 242 may determine match or mismatch so that the adjustment accuracy of Vcom is ensured at a predetermined accuracy or higher.

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

If the primary flag is the first flag "00", the flag selector 243 outputs the first flag "00" as it is as the secondary flag. If the primary flag is the second flag "11" or the third flag "01", the flag selector 243 switches the second flag "11" or the third flag "01" to the first flag "00". ” and output as a secondary flag (step S11 in FIG. 9). That is, if the comparison result signal is "0" indicating non-coincidence, the flag selector 243 fixedly selects the first flag "00" as the secondary flag regardless of the primary flag output from the flag generator 236. output as

The first flag "00" indicates that Vcom is the inversion center voltage and it is not necessary to correct Vcom. A second flag "11" indicates that Vcom is higher than the inversion center voltage and that Vcom needs to be corrected lower. A third flag "01" indicates that Vcom is lower than the inversion center voltage and that Vcom needs to be corrected higher. If two adjacent frames are different images, the determination result that 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 signals do not match is because the determination result may be incorrect. This is to avoid correcting Vcom.

The operation of the correction circuit 25b is as follows. The secondary flag output from the selection circuit 24b is input to the calculator 252. FIG. 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, even if Vcom is set based on the initial value of Vcom under various conditions such as variations in the characteristics of the pixel electrode driving transistor, asymmetry occurs between the positive polarity side and the negative polarity side of the AC voltage. and Vcom may need to be corrected. Note that it is not essential to hold the Vcom initial value in the data hold circuit 251 . Even if the Vcom initial value is not held in the data hold circuit 251, the Vcom correction values held in the data hold circuit 251 are sequentially updated, and the optimum Vcom correction value is obtained after a predetermined time.

The data hold circuit 251 reads the stored value when the 2-frame timing signal goes high. If the Vcom initial value is read from the data hold circuit 251 and the secondary flag is the first flag "00", the calculator 252 stores the Vcom initial value in the data hold circuit 251 without correcting it, and It is supplied to the DA converter 253 .

If the Vcom initial value is read from the data hold circuit 251 and the secondary flag is the second flag “11”, the computing unit 252 supplies the data hold circuit 251 with the Vcom correction value obtained by subtracting 1 bit from the Vcom initial value. It is stored and supplied to the DA converter 253 (step S12 in FIG. 9). If the Vcom initial value is read from the data hold circuit 251 and the secondary flag is the third flag “01”, the calculator 252 supplies the data hold circuit 251 with the Vcom correction value obtained by adding 1 bit to the Vcom initial value. It is stored and supplied to the DA converter 253 (step S12 in FIG. 9).

Similarly, after the Vcom correction value is stored in the data hold circuit 251, the calculator 252 reads out the Vcom correction value from the data hold circuit 251, and if the secondary flag is the second flag "11", the Vcom A new Vcom correction value obtained by subtracting 1 bit from the correction value is stored in the data hold circuit 251 and supplied to the DA converter 253 (step S12 in FIG. 9). If the Vcom correction value is read out from the data hold circuit 251 and the secondary flag is the third flag "01", the computing unit 252 adds a new Vcom correction value by adding 1 bit to the Vcom correction value, and stores it in the data hold circuit. 251 and supplied to the DA converter 253 (step S12 in FIG. 9).

The optimum Vcom correction value is supplied to the DA converter 253 by repeating the operation of updating the Vcom correction value by the data hold circuit 251 and the calculator 252 . The DA converter 253 DA-converts the input Vcom correction value and applies the analog value Vcom to the common electrode 122 (step S13 in FIG. 9).

In this manner, the correction circuit 25b does not correct Vcom when the secondary flag is the first flag "00", and corrects to lower Vcom when the secondary flag is the second flag "11". , and if the secondary flag is the third flag "01", Vcom is corrected to be higher. The correction circuit 25b can always apply Vcom matching the inversion center voltage to the common electrode 122 .

In step S14 of FIG. 9, when the power of the projection display device 1 is turned off, the projection display device 1 terminates the processing shown in FIG. Unless the power of the projection display device 1 is turned off, the projection display device 1 repeats the processing from step S1. The correction circuit 25b repeats the operation of correcting Vcom every two frames.

By the way, 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 or from the Vcom correction value (or the Vcom initial value) is expressed. "1" means subtraction, and "0" of the upper bit means addition. The arithmetic unit 252 can be configured by a digital circuit in which the upper bits and lower bits of the secondary flag are defined in this way. If the arithmetic unit 252 is configured with such a digital circuit, even if "10" indicating an undefined decimal number "2" is input by mistake, Vcom will not be corrected, thereby avoiding malfunction. can be done.

In FIG. 8, the timing generator 232 generates positive and negative trigger signals during the blanking period of the input image signal F(n) based on the horizontal and vertical synchronizing signals to hold the positive data. It is preferable to supply it to the circuit 233 and the negative data hold circuit 234 .

The optical sensor 21b is preferably arranged at a position where the reflected light modulated by the pixel at the position where the vertical scanning starts or the position where the vertical scanning ends in the reflective liquid crystal display elements 12r, 12g, and 12b is received. . 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 polarity or the negative polarity.

The operation of the projection display device 1 (light modulation device 60) will be described using the timing charts shown in FIGS. 10A to 10C. 10A, (a) conceptually shows waveforms of input image signals F(n), F(n+1), . . . , (b) shows input image signals F(n), F(n+1), . c) shows the image signals F(n-1), F(n), . . . one frame before. 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.

(d) of FIG. 10A shows comparison results C(n), C(n+2), . (e) of FIG. 10A shows comparison result signals 242(n−2), 242(n), and 242(n+2) indicating whether pixel values match at a predetermined ratio or more of all pixels in one frame. … is shown. Based on the comparison results C(n), C(n+2), . It outputs comparison result signals 242(n), 242(n+2), . . .

As shown in (f) of FIG. 10B, the liquid crystal drive circuits 22r, 22g, and 22b supply the timing generator 232 with polarity switching signals that alternately repeat high and low. The liquid crystal drive circuits 22r, 22g, and 22b invert the polarities of the input image signals F(n), F(n+1), . supply. Therefore, as shown in (g) of FIG. 10B, the liquid crystal drive voltage alternately repeats positive and negative polarities. While the polarity switching signal is high, the input image signals are +F(n), +F(n+2), . . . becomes.

In FIG. 10B, (h) indicates a vertical synchronization signal, (i) indicates a positive-side trigger signal supplied by the timing generator 232 to the positive-side data hold circuit 233, and (j) indicates that the timing generator 232 3 shows a negative trigger signal to be supplied to the data hold circuit 234. FIG. The positive and negative trigger signals go high at the beginning of each frame every two frames.

As shown in (k) of FIG. 10C, the positive data hold circuit 233 outputs positive peak absolute values 233(n), 233(n+2), . . . every two frames. As shown in (m) of FIG. 10C, the negative data hold circuit 234 outputs negative peak absolute values 234(n), 234(n+2), . . . every two frames. The timing of outputting the negative peak absolute values 234(n), 234(n+2), . . It should be noted that FIG. 10C shows the same trigger signals on the positive side and negative side as in (i) and (j) of FIG. 10B.

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

As shown in (q) of FIG. 10C, the data hold circuit 251 changes Vcom correction values 251(n−2), 251(n), 251( n+2) . As shown in (r) of FIG. 10C, the calculator 252 outputs new Vcom correction values 252(n), 252(n+2), 252(n+4), . .

The Vcom correction value 252(n) is the Vcom correction value 251(n−2)+secondary flag 243(n). The Vcom correction value 252(n+2) is the Vcom correction value 251(n)+secondary flag 243(n+2). The Vcom correction value 252(n+4) is the Vcom correction value 251(n+2)+secondary flag 243(n+4). However, if the secondary flags 243(n), 243(n+2), . Processing is executed, and if the third flag is "01", addition processing is executed.

As described above, the light modulation device 60 and the projection display device 1 including the light modulation device 60 do not need to project an image of a specific pattern in order to correct the deviation of Vcom. It is possible to always correct the deviation of Vcom while projecting the image of . As a result, it is possible to suppress the flicker that occurs in the projected image, and to suppress the secular change of the liquid crystal display elements (the reflective liquid crystal display elements 12r, 12g, and 12b). Since the flicker that occurs in the projected image is suppressed, the projection display device 1 can display a high-quality image. Since deterioration of the liquid crystal display element over time is suppressed, the reliability of the projection display device 1 can be improved.

According to the light modulation device 60 and the projection display device 1 including the light modulation device 60, there is no need to double the frame rate of the input image signal. Therefore, even if the frame rate of the input image signal is 120 Hz or higher, the deviation of Vcom can be corrected without causing a large increase in circuit scale and cost.

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. The presence of the optical sensors 21r, 21g, and 21b does not hinder replacement of the projection lens 17. FIG. Shadows of the optical sensors 21r, 21g, and 21b do not appear in the projection image projected onto the screen 18 by the projection lens 17 in an enlarged manner.

In the projection display apparatus 1 shown in FIG. 1, the 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. . Of the R light, G light, and B light, the light modulation device 60 may be provided only in the optical path of the G light, which is the brightest and causes conspicuous flicker. The optical modulator 60 may be provided only in the optical path of B light, which has a short wavelength and tends to affect organic materials used in optical components.

The conventional configuration in which the optical sensor is arranged in the vicinity of the projected image displayed on the screen 18 or within the projection lens 17 may be used in combination with the configuration of the present embodiment.

The present invention is not limited to the embodiments described above, 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 configured by integrated circuits, or at least a part of the circuits may be configured by a microcomputer. .

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 (4)

It has a pixel electrode, a common electrode to which a common electrode voltage is applied, and a liquid crystal sandwiched between the pixel electrode and the common electrode. a liquid crystal display element that modulates light based on and emits modulated light;
a reflective polarizing plate that transmits the first polarized light and reflects the second polarized light, which is linearly polarized light in one direction perpendicular to the first polarized light, out of the modulated light emitted from the liquid crystal display element;
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 driving circuit that inverts the polarity of the input image signal between positive and negative polarities with respect to the common electrode voltage every vertical period and supplies the input image signal to the pixel electrode;
a positive peak absolute value that 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 input image signal to the pixel electrode in positive polarity; The difference from the negative peak absolute value, which is the absolute value of the peak of the detection signal output from the photosensor during the vertical period in which the liquid crystal drive circuit supplies the input image signal to the pixel electrode with negative polarity, is 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, and if the difference is negative, a second flag is generated as a primary flag. a detection circuit that generates 3 flags;
comparing two adjacent frames in the input image signal to determine whether they are substantially the same image, and if it is determined that both are substantially the same image, the primary flag is left unchanged a selection circuit for outputting as a secondary flag and, if it is determined that the two are not substantially the same image, replacing the second and third flags with the first flag and outputting as the secondary flag;
If the secondary flag is the first flag, the common electrode voltage is not corrected; if the secondary flag is the second flag, the common electrode voltage is corrected to be low; is the third flag, a correction circuit for correcting the common electrode voltage to be higher;
A light modulating device comprising: 2. The light modulation device according to claim 1, wherein the optical sensor is arranged at a position for receiving reflected light modulated by a pixel at a position where vertical scanning starts or a position where vertical scanning ends in the liquid crystal display element. . One optical sensor that receives the first polarized light reflected by the transmissive polarizing plate with a plurality of light receiving units and outputs a detection signal, or a single optical sensor that receives the first polarized light reflected by the transmissive polarizing plate 3. The optical modulation device according to claim 1, comprising a plurality of optical sensors for receiving light with a light receiving portion and outputting a detection signal. a dichroic mirror that splits a white light flux emitted from a light source into randomly polarized red light, green light, and blue light fluxes;
a polarization conversion element that aligns each light flux of randomly polarized red light, green light, and blue light into a first polarized light that is linearly polarized light in one direction and emits the light;
the light modulation device according to any one of claims 1 to 3, provided in the optical paths of the red light, green light, and blue light beams aligned with the first polarized light;
Color-combining each light flux of second polarized light, which is linearly polarized light in one direction orthogonal to the first polarized light, of red light, green light, and blue light transmitted through the transmissive polarizing plate in the light modulation device. a color synthesizing prism;
a projection lens that enlarges and projects the combined light color-combined by the color-combining prism;
A projection display device.

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