PATENT DOCUMENT

Abstract:
The present invention provides a spatial light modulator comprises a plurality of deflectable mirror controllable to deflect from a horizontal state to first and second deflecting directions; an electrode connected to a memory and disposed in the first deflecting direction underneath each of the deflectable mirrors; and an electrode connected to a plate line and disposed in the second deflecting direction underneath each of the deflectable mirrors.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Non-provisional Application of a Provisional Application 61/069,278 filed on Mar. 13, 2008 and a Continuation in Part Application of another patent application Ser. No. 12/072,448 filed on Feb. 26, 2008. The application Ser. No. 12/072,448 is a Non-provisional Application of a Provisional Application of 60/903,467 filed on Feb. 26, 2007. This Application is further a Continuation in Part (CIP) Application of a Non-provisional patent application Ser. No. 11/121,543 filed on May 4, 2005 issued into Pat. No. 7,268,932 and another Non-provisional application Ser. No. 10/698,620 filed on Nov. 1, 2003. The application Ser. No. 11/121,543 is a Continuation In Part (CIP) Application of three previously filed Applications. These three Applications are 10/698,620 filed on Nov. 1, 2003; 10/699,140 filed on Nov. 1, 2003 now issued into Pat. No. 6,862,127; and 10/699,143 filed on Nov. 1, 2003 now issued into Pat. No. 6,903,860 by the Applicant of this Patent Applications. The disclosures made in these Patent Applications are hereby incorporated by reference in this Patent Application. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention generally relates to an image display system. More particularly, this invention relates to a system configuration and method to effectively control spatial light modulator implemented in an apparatus such as a projection apparatus. 
         [0004]    2. Description of the Related Art 
         [0005]    After the dominance of CRT technology in the display industry for over 100 years, Flat Panel Displays (hereafter FPD) and Projection Displays have gained popularity because the FDP display implements a more compact image projecting system while projecting images on a larger display screen. Of several types of projection displays, projection displays using micro-displays are gaining recognition among the consumers because of their high picture quality and a lower cost than FPDs. There are two types of micro-displays used for projection displays on the market, i.e., micro-LCDs (Liquid Crystal Displays) and micromirror technology. Because the micromirror devices display images with an unpolarized light, the images projected by the micromirror device have a brightness superior to that of micro-LCDs, which use polarized light. 
         [0006]    Even though there have been significant advances made in recent years in the technologies of implementing electromechanical micromirror devices as spatial light modulators (SLM), there are still limitations and difficulties when they are employed to display high quality images. Specifically, when the display images are digitally controlled, the quality of the images is adversely affected because the images are not displayed with a sufficient number of gray scale gradations. 
         [0007]    Electromechanical micromirror devices have drawn considerable interest because of their application as spatial light modulators (SLMs). A spatial light modulator requires an array of a relatively large number of micromirrors and each of these micromirrors are controlled for modulating and projecting a display pixel. Depending on the resolution requirements of the displayed images, the number of required micromirrors ranges from 60,000 to several million for each SLM. Referring to  FIG. 1A  for a digital video system  1  includes a display screen  2  disclosed in a relevant U.S. Pat. No. 5,214,420. A light source  10  is used to generate light beams to project illumination for the display images on the display screen  2 . The light  9  projected from the light source is further concentrated and directed toward lens  12  by way of mirror  11 . Lenses  12 ,  13  and  14  form a beam columnator operative to columnate the light  9  into a column of light  8 . A spatial light modulator  15  is controlled by a computer through data transmitted over data cable  18  to selectively redirect a portion of the light from path  7  toward lens  5  to display on screen  2 .  FIG. 1B  shows a SLM  15  that has a surface  16  that includes an array of switchable reflective elements  17 ,  27 ,  37 , and  47 , each of these reflective elements is attached to a hinge  30 . When the element  17  is in an ON position, a portion of the light from path  7  is reflected and redirected along path  6  to lens  5  where it is enlarged or spread along path  4  to impinge on the display screen  2  to form an illuminated pixel  3 . When the element  17  is in an OFF position, the light is reflected away from the display screen  2  and, hence, pixel  3  is dark. 
         [0008]    The on-and-off states of the micromirror control scheme as that implemented in the U.S. Pat. No. 5,214,420, and in most conventional display systems, impose a limitation on the quality of the display. Specifically, applying the conventional configuration of a control circuit limits the gray scale gradations produced in a conventional system (PWM between ON and OFF states) limited by the LSB (least significant bit, or the least pulse width). Due to the ON-OFF states implemented in the conventional systems, there is no way of providing a shorter pulse width than the duration represented by the LSB. The least intensity of light, which determines the gray scale, is the light reflected during the least pulse width. The limited levels of the gray scale lead to a degradation of the display image. 
         [0009]    Specifically,  FIG. 1C  exemplifies, as related disclosures, a circuit diagram for controlling a micromirror according to U.S. Pat. No. 5,285,407. The control circuit includes memory cell  32 . Various transistors are referred to as “M*” where “*” designates a transistor number and each transistor is an insulated gate field effect transistor. Transistors M 5 , and M 7  are p-channel transistors; transistors, M 6 , M 8 , and M 9  are n-channel transistors. The capacitances, C 1  and C 2 , represent the capacitive loads in the memory cell  32 . The memory cell  32  includes an access switch transistor M 9  and a latch  32   a  based on a Static Random Access switch Memory (SRAM) design. All access transistors M 9  on a Row line receive a DATA signal from a different Bit-line  31   a . The particular memory cell  32  is accessed for writing a bit to the cell by turning on the appropriate row select transistor M 9 , using the ROW signal functioning as a Word-line. Latch  32   a  consists of two cross-coupled inverters, M 5 /M 6  and M 7 /M 8 , which permit two stable states, including a state  1  when Node A is high and Node B is low and a state  2  when Node A is low and Node B is high. 
         [0010]      FIG. 1A  shows the operations of the switching between the dual states, as illustrated by the control circuit, to position the micromirrors in an ON or an OFF angular orientation. The brightness, i.e., the gray scales of a digitally controlled image system is determined by the length of time the micromirror stays in an ON position. The length of time a micromirror is in an ON position is controlled by a multiple bit word. As a simple illustration,  FIG. 1D  shows the “binary time intervals” when controlling micromirrors with a four-bit word. As shown in  FIG. 1D , the time durations have relative values of 1, 2, 4, 8, which in turn define the relative brightness for each of the four bits where “1” is the least significant bit and “8” is the most significant bit. According to the control mechanism as shown, the minimum controllable differences between gray scales for showing different levels of brightness is a represented by the “least significant bit” that maintains the micromirror at an ON position. 
         [0011]    For example, assuming n bits of gray scales, one time frame is divided into 2″-1 equal time periods. For a 16.7-millisecond frame period and n-bit intensity values, the time period is 16.7/(2″-1) milliseconds 
         [0012]    Having established these times for each pixel of each frame, pixel intensities are quantified such that black is a 0 time period, the intensity level represented by the LSB is 1 time period, and the maximum brightness is 2″-1 time periods. Each pixel&#39;s quantified intensity determines its ON-time during a time frame. Thus, during a time frame, each pixel with a quantified value of more than 0 is ON for the number of time periods that correspond to its intensity. The viewer&#39;s eye integrates the pixel brightness so that the image appears the same as if it were generated with analogous levels of light. 
         [0013]    For controlling deflectable mirror devices, the PWM applies data to be formatted into “bit-planes”, with each bit-plane corresponding to a bit weight of the intensity of light. Thus, if the brightness of each pixel is represented by an n-bit value, each frame of data has n bit-planes. Then, each bit-plane has a 0 or 1 value for each display element. According to the PWM control scheme as described in the preceding paragraphs, each bit-plane is separately loaded and the display elements are controlled on the basis of bit-plane values corresponding to the value of each bit within one frame. Specifically, the bit-plane according to the LSB of each pixel is displayed for 1 time period. 
         [0014]    In recent years, higher levels of resolution and higher gradation levels of gray scale for display (i.e., projection) images are in strong demand. More specifically, the strong demand is imposed on the projection apparatuses because of the requirements to comply with the display resolutions and gray scales for distribution of video images according to the high definition television (HDTV) broadcasting standards. 
         [0015]    However, as discussed above and shown in  FIG. 1D , the gray scale control for a display image by applying the pulse width modulation (PWM) control process is faced with the technical problem. The LSB and/or the frequency of rewriting a memory cell structured as SRAM actually limit the minimum controllable length of time and that further limits the minimum adjustable quantity of light for controlling and adjusting an expressible gray scale. 
         [0016]    Therefore, in order to attain a higher level of gradations of gray scale for a display image, it is required to increase the frequency of rewriting a memory cell by increasing the operation frequency of a control circuit that controls the memory cell. However, an increase in the operation frequency of such a control circuit increases the complexity of the circuit configuration and also the cost of manufacturing the circuit. U.S. Pat. No. 5,214,420 and U.S. Pat. No. 5,285,407 disclose more technical details of these conventional projection apparatuses. 
       SUMMARY OF THE INVENTION 
       [0017]    An aspect of the present invention is to provide a technique for applying a technology to display an image by implementing a new and improved spatial light modulator. The spatial light modulator is uniquely designed with the functions to change the control of modulation processes depending on the incident direction of light. 
         [0018]    A first exemplary embodiment of the present invention provides a spatial light modulator, comprises a plurality of deflectable mirror controllable to deflect from a horizontal state to first and second deflecting directions; an electrode connected to a memory and disposed in the first deflecting direction underneath each of the deflectable mirrors; and an electrode connected to a plate line and disposed in the second deflecting direction underneath each of the deflectable mirrors. 
         [0019]    A second exemplary embodiment of the present invention provides the spatial light modulator according to the first exemplary embodiment, wherein said plurality of deflectable mirrors are arranged along a row direction and a column direction substantially perpendicular to the row direction, wherein the plate line is connected to the plurality of electrodes along the ROW direction. 
         [0020]    A third exemplary embodiment of the present invention provides the spatial light modulator according to the first exemplary embodiment, further comprising a plurality of bit lines and word lines and the memory in each of the deflectable mirrors is controlled by one of the bit lines and by one of the word lines. 
         [0021]    A fourth exemplary embodiment of the present invention provides a spatial light modulator, including: a plurality of deflectable mirrors controllable to operate in a horizontal state, and to deflect to a first and a second deflecting directions; an electrode connected to a memory and disposed in the first deflecting direction underneath each of the deflectable mirrors; and an electrode connected to a word line and disposed in the second deflecting direction underneath each of the deflectable mirrors. 
         [0022]    A fifth exemplary embodiment of the present invention provides the spatial light modulator according to the fourth exemplary embodiment further comprising a plurality of bit lines and word lines and the memory in each of the deflectable mirrors is controlled by one of the bit lines and by one of the word lines. 
         [0000]    A sixth exemplary embodiment of the present invention provides a spatial light modulator, comprising: a plurality of pixel elements configured as a two-dimensional array; and a first and a second control circuits for controlling the pixel elements, wherein the first control circuit receives and applies a video signal to generate control signals for said pixel elements, and the second control circuit generates and changes control signals in a predetermined time interval. 
         [0023]    A seventh exemplary embodiment of the present invention provides the spatial light modulator according to the sixth exemplary embodiment, wherein the second control circuit is controlled to operate in an inactive state in at least one time in a subfield of a display frame for displaying a video image. 
         [0024]    An eighth exemplary embodiment of the present invention provides the spatial light modulator according to the sixth exemplary embodiment, wherein each of the pixel elements are controllable to operate in at least two modes, wherein the second control circuit controls and changes the control signals in accordance with the modes. 
         [0025]    A ninth exemplary embodiment of the present invention provides the spatial light modulator according to the sixth exemplary embodiment, wherein each of the pixel elements is controllable by applying a non-binary data to display an image. 
         [0026]    A tenth exemplary embodiment of the present invention provides the spatial light modulator according to the sixth exemplary embodiment, wherein the first control circuit further comprises a memory and a first electrode connected to a bit line and a word line, and the second control circuit further comprises a second electrode connected to a plate line. 
         [0027]    An eleventh exemplary embodiment of the present invention provides the spatial light modulator according to the sixth exemplary embodiment wherein each of said pixel elements further comprises a deflectable mirror configured as the two-dimensional array. 
         [0028]    A twelfth exemplary embodiment of the present invention provides a spatial light modulator, including: a plurality of pixel elements configured as a two-dimensional array; and each of the pixel elements further comprises a memory connected to a word line for controlling the memory and an electrode connected to the word line, wherein the word line is controllable to apply at least three level of voltages. 
         [0029]    A thirteenth exemplary embodiment of the present invention provides the spatial light modulator according to the twelfth exemplary embodiment, wherein the word line is controllable to operate at the three levels of voltages comprising: a first level of positive voltage for rewriting data to the memory, a second level of positive or negative voltage for controlling the pixel element by a control signal applied to the electrode, and a third level of zero voltage when the electrode is turned off with the pixel element free from a control of the electrode. 
         [0030]    A fourteenth exemplary embodiment of the present invention provides the spatial light modulator according to the twelfth exemplary embodiment wherein: each of said pixel elements further comprises a deflectable mirror configured as the two-dimensional array. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0031]    The present invention is described in detail below with reference to the following figures. 
           [0032]      FIG. 1A  illustrates the basic principle of a projection display using a micromirror device, as disclosed in a prior art patent. 
           [0033]      FIG. 1B  is a top view diagram showing the configuration of mirror elements of a portion of a micromirror array of a projection apparatus disclosed in a prior art patent. 
           [0034]      FIG. 1C  is a circuit diagram showing the configuration of a drive circuit of mirror elements of a projection apparatus disclosed in a prior art patent. 
           [0035]      FIG. 1D  shows the scheme of Binary Pulse Width Modulation (Binary PWM) of conventional digital micromirrors for generating a grayscale. 
           [0036]      FIG. 2  is a functional block diagram showing an exemplary configuration of a display system according to a preferred embodiment of the present invention. 
           [0037]      FIG. 3  is a diagram showing an exemplary configuration of a spatial light modulation element constituting a display system according to a preferred embodiment of the present invention. 
           [0038]      FIG. 4  is a conceptual diagram showing the configuration of an individual pixel unit constituting a spatial light modulator according to a preferred embodiment of the present invention. 
           [0039]      FIG. 5  is a top view for showing a diagonal perspective view of a mirror device comprised of, in two dimensions on a device substrate, a plurality of mirror elements, each controlling the reflecting direction of an incident light by the deflection a mirror 
           [0040]      FIG. 5A  is a table showing an exemplary specification of the structure of a spatial light modulation element constituting a display system according to a preferred embodiment of the present invention. 
           [0041]      FIG. 6  is a timing diagram showing an exemplary mirror control profile used in a display system according to a preferred embodiment of the present invention. 
           [0042]      FIG. 7A  is a cross-sectional diagram showing the ON state of a micromirror. 
           [0043]      FIG. 7B  is a timing diagram showing the intensity of light projected in the ON state of a micromirror. 
           [0044]      FIG. 7C  is a cross-sectional diagram showing the OFF state of a micromirror. 
           [0045]      FIG. 7D  is a timing diagram showing the intensity of light projected in the OFF state of a micromirror. 
           [0046]      FIG. 7E  is a cross-sectional diagram showing the oscillating state of a micromirror. 
           [0047]      FIG. 7F  is a timing diagram showing the intensity of light projected in the oscillating state of a micromirror. 
           [0048]      FIG. 8  is a functional circuit diagram showing an exemplary configuration of a pixel unit constituting the pixel array of a spatial light modulator according to a preferred embodiment of the present invention. 
           [0049]      FIG. 9  is a functional circuit diagram showing an exemplary modification of the configuration of the pixel unit shown in  FIG. 8 . 
           [0050]      FIG. 10  is a functional circuit diagram showing another exemplary modification of the configuration of the pixel unit shown in  FIG. 8 . 
           [0051]      FIG. 11  is a top view diagram depicting the layout of the capacitor used in the exemplary modification of a pixel unit of a display system according to a preferred embodiment of the present invention. 
           [0052]      FIG. 12A  is a cross-sectional diagram, in the ON state, of a pixel unit comprising two electrodes on the ON side, as shown in  FIG. 8 . 
           [0053]      FIG. 12B  is a cross-sectional diagram, in an OFF state, of a pixel unit comprising two electrodes on the ON side, as shown in  FIG. 8 . 
           [0054]      FIG. 12C  is an illustrative top view diagram showing an exemplary layout of the second ON electrode that is added to the pixel unit, as shown in  FIG. 8 . 
           [0055]      FIG. 12D  is an illustrative top view diagram showing another exemplary layout of the second ON electrode that is added to the pixel unit, as shown in  FIG. 8 . 
           [0056]      FIG. 13  is a functional circuit diagram showing an exemplary layout of the peripheral circuit of the pixel array used for a display system according to a preferred embodiment of the present invention. 
           [0057]      FIG. 14  is a functional circuit diagram showing an exemplary layout of the peripheral circuit describing the operation in accordance with the timing diagram showing the function of the pixel unit shown in  FIG. 8 . 
           [0058]      FIG. 15A  is a functional circuit diagram showing an exemplary modification of the layout configuration of the peripheral circuit of a pixel array according to a preferred embodiment of the present invention. 
           [0059]      FIG. 15B  is a functional circuit diagram showing an exemplary modification of the layout configuration of the peripheral circuit of a pixel array according to a preferred embodiment of the present invention. 
           [0060]      FIG. 15C  is a functional circuit diagram showing an exemplary modification of the layout configuration of the peripheral circuit of a pixel array according to a preferred embodiment of the present invention. 
           [0061]      FIG. 15D  is a functional circuit diagram showing an exemplary modification of the layout configuration of the peripheral circuit of a pixel array according to a preferred embodiment of the present invention. 
           [0062]      FIG. 16  is a table showing exemplary specifications of the frame, subfield and time slot of a spatial light modulator according to a preferred embodiment of the present invention. 
           [0063]      FIG. 17A  is a timing diagram showing an exemplary function of a spatial light modulator according to a preferred embodiment of the present invention. 
           [0064]      FIG. 17B  is a timing diagram showing an exemplary function of a spatial light modulator according to a preferred embodiment of the present invention. 
           [0065]      FIG. 17C  is a timing diagram showing an exemplary modification of the timing diagram shown in  FIG. 17A . 
           [0066]      FIG. 18  is a timing diagram showing an exemplary method for improving the number of gray scale levels for a spatial light modulator according to a preferred embodiment of the present invention. 
           [0067]      FIG. 18A  is a timing diagram showing an exemplary modification of the timing diagram shown in  FIG. 18 . 
           [0068]      FIG. 19  is a timing diagram showing an exemplary operation of a pixel unit according to a preferred embodiment of the present invention. 
           [0069]      FIG. 19A  is a timing diagram showing an exemplary modification of the exemplary operation shown in  FIG. 19 . 
           [0070]      FIG. 20  is a timing diagram showing an exemplary method for improving a gray scale representation in a single subfield of the pixel unit of a spatial light modulator according to a preferred embodiment of the present invention. 
           [0071]      FIG. 21  is a timing diagram showing an exemplary operation of a spatial light modulator according to a preferred embodiment of the present invention. 
           [0072]      FIG. 22  is a timing diagram showing an exemplary operation of a spatial light modulator according to a preferred embodiment of the present invention. 
           [0073]      FIG. 23  is a timing diagram showing an exemplary operation of a spatial light modulator according to a preferred embodiment of the present invention. 
           [0074]      FIG. 24  is a bit-structure diagram showing an exemplary configuration of a gamma table provided for a spatial light modulator according to a preferred embodiment of the present invention. 
           [0075]      FIG. 25  is a bit-structure diagram showing an exemplary method for generating data for controlling the allocation of a time slot for a spatial light modulator according to a preferred embodiment of the present invention. 
           [0076]      FIG. 26  is a flow chart showing an exemplary control for assigning a time slot, using a gamma table, for a spatial light modulator according to a preferred embodiment of the present invention. 
           [0077]      FIG. 27  is a table showing a specific setup example of a gamma table for a spatial light modulator according to a preferred embodiment of the present invention. 
           [0078]      FIG. 28  is a table showing an exemplary modification of the structure of a gamma table for a spatial light modulator according to a preferred embodiment of the present invention. 
           [0079]      FIG. 29  is a timing diagram showing an exemplary setup of a mirror control profile in order to describe the exemplary modification shown in  FIG. 28 . 
           [0080]      FIG. 30  is a functional circuit diagram showing an exemplary modification of the circuit configuration of the pixel unit shown in  FIG. 10 . 
           [0081]      FIG. 31  is a timing diagram showing an exemplary control for the pixel unit configured as shown in  FIG. 30 . 
           [0082]      FIG. 32  is a timing diagram showing an exemplary modification of the operation of the pixel unit configured as shown in  FIG. 30 . 
           [0083]      FIG. 33  is a timing diagram showing an exemplary modification of the operation of the pixel unit configured as shown in  FIG. 30 . 
           [0084]      FIG. 34  is a functional circuit diagram showing an exemplary modification of the circuit configuration of the pixel unit shown in  FIG. 30 . 
           [0085]      FIG. 35  is a timing diagram showing an exemplary operation of the pixel unit shown in  FIG. 34 . 
           [0086]      FIG. 36  is a timing diagram showing an exemplary modification of the control shown in  FIG. 35 . 
           [0087]      FIG. 37  is a timing diagram showing an exemplary modification of the control shown in  FIG. 35 . 
           [0088]      FIG. 38  is a functional circuit diagram showing an exemplary modification of the pixel unit shown in  FIG. 34 . 
           [0089]      FIG. 39  is a timing diagram showing the control waveform of the mirror control profile used for the pixel unit in a symmetrical configuration as shown in  FIG. 38 . 
           [0090]      FIG. 40  is a timing diagram showing the control waveform of the mirror control profile used for the pixel unit in a symmetrical configuration as shown in  FIG. 38 . 
           [0091]      FIG. 41  is a timing diagram showing the waveform of a mirror control profile in order to attain an intermediate oscillation in the pixel unit configured as shown in  FIG. 38 . 
           [0092]      FIG. 42  is a timing diagram showing the waveform of a mirror control profile in order to attain an intermediate oscillation in the pixel unit configured as shown in  FIG. 38 . 
           [0093]      FIG. 43  is a timing diagram showing an exemplary waveform in the case of performing a gray scale representation by driving, with a non-binary ON/OFF control pattern not including an oscillation control, the pixel unit configured as shown in  FIG. 38 . 
           [0094]      FIG. 44  is a timing diagram showing an exemplary waveform in the case of performing a gray scale representation by driving, with a non-binary ON/OFF control pattern not including an oscillation control, the pixel unit configured as shown in  FIG. 38 . 
           [0095]      FIG. 45  is a functional block diagram showing an exemplary control function equipped in the control apparatus of a projection apparatus according to a preferred embodiment of the present invention. 
           [0096]      FIG. 46  is a functional block diagram showing an exemplary control function equipped in the control apparatus of a projection apparatus according to a preferred embodiment of the present invention. 
           [0097]      FIG. 47  is a functional block diagram showing an exemplary control function of a projection apparatus according to a preferred embodiment of the present invention. 
           [0098]      FIG. 48A  is a timing diagram showing an exemplary waveform of a mirror control profile. 
           [0099]      FIG. 48B  is a timing diagram showing an exemplary waveform of a mirror control profile. 
           [0100]      FIG. 49  is a timing diagram showing an exemplary timing diagram shown in  FIG. 17A  with a part of the chart enlarged. 
           [0101]      FIG. 50  is a top view diagram illustratively exemplifying the layout configuration of an electrode of the pixel unit shown in  FIG. 8 . 
           [0102]      FIG. 51  is a timing diagram showing an exemplary modification of  FIG. 17A . 
           [0103]      FIG. 52  is a functional block diagram showing the configuration of a projection apparatus according to a preferred embodiment of the present invention. 
           [0104]      FIG. 53  is a functional block diagram showing an exemplary configuration of the control unit comprised in the projection apparatus shown in  FIG. 52 . 
           [0105]      FIG. 54  is a functional block diagram showing another exemplary modification of a multi-panel projection apparatus according to a preferred embodiment of the present invention. 
           [0106]      FIG. 55  is a functional block diagram showing an exemplary configuration of the control unit of a multi-panel projection apparatus according to a preferred embodiment of the present invention. 
           [0107]      FIG. 56  is a functional block diagram showing an exemplary modification of a multi-panel projection apparatus according to anther preferred embodiment of the present invention. 
           [0108]      FIG. 57  is a functional block diagram showing an exemplary configuration of a control unit comprised in the projection apparatus shown in  FIG. 56 . 
           [0109]      FIG. 58  is a timing diagram showing the waveform of a control signal of the projection apparatus shown in  FIG. 56 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0110]    The following is a description, in detail, of the preferred embodiment of the present invention with reference to the accompanying drawings. 
         [0111]      FIG. 2  is a functional block diagram showing an exemplary configuration of a display system according to a preferred embodiment of the present invention.  FIG. 3  is a block diagram showing an exemplary configuration of a spatial light modulation element implemented in a display system according to a preferred embodiment of the present invention.  FIG. 4  is a functional circuit diagram showing an exemplary configuration of a pixel unit  211  implemented in a spatial light modulator according to the present embodiment. 
         [0112]    The projection apparatus  100  according to the present embodiment comprises a spatial light modulator  200 , a control apparatus  300 , a light source  510  and a projection optical system  520 . 
         [0113]      FIG. 5  is a top view diagram showing a diagonal perspective of a spatial light modulator in which multiple mirror elements (i.e., pixel units), which control the reflecting direction of incident light by the deflection of the mirrors, are arrayed in two dimensions on a device substrate. 
         [0114]    As shown in  FIG. 5 , the spatial light modulator  200  is configured by arraying pixel units  211 , each of which comprises an address electrode (not shown in the drawing), an elastic hinge (not shown in the drawing), and a square mirror  212  supported by the elastic hinge, in a two-dimensional array on a substrate  214 . 
         [0115]    The mirror  212  of one pixel unit  211  is controlled by applying a voltage to an address electrode placed on the substrate  214 . 
         [0116]    Meanwhile, the pitch (i.e., the interval) between adjacent mirrors  212  is preferably set anywhere between 4 μm and 14 μm, or more preferably between 5 μm and 10 μm, in consideration of the number of pixels ranging from a super high definition television (i.e., a full HD TV) (e.g., 2048 by 4096 pixels) to a non-full HD TV, and of the sizes of mirror devices. Specifically, the pitch is defined as the distance between the deflection axes of adjacent mirrors  212 . 
         [0117]    Specifically, the area size of a mirror  212  may be anywhere between 16 square micrometers (μm 2 ) and 196 μm 2 , more preferably anywhere between 25 μm 2  and 100 μm 2 . 
         [0118]      FIG. 5A  is a table showing an exemplary specification of the structural elements of a spatial light modulation element constituting a display system according to a preferred embodiment of the present invention. 
         [0119]    The relationship between the pixel pitch and the transistor and capacitor of a pixel includes the combinations shown in  FIG. 5A  to show the relative ranges of size. The withstanding voltage of a transistor is proportional to the size as that listed in Table  5 A. As for the capacitor, in a comparison between an aluminum capacitor, in which the plate is made of aluminum, and a poly-capacitor, in which the plate is made of poly-silicon, the latter has a larger capacitance for the same plate area size. 
         [0120]    Referring to the combination number G 1  shown in  FIG. 5A , if one piece of dynamic random access memory (DRAM) is comprised for each of the ON and OFF zones of a mirror  212  with an 8-μm pixel pitch, two transistors possessing a 12-volt withstanding voltage will occupy the MOS substrate of the pixel zone. Therefore, the capacitors (i.e., OFF capacitor  215   b  and ON capacitor  216   b ) of the memory (i.e., memory cells M 1  and M 2 ) are exemplarily configured to place two aluminum capacitors between the transistors (i.e., gate transistors  215   c  and  216   c ) and the MEMS unit (i.e., mirror  212 , hinge  213  and address electrodes (i.e., OFF electrode  215  and ON electrode  216 )). 
         [0121]    The combination number G 2  shown in  FIG. 5A  is an exemplary configuration comprising one piece of DRAM memory in only the OFF zone of an 8 μm pixel pitch mirror and placing one transistor having a 12-volt withstanding voltage and one capacitor for a piece of memory on the substrate in the pixel zone. This circuit configuration is described later for  FIG. 34 . Compared to the configuration of G 1 , the configuration of G 2  has the advantages of reducing the number of masks used in the photolithography process and reducing the number of transistors by half thus improving the production yield. 
         [0122]    The configuration of the combination number G 3  shown in  FIG. 5A  is the result of changing, from that of G 2 , the withstanding voltage of the transistor to 24 volts and using an aluminum capacitor. The increase in the withstanding voltage of the transistor can further strengthen a hinge that may be required as a countermeasure to achieve the purpose of anti-stiction. 
         [0123]    The respective configurations of the other combination numbers G 4 , G 5  and G 6  which are shown in  FIG. 5A  are obtained by reducing the sizes of the respective configurations of the above described G 1 , G 2  and G 3 . 
         [0124]    Note that the form of the mirror  212  or the pitch between the adjacent mirrors is arbitrary. 
         [0125]    In  FIG. 5 , the dotted line shows the deflection axis  212   a  for deflecting the mirror  212 . An incident light  511  emitted from a coherent light source  510  is incident along a perpendicular or diagonal direction relative to the deflection axis  212   a  of the mirror  212 . The light source  510  may be implemented with a laser light source to emit a coherent characteristic. 
         [0126]    The following are descriptions of the configuration and operation of one pixel unit  211  with reference to the cross-sectional diagram, along the line II-II, of the pixel unit  211  of the spatial light modulator  200  shown in  FIG. 5 . 
         [0127]      FIG. 4  is an outline diagram of the cross-section, along the line II-II, of one mirror element of the spatial light modulator shown in  FIG. 5 . 
         [0128]    As shown in  FIGS. 3 ,  4  and other figures, the spatial light modulator  200  according to the present embodiment comprises the pixel array  210 , bit line driver unit  220  and word line driver unit  230 . 
         [0129]    In the pixel array  210 , pixel units  211  are positioned in a grid where individual bit lines  221  extending vertically from the bit line driver unit  220  cross individual word lines  231  extending horizontally from the word line driver unit  230 . 
         [0130]    As shown in  FIG. 4 , each pixel unit  211  comprises a mirror  212  which tilts freely while supported on the substrate  214  by a hinge  213 . 
         [0131]    An OFF electrode  215  (and an OFF stopper  215   a ) and the ON electrode  216  (and an ON stopper  216   a ) are positioned symmetrically across the hinge  213  that comprises a hinge electrode  213   a  on the substrate  214 . 
         [0132]    When a predetermined voltage is applied to the OFF electrode  215 , it attracts the mirror  212  with a Coulomb force and tilts the mirror  212  so that it abuts the OFF stopper  215   a.  This causes the incident light  511  to be reflected to the light path of an OFF position, which is not aligned with the optical axis of the projection optical system  130 . 
         [0133]    When a predetermined voltage is applied to the ON electrode  216 , it attracts the mirror  212  with a Coulomb force and tilts the mirror  212  so that it abuts the ON stopper  216   a.  This causes the incident light  311  to be reflected to the light path of an ON position, which is aligned with the optical axis of the projection optical system  130 . 
         [0134]    An OFF capacitor  215   b  is connected to the OFF electrode  215  and to the bit line  221 - 1  by way of a gate transistor  215   c  that is constituted by a field effect transistor (FET) and the like. 
         [0135]    Further, an ON capacitor  216   b  is connected to the ON electrode  216 , and to the bit line  221 - 2  by way of a gate transistor  216   c,  which is constituted by a field effect transistor (FET) and the like. The opening and closing of the gate transistor  215   c  and gate transistor  216   c  are controlled with the word line  231 . 
         [0136]    Specifically, one horizontal row of pixel units  211  that are lined up with an arbitrary word line  231  are simultaneously selected, and the charging and discharging of capacitance to and from the OFF capacitor  215   b  and ON capacitor  216   b  are controlled by way of the bit lines  221 - 1  and  221 - 2 , and thereby the individual ON/OFF controls of the micromirrors  212  of the respective pixel units  211  of one horizontal row are carried out. 
         [0137]    In other words, the OFF capacitor  215   b  and gate transistor  215   c  on the side of the OFF electrode  215  constitute a memory cell M 1  that is a so called DRAM structure. 
         [0138]    Likewise, the ON capacitor  216   b  and gate transistor  216   c  on the side of the ON electrode  216  constitute a DRAM-structured memory cell M 2 . 
         [0139]    With this configuration, the tilting operation of the mirror  212  is controlled in accordance with the presence and absence of writing data to the respective memory cells of the OFF electrode  215  and ON electrode  216 . 
         [0140]    As shown in  FIG. 2 , the light source  510  illuminates the spatial light modulator  200  with the incident light  511 , which is reflected by the individual micromirrors  212  as a reflection light  512 . The reflection light  512  then passes through a projection optical system  520  and is projected, as projection light  513 . 
         [0141]    A control apparatus  300 , according to the present embodiment, controlling the spatial light modulator  200  uses the ON/OFF states (i.e., an ON/OFF modulation) and oscillating state (i.e., an oscillation modulation) of the mirror  212 , thereby attaining an intermediate gray scale. 
         [0142]    A non-binary block  320  generates non-binary data  430  used for controlling the mirror  212  by converting an externally inputted binary video signal  400  into non-binary data. In this event, one LSB is different between the period of ON/OFF states of the mirror  212  and the period of intermediate oscillating state. 
         [0143]    A timing control unit  330  generates, on the basis of a synchronous signal  410  (Sync), a drive timing  420 , which is used for the non-binary block  320 , and also generates a PWM drive timing  440  and an OSC drive timing  441 , both of which are used for the mirror  212 . 
         [0144]    As shown in  FIG. 6 , the present embodiment is configured such that a desired number of bits of the upper bits  401  of the binary video signal  400  is assigned to the ON/OFF control pattern  451  of a mirror control profile  450  and the remaining lower bits  402  is assigned to an oscillation control pattern  452 . Further, according to the present embodiment, the control is such that the ON/OFF (positioning) state is controlled by the PWM drive timing  440  from the timing control unit  330  and the non-binary data  430 , while the oscillating state is controlled by the PWM drive timing  440  and OSC drive timing  441  from the timing control unit  330  and the non-binary data  430 . 
         [0145]    Next is a description of the basic control of the mirror  212  of the spatial light modulator  200  according to the present embodiment. 
         [0146]    Note that “Va (1, 0)” indicates an application of a predetermined voltage Va to the OFF electrode  215  and no application of voltage to the ON electrode  216  in the following description. Similarly, “Va (0, 1)” indicates no application of voltage to the OFF electrode  215  and an application of a voltage Va to the ON electrode  216 . “Va (0, 0)” indicates no application of voltage to either the OFF electrode  215  or ON electrode  216 . “Va (1, 1) indicates the application of a voltage Va to both the OFF electrode  215  and ON electrode  216 . 
         [0147]      FIGS. 7A ,  7 B,  7 C,  7 D,  7 E and  7 F show the configuration of the pixel unit  211  comprising the mirror  212 , hinge  213 , OFF electrode  215  and ON electrode  216 , and a basic example in which the mirror  212  is controlled under an ON/OFF state and under an oscillating state. 
         [0148]      FIG. 7A  shows the mirror  212  tilted from the neutral state to the ON state by being attracted to the ON electrode  216  as a result of applying a predetermined voltage (i.e., Va (0, 1)) to only the ON electrode  216 . In the ON state of the mirror  212 , the reflection light  512 , by way of the mirror  212 , is captured by the projection optical system  520  and projected as a projection light  513 .  FIG. 7B  shows the intensity of light projected in the ON state. 
         [0149]      FIG. 7C  shows the mirror  212  tilted from the neutral state to the OFF state by being attracted to the OFF electrode  215  as a result of applying a predetermined voltage (i.e., Va (1, 0)) to only the OFF electrode  215 . In the OFF state of the mirror  212 , the reflection light  512  is deflected from the projection optical system  520 , and therefore does not constitute a projection light  513 . The far right side of  FIG. 7B  shows the intensity of light projected in the OFF state.  FIG. 7D  shows the intensity of light projected in the OFF state. 
         [0150]      FIG. 7E  exemplifies a case of the mirror  212  performing a free oscillation in the maximum amplitude of AO between a tilted position (i.e., a Full ON) in contact with the ON electrode  216  and another tilted position (i.e., a Full OFF) in contact with the OFF electrode  215  (at Va (0, 0)). 
         [0151]    An incident light  511  is illuminated on the mirror  212  at a prescribed angle, and the intensity of light resulting from the incident light  511  reflecting in the ON direction and a portion of the light (i.e. the intensity of light of the reflection light  512 ) reflecting in a direction that is between the ON direction and OFF direction are incident to the projection optical system  520  so as to be projected as projection light  513 .  FIG. 7F  shows the intensity of light projected in an oscillating state. 
         [0152]    That is, in the ON state of the mirror  212  shown in  FIG. 7A , the flux of light of the reflected reflection light  512  is directed in the ON direction so as to be captured almost entirely by the projection optical system  520  and projected as the projection light  513 . 
         [0153]    In the OFF state of the mirror  212  shown in  FIG. 7C , the reflection light  512  is directed in an OFF direction away from the projection optical system  520 , and thus a light projected as a projection light  513  does not exist. 
         [0154]    In the oscillating state of the mirror  212  shown in  FIG. 7E , a portion of the light flux of the reflection light  512 , diffraction light, diffusion light and the like are captured by the projection optical system  520  and projected as a projection light  513 . 
         [0155]    Note that the examples shown in  FIGS. 7A ,  7 B,  7 C,  7 D,  7 E and  7 F described above have been described for a case of applying the voltage Va represented by a binary value of “0” or “1” to each of the OFF electrode  215  and ON electrode  216 . Alternatively, a more minute control of the tilting angle of the mirror  212  is available by increasing the steps of the magnitude of Coulomb force generated between the mirror  212  and the OFF electrode  215  or ON electrode  216  by increasing the steps of the voltage values Va to multiple values. 
         [0156]    Also note that the examples shown in  FIGS. 7A ,  7 B,  7 C,  7 D,  7 E and  7 F described above have been described for a case of setting the mirror  212  (i.e., the hinge electrode  213   a ) at the ground potential. Alternatively, a more minute control of the tilting angle of the mirror  212  may also be achieved by applying an offset voltage thereto. 
         [0157]    The present embodiment is configured to apply the voltages, i.e., Va (0, 1), Va (1, 0) and Va (0, 0), at appropriate timings in the midst of the tilting of the mirror  212  between the ON and OFF states so as to generate a free oscillation in an amplitude that is smaller than the maximum amplitude between the ON and OFF states, thereby accomplishing a more minute gray scale. 
         [0158]    The following shows a method for displaying a video image using the projection apparatus  100  according to the present embodiment shown in the above described  FIG. 2 . 
         [0159]    Non-binary data  430 , a PWM drive timing  440  and an OSC drive timing  441  are generated when a binary video signal  400  and a synchronous signal  410  are inputted into the control apparatus  300 . 
         [0160]    The non-binary block  320  and timing control unit  330  calculate, for each mirror of the SLM constituting a pixel of the video image of a frame, the period of time for controlling each mirror  212  under an ON state and under an oscillating state or the number of oscillations within one frame of a video image, in accordance with the binary video signal  400  and the drive timing  420  generated by the timing control unit  330  from the synchronous signal  410 . The non-binary block  320  and timing control unit  330  also generate non-binary data  430 , a PWM drive timing  440  and an OSC drive timing  441 . 
         [0161]    Specifically, the non-binary block  320  and timing control unit  330  that are comprised in the control apparatus  300  use the ratio of the intensity of a projection light  513  obtained by oscillating a predetermined mirror  212  in an oscillation time T to the intensity of a projection light  513  obtained by controlling the mirror  212  under an ON state during the oscillation time T, and calculate the period of time for controlling the mirror  212  under an ON state, the period of time for controlling the mirror  212  under the oscillating state or the number of oscillations during the period. 
         [0162]    The non-binary block  320  and timing control unit  330  carry out the ON/OFF control and oscillation control for each of the mirrors  212  constituting one frame of video image using non-binary data  430 , PWM drive timing  440  and OSC drive timing  441 , all of which are generated on the basis of the calculated value of the time or the number of times of oscillation. 
         [0163]    Next is a description of the pixel unit  211  that constitutes the pixel array  210  of the spatial light modulator  200  according to the present embodiment, with reference to  FIG. 8 , with the above described configuration in mind. 
         [0164]    In contrast to the pixel unit  211  according to the configuration shown in the above described  FIG. 4 , in which one pixel is equipped with one mirror, two electrodes and two DRAM-structured memory cells, the present embodiment 1 is configured to add plate lines  232  (PL-n; where “n” is the number of ROW lines) to the respective ROW lines and position the second ON electrode  235  (i.e., the electrode D) connected to the plate lines  232  close to the ON electrode  216 . 
         [0165]    In the case of each pixel unit  211  constituting the pixel array  210  according to the present embodiment, a memory cell on one side, the memory for controlling the mirror  212 , is a simple DRAM-structured requiring only one transistor, and therefore, it is possible to suppress the structure of the memory cell from becoming large even with the addition of the plate line  232  and second ON electrode  235 . Therefore a high definition projection image may be achieved by arraying a large number of pixel units  211  within a pixel array  210  of a more limited size. 
         [0166]    Furthermore, as described below, a gray scale representation may be drastically expanded by the addition of the plate line  232  and second ON electrode  235 . 
         [0167]    In other words, image projection with a high definition and a high grade of gray scale may be achieved by applying a projection technique implemented with a spatial light modulator with a configuration and control process described according to the spatial light modulator  200 . 
         [0168]      FIG. 9  is a conceptual diagram showing an exemplary modification of the configuration of the pixel unit  211  shown in the above described  FIG. 8 . The configuration shown in  FIG. 9  shows the case of placing a second OFF electrode  236  (i.e., an electrode B) on the side of the OFF electrode and connecting it to the plate line  232 . 
         [0169]    A spatial light modulator comprising the pixel unit configured as shown in  FIG. 9  is not designed as a different type of the spatial light modulator from the configuration described in  FIG. 8 . It is possible to attain the same operation with the spatial light modulator configuration of  FIG. 8  as that of the spatial light modulator configuration of  FIG. 9  by changing the direction of incident light by 180 degrees in the horizontal plane of the mirror and by inverting the image to be displayed 180 degrees in the plane of the image. 
         [0170]    As a result, the following operations using the configuration of  FIG. 9  can also be achieved with the configuration of  FIG. 8 . 
         [0171]    In this case, the ON electrode  216  (i.e., the electrode C), second ON electrode  235  (i.e., the electrode D) and OFF electrode  215 , which are shown in  FIG. 8 , perform the operations corresponding to the respective operations of the OFF electrode  215 , second OFF electrode  236  (i.e., the electrode B) and ON electrode  216 . With this configuration, the electrode that is not connected to memory changes roles by temporarily retaining the mirror in order to increase the number of gray scale levels by controlling the direction of incident light and by generating an intermediate oscillation of the mirror. 
         [0172]      FIG. 10  is a conceptual diagram showing another exemplary modification of the configuration of the pixel unit  11  shown in the above described  FIG. 8 . 
         [0173]    The exemplary modification shown in  FIG. 10  exemplifies the configuration of placing a second ON electrode  235  (i.e., the electrode D) and a second OFF electrode  236  (i.e., the electrode B) respectively on the ON side and OFF side of the mirror  212  and connecting them, respectively, to a plurality of second plate lines  233  and a plurality of plate lines  232 . 
         [0174]      FIG. 11  is a top view diagram showing an exemplary layout of the OFF capacitor  215   b  and ON capacitor  216   b  of the pixel unit  211  used in the exemplary configuration shown in  FIG. 8 . Specifically,  FIG. 11  shows the formation of the layer of the OFF capacitor  215   b  and ON capacitor  216   b  as viewed from the top of the mirror  212 . 
         [0175]    The OFF capacitor  215   b  and ON capacitor  216   b  are positioned in the regions obtained by dividing the placement region of the rectangular pixel unit  211  into two parts in the diagonal direction. 
         [0176]      FIGS. 12A and 12B  are cross-sectional diagrams of an ON state and OFF state, respectively, which are related to the pixel unit  211 , configured as shown in  FIG. 8 . The symbols assigned in  FIGS. 12A and 12B  follow the same conventions as that described in  FIG. 8 . 
         [0177]      FIGS. 12C and 12D  are illustrative top view diagrams showing an exemplary layout of the added second ON electrode  235 . 
         [0178]      FIG. 12C  shows an exemplary configuration that positions the OFF electrode  215  (i.e., an electrode A) and ON electrode  216  (i.e., an electrode C) at approximately symmetrical positions, sandwiching a hinge  213  that is positioned on the diagonal line of the rectangular placement region of a pixel unit  211 , and that positions a small triangular second ON electrode  235  (i.e., an electrode D) on the outside of the ON electrode  216 . 
         [0179]    Note that the pixel unit  211 , according to the exemplary modification shown in  FIG. 9 , is configured so that the second OFF electrode  236  (i.e., the electrode B) would be positioned on the outside of the OFF electrode  215  (i.e., the electrode A) in a similar configuration to that shown in  FIG. 12C . 
         [0180]      FIG. 12D  shows an exemplary configuration that divides the ON electrode  216 , shown in  FIG. 12C , into two parts, the aforementioned ON electrode  216  (i.e., the electrode C) and the second ON electrode  235  (i.e., an electrode D). 
         [0181]    Note that the pixel unit  211 , according to the exemplary modification shown in  FIG. 10 , is configured so that the placement region of the OFF electrode  215  would be divided into two parts and allocated to the OFF electrode  215  and second OFF electrode  236  shown in a similar configuration to that shown in  FIG. 12D . 
         [0182]      FIG. 13  shows an exemplary layout of the control circuit of the pixel array  210  arraying the pixel unit  211  shown in  FIG. 8 . 
         [0183]    Specifically, a plate line driver unit  250  used for controlling the plate line  232  (i.e., the second plate line  233 ) has been added to the configuration of the pixel array  210  shown in the above described  FIG. 3 . 
         [0184]    Specifically, this embodiment is configured to add the plate line driver unit  250  in the surroundings of the pixel array  210 , in addition to comprising the bit line driver unit  220  and word line driver unit  230 . 
         [0185]    The word line driver unit  230  is constituted by a first address decoder  230   a  and a word line driver  230   b,  which are used for selecting a word line  231  (WL). 
         [0186]    The plate line driver unit  250  is constituted by a plate line driver  251 , a plate line address decoders  252 - 1  and  252 - 2 , all of which are used for selecting a plate line  232  (PL). 
         [0187]    Each pixel unit  211  is connected to the bit lines  221 - 1  and  221 - 2  of the bit line driver unit  220  (Bitline driver) so that data is written to the pixel unit  211  belonging to the ROW line selected by the word line  231  (WL). 
         [0188]    A signal produced by an external input data though a serial word line (WL_ADDR 1) connected in parallel to an address decoder  230   a  (WL Address Decoder). A word line driver  230   b  (WL Driver) converts the input data into a designated voltage and applies the voltage to the word line  231  (WL). 
         [0189]    Furthermore, the plate line  232  (PL) controls the ON electrode  216  of each pixel unit  211  y separately from the word line  231  (WL). 
         [0190]    A plate line driver  251  (PL driver) converts the external input data PL_ADDRa or PL_ADDRb through series data line into a predefined voltage and apply the voltage through parallel signal lines to the plate line address decoder  252 - 1  (PL Address Decoder-a) and plate line address decoder  252 - 2  (PL Address Decoder-b) for selectively applied the signals to the plate line  232  (PL). 
         [0191]    Specifically, the number of ROW lines, constituted by a plurality of pixel units  211  lined up horizontally, may be configured to be, for example, at least 720 lines or more. 
         [0192]    In such a case, a data signal input to the memory cells M 1  and M 2  from each of the bit lines  221 - 1  and  221 - 2  is transmitted at 23 nsec or lower per one ROW line memory. 
         [0193]    That is, in order to process  720  ROW lines by dividing and assigning a display period into four colors red (R), green (G), blue (B) and white (W) at the rate of 60 frames per second, with each color in 256-bit gray scale, the transmission speed is as follows: 
         [0194]    1/60 [sec]/4 [divisions]/256 [bit gray scale]/720 [lines]=22.6 nsec. 
         [0195]    Further, in order to process 1080 ROW lines by dividing and assigning a display period into three colors R, G and B at the rate of 60 frames per second, with each color in 256-bit gray scale, the transmission speed is as follows: 
         [0196]    1/60/3/256/1080=20 nsec. 
         [0197]      FIG. 14  shows an example of the connecting relationship between the address decoder and bit line driver unit  220  (Bitline driver), which are used for selecting a word line  231  (WL) and a plate line  232  (PL) in the pixel array  210 . 
         [0198]    As shown in  FIG. 14 , it is simpler to connect one plate line address decoder  252 - 1  to the plate line driver  251  than to connect two plate line address decoders  252 - 1  and  252 - 2 , as shown in  FIG. 13 . 
         [0199]      FIG. 15A  is a conceptual diagram showing an exemplary modification of the configuration of the pixel array  210  according to the present embodiment. 
         [0200]    The configuration shown in  FIG. 15A  divides a plurality of ROW lines (ROW-1 through ROW-1080) into upper and lower groups (i.e., an upper row line area  210   a  and a lower row line area  210   b ), and comprises, for each group, an upper bit line driver part  220 - 1  and a lower bit line driver part  220 - 2  (Bitline Driver), a first address decoder  230   a  and a word line driver  230   b  (WL Address Decoder_up and WL Driver_up, WL Driver_down and WL Driver_down), a plate line driver  251 - 1  and a plate line address decoder  252 - 1 , a plate line address decoder  252 - 2  (PL Address Decoder-a_up, b_up and PL Driver_up, PL Address Decoder-a_down, b_down and PL Driver_up, down). 
         [0201]    That is, a plurality of row lines are divided into the upper row line area  210   a , which is constituted by the row lines ROW-1 through ROW-540, and the lower row line area  210   b,  which is constituted by the row lines ROW-541 through ROW-1080. 
         [0202]    In this case, the level change (i.e., the voltage Vd) of the plate line  232  is accomplished by changing the plate line address decoder  252 - 1  changing to H level and the plate line address decoder  252 - 2  to L level. 
         [0203]      FIG. 15B  shows an exemplary configuration in which the plate line driver  251 - 1  (PL Driver_up) and plate line driver  251 - 2  (PL Driver_down) that are equipped, respectively, for the upper and lower ROW line groups is equipped with one plate line address decoder  252  (PL Address Decode_up) and one plate line address decoder  252  (PL Address Decoder_down) in the comprisal of the pixel array  210  shown in the above described  FIG. 15A . 
         [0204]    In this case, the level change (i.e., the voltage Vd) of the plate line  232  (PL) is carried out by only the plate line  232  (PL). 
         [0205]      FIG. 15C  shows the configuration in which a first address decoder  230   a  and a word line driver  230   b,  a plate line driver  251  and a plate line address decoder  252 - 1  and a plate line address decoder  252 - 2  are equipped for each group in the configuration in which the ROW lines of a pixel array  210  is divided into the upper and lower groups, and each of the upper and lower ROW line groups is equipped with the upper bit line driver part  220 - 1  and lower bit line driver part  220 - 2 . 
         [0206]    In this case, for each group of the upper and lower ROW lines, the ROW lines applicable to the same address will be driven simultaneously; a combination of the respective ROW lines in the upper and lower groups to be simultaneously driven is determined by wirings. 
         [0207]    For example, the ROW lines applicable to the same address (in the example of  FIG. 15C , the first ROW-1 in the upper group and the first ROW-541 in the lower group) are simultaneously driven. 
         [0208]      FIG. 15D  shows an exemplary configuration in which the plate line driver  251  commonly equipped in the upper and lower groups is separated into a plate line driver  251 - 1  (PL Driver up) corresponding to the upper group and a plate line driver  251 - 2  (PL Driver down) corresponding to the lower group, and the divided drivers are placed correspondingly to the respective groups. 
         [0209]    In this case, the ROW lines belonging to the upper and lower groups are individually driven, unlike the configuration shown in  FIG. 15C . 
         [0210]    The following is a description of an exemplary operation of the pixel unit  211  configured as shown in  FIG. 8 . 
         [0211]      FIG. 16  is a table showing the exemplary specifications of frame, subfield and time slot ts in the following description. 
         [0212]    In the case of the present embodiment, for example, in a color sequential display, one frame is constituted by a plurality of fields corresponding to each of a plurality of colors, and the field of each color is further constituted by a plurality of subfields. The period of the field of each color do not necessarily have to be the same. 
         [0213]    If one frame is 60 Hz (16.66667 msec.), the width of a subfield assigned to one color is between 5.00 msec (at the shortest) and 10.00 msec (at the longest). 
         [0214]    Further, each subfield is constituted by a plurality of time slots ts, and the length of the time slot ts is different depending on the bit width of data used for a gray scale representation and on the length of the subfield. 
         [0215]    For example, in the case of 8-bit (i.e., 255-level gray scale), the length of a time slot ts is 19.61 μsec if one subfield is 5.0 msec, and the length of a time slot ts is 39.22 μsec if one subfield is 10.0 msec, as shown in  FIG. 16 . 
       &lt;Exemplary Operation - A&gt; 
       [0216]      FIGS. 17A and 17B  are timing charts showing an exemplary action of the present embodiment. 
         [0217]    When a gray scale display is carried out with a control that is a combination between OSC and PWM using a mirror control profile  450  consisting of an ON/OFF control pattern  451  (PWM) and an oscillation control pattern  452  (OSC), a gray scale level is determined by the write cycle (i.e., the time slot cycle) to the memory cells M 1  and M 2 . 
         [0218]    Accordingly, the present embodiment is configured to use the second ON electrode  235  (i.e., the electrode D) in  FIG. 8  connected to the plate line  232  for maintaining the state of the mirror  212  even if the data of the memory cells M 1  and M 2  are changed, and maintaining the state for a period shorter than a time slot ts, and thereby enabling a control of light intensity for a period shorter than the time slot ts. 
         [0219]    The following is a description of a method for improving gray scale when using a mirror control profile  450  in the control that is a combination between OSC and PWM consisting of the oscillation control pattern  452  and ON/OFF control pattern  451 , in the case of the present embodiment. 
         [0220]      FIG. 17A  exemplifies the case of structuring one frame (i.e., one screen) of each color with a plurality of subfield: the first subfield  601 , second subfield  602 , third subfield  603  and fourth subfield  604 . 
         [0221]    In the pixel unit  211 , the ON state of the mirror  212  can be maintained for a predetermined period of time even when the OFF electrode  215  and ON electrode  216 , which are connected to the memory cells M 1  and M 2 , respectively, are shifted from (0, 1) to (1, 0), if a pulse Vd 2  is given to the second ON electrode  235  (i.e., an electrode D, the plate line  232 ) that is placed on the ON side (refer to the circuit configuration shown in  FIG. 8 ). 
         [0222]    The intensity of light during the aforementioned period through the application of the pulse Vd 2  is controlled to be lower than the intensity of light of the oscillation control pattern  452  (OSC) in one time-slot ts and is also controlled to differ in each subfield (i.e., the first subfield  601 , second subfield  602 , third subfield  603 ), and thereby projecting images with an increased gradations of gray scale levels. 
         [0223]    That is, the width of the pulse Vd 2  changes with each of the first subfield  601  through the third subfield  603  as follows: 
         [0224]    pulse width t 1 &lt;pulse width t 2 &lt;pulse width t 3   
         [0225]    The pulse width t 1  of the pulse Vd 2  in the first subfield  601  is set at a value that is ⅛ the intensity of light (noted as “⅛ OSC” hereinafter) in one time-slot of the oscillation control pattern  452 ; the pulse width t 2  of the second subfield  602  is set at ¼ OSC; the pulse width t 3  of the third subfield is set at ½ OSC. 
         [0226]    The interval of the pulse Vd 2  is set so that the electrode D maintaining the state of the mirror  212  is carried out for every other time slot ts. In order to correct the gray scale for one subfield (i.e., the last subfield, the fourth subfield  604  in this case), the voltage Vd of the second ON electrode  235  is equipped with only a pulse Vd 1 , not a pulse Vd 2 , and the state of the mirror  212  is not maintained by the second ON electrode  235  (i.e., the electrode D). Instead, the number of time slots ts is adjusted as described later. In adjusting the number of time slots ts, the control process may prevent all the time slots from turning to the ON state in the fourth subfield  604  even if a video signal at a saturated level is inputted into the control apparatus  300 . 
         [0227]      FIG. 17B  shows, as an example, the result of reducing the grades of gray scale equivalent to the intensity of light by ⅛ OSC from that of the example shown in  FIG. 17A . 
         [0228]    When a data loading of the ON/OFF control pattern  451  (PWM) for the first subfield  601  of  FIG. 17A  is shortened by the equivalent of one time-slot, the intensity of light is reduced by 1+⅛ OSC in the first subfield  601 . 
         [0229]    Accordingly, if a data loading for PWM for the fourth subfield  604  is extended by the equivalent of one time-slot, a reduction in the intensity of light by ⅛ OSC can be attained for the entirety of one frame. 
         [0230]    With this control, a combination of a light intensity control by means of a pulse Vd 2  in each of the first subfield  601  through the third subfield  603  makes it possible to attain a gray scale representation eight times (8×) the gray scale control achieved by means of the ON/OFF control pattern  451  or oscillation control pattern  452  in units of time slot ts. 
         [0231]    Specifically, the mirror  212  is drawn to the ON side by the electrode D only for the period of the pulse Vd 1  by turning on the electrode D at the time when the mirror is switched from the oscillation control pattern  452  (OSC) to the ON/OFF control pattern  451  (PWM) by controlling the voltage Vd of the second ON electrode  235  (i.e., an electrode D) for each of the first subfield  601  through the fourth subfield  604 . The switch of operation occurs when the mirror  212  is operated in the oscillating state under the control of the oscillation control pattern  452  and the mirror is switched smoothly to the ON state on the ON/OFF control pattern  451  in a short time. 
         [0232]    Application of the pulse Vd 1  as described above is advantageous in that it lowers the voltage applied to the OFF electrode  215  and ON electrode  216 , which are connected to the memory cells M 1  and M 2 , respectively, and lowers the power consumption and also acts as a countermeasure to stiction. [[NOTE: don&#39;t know if I&#39;m interpreting this correctly]] 
         [0233]    The pulse Vd 1  may also be applied to control a mirror  212  to switch from the horizontal state to an ON state immediately after turning on the power to a display element. For example, if a mirror  212  cannot be shifted from the horizontal state to the ON state even though the mirror  212  is successfully shifted from the OFF state to the ON state by only the ON electrode  216 , to which 5 volts as the voltage Vc is applied, 10 volts can be applied as a pulse Vd 1  to the electrode D simultaneously with the application of 5 volts (i.e., the voltage Vc) to the ON electrode  216  when the mirror  212  is in the horizontal state, and then the voltage Vd of the electrode D is returned to zero (0) volts after the elapse of time necessary for the mirror  212  to shift to the ON state. This operation eliminates the need to apply an unnecessarily high voltage for shifting the mirror  212  from the OFF state to the ON state and also reduces stiction. In this case, a voltage (i.e., a snap-in voltage or a pull-in voltage) necessary for shifting the mirror  212  from the horizontal state to the ON state is 5 volts plus 10 volts. The voltages at the electrode D and ON electrode  216  can be set independently, as shown in  FIG. 51  (to be described later). 
       &lt;Exemplary Operation - A′&gt; 
       [0234]      FIG. 17C  is a timing diagram showing an exemplary modification of the above described Exemplary Operation A.  FIG. 17C  exemplifies the case in which the mirror  212  performs an intermediate oscillation under the control of the oscillation control pattern  452 , shown in the above described  FIG. 17A . 
         [0235]    In this case, the pixel unit  211 , as shown in  FIG. 10 , is configured so that the second OFF electrode  236  (i.e., the electrode B) is placed on the side where the OFF electrode  215  is placed, and the second ON electrode  235  (i.e., the electrode D) is placed on the side where the ON electrode  216  is placed, with the second OFF electrode  236  and second ON electrode  235  respectively connected to the plate line  232  and second plate line  233 , which are independent of each other. 
         [0236]    In the case of  FIG. 17C , the mirror control profile  450  is assigned in order of the ON/OFF control pattern  451  (PWM) and oscillation control pattern  452  so that the OFF state of the mirror  212  is maintained for a predetermined period of time by means of the electrode B placed on the OFF side, and the intermediate oscillation of the mirror  212  is generated by means of the electrode D placed on the ON side. In this case, for a voltage Vb applied to the plate line  232  connected to the electrode B, a pulse Vb 1  is applied during every other time slot ts during a period of the ON/OFF control pattern  451 . 
         [0237]    The width of the pulse Vb 1  is differentiated for each of the first subfield  601  through third subfield  603  as follows: 
         [0238]    pulse width t 4 &gt;pulse width t 5 &gt;pulse width t 6   
         [0239]    The pulse width t 4  is set at a value for maintaining the mirror  212  in the OFF state only for the period during which the reflection light intensity of ⅛ OSC is obtained within one time-slot. 
         [0240]    Likewise, the pulse width t 5  is set at a value for maintaining the mirror  212  in the OFF state only for the period during which the reflection light intensity of ¼ OSC is obtained within one time-slot. 
         [0241]    Likewise, the pulse width t 6  is set at a value for maintaining the mirror  212  in the OFF state only for the period during which the reflection light intensity of ½ OSC is obtained within one time-slot. 
         [0242]    This operation changes the timing of shifting from the OFF state to ON state by one time-slot in the ON/OFF control pattern  451 , and thereby, it is possible to reduce the light intensity by “1 -(⅛ OSC)” in the time slot ts corresponding to the pulse Vb 1 , for example, in the first subfield  601 . A similar operation may also be applied to the other subfields, i.e., the second subfield  602  and third subfield  603 . 
         [0243]    Further, in the fourth subfield  604 , an OFF period the length of three time slots is set at the beginning of the ON/OFF control pattern  451  so as to compensate for the equivalent of one time-slot for each of the first subfield  601  through third subfield  603 . 
         [0244]    This operation makes it possible to achieve a gray scale level eight times (8×) that of the control in units of time slot ts, similar to the case described in  FIG. 17A . 
         [0245]    Further, using a pulse Vd 1  as the voltage Vd of the electrode on the ON side when shifting from the ON/OFF control pattern  451  to oscillation control pattern  452  attracts the mirror  212 , which has just started to shift from the ON side to OFF side, in the direction returning to the ON side, thereby shifting the mirror  212  to an intermediate oscillation under the control of the oscillation control pattern  452 . 
       &lt;Exemplary Operation - B&gt; 
       [0246]      FIG. 18  is a timing diagram showing an exemplary method for improving the number of gray scale levels when using a non-binary PWM. 
         [0247]    In this case, the circuit configuration of a pixel unit  211  uses a configuration that places the second ON electrode  235  (i.e., an electrode D) on the side where the ON electrode  216  (i.e., the electrode C) is placed, as shown in  FIG. 8 . 
         [0248]    Further, one frame is constituted by two subfields, that is, the first subfield  601  and the second subfield  602 . 
         [0249]    In the case of non-binary PWM, the ON state of the mirror  212  is expressed by a bit string corresponding to the number of gray scale levels, and therefore a gray scale control is performed by setting a continuous ON state during an arbitrary period within a subfield. 
         [0250]    In this event, the present embodiment is configured to control, for the pixel unit  211  in which the mirror  212  is in the ON state, the voltage Vd of a plate line  232  so as to maintain the ON state of the mirror  212  only for a predetermined period (i.e., during a pulse Vd 2 ) by means of the electrode D placed on the ON side even when the OFF electrode  215  and ON electrode  216 , which are connected to the memory M 1  and M 2 , respectively, are changed from (0, 1) to (1, 0). 
         [0251]    The intensity of light during the period of maintaining the pulse Vd 2  is set to be lower than the intensity of light under the control of the ON/OFF control pattern  451  (i.e., a PWM control) for the length of one time-slot, and is set to be different for each of a plurality of subfields (in this case, the first subfield  601  and the second subfield  602 ), and thereby the number of gray scale levels can be increased. 
         [0252]    In this case, for the first subfield  601 , a pulse width t 7  that is equivalent to a ¼ of the intensity of light (noted as “¼ PWM” hereinafter) of the ON state during one time-slot under a PWM control is set as a pulse Vd 2  at a position corresponding to the time slot ts at the tail end of the ON/OFF control pattern  451 . 
         [0253]    Likewise, for the second subfield  602 , a pulse width t 8  that is equivalent to ½ of the intensity of light (noted as “½ PWM” hereinafter) of the ON state during one time-slot under a PWM control is set as a pulse Vd 2  at a position corresponding to the time slot ts at the tail end. 
         [0254]    As such, the ON state is maintained by means of the pulse Vd 2  of the electrode D at the last time slot of each subfield. If the ON state is not maintained during this period, the PWM waveform of the ON/OFF control pattern  451  is moved to the start of the subfield so as to not use the last two time slots. 
         [0255]    By combining the aforementioned control with the presence/absence of controlling the pulse Vd 2  in the first subfield  601  and second subfield  602 , an improvement in the gray scale representation four times (in this example), that of a simple gray scale control by means of an ON/OFF control in units of time slots ts is achieved. 
         [0256]    As described above, the example shown in  FIG. 18  has two subfields, that is, the first subfield  601  and second subfield  602 , and operates the electrode D in the last time slot ts so as to enable a gray scale representation of ¼ PWM for the first subfield  601  and ½ PWM for the second subfield  602 . 
         [0257]    Specifically, the control processes switch the mirror from the ON/OFF control pattern  451  to turn on the time slot ts immediately before the pulse Vd 2  in the case of turning on a light intensity control using the pulse Vd 2  of the electrode D. The control processes switch the of the ON/OFF control pattern  451  toward the beginning of the subfield in the case to turn off the light intensity control. 
         [0258]    Furthermore,  FIG. 18  exemplifies the combination between the first subfield  601  and second subfield  602  when the gray scale representations are changed in increments of the light intensity of ¼ PWM starting from the top left. 
         [0259]      FIG. 18A  is a timing diagram showing an exemplary modification of the operation shown in  FIG. 18 . The operation of  FIG. 18A  is applicable to a pixel unit  211  configured to place an electrode B on the OFF side, as shown in  FIG. 9 . 
         [0260]    Further, the operation of the electrode B is controlled in the first time slot of each subfield so as to maintain the OFF state of the mirror  212  when it starts to shift from the OFF state to ON state. 
         [0261]    That is, in the control of the voltage Vb of the electrode B connected to the plate line  232 , the pulse Vb 1  by pulse widths t 9  and t 10  are set for the second time slot ts position at the start of the first subfield  601  and second subfield  602 , respectively, and the operation of the electrode B is controlled so as to maintain the OFF state of the mirror  212  when it starts to shift from the OFF state to ON state, and thereby the control for obtaining the light intensity of ¼ PWM and ½ PWM is attained. Specifically, while the above description defines the controlled light intensity as ⅛ PWM, ¼ PWM, ½ PWM and 1/1 PWM, they may also be defined as 1/4 PWM, 1/2 PWM, 1/1 PWM and 1/1 PWM, or as ½ PWM, 1/1 PWM, 1/1 PWM and 1/1 PWM. 
         [0262]    As described above, this configuration makes it possible to control the mirror  212  with different resolutions for each subfield, thereby providing an image with a high level of gray scale without requiring high speed data transmission. 
       &lt;Exemplary Operation - C&gt; 
       [0263]      FIG. 19  is a timing diagram showing Exemplary Operation C of the pixel unit  211  according to the present embodiment. 
         [0264]      FIG. 19  exemplifies a method for improving the number of gray scale levels by means of a binary PWM control in a single field. 
         [0265]    In this case, the circuit of the pixel unit  211  is configured to place a second OFF electrode  236  (i.e., an electrode B) on the OFF side, as shown in  FIG. 9 . 
         [0266]    When the mirror  212  is in the OFF state, even if the OFF electrode  215  and ON electrode  216 , which are respectively connected to the memory cells M 1  and M 2  are shifted from (1, 0) to (0, 1), the OFF state of the mirror  212  is maintained for a predetermined period of time by means of the pulse Vb 1  of the electrode B placed on the OFF side, whereas when the pulse Vb 1  of the electrode B is turned to L, the mirror  212  is shifted to the ON side. 
         [0267]    It is possible to control gray scale to have more levels than the gray scale control in units of time slots ts by making the light intensity obtained during the period of maintaining the pulse Vb 1  of the electrode B lower than the controlled light intensity by means of PWM for the length of one time-slot. 
         [0268]    Specifically, in the example of  FIG. 19 , the OFF state is maintained in the last time slot in a single subfield  600  by means of the pulse Vb 1  of the electrode B, whereas the last time-slot is set at (0, 1) when a ½ PWM gray scale representation is not carried out. 
         [0269]    In order to represent the ½ /PWM, the immediate prior time slot is turned OFF. In a binary PWM, a gray scale control is carried out by combining the ON state and OFF state of a continuous multiple time slots ts on the basis of the weighting of each bit of a bit string assigned to the gray scale control, whereas the present exemplary operation is configured to add one extra time slot ts to the tail end of the subfield  600  and to set the pulse Vb 1  (i.e., the pulse width t 11  corresponding to ½ PWM) of the electrode B at the position of the tail-end time slot ts. 
         [0270]    Note that  FIG. 19  exemplifies the subfield  600  in the case of decreasing the light intensity by an increment of ½ PWM starting from the top. 
         [0271]    Specifically, in  FIG. 19 , while the state is maintained by means of the pulse Vb 1  of the electrode B in the last time slot ts, the placement of pulse Vb 1  in the subfield  600  is arbitrary. 
         [0272]    As described above, Exemplary Operation C shown in  FIG. 19  makes it possible to represent a gray scale twice the number of gray scale levels as in the case of controlling a gray scale in units of time slots ts. 
         [0273]      FIG. 19A  is a timing diagram showing an exemplary modification of the exemplary operation shown in  FIG. 19 . 
         [0274]      FIG. 19A  exemplifies the case of using the circuit configuration of a pixel unit  211  that places an electrode D on the ON side, as shown in  FIG. 8  and maintaining the ON state of the mirror  212 , thereby controlling a gray scale in units of ½ PWM. 
         [0275]    That is, the control is such as to set the pulse Vd 2  of the electrode D in the last time slot ts of the subfield  600  and to maintain the mirror  212  in the ON state only for the period of the pulse width t 12  of the pulse Vd 2  when the mirror  212  is shifting from the ON state to OFF state. 
         [0276]    In this case, the time slot ts immediately prior to a time slot ts to which the pulse Vd 2  is set is controlled under the ON state. 
       &lt;Exemplary Operation - C′&gt; 
       [0277]      FIG. 20  is a timing diagram showing an exemplary method of combining a non-binary PWM and an oscillation control for improving a gray scale representation in a single subfield. 
         [0278]    The basic concept of the method is the same as that of the Exemplary Operation C shown in  FIG. 19 . 
         [0279]    Further, the circuit of a pixel unit  211  uses the configuration shown in  FIG. 9 , in which the electrode B is placed on the OFF side. 
         [0280]    In this case, when the mirror  212  is controlled under a mirror control profile  450  that combines an ON/OFF control pattern  451  (PWM) and an oscillation control pattern  452 , a pulse Vb 1  is set correspondingly to the tail end time slot ts of the oscillation control pattern  452  in a single subfield  600 . 
         [0281]    In the pixel unit in which the mirror  212  is in an oscillating state (OSC), the mirror  212  can be placed under the OFF state by setting a pulse Vb 1  on the voltage Vb of the electrode B placed on the OFF side even when the OFF electrode  215  and ON electrode  216 , which are respectively connected to the memory cells M 1  and M 2 , are maintained to be (0, 0). 
         [0282]    The number of gray scale levels can be increased by making the light intensity obtained while maintaining the pulse Vb 1  lower than the OSC light intensity. 
         [0283]    The example shown in  FIG. 20  is configured to maintain the pulse Vb 1  by means of the electrode B in the last time slot ts in one subfield  600 , whereas the last time slot ts is maintained to be (0, 1) when a ½ OSC gray scale control is not used. 
         [0284]      FIG. 20  exemplifies the case of increasing the light intensity in increments of ½ OSC in sequence, starting from the top. 
         [0285]    Specifically, the example of  FIG. 20  has been provided by exemplifying the case of shifting from the ON/OFF control pattern  451  (PWM) to the oscillation control pattern  452  (OSC) within a subfield  600 ; the same result can be obtained by using the mirror control profile  450  to shift from the oscillation control pattern  452  (OSC) to the ON/OFF control pattern  451  (PWM) and maintaining the electrode B by means of pulse Vb in the first time slot ts within the subfield  600 . 
       &lt;Exemplary Operation - D&gt; 
       [0286]      FIG. 21  is a timing diagram showing an Exemplary Operation D according to the present embodiment, in which a method of light intensity control in the oscillating state (OSC) of a mirror  212  is described. 
         [0287]    The circuit of a pixel unit  211  uses the configuration shown in  FIG. 9 , in which the electrode B is placed on the OFF side. 
         [0288]    When a gray scale control is carried out using, for example, the mirror control profile  450  that combines the ON/OFF control pattern  451  and oscillation control pattern  452 , and if the number of assigned time slots ts of the oscillation control pattern  452  (OSC) is seven (7), the light intensity in one time-slot of the oscillation control pattern  452  (OSC) is preferred to be 12.5% (i.e., 12.5[%]*(7+1)=100[%]) of the light intensity that will be obtained in one time-slot ts of the ON/OFF control pattern  451  (PWM). 
         [0289]    However, the light intensity may sometimes be more than 12.5% due to variations in the amplitude of the mirror  212  under the control of the oscillation control pattern  452  (OSC), variations in the optical system, or other variations. In such a case, the linearity of the gray scale represented by the mirror control profile  450  is damaged. 
         [0290]    Accordingly, Exemplary Operation D is configured to provide a period, in which the mirror  212  is maintained on the OFF side by means of the pulse Vb 2  (in a pulse width t 13 ) on the voltage Vb that is applied to electrode B, in each time slot ts during the period of a oscillation control pattern  452  (OSC) so as to control the light intensity obtained by the OSC during the period at 12.5%. Alternatively, the light intensity may be controlled at values that are the products of 12.5% times an odd number (i.e., 37.5%, 62.5% and 87.5%) so as to make a corresponding gray scale when an externally inputted video signal is converted into a video signal to be sent to the spatial light modulator  200  (i.e., the display panel). 
         [0291]    As described above, when the number of time slots ts of the oscillation control pattern  452  (OSC) is set at seven (7), the light intensity of one time-slot of the OSC is preferred to be 12.5% of the light intensity of one time-slot of the PWM. However, when the number of time slots ts of the OSC is three (3), the light intensity is preferred to be 25%, and to be 6.5% when the number of time slots ts of the OSC is fifteen (15). These numbers may also be multiplied by odd numbers. This is especially necessary if the light intensity of one time-slot of the OSC is set at 6.5% (when there are fifteen time slots ts of the OSC) since there will be a large loss in light intensity, and therefore, in this case, it is better to use a value obtained by multiplication with an odd number. 
         [0292]    Specifically,  FIG. 21  exemplifies the case of placing the pulse Vb 2  of the electrode B in the last half of one time-slot of the oscillation control pattern  452  (OSC); alternatively, the pulse Vb 2  may be placed in the first half. 
         [0293]    Furthermore, while the example of  FIG. 21  shows the ON/OFF control pattern  451  (PWM) followed by the oscillation control pattern  452  (OSC) in the mirror control profile  450 ; the operation will be the same if they are placed in reverse order, with the oscillation control pattern  452  (OSC) followed by the ON/OFF control pattern  451  (PWM). 
         [0294]    The above described configuration makes it possible to attain a gray scale control with good linearity by appropriately setting both the position of the pulse Vb 2  on a voltage Vb, which is applied to the electrode B, and a pulse width t 13 , even if there is non-linearity in the gray scale caused by a variation in the optical system or other causes. In other words, a gray scale control with good linearity can be attained without being affected by a variation in the production process for the pixel unit  211 . 
       &lt;Exemplary Operation - E&gt; 
       [0295]      FIG. 22  is a timing diagram showing Exemplary Operation E. The following description exemplifies a method for adjusting (i.e., offsetting) the intensity of light when using a mirror control profile that combines a non-binary PWM and an oscillation control (OSC). 
         [0296]    Note that the circuit of a pixel unit  211  uses the configuration shown in  FIG. 8 , in which the second ON electrode  235  (i.e., the electrode D) connected to the plate line  232  is placed on the ON side. 
         [0297]    At a timing of the time slot ts at the start of the oscillation control pattern  452 , during the transition between the ON/OFF control pattern  451  and oscillation control pattern  452 , a pulse Vd 3  (in a pulse width t 14 ) is applied to the electrode D, on an as-needed basis, in order to shift the start timing of the oscillation control pattern  452  (OSC) by the length of the pulse width t 13 , and thereby the period of the ON state of the preceding ON/OFF control pattern  451  is increased or decreased. 
         [0298]    Specifically, in  FIG. 22 , the waveform on the upper half of the figure exemplifies the case in which an operation (by means of a pulse Vd 3 ) performed by the electrode D is not carried out (i.e., the voltage Vd is flat), while the waveform on the lower half exemplifies the case in which the electrode D is turned to High (i.e., by applying a pulse Vd 3 ) at the timing of starting the oscillation control pattern  452  (OSC) to extend the ON period of the mirror  212  by approximately the length of the pulse width t 14  of the pulse Vd 3 . 
         [0299]    Note that the example of  FIG. 22  shows the ON/OFF control pattern  451  (PWM) followed by the oscillation control pattern  452  (OSC) in the configuration of the mirror control profile  450 ; while the operation will be the same if the oscillation control pattern  452  (OSC) and ON/OFF control pattern  451  (PWM) are applied in this reverse order. 
       &lt;Exemplary Operation - E′&gt; 
       [0300]      FIG. 23  is a timing diagram showing Exemplary Operation E′, an exemplary modification of the above described Exemplary Operation E. Specifically, Exemplary Operation E′ shows the case in which a pulse Vd 4  (in the pulse width t 15 ), a voltage inverted from the pulse Vd 3 , is applied at the timing of the tail end time slot ts of the ON/OFF control pattern  451  in the pixel unit  211  configured as shown in  FIG. 8 , and thereby, the start timing of the oscillation control pattern  452  is advanced. 
         [0301]    In  FIG. 23 , the waveform on the upper half of the figure exemplifies the case in which an operation (by means of a pulse Vd 4 ) performed by the electrode D is not carried out, while the waveform on the lower half exemplifies the case in which a negative bias (by means of the pulse Vd 4 ) is applied to the electrode D at a timing earlier than the start of an oscillation control (OSC) to advance a transition to the oscillation control (OSC) for the mirror  212 . 
         [0302]    Similar to the above described Exemplary Operation E, the operation is the same even if the sequence of the ON/OFF control pattern  451  and oscillation control pattern  452  is reversed. 
         [0303]    The present Exemplary Operation E and Operation E′ can also be used for improving a gray scale level as shown in the above described  FIG. 17 . When one frame is divided into a plurality of sub-frames for a display, the periods of the ON state or oscillation state of the mirror  212  may be changed for individual sub-frames by changing the timings and/or pulse widths of the pulse Vd 4  or pulse Vd 3  for each respective sub-frame. 
       &lt;Exemplary Operation - F&gt; 
       [0304]      FIG. 24  is a conceptual diagram showing an exemplary configuration of a gamma table according to the present exemplary operation. 
         [0305]    The present exemplary operation shows an exemplary structure of a gamma table when an improvement in a gray scale performance is attained by combining an oscillation control (OSC) and a PWM control. 
         [0306]    The above described individual exemplary operations dynamically changes the allocation of ON/OFF of time slots to the ON/OFF control pattern  451  and oscillation control pattern  452 , thereby attaining a higher number of gray scale levels than that attained by the control of the memory cells M 1  and M 2  in units of time slots. 
         [0307]    A description of Exemplary Operation F is provided for a gamma table  700  used for controlling a dynamic allocation of a time slot to the ON/OFF control pattern  451  and oscillation control pattern  452  for the above described Exemplary Operation A and so on. 
         [0308]    The present embodiment is configured to attain an improvement in the gray scale by distributing data (i.e., an ON/OFF setup) to the time slots ts of each subfield of the first subfield  601  through fourth subfield  604 , requiring a table corresponding to each subfield. 
         [0309]      FIG. 24  exemplifies the case in which the input gray scale data is 12-bit and the total number of time slots ts of one field consisting of the first subfield  601  through fourth subfield  604  is “ 155 ”. 
         [0310]    The 12-bit input gray scale data consists of four regions corresponding to the first subfield  601  through fourth subfield  604 , and a combination between OSC data  701 , which corresponds to the ON/OFF control pattern  451 , and PWM data  702 , which corresponds to the oscillation control pattern  452 , which is set to an individual region by a number equivalent to 12-bit gray scale levels. 
         [0311]    In the example shown in  FIG. 24 , 3 bits are assigned to the OSC data  701  and 9 bits are assigned to the PWM data  702 . 
         [0312]      FIG. 25  is a conceptual diagram showing an exemplary method for generating data for controlling the allocation of time slots ts to the ON/OFF control pattern  451  and oscillation control pattern  452  using the setup data of gamma table  700 . 
         [0313]      FIG. 25  exemplifies the control for the first subfield  601 . The control is the same for other subfields, i.e., the second subfield  602  through fourth subfield  604 . 
         [0314]    Defining the maximum number of time slots ts allocated to a predetermined oscillation control pattern  452  as “the number of within-OSC period time slots n 1 ”, a value (i.e., “011” in this case) obtained by subtracting the data of the ON/OFF control pattern  451  from the number of within-OSC period time slots n 1  is set to an OSC comparator setup value n 2 . 
         [0315]    The value of the OSC comparator setup value n 2  indicates a predetermined period (i.e., the number of OFF time slots ts) of maintaining the OFF state at the start of the oscillation control pattern  452 . 
         [0316]    Further, the number of total time slots of the first subfield  601  is set to the number of within-subfield total time slots n 3 . 
         [0317]    Further, the PWM data  702  (“001101” in this case) corresponding to the oscillation control pattern  452  is set to a PWM comparator setup value n 4 . 
         [0318]      FIG. 26  is a flow chart showing an exemplary control for assigning a time slot using the above described gamma table. 
         [0319]    The following is a description of the operation under the control of mirror control profile  450  in which the ON/OFF control pattern  451  follows after the oscillation control pattern  452 . 
         [0320]    First, a control variable N indicating the position of a focused time slot ts within a subfield is initialized to “0” (step  801 ). 
         [0321]    Then, it is determined in step  802  whether or not the control variable N has exceeded the number of within-subfield total time slots n 3 . If it has exceeded, the process for the present subfield is ended, the time slot ts is turned to OFF (i.e., the binary data=0) (step  813 ), and the process shifts to the processing of the next subfield (step  814 ). 
         [0322]    In contrast, if it is determined in step  802  that the control variable N does not exceed the number n 3 , then it is determined in step  803  whether or not the control variable N has exceeded the number of within-OSC period time slots n 1 ; that is, whether or not the processing of a time slot corresponding to the oscillation control pattern  452  has been completed. 
         [0323]    If the control variable N is no larger than the number n 1  (i.e., the result of step  803  is “No”), OSC mode=1 is set (step  804 ). Setting the “OSC mode=1” means that the mirror  212  is operated in the oscillation (OSC) mode by setting data (0, 0) to the memory cells M 1  and M 2  of the pixel unit  211  of the spatial light modulator  200 . 
         [0324]    In step  805 , whether or not the control variable N has exceeded the OSC comparator setup value n 2  is discerned. If not, (i.e., N≦n 2 ), the time slot ts corresponding to the present control variable N is turned to OFF (i.e., the binary data=0) (step  806 ). 
         [0325]    If in step  805 , N is determined to have a value greater than n 2  (i.e., N&gt;n 2 ), the time slot ts corresponding to the present control variable N is turned to ON (i.e., the binary data=1) (step  807 ). 
         [0326]    On the other hand, if the result of the above described step  803  is “yes” (i.e., N&gt;n 1 ), it indicates a transition to the range of time slots ts corresponding to the succeeding ON/OFF control pattern  451 , and therefore OSC mode=0 is set (step  809 ). The mirror  212  is operated in the ON/OFF mode by setting data (1, 0) or (0, 1) to the memory cells M 1  and M 2  of the pixel unit  211  of the spatial light modulator  200 . 
         [0327]    Then, it is determined in step  810  whether or not [N-n 1 ] has exceeded the PWM comparator setup value n 4 . The ON/OFF control pattern  451  is turned on (i.e., the binary data=1) in step  811  as long as the [N-n 1 ] does not exceed the value n 4  (i.e., [N-n 1 ]≦n 4 ). If the [N-n 1 ] value exceeds the value n 4 , then the ON/OFF control pattern  451  is turned off (i.e., the binary data=0) in step  812 . 
         [0328]    Then, following the above described steps  806 ,  807 ,  811  and  812 , the control variable N is incremented (step  808 ), and the process returns to step  802 . 
         [0329]    The above described control makes it possible to dynamically set and control the ON/OFF of each time slot ts in the oscillation control pattern  452  and ON/OFF control pattern  451  for each of the first subfield  601  through fourth subfield  604  in accordance with the input gray scale data. 
         [0330]      FIG. 27  is a table showing a specific setup example of the above described gamma table. 
         [0331]    Referring to  FIG. 27 , the gamma table  700  exemplifies a data structure in the case of controlling the reflection light intensity of the mirror  212  so as to decrease it by ⅛ OSC for each step (i.e., each row) starting from the top step. 
         [0332]    For example, the pixel unit  211  is implemented with the second OFF electrode  236  (i.e., the electrode B) shown in  FIG. 9 . When the bit in the bold line box is a bit “1”, with the bit on the right side set as a bit “0”, each piece of data of the first subfield  601  through third subfield  603  is applied to the electrode B to carry out the mirror control process according to the data in for each of the first subfield  601  through third subfield  603 . 
         [0333]    In this case, even if the number of time slots in which the data is “1” is the same, the light intensities can be changed (i.e., a gray scale control) by a method of setting the data to each time slot ts. 
         [0334]    In the gamma table  700  of  FIG. 27 , the first and second rows from the top have the same number of time slots with the data “1” (26 slots). The difference in light intensity, i.e., 1721.875 (for the first row) and 1709.375 (for the second row), is due to the different positions of the time slots ts in which the data is “1”. 
         [0335]      FIG. 28  is a table showing an exemplary modification of the structure of a gamma table; and  FIG. 29  is a timing diagram showing an exemplary setup of a mirror control profile in order to describe the exemplary modification shown in  FIG. 28 . 
         [0336]    As an example, consider the case shown in  FIG. 29  in which, assuming that a light intensity at one time-slot ts of the oscillation control pattern  452  is 25% of the light intensity at one time-slot ts of the ON/OFF control pattern  451 , three time-slots ts are allocated to the oscillation control pattern  452  and a stepwise change in the gray scale is attempted by the number of ON time slots ts in the oscillation control pattern  452  so as to increase the number of gray scale levels by one step, such as 0% (when the number of ON time slot ts is “0”), 25% (when the number of ON time slots ts is “1”), 50% (when the number of ON time slots ts is “2”) and 75% (when the number of ON time slots ts is “3”)shown. 
         [0337]    As such, assuming that the OSC light intensity of one time-slot ts of the oscillation control pattern  452  is 25% of the PWM light intensity of one time-slot ts of the ON/OFF control pattern  451 , the OSC changes by one level of gray scale for every one time-slot, and therefore the change is one PWM for four gray scale levels of the OSC. 
         [0338]    In this event, if a light intensity obtained in one ON time slot ts of the oscillation control pattern  452  is, for example, 40% of the light intensity obtained in the ON time slot ts of the ON/OFF control pattern  451  (i.e., the case of the gamma table  700 A shown in  FIG. 28 ) caused by a variation in the reflectance of the mirror  212  or another variation, a control to increase the number of ON time slots ts of the oscillation control pattern  452  one by one generates a reversal of gray scale levels (i.e., the number of gray scale levels decreases with the number of ON time slots ts), making it difficult to carry out an accurate gray scale control. 
         [0339]    In such a case, shown by replacing data, such as replacing the data in gamma table  700 A replaced with the data in gamma table  700 B ( FIG. 28 ), an accurate a gray scale representation is attained without being affected by variations in the production of the mirror  212 , et cetera. This configuration can also be applied to a case in which the light intensity adjustment of the OSC is designated at an odd number times (excluding “1”), the desired adjustment in Exemplary Operation D. 
       &lt;Exemplary Operation - J&gt; 
       [0340]      FIG. 30  is a conceptual diagram showing an exemplary modification of the circuit configuration of the pixel unit shown in  FIG. 10 . 
         [0341]    The circuit of a pixel unit  211  according to the exemplary modification shown in  FIG. 30  is configured such that the ON electrode  216  (i.e., the electrode C) and memory cell M 2  are removed from the comprisal of  FIG. 24  and such that the control for the ON side of the mirror  212  is carried out using the second ON electrode  235  (i.e., an electrode D) connected to the plate line  232 . 
         [0342]      FIG. 31  is a timing diagram showing an exemplary control of a pixel unit configured as shown in  FIG. 30 . The circuit requires only one OFF capacitor  215   b  that can be placed in the entire area under the mirror  212  to increase the capacitance of the capacitor. This configuration makes it possible to attain an element structure that is robust against a voltage drop due to leakage and against voltage fluctuations due to a photoelectric effect. 
         [0343]    As shown in  FIG. 31 , starting from a state in which the mirror  212  is in the OFF state (i.e., the voltage Va of the electrode A is maintained at H (“1”), and the memory cell M 1  is maintained at H (“1”)) and in which the voltage Vd of the electrode D placed on the ON side is maintained at H (“1”), the value of the voltage Va of the electrode A is turned to L (i.e., the memory cell M 1  is turned to L (“0”)) at a timing of the time slot number corresponding to the number of gray scale levels to be displayed. The mirror  212  is then turned to the ON state because the voltage Vd of the electrode D placed on the ON side is maintained at H. 
         [0344]    After entering the control period under the oscillation control pattern  452  (OSC), the voltage Vd of the electrode D is turned to L (“0”) and the mirror  212  starts oscillating (OSC). If the oscillation (under the oscillation control pattern  452 ) of the mirror  212  needs to be ended, the value of the voltage Va of the electrode D is turned to H (i.e., the memory cell M 1  is turned to H (“1”)). 
         [0345]    Further, if the voltage Va of the electrode A is maintained in the state of H (“1”), the mirror  212  is maintained in the OFF state regardless of a change in the voltages Vd of the electrode D. In the above description, the electrode D is commonly connected for each ROW in the exemplary configuration. It is, however, also possible to commonly connect the electrode D for all pixels and turn off the entirety in synch with the end of the ON state of the mirror  212 . Further, it is also possible to fix the electrode D to a ground potential (GND) and apply a voltage only to the ON side of the mirror  212 . 
         [0346]      FIG. 32  is a timing diagram showing an exemplary modification of the operation of a pixel unit configured as shown in  FIG. 30 . 
         [0347]      FIG. 32  shows the waveform of a mirror control profile  450  in the case of generating an intermediate oscillation using the electrode D. 
         [0348]    Specifically, a mirror  212  shifting from the ON state to the OFF state is brought back to the ON side temporarily by applying a Vd 5  to the voltage Vd of the electrode D immediately after the voltage Vd is turned to L (“0”) for shifting from the ON/OFF control pattern  451  to the oscillation control pattern  452 . Thereby, an oscillation control pattern  452  for an intermediate oscillation causing the mirror  212  to oscillate in a narrow amplitude is attained. 
         [0349]    Further, by maintaining the voltage Va of the electrode A at H (“1”), the mirror  212  is maintained in the OFF state even if the voltage Vd of the electrode D is given a change, including a pulse Vd 5 . 
         [0350]      FIG. 33  is a timing diagram showing an exemplary modification of the operation of a pixel unit configured as shown in  FIG. 30 . 
         [0351]      FIG. 33  exemplifies a waveform when a gray scale is represented by the mirror control profile  450  consisting of only the non-binary ON/OFF control pattern  451  (that is, not including an OSC, i.e., a full oscillation or intermediate oscillation of the mirror  212 ). 
         [0352]    In the case of  FIG. 33 , the control is such that, within a subfield, either the voltage Va of the electrode A or the voltage Vd of the electrode D is turned to H (“1”) and the other is turned to L (“0”). 
         [0353]    As such, the pixel unit  211  shown in  FIG. 30  is configured to connect the electrode D on the ON side to the plate line  232  and to eliminate a memory cell M 2  and ON electrode  216  (i.e., an electrode C), decreasing the number of circuit elements than a configuration in which the OFF side and ON side are furnished individually with the memory cells M 1  and M 2 , respectively. Therefore, the production yield of pixel arrays  210  (i.e., the spatial light modulator  200 ) comprising a large number of pixel units  211  is improved. 
         [0354]    Also, in order to reduce the size each pixel unit  211  so as to place a larger number of pixel units  211  within a pixel array  210  of a certain size, a transistor of the same size (that is, the same withstanding voltage), as a transistor constituting the memory cell M 1  on the OFF side, can be used. Thereby the reliability of the operations of the pixel units  211  and spatial light modulator  200  can be maintained and improved. 
         [0355]    Further, even for the same pixel size, it is possible to enlarge a gate transistor  216   c,  which improves the withstanding voltage. A high drive voltage enables high speed operation of the mirror  212  and the tilting of the mirror  212 , even if the hinge  213  is strengthened as a countermeasure to stiction. Meanwhile, the number of masks used in the production process employing a photolithography process can be reduced by configuring the OFF capacitor  215   b  of the memory cell M 1  using a poly-capacitor (i.e., a MOS capacitor) in place of the aluminum capacitor. Also, even for the same area size of poly-capacitor, a larger size lengthens the voltage support time of the memory cell M 1 , enabling a lower speed (i.e., a required speed is relaxed) write cycle of the memory cell M 1 . 
       &lt;Exemplary Operation - J′&gt; 
       [0356]      FIG. 34  is a conceptual diagram showing an exemplary modification of the circuit configuration of the pixel unit shown in  FIG. 30 . 
         [0357]    The exemplary configuration of the pixel unit  211  shown in  FIG. 34  is a configuration that combines the word line  231  and plate line  232 , eliminating the latter. 
         [0358]      FIG. 35  is a timing diagram showing an exemplary operation of the pixel unit  211  shown in  FIG. 34 . In this case, the ON/OFF control and oscillation control of the mirror  212  is the same as those for the configuration in  FIG. 30 . The difference in this case is in the control, where voltage Vd is a positive (+) level (i.e., a pulse Vd 6 ) when the word line writes data to the memory cell M 1 , and where voltage Vd is switched to a negative (−) level during the period of attracting the mirror  212  to the ON side, and such that the voltage Vd is at zero potential during the period of an oscillation control (OSC). 
         [0359]      FIG. 36  is a timing diagram showing an exemplary modification of the control shown in  FIG. 35 . 
         [0360]    The mirror control profile  450  of  FIG. 36  shows the waveform for generating an intermediate oscillation of the mirror  212  using the electrode D in the configuration shown in  FIG. 34 . 
         [0361]    In this case, a pulse Vd 7  is applied, as the voltage Vd of the electrode D, in order to attain the intermediate oscillation of the mirror  212  by temporarily returning the mirror  212  to the ON side when it shifts from the ON to OFF states. In addition, for each time slot, ts, a pulse Vd 6  is applied for writing data to the memory cell M 1 . 
         [0362]    Specifically, the gate transistor  215   c  driven by the word line  231  is not operated when the voltage Vd is in a negative bias and therefore the voltage Va of the electrode A is not changed. The electrodes A and D are controlled by utilizing the generation of Coulomb force in the electrode D, to which the voltage Vd is applied, even if the aforementioned voltage Vd is negative. 
         [0363]      FIG. 37  is a timing diagram showing an exemplary modification of the control shown in  FIG. 35 . 
         [0364]      FIG. 37  shows the waveform of a mirror control profile  450  when a gray scale representation is carried out only by a non-binary ON/OFF control pattern  451  for the mirror  212 . 
         [0365]    In this case, the voltage Vd of the electrode D is maintained at negative (−) other than during pulse Vd 6 . 
         [0366]    As such, the pixel unit  211  shown in  FIG. 34  is configured to control the OFF electrode  215  (i.e., the electrode A) and second ON electrode  235  (i.e., the electrode D) using only the word line  231 , leaving only one string of the word line  231  as the wiring along the ROW direction of the pixel unit  211  of the pixel array  210 , thereby making it possible to increase the speed of driving the word line  231  because of the reduction of the stray capacitance of the wiring. 
         [0367]    It is further possible to miniaturize the spatial light modulator  200  by eliminating a line driver (i.e., the word line driver  230   b ) used for driving the word line  231 . 
       &lt;Exemplary Operation - J″&gt; 
       [0368]      FIG. 38  is a conceptual diagram showing an exemplary modification of the pixel unit shown in  FIG. 34 .  FIG. 38  is different from the configuration shown in  FIG. 34  in that the ON side and OFF side are symmetrical. 
         [0369]    The OFF electrode  215  (i.e., the electrode A and the memory cell M 1 ) on the OFF side and the second ON electrode  235  (i.e., the electrode D) on the ON side are controlled by a common word line  231   a.  Likewise, the ON electrode  216  (i.e., an electrode C and the memory cell M 2 ) on the ON side and the second OFF electrode  236  (i.e., the electrode B) on the OFF side are controlled by a common word line  231   b.    
         [0370]    This configuration inversely controls the set of electrodes A and D using the word line  231   a  (and the bit line  221 - 1 ) and the set of electrodes C and B using the word line  231   b  (and the bit line  221 - 2 ), thereby making it possible to symmetrically change over the ON operation of the mirror  212  and the OFF operation. 
         [0371]    For example, if the direction of a light  511  incident to a spatial light modulator  200  is completely reversed, the ON/OFF operation of a mirror  212  can be changed over in accordance with the incidence direction of the light  511  by controlling the word line  231   a  and word line  231   b.    
         [0372]      FIGS. 39 and 40  are timing charts showing the control waveform of the mirror control profile used for the pixel unit in a symmetrical configuration, as shown in  FIG. 38 . 
         [0373]    In  FIGS. 39 and 40 , the signal levels of all signal waveforms are symmetrical to each other. 
         [0374]    Specifically, in  FIG. 39 , the control for the voltage Va of the electrode A and the voltage Vd of the electrode D, both of which are controlled by the word line  231   a , is similar to the case of the above described  FIG. 35 . 
         [0375]    In contrast, the electrode C (at the voltage Vc) and the electrode B (at the voltage Vb), both of which are controlled by the word line  231   b , are supplied with a pulse Vb 6  by the cycle of time slots ts against the voltage Vb, while a data loading to the memory cell M 2  (i.e., the ON side) from the bit line  221 - 2  is suppressed, and therefore the operation of the mirror  212  moving towards the ON side is carried out by the voltage Vc of the electrode C. 
         [0376]    Meanwhile, in  FIG. 40 , in which the waveforms of the individual signals are symmetrical to those of  FIG. 39 , a reverse operation to the above description is carried out so that the OFF operation of the mirror  212  is carried out by the pulse Vb 6  on the voltage Vb loading data onto the memory cell M 2  (i.e., on the OFF side) using the bit line  221 - 2 . While, in electrodes A and B, both of which are controlled to the ON side, a data loading onto the electrode A (i.e., the memory cell M 1 ) using the bit line  221 - 1  is not carried out, and therefore the operation for attracting the mirror  212  to the ON side is controlled by the change in potentials (i.e., negative, zero and positive) of the voltage Vb (i.e., the pulse Vb 6 ) of electrode B. 
         [0377]      FIGS. 41 and 42  are timing charts showing the waveform of a mirror control profile in order to attain an intermediate oscillation in the pixel unit configured as shown in  FIG. 38 . 
         [0378]      FIG. 41  shows a waveform when operating the electrode B as the OFF side and the electrode D as the ON side. With the operation, the mirror is returned to the ON side to attain an intermediate oscillation by applying a pulse Vd 7  to the voltage Vd of the electrode D when the mirror  212  is shifting from the ON to OFF states. 
         [0379]    Meanwhile,  FIG. 42  shows a waveform when operating the electrode B as the ON side and the electrode D as the OFF side. With the operation, an intermediate oscillation of the mirror  212  is attained by applying a pulse Vb 7  to the voltage Vb of the electrode B. 
         [0380]      FIGS. 43 and 44  are timing charts showing an exemplary waveform in the case of performing a gray scale representation by driving the pixel unit configured as shown in  FIG. 38  with a non-binary ON/OFF control pattern, not including an oscillation control. 
         [0381]    Specifically,  FIG. 43  shows an example of making the electrode A (or electrode B) function as the OFF side and making the electrode D (or electrode C) function as the ON side. In contrast,  FIG. 44  shows an example of making the electrode A (or electrode B) function as the ON side and making the electrode D (or electrode C) functions as the OFF side. 
         [0382]    A spatial light modulator  200  comprising the pixel unit  211 , configured as shown in  FIG. 38 , in which the ON side and OFF side are symmetrically configured, may be placed among a plurality of light sources of varying colors The ON operation and OFF operation may be mutually reversed by means of controlling. the word lines  231   a  and  231   b  when, for example, a color display is implemented by synthesizing a plurality of incident lights  511  using a plurality of spatial light modulators  200  assigned to the respective colors, thereby eliminating the need for a spatial light modulator  200  comprising pixel units  211  configured differently for the individual light sources with different incidence directions of the lights  511 , and thus making it possible to manufacture a lower cost display apparatus carrying out a color display by means of a synthesis using an optical system comprising a plurality of spatial light modulators  200 . 
         [0383]      FIG. 45  is a functional block diagram showing an exemplary control function equipped in the control apparatus of a projection apparatus according to the present embodiment. 
         [0384]    The control apparatus  300  shown in  FIG. 45  is equipped. with a control logic  301  for determining whether or not to improve a gray scale representation by means of a light intensity control in the equivalence of a time slot ts, or less, with the signal width (i.e., 10-bit or 12-bit in this case) of a binary video signal  400  to the control apparatus  300  by placing the electrodes D and B, as described above in the preferred embodiments. 
         [0385]    Further, as shown in the upper half of  FIG. 45 , when a 12-bit width binary video signal  400  is inputted to the control apparatus  300 , the control logic  301  instructs the spatial light modulators  200  to carry out a light intensity control in no more than the time width of the time slot ts shown in  FIG. 17A  and other figures. 
         [0386]    Meanwhile, as shown on the lower half of  FIG. 45 , when a 10-bit width binary video signal  400  is inputted to the control apparatus  300 , the control logic  301  instructs the spatial light modulators  200  to carry out a light intensity control in no more than the time width of the time slot ts, shown in  FIG. 17A  and other figures, for only the first subfield  601  and not to carry it out for the rest of the subfields, i.e., the second subfield  602  through fourth subfield  604 . 
         [0387]      FIG. 46  is a functional block diagram showing an exemplary control function equipped in the control apparatus of a projection apparatus according to the present embodiment. 
         [0388]      FIG. 46  exemplifies the case of changing over light intensity controls in no more than the time width of a time slot ts for each subfield in accordance with the average picture level (APL) of a binary video signal  400  inputted to the control apparatus  300 . 
         [0389]    Specifically, the control apparatus  300  is equipped with a subfield sequencer  303  for changing over light intensity controls in no more than the time width of a time slot ts for each subfield and with an APL detector  304  for detecting the APL of the binary video signal  400 . 
         [0390]    Further, the subfield sequencer  303  performs a light intensity control in no more than the time width of a time slot ts in each of the first subfield  601  through fourth subfield  604 , as described above in accordance with the value of the average picture level (APL) of the binary video signal  400  inputted from the APL detector  304 . The necessary gray scale characteristic and gamma characteristic may be obtained by a configuration by means of the control in accordance with the APL. 
         [0391]      FIG. 47  is a functional block diagram showing an exemplary control function of a projection apparatus according to the present embodiment. 
         [0392]    In addition to being equipped with the control apparatus  300 , the projection apparatus  100  shown in  FIG. 47  is equipped with an input source detector  340  for discerning the category of an input binary video signal  400 . 
         [0393]    The input source detector  340  discerns, for example, whether a binary video signal  400  is a digital input video signal  400   a  such as a digital visual interface (DVI) or an analog input video signal  400   b.  It inputs the discernment result to the control apparatus  300  so that it instructs the spatial light modulator  200  to change over light intensity controls in no more than the time width of a time slot ts in accordance with the appropriate category of the video signal inputted from the input source detector  340   
         [0394]      FIGS. 48A and 48B  are timing charts showing an exemplary waveform of a mirror control profile. 
         [0395]      FIGS. 48A and 48B  exemplifies the case of changing over light intensity controls in no more than the time width of a time slot ts for each frame of a color sequence display (consisting of a plurality of subfields, i.e., the first subfield  601  through fourth subfield  604 ). 
         [0396]    Specifically,  FIG. 48A  exemplifies the control waveforms for the first subfield  601  through fourth subfield  604  constituting the frame corresponding to green (G);  FIG. 48B  exemplifies the control waveforms for the first subfield  601  through fourth subfield  604  constituting the frame corresponding to red (R). 
         [0397]    The frame of green shown in  FIG. 48A  exemplifies the case in which the light intensity controls of 1+⅛ (OSC), 1+¼ (OSC) and 1+½ (OSC) for the first subfield  601  through third subfield  603 ,, totaling 3+⅞ (OSC), are carried out, and the light intensity control of −3 for the fourth subfield  604  is carried out. As a result, light intensity is increased by the amount of ⅞ (OSC) for the entirety of the green frame. 
         [0398]    Meanwhile, the frame of red shown in  FIG. 48B  exemplifies the case in which the light intensity controls of +1, +1 and 1+½ for first subfield  601  through third subfield  603 , totaling 2+½, are carried out, and the light intensity control of −3 for the fourth subfield  604  is carried out. As a result, the light intensity control of −½ (OSC) is carried out for the entirety of the red frame. 
         [0399]    As such, the examples shown in  FIGS. 48A and 48B  are configured to perform the light intensity controls in which the time widths of a time slot ts are different for the green frame and red frame. 
         [0400]    These controls improve the gradation of an image by, for example, making a change in gray scale levels large for the green frame with which the sensitivity of the human eye is high, while making a change in gray scale levels small for colors with which the sensitivity of human eye is low, such as red and blue. 
         [0401]      FIG. 49  is a timing diagram showing an exemplary timing diagram shown in  FIG. 17A , with a part of the chart enlarged. 
         [0402]    With reference to  FIG. 49 , the relationship between the pulse Vd 2 , on the voltage Vd of the electrode D, and a pulse Vw 1 , on the voltage Vw of the word line  231 , used for determining the timing of a data loading onto the memory cell M 1  (and the memory cell M 2 ) for each time slot ts will be examined. 
         [0403]    The exemplary timing control (c) on the right side of  FIG. 49  exemplifies the case of setting the start timing of the pulse Vd 2  earlier than the start timing of the pulse Vw 1  and also of setting the width of the pulse Vd 2  wider than that of the pulse Vw 1 . 
         [0404]    Under the exemplary timing control (c), the mirror  212  is stopped in the ON state by the Coulomb force generated by the ON electrode  216  (i.e., the electrode C). In this state, the Coulomb force generated by the electrode D (i.e., the second ON electrode  235 ) placed on the ON side is applied to the mirror  212 , and thereby the mirror  212  is tilted onto the ON electrode  216 . This operation makes it possible to maintain the mirror  212  stationary in the ON state. 
         [0405]    In the exemplary timing control (c), however, there may be the possibility of stiction. That is, the mirror  212  may be stuck on the ON side. 
         [0406]    Accordingly, the exemplary timing control (b) at the center of  FIG. 49  is configured to set the timing so as to start the pulse Vd 2  on the electrode D after the pulse Vw 1  on the word line  231  and to turn ON the electrode D by giving the pulse Vd 2  after the data of the memory cell M 1  (and the memory cell M 2 ) are exchanged by the pulse Vw 1  on the word line  231 . In this case, although there is no concern for a problem of stiction, the mirror  212  may start to freely move immediately depending on the state of data transition in the memory cell M 1  (and the memory cell M 2 ). 
         [0407]    As an intermediate case between the above described exemplary timing controls (b) and (c), the exemplary timing control (a) on the left side of  FIG. 49  is configured to set the start timing of the pulse Vw 1  on the word line  231  and that of the pulse Vd 2  on the electrode D to be simultaneous. By doing so, the control of the word line  231  and plate line  232  can be simplified. 
         [0408]      FIG. 50  is a top view diagram showing the layout configuration of an electrode of the pixel unit shown in  FIG. 12C  (and  FIG. 8 ). 
         [0409]      FIG. 51  is a timing diagram showing an exemplary modification of d  FIG. 17 . 
         [0410]    As shown in  FIG. 50 , on the ON side of the pixel unit  211 , the area size of the electrode C is larger than that of the electrode D. 
         [0411]    Therefore, if the voltage Vc of the electrode C and the voltage Vd of the electrode D are the same, the Coulomb force Fc functioning between the electrode C and the mirror  212  is larger than the Coulomb force Fd functioning between the electrode D and the mirror  212 . 
         [0412]    The timing diagram shown in  FIG. 51  exemplifies the setting of mutually different values between the voltage value V 2  of the pulse Vd 2  applied to the electrode D and voltage value VI at H (“1”) of the voltage Vc of the electrode C, thereby allowing for the discretionary adjustment of the magnitude between Coulomb forces Fd and Fc. 
         [0413]      FIG. 52  is a conceptual diagram showing the configuration of a projection apparatus according to a preferred embodiment of the present invention. 
         [0414]    The following is a description of an exemplary configuration of a projection apparatus  100  using, as a spatial light modulator  5100 , the spatial light modulator  200  comprising the above described pixel unit  211  shown in  FIGS. 8 ,  9  and  10 , and further exemplary modification thereof. 
         [0415]    As shown in  FIG. 52 , a projection apparatus  5010  according to the present embodiment comprises a single spatial light modulator (SLM)  5100  (i.e., the spatial light modulator  200 ), a control unit  5500  (i.e., the control apparatus  300 ), a Total Internal Reflection (TIR) prism  5300 , a projection optical system  5400  and a light source optical system  5200 . 
         [0416]    The spatial light modulator  5100  is constituted by the above described spatial light modulator  200  comprising the plate line  232 . 
         [0417]    The projection apparatus  5010  is commonly referred to as a single-panel projection apparatus  5010  comprising a single spatial light modulator  5100 . 
         [0418]    The projection optical system  5400  is equipped with the spatial light modulator  5100  and TIR prism  5300  in the optical axis of the projection optical system  5400 , and the light source optical system  5200 , which is equipped in such a manner that the optical axis thereof matches that of the projection optical system  5400 . 
         [0419]    The TIR prism  5300  causes the illumination light  5600 , incoming from the light source optical system  5200  placed onto the side, to enter the spatial light modulator  5100  at a prescribed inclination angle as incident light  5601  and causes a reflection light  5602 , reflected by the spatial light modulator  5100 , to transmit to the projection optical system  5400 . 
         [0420]    The projection optical system  5400  projects the reflection light  5602  as projection light  5603  to a screen  5900 . 
         [0421]    The light source optical system  5200  comprises a variable light source  5210  for generating the illumination light  5600 , a condenser lens  5220  for focusing the illumination light  5600 , a rod type condenser body  5230 , and a condenser lens  5240 , all of which are sequentially placed in the aforementioned order in the optical axis of the illumination light  5600 , which is emitted from the variable light source  5210  and incident to the side face of the TIR prism  5300 . 
         [0422]    The projection apparatus  5010  employs a single spatial light modulator  5100  for implementing a color display on the screen  5900  by means of a sequential color display method. 
         [0423]    Specifically, the variable light source  5210 , comprising a red laser light source  5211 , a green laser light source  5212  and a blue laser light source  5213  (which are not shown in the drawing), allows independent controls for the light emission states and divides one frame of display data into a plurality of sub-fields (i.e., three sub-fields, that is, red (R), green (G) and blue (B) in the present case). It further causes each of the red  5211 , green  5212  and blue  5213  laser light sources to emit each respective light in a time series at the time band corresponding to the sub-field of each color, as described later. 
         [0424]      FIG. 53  is a functional block diagram for showing a configuration of the control unit  5500  implemented in the above described single-panel projection apparatus  5010 . The control unit  5500  comprises a frame memory  5520 , an SLM controller  5530 , a sequencer  5540 , a light source control unit  5560  and a light source drive circuit  5570 . 
         [0425]    The sequencer  5540 , includes a microprocessor to control the operation timing of the entire control unit  5500  and the spatial light modulators  5100 . 
         [0426]    In one exemplary embodiment, the frame memory  5520  retains one frame of input digital video data  5700  received from an external device (not shown in the figure) connected to a video signal input unit  5510 . The input digital video data  5700  is updated in real time whenever the display of one frame is completed. 
         [0427]    The SLM controller  5530  processes the input digital video data  5700  read from the frame memory  5520 , as described later. The SLM controller separates the data, read from the memory  5520 , into a plurality of sub-fields according to detailed descriptions below. The SLM controller outputs the data subdivided into subfields to the spatial light modulators  5100  as binary data  5704  and non-binary data  5705 , which are used for implementing an the ON/OFF control and oscillation control (which are described later) of a mirror  5112  of the spatial light modulator  5100 . 
         [0428]    The sequencer  5540  outputs a timing signal to the spatial light modulators  5100  in sync with the generation of the binary data  5704  and non-binary data  5705  at the SLM controller  5530 . 
         [0429]    The video image analysis unit  5550  outputs a image analysis signal  5800  used for generating various light source pulse patterns (which are described later) corresponding to the input digital video data  5700  inputted from the video signal input unit  5510 . 
         [0430]    The light source control unit  5560  controls, by way of the light source drive circuit  5570 , the operation of the variable light source  5210  emitting the illumination light  5600  on the basis of the video image analysis signal  6800  obtained from the video image analysis unit  5550 , by way of the sequencer  5540 . 
         [0431]    The light source drive circuit  5570  drives the red laser light source  5211 , green laser light source  5212  and blue laser light source  5213  of the variable light source  5210  to emit light on the basis of instruction from the light source control unit  5560 . 
         [0432]      FIG. 54  is a conceptual diagram showing another exemplary modification of a multi-panel projection apparatus according to the present embodiment. 
         [0433]    The projection apparatus  5040  is configured to position, so as to be adjacent to one another in the same plane, a plurality of spatial light modulators  5100  (i.e., the spatial light modulators  200 ) corresponding to the three colors R, G and B on one side of a light separation/synthesis optical system  5330 . 
         [0434]    This configuration makes it possible to consolidate a plurality of spatial light modulators  5100  into the same packaging unit, for example, a package  201 , thereby saving space. 
         [0435]    The light separation/synthesis optical system  5330  comprises a TIR prism  5331 , a TIR prism  5332  and a TIR prism  5333 . 
         [0436]    The TIR prism  5331  has the function of guiding illumination light  5600 , incident in the lateral direction of the optical axis of the projection optical system  5400 , to the spatial light modulators  5100  as incident light  5601 . 
         [0437]    The TIR prism  5332  has the functions of separating red light from the incident light  5601  and guiding it to the red color-use spatial light modulator  5100  and also of capturing the reflection light  5602  of the separated incident light and guiding it to the projection optical system  5400 . 
         [0438]    Likewise, the TIR prism  5333  has the functions of separating the incident green and blue lights from the incident light  5601 , making them incident to the individual spatial light modulators  5100  equipped correspondently to the each color, and of capturing the reflection lights  5602  of the respective colors to guide them to the projection optical system  5400 . 
         [0439]      FIG. 55  is a block diagram showing an exemplary configuration of the control unit of a multi-panel projection apparatus according to the present embodiment. 
         [0440]    The control unit  5502  comprises a plurality of SLM controllers  5531 ,  5532  and  5533  used for controlling each of the spatial light modulators  5100  equipped for the respective colors R, G and B, and the configuration of the controllers is the main difference from the above described control unit  5500 . 
         [0441]    Specifically, each of the SLM controller  5531 , SLM controller  5532  and SLM controller  5533 , is implemented to process the modulation of a specific color, Red, Green, and Blue. Each modulator is supported on the same substrate as those of the other spatial light modulators  5100 . This configuration makes it possible to place the individual spatial light modulators  5100  and the corresponding SLM controller  5531 , SLM controller  5532  and SLM controller  5533  close to each other, thereby enabling a high speed data transfer rate. 
         [0442]    Further, a system bus  5580  is used to connect the frame memory  5520 , light source control unit  5560 , sequencer  5540  and SLM controllers  5531  through  5533 , in order to speed up and simplify the connection path of each connecting element. 
         [0443]      FIG. 56  is a conceptual diagram showing an exemplary modification of a multi-panel projection apparatus according to another preferred embodiment of the present invention. 
         [0444]    An exemplary case of the projection apparatus  5020  shown in  FIG. 56  is equipped with two spatial light modulators  5100  (i.e., the spatial light modulators  200 ), each of which comprises the above described plate line  232 . One spatial light modulator  200  modulates the green light, while the other spatial light modulator  200  modulates the red and blue lights. 
         [0445]    The projection apparatus  5020  comprises a dichroic mirror  5320  as a light separation/synthesis optical system. The dichroic mirror  5320  separates the wavelength component of green light and the wavelength components of red and blue lights from the incident light  5601  from the light source optical system  5200 , causing them to branch into the two spatial light modulators  200 , respectively. The dichroic mirror  5320  further synthesizes the reflection lights  5602  of the green light with the reflection lights of the red and blue light, each reflected (i.e., modulated) by the corresponding spatial light modulators  200 , to guide the synthesized light to the optical axis of the projection optical system  5400 , which projects the synthesized light onto a screen  5900  as projection light  5603 . 
         [0446]      FIG. 57  is a functional block diagram showing an exemplary configuration of a control unit  5506  equipped in the projection apparatus  5020  comprising the above described two spatial light modulators  200 . In this case, the SLM controller  5530  controls two spatial light modulators  5100  (i.e., the spatial light modulators  200 ), which is the only difference from the configuration shown in  FIG. 53 . 
         [0447]      FIG. 58  is a chart showing the waveform of a control signal of the projection apparatus according to the present embodiment. 
         [0448]    A drive signal (i.e., a mirror control profile  450  shown in  FIG. 58 ) generated by the SLM controller  5530  drives a plurality of spatial light modulators  5100 . 
         [0449]    The light source control unit  5560  generates a light source profile control signal  5800  corresponding to the mirror control profile  450 , a signal for driving an individual spatial light modulators  5100 , and inputs the generated signal to the light source drive circuit  5570 , which then adjusts the intensity of the laser light (i.e., the illumination light  5600 ) emitted from each of the red  5211 , green  5212  and blue  5213  laser light source. 
         [0450]    The control unit  5506  comprised in the projection apparatus  5020  is configured such that a single SLM controller  5530  drives the plurality of spatial light modulators  5100 , thereby enabling the irradiation of the illumination light  5600  on the respective spatial light modulators  5100  with the optimal intensity of light without the need to comprise a light source control unit  5560  or light source drive circuit  5570  for each spatial light modulator  5100 . This configuration simplifies the circuit configuration of the control unit  5506 . 
         [0451]    As shown in  FIG. 58 , the light source control unit  5560  and light source drive circuit  5570  drives the red  5211 , green  5212  and blue  5213  laser light source so as to adjust the intensities of individual lasers (i.e., illumination light  5600 ) of the colors R, G and B in synch with the respective SLM drive signals (i.e., the mirror control profile  450 ) that is generated by the SLM controller  5530 . 
         [0452]    In this case, two colors R and B share one spatial light modulator  5100 , and therefore, the control is a color sequential method. 
         [0453]    Specifically, one frame is constituted by a plurality of subfields, that is, subfields  6701 ,  6702  and  6703 , and the same light source pulse pattern  6815  is repeated in each subfield in one spatial light modulator  5100  corresponding to green (G). 
         [0454]    Meanwhile, for the red (R) and blue (B) lights that share one spatial light modulator  5100 , the pulse emission of the red laser light source  5211  and blue laser light source  5213  are respectively controlled so that the subfields, that is, subfields  6701  through  6703 , are alternately used in a time series as indicated by the light source pulse pattern  6816  and light source pulse pattern  6817 . 
         [0455]    Further, in this case, the emission pulse intervals ti and emission pulse widths tp can be changed in each of the light source pulse pattern  6815  of the green laser, the light source pulse pattern  6816  of the red laser, and the light source pulse pattern  6817  of the blue laser. 
         [0456]    The present embodiment makes it possible to improve the number of gray scale levels for each of the colors R, G and B. Combined with the above described method of mirror control achieving a higher number of gray scale levels, it is possible to attain an extremely high grade gray scale up to 12-bit, 14-bit, 16-bit, 18-bit and higher without a need to change a low image transfer rate likewise the conventional 6- to 8-bit. Furthermore, the capability makes it possible to set for a free grayscale characteristic. 
         [0457]    The present invention makes it possible to provide a technique enabling the implementation of a higher-grade gray scale of a display image in a technique for displaying an image employing a spatial light modulation technique without increasing the operating frequency of a control circuit for controlling a spatial light modulator. 
         [0458]    The present invention may be modified or changed in various manners possible within the spirit and scope of the present invention and is not limited to the configurations put forth in the above described embodiments. 
         [0459]    More specifically, the present invention may include embodiments in various manners possible and would be within the scope of the present invention. Although the present invention has been described by exemplifying the presently preferred embodiments, it shall be understood that such disclosure is not to be interpreted as limiting. Various alternations and modifications will no doubt become apparent to those skilled in the art after reading the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alternations and modifications as falling within the true spirit and scope of the invention.