JP2008197363A - Liquid crystal projector and flicker adjustment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance an effect of suppressing a flicker by exactly obtaining an optimum value of a common voltage. <P>SOLUTION: A liquid crystal projector comprises: a test pattern generation section 105 which generates video data for testing for forming the image for adjustment comprising first and second bright spots formed by first and second liquid crystal cells held inverted in the mutual polarity on a liquid crystal panel 10; a controller 101 which supplies the video data for testing to a liquid crystal driving circuit 106 and makes the set level of a common voltage created in a common voltage generation section 104 change stepwise; and a PSD 103 which photodetects the light from the first and second bright spots in the projected image of the image for adjustment respectively at each of the set levels of the common voltage. The controller 101 determines the set level which is highest in the peak value of the output of the PSD 103 among the set levels of the common voltage as the optimum voltage. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal projector, and more particularly to a liquid crystal projector in which a common voltage is supplied to a common electrode to which a plurality of liquid crystal cells are connected in common.

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

  FIG. 6 shows the waveform of video data for line inversion driving. In the video data shown in FIG. 6, positive-polarity video data and negative-polarity video data whose polarity is inverted with reference to the reference voltage Vref are alternately switched every horizontal scanning period. In the line inversion driving, as shown in FIG. 6, the polarity of the video signal is inverted every horizontal scanning period. The positive video data and the negative video data are vertically symmetrical about the reference voltage Vref. The common voltage Vcom is a voltage applied to the common electrode of each liquid crystal cell, and is adjusted so as to minimize flicker (brightness flicker) generated when the video data is inverted.

  FIG. 7 shows an equivalent circuit of a liquid crystal cell of a liquid crystal panel in which AC driving is performed. A TFT is provided at the intersection of the video signal line L1 and the gate line L2. CLC indicates the capacitance of the liquid crystal cell, CS indicates the additional capacitance, and CGD indicates the parasitic capacitance between the gate and the drain of the TFT. When a voltage is applied to the target liquid crystal cell (that is, when a video signal is written), the gate line L2 becomes High, and the TFT is energized. After the video signal is written, the gate line L2 becomes Low, and the written video signal is held thereafter. When the gate line L2 changes from High to Low, the liquid crystal cell potential VLC decreases due to the differential effect of the parasitic capacitance CGD. This voltage drop is constant regardless of the polarity of the video signal. Further, due to the influence of the voltage drop due to the combined capacitance of the liquid crystal cell capacitor CLC and the additional capacitor CS, the common voltage Vcom becomes an optimum adjustment value at a voltage lower than the reference voltage Vref that is the central value of the video data.

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

  Thus, a liquid crystal projector that allows a user to easily adjust the common voltage has been proposed (see Patent Document 1). This liquid crystal projector has a liquid crystal panel composed of a plurality of liquid crystal cells, and a counter electrode adjustment circuit that supplies a common voltage to a common electrode to which the liquid crystal cells are connected in common. The main part of the counter electrode adjustment circuit includes a light receiving part, a voltage conversion part, and a data processing circuit. The light receiving unit is an optical sensor composed of a phototransistor or the like, and is provided in a wired remote controller (hereinafter simply referred to as a remote controller) for operating a liquid crystal projector. The voltage conversion unit is a low-pass filter that extracts a low-frequency component of the output signal of the light-receiving unit, and a positive peak value hold circuit and a negative peak value hold circuit that receive the low-frequency component signal extracted by the low-pass filter, And a subtractor for outputting a difference between outputs of the positive and negative peak value hold circuits. The data processing circuit supplies a common voltage to the common electrode of the liquid crystal panel and determines an optimum value of the common voltage based on the output of the voltage conversion unit.

In the above liquid crystal projector, when flicker adjustment is performed, positive and negative images that are halftone checkered patterns are displayed on a liquid crystal panel by AC driving, and the display image is projected on a screen. Point the remote control's light-receiving part toward the screen In this state, the data processing circuit changes the common voltage stepwise from a high level to a low level. In the voltage converter, for each common voltage level, the positive peak value hold circuit and the negative peak value hold circuit hold the positive peak value and negative peak value of the light receiving unit output, and the subtractor The difference between the positive and negative peak values held is output. The difference between the positive and negative peak values corresponds to the flicker size. The data processing circuit holds the difference value (flicker value) between the positive and negative peak values output from the voltage conversion unit for each common voltage level, and sets the common voltage level at which this difference value is minimum to the optimum common voltage value. Judge.
JP-A-8-286169

  However, in the liquid crystal projector described in Patent Document 1, the difference between the peak value of the light reception level of the projection video based on the positive video data and the peak value of the light reception level of the projection video based on the negative video data, that is, projection. Since the optimum value of the common voltage is determined based on the difference in the contrast of the video, the following problem occurs.

  The common voltage supplied to the common electrode of each liquid crystal cell is not uniform throughout the liquid crystal panel due to factors such as a voltage drop due to the resistance component of the common electrode. For this reason, the size of the flicker generated in the liquid crystal cell located at the center of the panel is different from the size of the flicker in the liquid crystal cell located at the outer periphery of the panel. Since the difference in the contrast of the projected image includes the influence of such flicker variations, it is difficult for the liquid crystal projector described in Patent Document 1 to accurately determine the optimum value of the common voltage.

  An object of the present invention is to provide a liquid crystal projector that can solve the above-described problems and can further improve the effect of suppressing flicker by accurately obtaining the optimum value of the common voltage.

  In order to achieve the above object, a liquid crystal projector of the present invention is a liquid crystal projector including a liquid crystal panel and a projection optical system for projecting an image displayed on the liquid crystal panel, and a plurality of liquid crystal cells constituting the liquid crystal panel. A common voltage generator for supplying a common voltage to a common electrode connected in common, and an image based on the video data on the liquid crystal panel by supplying a voltage corresponding to the input video data to the plurality of liquid crystal cells. And a first and second liquid crystal cell formed by the first and second liquid crystal cells in which the polarities of the supplied voltages are opposite to each other among the plurality of liquid crystal cells A test pattern generator for generating test image data for forming an adjustment image consisting only of bright spots on the liquid crystal panel, and a light receiving surface, and incident on the light receiving surface A light detection element that outputs data indicating a light intensity distribution in accordance with the amount of light that has been transmitted; and image data for testing generated by the test pattern generator is supplied to the liquid crystal driving circuit to display the adjustment image in the liquid crystal And a control unit that changes the setting level of the common voltage supplied by the common voltage generation unit stepwise while being formed on the panel, and the photodetecting element at each of the setting levels of the common voltage, Each of the light from the first and second bright spots in the projected image of the adjustment image projected by the projection optical system is received and the data is output, and the control unit outputs from the light detection element The setting level of the common voltage having the highest peak value of the intensity distribution in the obtained data is determined as the optimum value.

  According to the above configuration, the luminance levels of the first and second bright spots when the common voltage is out of the optimum value are the brightness levels of the first and second bright spots when the common voltage is the optimum value. Since it is lower than the level, the peak of the intensity distribution in the output data of the photodetecting element is highest when the common voltage is the optimum value. Therefore, the optimum value of the common voltage can be determined by changing the setting level of the common voltage stepwise and comparing the peak values of the output data of the light detection elements at the respective setting levels.

  Another liquid crystal projector of the present invention is a liquid crystal projector including a liquid crystal panel and a projection optical system for projecting an image displayed on the liquid crystal panel, and a plurality of liquid crystal cells constituting the liquid crystal panel are commonly used. A common voltage generator for supplying a common voltage to the connected common electrode, and a voltage corresponding to the input video data are supplied to the plurality of liquid crystal cells to display an image based on the video data on the liquid crystal panel. Only the first and second bright spots formed by the liquid crystal driving circuit and the first and second liquid crystal cells in which the polarity of the supplied voltage is opposite to each other among the plurality of liquid crystal cells A test pattern generator for generating test video data for forming an adjustment image on the liquid crystal panel, and a light receiving surface, and the amount of light incident on the light receiving surface A light detecting element for detecting the position of the center of gravity of the light quantity based on the light intensity distribution, and the test image data generated by the test pattern generator is supplied to the liquid crystal driving circuit to display the adjustment image on the liquid crystal. And a control unit that changes the setting level of the common voltage supplied by the common voltage generation unit in a stepwise manner, and the photodetecting element is set at each of the setting levels of the common voltage. Receiving the light from the first and second bright spots in the projection image of the adjustment image projected by the projection optical system to detect the position of the center of gravity, and the control unit sets the common voltage Of the levels, the center of gravity position detected by the light detection element is the center of gravity position detected in the state where the setting level of the common voltage is the lowest and the setting level of the common voltage And determining an optimum value of the set level of the common voltage becomes an intermediate position between the detected gravity center position at the highest state.

  According to the above configuration, for example, when the first liquid crystal cell is positive and the second liquid crystal cell is negative, if the common voltage is lower than the optimum value, When the brightness level is lower than the brightness level when the common voltage is the optimum value, and when the common voltage is higher than the optimum value, the brightness level of the first bright spot is the optimum value of the common voltage. Lower than the brightness level of When the setting level of the common voltage is set to the lowest state, the light amount from the first bright spot on the light receiving surface becomes extremely larger than the light quantity from the second bright spot, and the center of gravity is obtained. The position is approximately the position of the center of gravity of the first bright spot. On the contrary, when the setting level of the common voltage is the highest, the amount of light from the second luminescent spot on the light receiving surface becomes extremely larger than the amount of light from the first luminescent spot. Therefore, the position of the center of gravity is substantially the position of the center of gravity of the second bright spot. When the common voltage is an optimum value, the luminance levels of the first and second luminescent spots are the same, and the amount of light from the first and second luminescent spots on the light receiving surface is also the same. In this case, the barycentric position is located between the barycentric position of the first bright spot and the barycentric position of the second bright spot. Therefore, the optimum value of the common voltage can be obtained by obtaining the center-of-gravity position as the intermediate position.

  In any of the above-described inventions, the optimum value of the common voltage is determined between the liquid crystal cells in which the polarities of the voltages supplied to the pixel electrodes are reversed. It is possible to accurately determine the optimum value of the common voltage without being affected by flicker variations.

  According to the present invention, since the optimum value of the common voltage can be accurately determined, the occurrence of flicker can be more effectively suppressed.

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

  FIG. 1 is a block diagram showing a main part of a liquid crystal projector according to an embodiment of the present invention.

  Referring to FIG. 1, the main parts of the liquid crystal projector are a control unit 101, a PSD (Position Sensitive Detector) signal processing unit 102, a PSD 103, a common voltage generation unit 104, a test pattern generation unit 105, a liquid crystal drive unit 106, and a liquid crystal panel 107. Consists of. In FIG. 1, it is supplied from a projection optical system that projects an image displayed on the liquid crystal panel 107 onto a screen (or a member corresponding to the screen), or an external image supply device typified by a personal computer. Well-known components constituting the liquid crystal projector such as a circuit for processing video data are omitted.

  The liquid crystal panel 107 is a liquid crystal panel in which AC driving is performed in which the polarity of the voltage applied to the pixel electrode of the liquid crystal is inverted at a predetermined period, and the configuration shown in FIG. 7 can be applied, for example. For AC driving, one or a combination of dot inversion driving, line inversion driving, and frame inversion driving can be applied. Here, it is assumed that line inversion driving is applied. In the line inversion driving, the polarities of the voltages supplied to each other are inverted between the odd lines and the even lines in the liquid crystal cell columns (horizontal lines) arranged in the horizontal direction of the liquid crystal panel. In this line inversion drive, for example, the odd line is fixed to positive polarity and the even line is fixed to negative polarity, and the polarity of the odd line and even line is inverted for each frame (or field). However, any method may be applied.

  The test pattern generation unit 105 generates video data for flicker adjustment according to a control signal from the control unit 101. Among the liquid crystal cells constituting the liquid crystal panel 107, the first and second liquid crystal cells to which voltages having different polarities are supplied and whose distances are within a predetermined distance are determined as flicker adjustment target cells. Yes. The video data for flicker adjustment is video data for operating these first and second liquid crystal cells.

  Here, the first and second liquid crystal cells will be specifically described. FIG. 2 schematically shows a dot image of a liquid crystal panel in which line inversion driving is performed. In FIG. 2, horizontal scanning periods L1 to L4 indicate horizontal scanning periods in four horizontal lines adjacent in the vertical direction among the horizontal lines of the liquid crystal panel. When positive video data is supplied during the horizontal scanning periods L1 and L3, negative video data is supplied during the horizontal scanning periods L2 and L4. Conversely, when negative video data is supplied during the horizontal scanning periods L1 and L3, positive video data is supplied during the horizontal scanning periods L2 and L4. When frame inversion is combined with line inversion driving, the polarities of the horizontal scanning periods L1 and L3 and the polarities of the horizontal scanning periods L2 and L4 are inverted for each frame. The dot image 301 is a dot representation of a liquid crystal cell that is driven based on a video signal supplied during the horizontal scanning periods L1 to L4. The dot A in the horizontal scanning period L1 and the dot C in the horizontal scanning period L3 are supplied with the same polarity data, and the dot B in the horizontal scanning period L2 and the dot D in the horizontal scanning period L4 are supplied with the same polarity data. . The dots A and C are supplied with data having a polarity opposite to that of the data supplied to the dots B and D.

  In this embodiment, since a system that combines frame inversion with line inversion driving or line inversion driving is assumed, when the first liquid crystal cell is set to dot A in the flicker adjustment target cell setting, The liquid crystal cell is a dot B or a dot D. The dots corresponding to the second liquid crystal cell are not limited to the dots B and D, but are data at a predetermined distance from the first liquid crystal cell and having a polarity opposite to that of the first liquid crystal cell. Any liquid crystal cell (dot) may be used. Here, the predetermined distance is a distance at which the optimum value of the common voltage can be determined based on the output signal of the PSD 103. The video data for flicker adjustment is data that supplies voltages having different polarities to the first liquid crystal cell and the second liquid crystal cell. For example, when the first liquid crystal cell is the dot A and the second liquid crystal cell is the dot D, the video data for flicker adjustment applies a positive voltage to the dot A, and the dot D The data is such that a negative voltage is applied, and the polarity for each dot is fixed.

  The liquid crystal driving unit 106 AC drives the liquid crystal panel 107 based on the supplied video data. In the flicker adjustment mode, the output (video data for flicker adjustment) of the test pattern generation unit 105 is supplied to the liquid crystal driving unit 106, and in the normal operation mode, the video data input from an external video supply device (not shown) is liquid crystal. It is supplied to the drive unit 106. Although not shown in FIG. 1, the input stage of the liquid crystal driving unit 106 is provided with switch means that can switch the input according to such a mode. In addition, the liquid crystal projector is provided with an operation unit (not shown) having an operation mode selection button, and the user can switch the mode such as the flicker adjustment mode and the normal operation mode by using the operation mode selection button. Can be done freely.

  The common voltage generation unit 104 supplies a common voltage to a common electrode to which the liquid crystal cells constituting the liquid crystal panel 107 are connected in common, and the level of the common voltage supplied to the common electrode according to a control signal from the control unit 101. Is gradually changed from high to low, or from low to high. The range in which the common voltage is changed is determined in advance.

  The PSD 103 is a position detection element that can detect the incident position of light (the center of gravity of the light amount) on the light receiving surface. The light receiving surface is composed of a semiconductor layer (PIN structure) constituting the photodiode and a resistance layer formed on the semiconductor layer, and at least one output terminal pair disposed opposite to the resistance layer. Is provided. When light enters the light receiving surface, the current output from each output terminal changes due to the resistance proportional to the distance between the incident position and each output terminal. The incident position can be obtained from the ratio of each output current (corresponding to the ratio of the resistance between the incident position and each output terminal). The output of the PSD 103 is given by [(A−B) / (A + B)] where, for example, A is one output current of the output terminal pair and B is the other output current. The output of the PSD 103 includes data indicating the light intensity distribution according to the light reception level of the incident light.

  A condensing optical system for condensing light is provided on the light receiving surface side of the PSD 103. The PSD 103 projects light on the screen (or a member corresponding to the screen) through the condensing optical system, and the light (first and second liquid crystal cells corresponding to the first and second liquid crystal cells) from the projected image of the flicker adjustment target cell. And light from the second bright spot). The PSD 103 may be a one-dimensional PSD or a two-dimensional PSD. Here, a one-dimensional PSD is used.

  The PSD signal processing unit 102 converts light incident area data (light receiving point data) obtained from the output signal of the PSD 103 into a signal (digital) that can be processed by the control unit 101.

  The control unit 101 controls input switching in the liquid crystal driving unit 106 and operations of the test pattern generation unit 105 and the common voltage generation unit 104. Further, the control unit 101 determines an optimum value of the common voltage based on the light reception point data supplied from the PSD signal processing unit 102.

  Next, the flicker adjustment operation performed in the liquid crystal projector of this embodiment will be described.

(1) Flicker adjustment using the peak value of the output data of the PSD 103:
When the flicker adjustment mode is selected, the control unit 101 first transmits a control signal for instructing the test pattern generation unit 105 to start generation of video data for flicker adjustment and to the common voltage generation unit 104. On the other hand, a control signal instructing the start of supply of the common voltage to the common electrode of the liquid crystal panel 107 is transmitted.

  The common voltage generator 104 supplies a common voltage to the common electrode of the liquid crystal panel 107 in accordance with a control signal from the controller 101. The level of the common voltage supplied to the common electrode is set by the control unit 101. The common voltage setting range is given in advance, the control unit 101 sets the lowest level in the setting range, and the common voltage generation unit 104 supplies the common voltage of the set level to the common electrode. To do.

  The test pattern generation unit 105 generates video data for flicker adjustment according to a control signal from the control unit 101. Here, the image data for flicker adjustment is image data for operating the liquid crystal cells corresponding to the dots A and D shown in FIG. 2, and the dot A is fixed to the positive electrode and the dot D is fixed to the negative electrode. Yes. The video data for flicker adjustment is supplied to the liquid crystal driving unit 106.

  The liquid crystal driving unit 106 drives the liquid crystal panel 107 based on the video data for flicker adjustment supplied from the test pattern generating unit 105. By the line inversion driving based on the video data for flicker adjustment, the liquid crystal panel 107 performs display by the dot A (positive electrode) in the horizontal scanning period L1, and then by the dot D (negative electrode) in the horizontal scanning period L4. Display is performed.

  On the liquid crystal panel 107, an adjustment image based on the dots A and D is displayed, and the adjustment image is projected on the screen through the projection optical system. FIG. 3 schematically shows an adjustment image projected on the screen. In FIG. 3, reference numeral 602 denotes the liquid crystal projector according to the present embodiment, and reference numeral 603 denotes an adjustment image projected from the liquid crystal projector 602 onto the screen 601. The projection adjustment image 603 is an adjustment image in which the dots A and D are set to the white level and the other dots are set to the black level.

  Light (images of dots A and D) from the projection adjustment image 603 on the screen 601 enters the light receiving surface of the PSD 103 through the condensing optical system. The PSD 103 outputs data (light receiving point data) indicating the position on the light receiving surface where the light of the projection adjustment image is incident. The received light point data is supplied to the control unit 101 via the PSD signal processing unit 102. The control unit 101 associates the light reception point data supplied from the PSD signal processing unit 102 with the common voltage level set in the common voltage generation unit 104 and stores it in a storage unit (not shown).

  Next, the control unit 101 increases the setting level of the common voltage in the common voltage generation unit 104 by one step. In this state, the above-described display operation of the dots A and D is performed, and an adjustment image based on the dots A and D is displayed on the liquid crystal panel 107. Light from the projection adjustment image on the screen is incident on the light receiving surface of the PSD 103 through the condensing optical system. The PSD 103 outputs light receiving point data indicating the incident position of light from the projection adjustment image on the light receiving surface. The control unit 101 receives the light reception point data via the PSD signal processing unit 102 and associates the received light reception point data with the level of the common voltage set in the common voltage generation unit 104 and stores it in the storage unit. .

  As described above, the control unit 101 increases the setting level of the common voltage in the common voltage generation unit 104 in a stepwise manner, and stores the light reception point data for each setting level in the storage unit. When the light receiving point data is stored in the storage unit for all the setting levels of the common voltage setting range, the control unit 101 determines the optimum value of the common voltage based on the stored light receiving point data.

  FIG. 4 shows the transition of the light receiving point data when the level of the common voltage is changed stepwise. This light receiving point data is the output data of the PSD 103 when the dots A and D shown in FIG. 2 have the positive polarity and the dot D has the negative polarity. The X axis indicates the position on the light receiving surface, and the Y axis indicates the current value.

  A broken line 501 indicates a current waveform of light reception point data obtained when the common voltage is set to the lowest level. Since the common voltage is lower than the optimum value, the luminance level of the dot D is lower than the luminance level of the dot A on the liquid crystal panel. For this reason, on the light receiving surface, the amount of light in the region where the light from the projected image of the dot A is incident (hereinafter referred to as the dot A spot) is the same as the region where the light from the projected image of the dot D is incident (hereinafter referred to as the dot D). It is more than the amount of light (referred to as a spot). Since the light amount of the dot A spot is larger than the light amount of the dot D spot, the peak of the current waveform indicated by the broken line 501 is located on the dot A spot side.

  A solid line 502 indicates a current waveform of light reception point data when the common voltage is set to an optimum value. Since the common voltage is an optimum value, the luminance level of the dot A and the luminance level of the dot D on the liquid crystal panel are substantially the same, and the light amount of the dot A spot and the light amount of the dot D spot on the light receiving surface are also substantially the same. In this case, the peak of the current waveform indicated by the solid line 502 is theoretically located at an intermediate point between the dot A spot and the dot D spot.

  A broken line 503 indicates a current waveform of light reception point data obtained when the common voltage is set to the highest level. Since the common voltage is higher than the optimum value, the luminance level of the dot A on the liquid crystal panel is lower than the luminance level of the dot D. As a result, the light amount of the dot A spot is larger than the light amount of the dot D spot on the light receiving surface. Less. In this case, the peak of the current waveform of the broken line 502 is located on the dot B spot side.

  When the level of the common voltage is changed stepwise from low to high, the light receiving point data waveform changes stepwise from the waveform of the broken line 501 to the waveform of the solid line 502 and further to the waveform of the broken line 503. Changes. The brightness levels of the dots A and D on the liquid crystal panel are the highest when the common voltage reaches the optimum value, and gradually decrease as the common voltage deviates from the optimum value. Therefore, when the level of the common voltage is changed stepwise from the lower level to the higher level, the peak value of the waveform of the light receiving point data becomes the highest when the waveform of the solid line 502 where the common voltage is the optimum value. The control unit 101 determines the light reception point data having the highest waveform peak value among the light reception point data stored in the storage unit as the light reception point data when the common voltage is the optimum value, and associates the light reception point data with the light reception point data. The common voltage is determined to be the optimum value for the stored setting level.

  According to the above flicker adjustment, an adjustment image consisting only of the first and second bright spots formed by the first and second liquid crystal cells to which voltages having opposite polarities are supplied is displayed on the liquid crystal panel. The light from the first and second bright spots of the projection image of the adjustment image is detected by PSD. The PSD outputs data indicating the intensity distribution of light spots from the first and second bright spots. The luminance levels of the first and second luminescent spots when the common voltage deviates from the optimum value are lower than the luminance levels of the first and second luminescent spots when the common voltage is the optimum value. For example, when the first liquid crystal cell is positive and the second liquid crystal cell is negative, if the common voltage is lower than the optimum value, the luminance level of the second bright spot is On the contrary, when the common voltage is higher than the optimal value, the luminance level of the first bright spot is lower than the luminance level when the common voltage is the optimal value. Therefore, the peak of the intensity distribution in the PSD output data is highest when the common voltage is the optimum value. Therefore, the optimum value of the common voltage can be determined by changing the setting level of the common voltage stepwise and comparing the peak value of the PSD output data at each setting level.

  As described above, since the optimum value of the common voltage can be determined for each liquid crystal cell, the optimum value of the common voltage in the liquid crystal cell at any part of the liquid crystal panel is determined, and the entire liquid crystal panel is determined based on the optimum value. The optimum value of the common voltage can be determined. In addition, since there is no influence of flicker variation occurring in the entire liquid crystal panel, the occurrence of flicker can be more effectively suppressed.

(2) Flicker adjustment using the incident position of the output data of PSD 103:
In the flicker adjustment operation of (1) above, the control unit 101 changes the level of the common voltage at the beginning, and optimizes the level of the common voltage at the maximum peak of the output waveform of the PSD 103 (the maximum point on the Y axis). Although it is determined to be a value, the optimum value of the common voltage can be determined using the incident position.

  The control unit 101 changes the level of the common voltage at the beginning, and the PSD 103 has the dots A and D (first in the projection image of the adjustment image projected by the projection optical system at each of the common voltage setting levels. And the center of gravity position is detected by receiving light from the second bright spot). And the control part 101 is the state in which the center-of-gravity position detected by PSD103 among the setting levels of the common voltage is the highest in the state of the center-of-gravity position detected in the state where the setting level of the common voltage is the lowest. The setting level of the common voltage that is an intermediate position between the detected center of gravity position is determined as the optimum value.

  When the first liquid crystal cell has a positive polarity and the second liquid crystal cell has a negative polarity, when the common voltage is lower than the optimum value, the luminance level of the second bright spot is the optimum value of the common voltage. In contrast, when the common voltage is higher than the optimum value, the luminance level of the first bright spot is lower than the luminance level when the common voltage is the optimum value. When the setting level of the common voltage is set to the lowest state, the light amount from the first bright spot on the light receiving surface becomes extremely larger than the light quantity from the second bright spot, and the center of gravity is obtained. The position is approximately the position of the center of gravity of the first bright spot. On the contrary, when the setting level of the common voltage is the highest, the amount of light from the second luminescent spot on the light receiving surface becomes extremely larger than the amount of light from the first luminescent spot. Therefore, the position of the center of gravity is substantially the position of the center of gravity of the second bright spot. When the common voltage is an optimum value, the luminance levels of the first and second luminescent spots are the same, and the amount of light from the first and second luminescent spots on the light receiving surface is also the same. In this case, the barycentric position is located between the barycentric position of the first bright spot and the barycentric position of the second bright spot. Therefore, the optimum value of the common voltage can be obtained by obtaining the center-of-gravity position as the intermediate position.

  For example, in FIG. 4, the barycentric position of the broken line 501 is the barycentric position detected with the lowest common voltage setting level, and the barycentric position of the broken line 503 is detected with the highest common voltage setting level. The center of gravity position. In this case, the barycentric position of the solid line 502 at which the common voltage is the optimum value is located at an intermediate position between the barycentric position of the broken line 501 and the barycentric position of the broken line 503. Therefore, the optimum value of the common voltage can be determined by changing the setting level of the common voltage stepwise and comparing the output data (center of gravity position) of the PSD 103 at each setting level. Also in this case, since the optimum value of the common voltage can be determined in units of liquid crystal cells, the same effect as the flicker adjustment operation (1) is achieved. In addition, according to the detection of the barycentric position of the light amount by PSD, it is difficult to be influenced by external light or the like, and therefore the optimum value of the common voltage can be determined more accurately.

  The liquid crystal projector of the present embodiment described above is an example of the present invention, and the configuration and operation thereof can be changed as appropriate without departing from the spirit of the invention.

  For example, the settings of the first and second liquid crystal cells, which are adjustment target cells, differ depending on the AC driving method. In the case of line inversion driving, the first liquid crystal cell is a cell on the odd line, and the second liquid crystal cell is a cell on the even line. On the other hand, in the case of dot inversion driving, two liquid crystal cells having opposite polarities on the same line or different lines are used as the first and second liquid crystal cells. However, the distance between the first and second liquid crystal cells needs to be determined in consideration of PSD detection accuracy. For example, if the PSD detection accuracy is high, adjacent cells can be set as the first and second liquid crystal cells. If the PSD detection accuracy is low, the first and second liquid crystal cells are considered in consideration of the accuracy. It is desirable to set a cell having a certain distance as the two liquid crystal cells.

  A plurality of adjustment target cells (a pair of first and second liquid crystal cells) may be set on the liquid crystal panel. FIG. 5 shows an example of a projected image when a plurality of adjustment target cells are set. In this example, a measurement point 402 is set at the center of the projected image 401, a measurement point 403 is set at the upper left, a measurement point 404 is set at the lower left, a measurement point 405 is set at the upper right, and a measurement point 406 is set at the lower right. An adjustment target cell is set corresponding to each of the measurement points 402 to 406. At the time of flicker adjustment, the control unit 101 determines the optimum value of the common voltage for each measurement point, and determines the average value of the optimum values at each measurement point as the optimum value of the common voltage in the entire liquid crystal panel. Thereby, the influence of the flicker variation on the liquid crystal panel can be more effectively suppressed. In addition, the number and position of a measurement point are not limited to what was shown in FIG. 5, but can be set suitably.

  In general, when a human views an image, the viewpoint is often located at the center of the image. Therefore, even if the flicker adjustment is performed by specializing the measurement point at the center of the screen, a great effect can be obtained.

  The PSD is usually provided in the projector main body, but may be separate from the projector main body.

  Instead of PSD, an image sensor composed of a plurality of light receiving elements that convert incident light into an electrical signal, such as a CCD sensor or a CMOS sensor, may be used.

  In addition, because of the characteristics of the human eye, the brightness with a luminance level of 50% is the brightness at which flicker is most easily detected, so the first and second liquid crystal cells formed by the first and second liquid crystal cells. The brightness level of the bright spot is preferably about 50% of the dynamic range.

  The liquid crystal projector of the present invention can be applied not only to a single plate type but also to a projector using three liquid crystal panels. For example, when the liquid crystal panel for red, the liquid crystal panel for blue, and the liquid crystal panel for green are provided, the test pattern generator generates a test pattern for red that generates video data for flicker adjustment related to the liquid crystal panel for red Generating unit, blue test pattern generating unit for generating video data for flicker adjustment relating to the blue liquid crystal panel, and green test pattern generating unit for generating video data for flicker adjustment relating to the liquid crystal panel for green And provide. A liquid crystal drive circuit and a common voltage generator are also provided for each liquid crystal panel. The control unit performs the aforementioned flicker adjustment operation for each of the liquid crystal panels.

It is a block diagram which shows the principal part of the liquid crystal projector which is one Embodiment of this invention. It is a schematic diagram which shows an example of the dot image of the liquid crystal panel in which line inversion drive is performed. It is a schematic diagram which shows an example of the image for adjustment projected on the screen. It is a schematic diagram which shows transition of the light reception point data at the time of changing the level of a common voltage in steps. It is a schematic diagram which shows an example of the projection image at the time of setting several adjustment object cell. It is a figure which shows the waveform of the video data of a line inversion drive. It is a circuit diagram which shows an example of a liquid crystal panel.

Explanation of symbols

101 control unit 102 PSD signal processing unit 103 PSD
104 Common voltage generator 105 Test pattern generator 106 Liquid crystal drive circuit 107 Liquid crystal panel

Claims (7)

A liquid crystal projector comprising a liquid crystal panel and a projection optical system for projecting an image displayed on the liquid crystal panel,
A common voltage generator for supplying a common voltage to a common electrode to which a plurality of liquid crystal cells constituting the liquid crystal panel are connected in common;
A liquid crystal driving circuit for supplying a voltage corresponding to input video data to the plurality of liquid crystal cells and displaying an image based on the video data on the liquid crystal panel;
An adjustment image composed of only first and second bright spots formed by first and second liquid crystal cells in which the polarity of the supplied voltage is opposite to each other among the plurality of liquid crystal cells. A test pattern generator for generating video data for testing for forming on the liquid crystal panel;
A light detecting element that includes a light receiving surface and outputs data indicating a light intensity distribution according to the amount of light incident on the light receiving surface;
The test video data generated by the test pattern generator is supplied to the liquid crystal drive circuit to form the adjustment image on the liquid crystal panel, and the common voltage setting level supplied by the common voltage generator is set. A control unit that changes in stages,
The light detecting element receives light from the first and second bright spots in the projection image of the adjustment image projected by the projection optical system at each of the common voltage setting levels, respectively. Output data,
The liquid crystal projector, wherein the control unit determines a setting level of the common voltage having the highest peak value of the intensity distribution in the data output from the light detection element as an optimum value. A liquid crystal projector comprising a liquid crystal panel and a projection optical system for projecting an image displayed on the liquid crystal panel,
A common voltage generator for supplying a common voltage to a common electrode to which a plurality of liquid crystal cells constituting the liquid crystal panel are connected in common;
A liquid crystal driving circuit for supplying a voltage corresponding to input video data to the plurality of liquid crystal cells and displaying an image based on the video data on the liquid crystal panel;
An adjustment image composed of only first and second bright spots formed by first and second liquid crystal cells in which the polarity of the supplied voltage is opposite to each other among the plurality of liquid crystal cells. A test pattern generator for generating video data for testing for forming on the liquid crystal panel;
A light detecting element that includes a light receiving surface, and detects a position of the center of gravity of the light amount based on a light intensity distribution according to the light amount of light incident on the light receiving surface;
The test image data generated by the test pattern generator is supplied to the liquid crystal drive circuit to form the adjustment image on the liquid crystal panel, and the setting level of the common voltage supplied by the common voltage generator And a control unit that gradually changes
The light detection element receives light from the first and second bright spots in the projection image of the adjustment image projected by the projection optical system at each of the setting levels of the common voltage and receives the center of gravity. Detect the position,
The control unit is configured such that, among the setting levels of the common voltage, the position of the center of gravity detected by the photodetecting element is the position of the center of gravity detected with the lowest setting level of the common voltage and the setting level of the common voltage. A liquid crystal projector that determines a setting level of a common voltage that is an intermediate position between the center of gravity detected in the highest state as an optimum value.   The photodetecting element includes a semiconductor layer constituting a photodiode, a resistance layer formed on the semiconductor layer, and a plurality of output terminals arranged opposite to the resistance layer, and light is transmitted to the semiconductor 2. The position detection element according to claim 1, wherein when the light is incident on the layer, the current output from each of the plurality of output terminals is changed by a resistance proportional to a distance between the incident position and each of the plurality of output terminals. 2. A liquid crystal projector according to 2.   The liquid crystal projector according to claim 1, wherein the light detection element is an image sensor including a plurality of light receiving elements that convert incident light into an electric signal.   5. The liquid crystal projector according to claim 1, wherein a plurality of adjustment target cells including the first and second liquid crystal cells are set on the liquid crystal panel. 6. A flicker adjustment method performed in a liquid crystal projector including a liquid crystal panel and a projection optical system that projects an image displayed on the liquid crystal panel,
Supplying a common voltage to a common electrode to which a plurality of liquid crystal cells constituting the liquid crystal panel are connected in common;
Supplying a voltage corresponding to input video data to the plurality of liquid crystal cells to display an image based on the video data on the liquid crystal panel;
An adjustment image composed of only first and second bright spots formed by first and second liquid crystal cells in which the polarity of the supplied voltage is opposite to each other among the plurality of liquid crystal cells. Generating test video data for forming on the liquid crystal panel;
Supplying the test video data to the liquid crystal drive circuit to form the adjustment image on the liquid crystal panel, and changing the setting level of the common voltage stepwise;
A light detection element that includes a light receiving surface and outputs data indicating a light intensity distribution according to the amount of light incident on the light receiving surface is projected by the projection optical system at each of the common voltage setting levels. Receiving light from the first and second bright spots in the projection image of the adjustment image and outputting the data;
Determining a setting level of the common voltage having the highest peak value of the intensity distribution in the data output from the light detection element as an optimum value. A flicker adjustment method performed in a liquid crystal projector including a liquid crystal panel and a projection optical system that projects an image displayed on the liquid crystal panel,
Supplying a common voltage to a common electrode to which a plurality of liquid crystal cells constituting the liquid crystal panel are connected in common;
Supplying a voltage corresponding to input video data to the plurality of liquid crystal cells to display an image based on the video data on the liquid crystal panel;
An adjustment image composed of only first and second bright spots formed by first and second liquid crystal cells in which the polarity of the supplied voltage is opposite to each other among the plurality of liquid crystal cells. Generating test video data for forming on the liquid crystal panel;
Supplying the test video data to the liquid crystal drive circuit to form the adjustment image on the liquid crystal panel, and changing the setting level of the common voltage stepwise;
A light detection element that includes a light receiving surface and outputs data indicating a light intensity distribution according to the amount of light incident on the light receiving surface is projected by the projection optical system at each of the common voltage setting levels. Receiving the light from the first and second bright spots in the projected image of the adjustment image and detecting the position of the center of gravity;
Among the set levels of the common voltage, the barycentric position detected by the photodetecting element is detected in the state where the barycentric position detected in the state where the set level of the common voltage is the lowest and the set level of the common voltage are the highest. And a step of determining a setting level of a common voltage that is an intermediate position between the center of gravity position and an optimum value as an optimum value.

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