Abstract:
In the case of conducting an overdriving with a liquid crystal display device, the circuit for comparing the previous and present gray-scale data, the circuit for converting the gray-scale data upon the comparison result, and the like complicate the structure of the liquid crystal display device. Further, since hold driving by which the voltage applied is kept throughout one frame period is conducted in a liquid crystal display device, it is not sufficient to decrease the rise time due to high applied voltage for a countermeasure against blur of moving images. In the present invention, in one frame period, a high voltage is applied to a liquid crystal element and a constant voltage is applied after the high voltage is applied. The absolute value of the high voltage is equal to or higher than the constant voltage, in other words, equal to or higher than a reference voltage. Further, a rectangular wave within the high voltage application period (also referred to as a pulse) has a plurality of pulses having periods shorter than the rise time τ ON .

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a liquid crystal display device having high response speed and a method for driving the same using applied voltage waveform for achieving high response speed. 
     2. Description of the Related Art 
     An active matrix driving method has conventionally been used for conducting multiple gray-scale display using a liquid crystal display device. The active matrix driving method is a method in which a reference voltage corresponding to a display gray-scale is selected with an analog switch, and the selected voltage is applied to a liquid crystal display device to display a desired display gray-scale. One gray-scale is generally displayed in a period in which an image is displayed (one frame), and a predetermined reference voltage corresponding to the desired gray-scale is applied to the liquid crystal display device. 
     When change in the voltage applied to the liquid crystal display device is small, the time within which the desired gray-scale is obtained (response time, namely, rise time plus fall time) tends to increase. Increase in response time cause a problem of blur since the response of a liquid crystal is late when the change in voltage applied to the liquid crystal display device, for example, change from a halftone  1  to a halftone  2  is small. Correspondingly, for example, comparing the gray-scale data for the previous time and the next time, the voltage to be applied is increased when the gray-scale data for the previous time is more, and is reduced when the gray-scale data for the present time is less, conventionally. Thus, the rise time is reduced by overdriving, for example, by making the voltage actually applied or a part thereof higher or lower than the reference voltage corresponding to the desired gray-scale, thereby solving the problem. 
     In the case of conducting such overdriving, the scale of circuit becomes larger, which causes a fear of high cost. Correspondingly, a driving method with which response speed of gray-scale change of a liquid crystal display panel can be improved using small memory capacitance has been proposed (Reference 1: Japanese Patent Laid-Open No. 07-121143). 
     However, in the case of conducting such overdriving with a liquid crystal display device, the circuit for comparing the previous and present gray-scale data, the circuit for converting the gray-scale data upon the comparison result, and the like complicate the structure of the liquid crystal display device. 
     Further, since hold driving by which the voltage applied is kept throughout one frame period is conducted in a liquid crystal display device, it is not sufficient to decrease the rise time due to high applied voltage for a countermeasure against blur of moving images. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above problems and it is a feature of the present invention that one frame period includes a high voltage application period for applying a high voltage to a liquid crystal element and a constant voltage application period for applying a constant voltage after the high voltage application period. The high voltage application period includes a plurality of pulses having periods shorter than the rise time of a liquid crystal display device, and the absolute value of the high voltage is higher than the constant voltage, in other words, higher than a reference voltage. Note that, in this specification, a period in which high voltage is applied is referred to as a high voltage application period and a period in which a constant voltage is applied is referred to as a constant voltage application period, as above. Further, a short waveform within the high voltage application period (also referred to as a pulse) has a plurality of pulses having periods shorter than the rise time τ ON . The period in which a short period pulse is applied is also referred to a short period pulse period. 
     Thus, using a pulse for applying high voltage, the rise time of a liquid crystal element in the liquid crystal display device can be reduced. Further, since the rise time is reduced, the response time (rise time (τ ON ) plus fall time (τ OFF )) is also reduced. Therefore, even in the case where a no-voltage application period is provided in addition, multiple gray scales can be controlled in one frame. Further, the light transmission intensity characteristics can be impulse type. 
     The present invention provides a method for driving a liquid crystal display device, in which one frame period includes a high voltage application period for applying a high voltage to a liquid crystal element and a constant voltage application period for applying a constant voltage after the high voltage application period. The high voltage application period includes a plurality of pulses having periods shorter than the rise time of a liquid crystal display device, and the absolute value of the high voltage is higher than the constant voltage. 
     In order to achieve such a driving method, a function of applying high voltage to a liquid crystal element, and a function of applying a constant voltage thereto after the high voltage application are provided. These functions may be integrated on a glass substrate where a pixel area is formed, or may be mounted on a printed substrate. 
     Further, preferably, in the present invention, it is a feature of the present invention that after a constant voltage application period in which a constant voltage is applied to a liquid crystal element, a period in which a voltage that is lower than the absolute value of the threshold voltage is applied or a period in which any voltage is not applied (hereinafter referred to as a no voltage application period) is provided. By providing a period in which a voltage that is lower than the absolute value of threshold voltage is applied, liquid crystal molecules can always be once returned to the reference state. Accordingly, without comparing two successive data, the present time data may be compared with only the reference state. Therefore, a complicated process circuit is not required, and the complexity of circuitry can be prevented. Note that the threshold voltage here is referred to a voltage at which the director direction (an average direction of long axes of liquid crystal molecules is referred to as director) of liquid molecules begins to change by an electric filed applied to a liquid crystal element included in a liquid crystal display device. 
     Thus, the present invention provides a method for driving a liquid crystal display device, in one frame period, having a period in which a high voltage application period in which a high voltage is applied to a liquid crystal element, a constant voltage application period in which a constant voltage is applied after the high voltage application period, and a no-voltage application period after the constant voltage application period. Further, the high voltage application period includes a plurality of pulses each having shorter frequency than the rise time of the liquid crystal display device, and the absolute value of the high voltage value is higher than the voltage value of the constant voltage. 
     In order to achieve such a driving method, a function of controlling so as to apply a voltage that is lower than an absolute value of a threshold voltage or a function for controlling so as not to apply any voltage is provided after the constant voltage application period for applying a constant voltage. The function may be integrated on a glass substrate where a pixel area is formed, or may be mounted on a printed substrate. 
     The present invention provides a liquid crystal display device including a function of applying a high voltage to a liquid crystal element, and a function of applying a constant voltage. Further, one frame period includes a high voltage application period for applying a high voltage and a constant voltage application period for applying a constant voltage after the period for applying a high voltage. The period for applying a high voltage includes a plurality of pulses having periods shorter than the rise time of the liquid crystal display device, and the absolute value of the high voltage value is higher than the voltage value of the constant voltage. 
     The present invention provides a liquid crystal display device including a function of applying a high voltage to a liquid crystal element, a function of applying a constant voltage, and a function of controlling so as to apply a voltage that is lower than an absolute value of a threshold voltage (or a function for controlling so as not to apply any voltage). Further, one frame period includes a high voltage application period for applying the high voltage; a constant voltage application period for applying the constant voltage after the period for applying the high voltage; and a no-voltage application period for applying the voltage that is lower than an absolute voltage of a threshold voltage (or for controlling so as not to apply any voltage) after the period for applying the constant voltage. The period for applying the high voltage includes a plurality of pulses having periods shorter than the rise time of the liquid crystal display device, and the absolute value of the high voltage value is higher than the voltage value of the constant voltage. 
     In the above driving method and a liquid crystal display device using the above driving method, a voltage of at least one of the plurality of pulses may have a polarity opposite to the voltage of the constant voltage. The period for applying the plurality of pulses may be almost equal to the rise time of the liquid crystal display device. Further, the period for applying the voltage that is lower than an absolute voltage of a threshold voltage (or for controlling so as not to apply any voltage) may be almost equal to the fall time of the liquid crystal display device. 
     A waveform for applying such above voltage (hereinafter referred to as a voltage application waveform, or simply a voltage waveform or a voltage application pattern) is applied to a normally black liquid crystal display device. Thus, a black display period can be inserted between two frames that are temporally successive, preferably, in the no-voltage application period, and blur of moving images can be reduced. 
     In other words, the black display period may be inserted using the no-voltage application period in which a voltage that is lower than the absolute value of the threshold voltage is applied (or any voltage is not applied). 
     The present invention can provide a method for driving a liquid crystal display device, one frame period has a voltage application waveform including a high voltage application period using the above pulses and a constant voltage application period for keeping the desired gray-scale. One of specific method for driving a liquid crystal display device of the present invention is as follows. As a method for applying the above voltage application waveform to the liquid crystal display device, a frame period for displaying an image (gray-scale) is divided into equal subframes having a unit time of the application time of a pulse (that is, the pulse width) in the above high voltage application period, and the liquid crystal display device is driven by an active matrix driving method using the subframe as one unit time. The above method for driving a liquid crystal display device can be achieved by increasing the frame frequency from that of a conventional active matrix driving method. Therefore, the driving method can be conducted without the complexity of circuitry. 
     The present invention provides a method for driving a liquid crystal display device, in which one frame period includes a high voltage application period for applying a high voltage to a liquid crystal element and a constant voltage application period for applying a constant voltage after the high voltage application period. The high voltage application period includes a plurality of pulses having periods shorter than the rise time of a liquid crystal display device, and the absolute value of the high voltage is higher than the constant voltage. Further, the liquid crystal display device can be driven using the width of the pulse as one time unit. 
     The present invention provides a method for driving a liquid crystal display device, in which one frame period includes a high voltage application period for applying a high voltage to a liquid crystal element, a constant voltage application period for applying a constant voltage after the period for applying a high voltage, and a period for applying a voltage that is lower than an absolute voltage of a threshold voltage (or for not applying any voltage) after the period for applying a constant voltage. The period for applying a high voltage includes a plurality of pulses having periods shorter than a rise time of the liquid crystal display device, and the absolute value of the high voltage value is higher than a voltage value of the constant voltage. Further, the liquid crystal display device can be driven using the width of the pulse as one time unit. 
     The present invention can reduce blur of moving images of a liquid crystal display device. That is because the transmitted light intensity characteristics can be an impulse type instead of a hold type due to a voltage application waveform according to the present invention. Further, in that case, the voltage application waveform and the application method according to the present invention can be obtained by increasing the frame frequency from that of a conventional active matrix driving method. Therefore, the circuit is not complicated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIGS. 1A to 1E  show voltage application waveforms for a liquid crystal display device in the present invention. 
         FIGS. 2A and 2B  show a voltage application waveform for a liquid crystal display device in the present invention and a voltage application waveform for a conventional method. 
         FIG. 3  shows a transmitted light intensity transient response characteristics of a liquid crystal display device due to voltage application. 
         FIG. 4  shows a transmitted light intensity transient response characteristics of a liquid crystal display device due to voltage elimination. 
         FIG. 5  shows a rising characteristic of a liquid crystal display device compared with the falling characteristic. 
         FIG. 6  shows change in rise time by the increase and decrease in the applied voltage. 
         FIG. 7  shows a structure of a liquid crystal display device in the present invention. 
         FIGS. 8A and 8B  each show a voltage application waveform in the present invention. 
         FIG. 9  shows transient response characteristics of transmitted light intensity of a liquid crystal display device in the embodiment. 
         FIG. 10  shows a cellular phone using a liquid crystal display device of the present invention. 
         FIGS. 11A to 11E  show examples of electronic devices using a liquid crystal display device of the present invention. 
         FIGS. 12A and 12B  show a rear-projection display device using a liquid crystal display device of the present invention. 
         FIG. 13  shows a front-projection display device using a liquid crystal display device of the present invention. 
         FIG. 14  shows a projector unit using a liquid crystal display device of the present invention. 
         FIG. 15  shows a projector unit using a liquid crystal display device of the present invention. 
         FIGS. 16A to 16C  show projector units using a liquid crystal display device of the present invention. 
         FIG. 17  shows a voltage application waveform and a transient response characteristic of transmitted light intensity of a liquid crystal display device in the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiment modes of the invention will be described below with reference to the drawings. Note that the invention is not limited to the following descriptions and various changes may be made in modes and details without departing from the spirit and the scope of the invention. In the drawings for describing the embodiment modes, the same reference numerals are commonly given to like components, and the components will not be described repeatedly. 
     Embodiment Mode 1 
     In embodiment mode, a gray scale display method will be described with reference to  FIGS. 3 to 6 . 
     As for a transmitted light intensity characteristics showing the transmitted light intensity corresponding to the voltage applied to a liquid crystal display device, in  FIG. 3 , the rise time of the voltage of OFF to ON is equivalent to time within which the transmitted light intensity changes from 0 to 0.9, and is represented by τ ON . Further, in  FIG. 4 , the fall time of the voltage of ON to OFF is equivalent to time within which the transmitted light intensity changes from 1.0 to 0.1, and is represented by τ OFF . 
     τ ON  and τ OFF  differ in actual liquid crystal driving. Specifically, as shown in  FIG. 5 , τ OFF  would be longer than τ ON . Further, since τ OFF  is longer than τ ON , when a voltage application waveform having extremely short frequency with respect to the response speed (τ ON +τ OFF ) is successively applied, the voltage applied state would almost kept because the liquid crystal molecules can not respond in accordance with the voltage application waveform. 
     Further, as for a voltage application waveform in accordance with the present invention, since the pulse width of one pulse in the initial stage of the voltage application period is shorter than τ ON , the maximum change in the transmitted light intensity can not be achieved with one pulse. However, since the time before the next pulse is applied is much shorter than (τ ON  plus τ OFF ), the next pulse is applied before the transmitted light intensity of the liquid crystal recovers OFF state even when the applied voltage is temporally OFF. Consequently, the liquid crystal element can be controlled accurately. 
     Further, by successively conducting the pulse application, the maximum value of transmitted light intensity can be obtained with a liquid crystal display device. 
       FIG. 6  shows respective transmitted light intensities in the case where the voltages V 1  and V 2  (V 1 &gt;V 2 ) are applied respectively. The rise time τ ON  of the liquid crystal display device in the case where the voltages V 1  and V 2  (V 1 &gt;V 2 ) are respectively applied has a characteristic that the rise time is shorter when the higher voltage V 1  is applied as shown in  FIG. 6 . Further, this characteristic is the same in the case of a pulse voltage having a shorter period with respect to the rise time; thus, τ ON  becomes shorter when the applied voltage of the pulse application voltage is higher. 
       FIG. 17  shows a voltage application waveform and the transmitted light intensity of a liquid crystal display device according to the present invention. The pulse width of one pulse in a high voltage application period A is shorter than τ ON ; accordingly, transmitted light intensity for a desired gray-scale is not achieved. However, since the time before the next pulse is applied is much shorter than τ OFF , the next pulse is applied before the transmitted light intensity of the liquid crystal recovers OFF state even when the applied voltage is temporally OFF. By successively conducting the pulse application, a desired gray-scale can be obtained with transmitted light intensity of a liquid crystal display device. Further, the desired gray-scale obtained in the period A is kept in a period B within which a constant voltage is applied; subsequently, the transmitted light intensity is returned back to an OFF state. Consequently, the response waveform of the liquid crystal element becomes an impulse type, and blur of moving images is reduced. 
     A liquid crystal display device using a conventional active matrix driving method has slow response speed; therefore, hold type driving, in which an applied voltage is kept until the next data is written, is conducted. In the hold type driving, a desired gray-scale cannot be obtained immediately after the next data is written, which cause blur. On the other hand, in the case of the applied voltage waveform in the present invention has faster response speed; thus, a no-voltage application period can be provided at the end. Further, a black display period can be inserted in the no-voltage application period before the next data is written. Accordingly, the transmitted light intensity characteristics can be an impulse type instead of a hold type. Consequently, blur of moving images can be reduced. 
     Embodiment Mode 2 
     In this embodiment mode, a specific voltage application waveform of the present invention will be described in comparison with a voltage application waveform used for a conventional active matrix driving method. 
     In a voltage application waveform used for a conventional active matrix driving method, which is shown in  FIG. 2B , one pulse per one frame is applied throughout the frame period at a voltage value corresponding to a desired gray-scale for display (reference voltage). On the other hand, in a voltage application waveform for a liquid crystal display device of the present invention, which is shown in  FIG. 2A , a plurality of pulses having a frequency shorter than τ ON  are included in a period A provided in the initial stage. Further, the applied voltage is higher than the reference voltage, and the application time in the period is about τ ON  at the longest, namely, as long as τ ON . The period A shall be a high voltage application period. Further, a middle stage, a period B shall be a constant voltage application period within which a reference voltage corresponding to a desired gray-scale is applied. Further, a period C at the end shall be a no-voltage application period. The application time in the period is about τ OFF  at the longest, namely, as long as τ OFF . Note that the applied voltage shown in  FIG. 2B  is the same as the applied voltage in the period B of  FIG. 2A . 
     The period A in the voltage application time in  FIG. 2A  is to be τ ON  at the longest, and the period C to be τ OFF . Specific voltage application waveform can be referred to  FIG. 1A . Further, the frequency of the application time in the frame period including the periods A to C corresponds to a frame frequency. Accordingly, when a liquid crystal display device is driven with a frame frequency of X Hz, a frame frequency of this embodiment mode is also X Hz, and the frame period is 1/X sec. 
     By using such a driving method for driving a liquid crystal display device, the transmitted light intensity characteristics can be an impulse type; thus, blur of moving images can be reduced. Further, in that case, the voltage application waveform and the application method according to the present invention can be obtained by increasing the frame frequency from that of a conventional active matrix driving method. Therefore, the circuit is not complicated. 
     Embodiment Mode 3 
     In this embodiment mode, a voltage application waveform different from the above embodiment modes will be described. 
     In a liquid crystal display device using TN liquid crystal, the transmitted light intensity is determined by the absolute value of an applied voltage independently of the polarity. Therefore, the polarity of the applied voltage of a period A is opposite to that of a period B in  FIG. 2A . The specific voltage application waveform can be referred to  FIG. 1B . 
     Thus, deflection of a residual ion inside the liquid crystal display device, and the reduction in contrast due to the deflection of a residual ion can be reduced in addition to the effect of the above embodiment modes. 
     Embodiment Mode 4 
     In this embodiment mode, a voltage application waveform different from the above embodiment modes will be described. 
     Different from the above Embodiment Mode 1, the polarity of the voltages applied in the period A is alternately opposite to that of the period B. The specific voltage application waveform can be referred to  FIG. 1C . 
     Thus, deflection of a residual ion inside the liquid crystal display device, and the reduction in contrast due to the deflection of a residual ion can be reduced in addition to the effect of the above embodiment modes. 
     Embodiment Mode 5 
     In this embodiment mode, a voltage application waveform different from the above embodiment modes will be described. 
     Short frequency pulses in a voltage application waveform in the present invention are applied to improve τ ON  by applying high voltage at the beginning of pulse application. Accordingly, the absolute value of the applied voltage is not required to be always constant, and it can changed in the period A, for example, reduce gradually, increase gradually, and varies one by one. The specific voltage application waveform can be referred to  FIG. 1D . 
     Embodiment Mode 6 
     In this embodiment mode, a voltage application waveform different from the above embodiment modes will be described. 
     Different from the above Embodiment Mode 1, voltage having polarity opposite to that of the period B is applied in no-voltage application part of the period A. The specific voltage application waveform can be referred to  FIG. 1E . 
     Thus, deflection of a residual ion inside the liquid crystal display device, and the reduction in contrast due to the deflection of a residual ion can be reduced in addition to the effect of the above embodiment modes. 
     Further, no-voltage application part is not included in the period A; thus, high response speed can be achieved. 
     Embodiment Mode 7 
     In this embodiment mode, a structure of a liquid crystal display device will be described. 
       FIG. 7  is a structural figure of a liquid crystal display device of the present invention. The liquid crystal display device includes an active matrix liquid crystal panel  101 , a gate line driver circuit  102  for driving a gate line of the panel, and a source line driver circuit  103  for driving a source line of the panel. 
     A signal for turning a switching transistor ON is inputted from the gate line driver circuit  102  into a gate line  1  (G 1 ). Subsequently, a video signal is inputted from a source line  1  (S 1 ) into a source line x (Sx) from the source line driver circuit  103 , so that a voltage corresponding to the video signal is applied to a pixel x (Pix (x)) from a pixel  11  of the active matrix liquid crystal panel. The series of operation is repeated to a gate line y (Gy). When 1/n second is required to scan from the gate line  1  (G 1 ) to the gate line y (Gy) once for each, the frame frequency is n Hz. The method in which each pixel connected to one gate line is thus driven is referred to as a line sequential driving. 
     In the present invention, when the width of one pulse (pulse width) in plural pulse application part is 1/m sec, the driving is conducted with the frame frequency of m Hz. 
     Further, as described in Embodiment Mode 1, the subframe period 1/m is shorter than τ ON . In a conventional active matrix driving method, one image is displayed with one frame. On the other hand, in the case of employing the present invention, a desired image is not displayed with a frequency of the conventional one frame. In the present invention, a method in which one image is displayed in a frame period including a plurality of (here, the number is assumed to be a) subframes each having the frequency of 1/m can be employed. The frame period including a plurality of subframes corresponds to the voltage application waveform shown in  FIG. 1A to 1E . Accordingly, the time required for displaying one image, that is, the frame period is a/m sec. Further, a frame frequency indicates the number of displayed images per one second, and a substantial frame frequency of the present invention is m/a Hz. 
     As for the above driving method, the frame frequency is simply increased compared with a conventional active matrix driver circuit. Therefore, there are no major changes in the liquid crystal display device structure, and the driving can be carried out without complexity of the circuit configuration. 
     However, a circuit in the gate line driver circuit or the source line driver circuit has a function of applying high voltage to a liquid crystal element and a function of applying a constant voltage after the high voltage application. These functions may be integrated on a glass substrate where a pixel area is formed, or may be mounted on a printed substrate. A circuit in the gate line driver circuit or the source line driver circuit further has a function of applying a voltage that is lower than the absolute value of the threshold voltage or a function of controlling so as not to apply any voltage. 
     In such a liquid crystal display device, the voltage application waveform shown in Embodiment Mode 2 is applied, and the driving can be conducted with the period A: 3 ms, the period B: 3 ms, and the period C: 9 ms, for example. 
     Note that a driving method of the present invention can be applied to a point sequential driving for independently driving each pixel, in which a video signal is sequentially inputted to one source line when an ON signal is inputted to the gate line  1  (G 1 ). 
     Embodiment Mode 8 
     In this embodiment mode, a cellular phone using a liquid crystal display device of the present invention will be described. 
       FIG. 10  shows one example of a cellular phone using a liquid crystal display device according to the present invention. A display panel  401  equivalent to a liquid crystal display device of the present invention is detachably incorporated in a housing  402 . The shape and the size of the housing  402  can be determined appropriately in accordance with the size of the display panel  401 . The housing  402 , in which the display panel  401  is fixed, is attached to a printed substrate  403 , so as to fabricate a module. 
     The display panel  401  is connected to the printed substrate  403  through an FPC  404 . Over the printed substrate  403 , a signal processing circuit  408  is provided, which includes a speaker  405 , a microphone  406 , a transmit/receive circuit  407 , a CPU, a controller and the like. The module, an input means  409 , and a battery  410  are combined and stored in a frame  411 . A pixel portion of the display panel  401  is placed so as to be seen through an aperture window that is formed in the frame  411 . 
     The display panel is driven using the voltage application waveform as described in the above embodiment mode to improve the response speed. Further, a driving method using a voltage application waveform according to the present invention can be achieved by increasing the frame frequency; thus, the circuits to be provided on the printed substrate  403  or the like are not complicated. Therefore, the miniaturization and light weight of the cellular phone can be achieved. 
     The cellular phone in accordance with this embodiment mode can be changed into various modes depending on the function or the usage thereof. For example, even when the cellular phone has a plurality of display panels or has a hinged open and shut structure in which a frame is appropriately separated into a plurality of frames, the advantages described above can be obtained. 
     Embodiment Mode 9 
     The following can be given as an example of an electronic device using a liquid crystal display device of the present invention other than the above cellular phone: a television apparatus (also simply referred to as a television or a television receiver), a camera such as a digital camera or a digital video camera, a portable information terminal such as PDA, a portable game machine, a computer monitor, a computer, an audio reproducing device such as a car audio, an image reproducing device provided with a recording medium, such as a home game machine, or the like. The specific examples will be explained with reference to  FIGS. 11A to 11E . 
     A personal digital assistant device shown in  FIG. 11A  includes a main body  9201 , a display area  9202 , and the like. The liquid crystal display device of the present invention can be applied to the display area  9202 . Consequently, a high-speed response personal digital assistant device can be provided without the complexity of circuitry. 
     A digital video camera shown in  FIG. 11B  includes a display area  9701 , a display area  9702 , and the like. The liquid crystal display device of the present invention can be applied to the display area  9701 . Consequently, a high-speed response digital video camera can be provided without the complexity of circuitry. 
     A portable television apparatus shown in  FIG. 11C  includes a main body  9301 , a display area  9302 , and the like. The liquid crystal display device of the present invention can be applied to the display area  9302 . Consequently, a high-speed response portable television apparatus can be provided without the complexity of circuitry. In addition, as for a television apparatus, the liquid crystal display device of the present invention can be widely applied to a small-sized television to be mounted on a portable terminal such as a cellular phone, a portable middle-sized television, a large-sized television (for example, 40 inch or more), and the like. 
     A portable computer shown in  FIG. 11D  includes a main body  9401 , a display area  9402 , and the like. The liquid crystal display device of the present invention can be applied to the display area  9402 . Consequently, a high-speed response portable computer can be provided without the complexity of circuitry. 
     A television apparatus shown in  FIG. 11E  includes a main body  9501 , a display area  9502 , and the like. The liquid crystal display device of the present invention can be applied to the display area  9502 . Consequently, a high-speed response television apparatus can be provided without the complexity of circuitry. 
     Thus, high-speed response electronic devices can be provided without the complexity of circuitry using a liquid crystal display device of the present invention. 
     Embodiment Mode 10 
     In this embodiment mode, a rear-projection display device using a liquid crystal display device of the present invention will be described. 
     A rear-projection display device  501  shown in a general view of  FIG. 12A  and a cross-sectional view of  12 B includes a projector unit  502 , a mirror  503  and a screen panel  504 . In addition, a speaker  505  and operation switches  506  may also be provided. The projector unit  502  is placed in a lower position of a frame  507  of the rear-projection display device  501 , and projects light for displaying an image toward the mirror  503 , based on an image signal. The rear-projection display device  501  displays an image that is projected from the backside of the screen panel  504 . 
     Meanwhile,  FIG. 13  shows a front-projection display device  541 . The front-projection display device  541  includes a projector unit  502  and a projection optical system  603 . The front-projection display device  541  projects an image on a screen or the like placed in front. 
     The structures of projector units  502  that are applied to the rear-projection display device  501  shown in  FIGS. 12A and 12B  and the front-projection display device  541  shown in  FIG. 13  will be described below. 
       FIG. 14  shows one structural example of a projector unit  502 . The projector unit  502  includes a light source unit  511  and a modulation unit  512 . The light source unit  511  includes a light source optical system  513  having lenses and a light source lamp  514 . The light source lamp  514  is stored in a frame not to diffuse stray light. As the light source lamp  514 , for example, a high pressure mercury lamp, a xenon lamp or the like is used, which is capable of emitting a large amount of light. The light source optical system  513  is composed by appropriately providing an optical lens, a film that has a polarizing function, a film for controlling phase difference, an IR film, and the like. The light source unit  511  is placed so that emitted light enters the modulation unit  512 . The modulation unit  512  includes a plurality of liquid crystal panels  515 , a color filter provided on or in the vicinity of the panel, dichroic mirrors  516 , total reflection mirrors  517  provided at plural comers, a prism  518 , and a projection optical system  519 . Light emitted from the light source lamp  514  is divided into a plurality of light paths by the dichroic mirrors  516 . 
     Each light path is provided with a liquid crystal panel  515  transmitting light of a predetermined wavelength or wavelength range and a color filter provided on or in the vicinity of the crystal panel  515 , a phase difference plate  540  provided outside the color filter. Such a liquid crystal panel, which is transmits light includes a pixel electrode formed of a transparent electrode material such as ITO. The transmissive liquid crystal panel  515  modulates transmitted light based on an image signal. Light of each color transmitted by the liquid crystal panel  515  enters the prism  518  and displays an image on a screen panel  504  through a lens of the projection optical system  519 . In the case of a rear-projection display device  501 , a fresnel lens is provided between the mirror  503  and the screen panel  504 . The projection light that is projected by the projector unit  502  and reflected by the mirror  503  is converted to almost parallel light by this fresnel lens and projected on the screen panel  504 . 
     A liquid crystal display device using a driving method according to the present invention can be applied to the liquid crystal panel  515 . Consequently, blur of moving images can be reduced. In that case, a driving method using a voltage application waveform according to the present invention can be achieved by increasing the frame frequency from that of a conventional active matrix driving method. Therefore, the circuitry is not complicated, which is preferable. 
     A projector unit  502  shown in  FIG. 15  has a structure which is provided with reflective liquid crystal panels  525 R,  525 Q and  525 B. The reflective liquid crystal panels  525 R,  525 C; and  525 B each have a structure in which the pixel electrode is formed using aluminum (Al), Ti (titanium), an alloy of those metals, or the like. 
     The projector unit  502  includes a light source unit  521  and a modulation unit  522 . The light source unit  521  has the same structure as in  FIG. 14 . Light from the light source unit  521  is divided into a plurality of light paths by dichroic mirrors  526 R and  526 G and a total reflection mirror  527 R, and enters polarizing beam splitter  530 R,  530 Q and  530 B. The polarizing beam splitter  530 R,  530 Q and  530 B are provided with respect to the reflective liquid crystal panels  525 R,  525 G, and  525 B corresponding to each color. The reflective liquid crystal panels  525 R,  525 G, and  525 B modulate transmitted light based on an image signal. Light of each color that is reflected by the reflective liquid crystal panels  525 R,  525 Q and  525 B enters a prism  528 , and is projected through a lens of a projection optical system  529 . 
     Of light that is emitted from the light source unit  521 , only light of a red wavelength range is transmitted through the dichroic mirror  526 R, and light of a green or blue wavelength range is reflected by the dichroic mirror  526 R. Further, only light of a green wavelength range is reflected by the dichroic mirror  526 G. The light of a red wavelength range, which has been transmitted through the dichroic mirror  526 R, is reflected by the total reflection mirror  527 R, and enters the polarizing beam splitter  530 R. The light of a green wavelength range enters the polarizing beam splitter  530 G, and the light of a blue wavelength range enters the polarizing beam splitter  530 B. The polarizing beam splitters  530 R,  530 G, and  530 B each have a function of splitting incident light into P-polarized light and S-polarized light, and a function of transmitting only the P-polarized light. The reflective liquid crystal panels  525 R,  525 G, and  525 B polarize light incident from the polarizing beam splitters based on an image signal. 
     Only the S-polarized light corresponding to each color enters the reflective liquid crystal panels  525 R,  525 G, and  525 B corresponding to each color. The reflective liquid crystal panels  525 R,  525 G, and  525 B can be operated in an electrically controlled birefringence mode (ECB). Since a liquid crystal molecule is orientated perpendicularly at an angle to a substrate. Therefore, in the reflective liquid crystal panels  525 R,  525 C, and  525 B, incident light is reflected with no change in the polarizing state when a pixel is in an OFF state. When a pixel is in an ON state, the orientation state of the liquid crystal molecule is changed and the polarizing state of incident light is changed to reflect the incident light. 
     The projector unit  502  shown in  FIG. 15  can be applied to the rear-projection display device  501  shown in  FIGS. 12A and 12B  and the front-projection display device  541  shown in  FIG. 13 . 
     Next, structures different from the projector unit will be described.  FIG. 16A to 16C  show single-plate projector units. The projector unit  502  shown in  FIG. 16A  includes a light source unit  601 , a liquid crystal panel  605 , a projection optical system  609 , and a phase difference plate  600 . The projection optical system  609  includes one or a plurality of lenses. Further, the projector unit  502  is provided with a color filter provided on or in the vicinity of the liquid crystal panel  605 . Note that a single-plate mode includes a field sequential mode in which one liquid crystal display device is temporally divided into three periods of an R period, a G period, and a B period; and a color filter method in which one pixel of one liquid crystal display device is divided into regions of three colors of RGB. The former field sequential method is applied in this embodiment mode. 
       FIG. 16B  shows the structure of a projector unit  502  which operates in a field sequential mode. The field sequential mode is a mode in which light of each color such as red, green, or blue is made enter a liquid crystal panel sequentially with a time lag, and color display is conducted without a color filter. In particular, when the field sequential mode and a fast-response liquid crystal panel are combined, high-definition images can be displayed. In  FIG. 16B , a rotary color filter plate  610  provided with a plurality of color filters for red, green and blue is provided between a light source unit  601  and a liquid crystal panel  605 . 
     A projector unit  502  shown in  FIG. 16C  has a structure of a color separation system that uses a micro lens for a color display method. In this method, a micro lens array  611  is provided on a light incidence side of a liquid crystal panel  605 , and light of each color is illuminated from each direction to achieve color display. In a projector unit  502  that uses this method, no light is lost due to a color filter; thus, the projector unit  502  has a feature that light from the light source unit  601  can be used effectively. The projector unit  502  includes a dichroic mirror  606 R for R, a dichroic mirror  606 G for G and a dichroic mirror  606 B for B so that light of each color is illuminated from each direction to the liquid crystal panel  605 . 
     A liquid crystal display device employing a driving method of the present invention can be applied to the liquid crystal panel  605 . As a result, blur of moving images can be reduced in a display device including a single-plate projector unit. Further, in that case, a voltage application waveform in accordance with the present invention and a driving method using the voltage application waveform can be obtained by increase frame frequency of a conventional active matrix driving method; thus, a circuit can be prevented from being complicated, which is preferable. 
     Thus, according to the present invention, a projection display device (projection television apparatus) in which blur of moving images can be reduced can be provided without the complexity of a circuit. 
     Embodiment 
     In this embodiment, normally white display is conducted with polarizers arranged as crossed nichols using a TN liquid crystal display device. As shown in  FIG. 8A , one frame is 15 msec, the initial period is 3 msec, the duty ratio is 50%, and the pulse has a period of 0.1 msec. Accordingly, the subframe is 0.05 msec. A constant voltage application period of 3 msec is provided thereafter, and the value of the constant voltage is to be the reference voltage corresponding to a display gray-scale. The applied voltage of the first half is to be twice the applied voltage of the last half Further, no voltage is applied in the remaining 9 msec. 
     The response characteristics of the transmitted light intensity of the above voltage application waveform is compared with a conventional voltage application waveform shown in  FIG. 8B , in which the initial period (period D) of 6 msec is to be a voltage application period, a reference voltage equivalent to a period B of  FIG. 8A , that is a voltage at which the applied voltage of the period B of  FIG. 8A  is equal to the applied voltage of  FIG. 8B  is applied. 
     The result is shown in  FIG. 9 . The transient response characteristics of the transmitted light intensity of the voltage application waveform shown in  FIG. 8A  is shown in ( 1 ) to ( 3 ). In ( 1 ), the voltage of the period A is 8 V and the voltage of the period B is 4 V. In ( 2 ), the voltage period A is 4.5 V and the voltage of the period B is 2.25 V. In ( 3 ), the voltage period A is 3.5 V and the voltage of the period B is 1.75 V. The response characteristics of the transmitted light intensity of the voltage application waveform shown in  FIG. 8B  equivalent to the reference voltage are shown in ( 4 ) to ( 6 ). In ( 4 ), the voltage of the period D is 4 V. In ( 5 ), the voltage of the period D is 2.25 V. In ( 6 ), the voltage of the period D is 1.75 V. 
     In ( 1 ) to ( 3 ), τ ON  is improved. This is because a voltage higher than ( 4 ) to ( 6 ) is applied at the beginning of the initial period of voltage application, and τ ON  is influenced by the voltage. 
     On the other hand, when the conventional voltage application waveform shown in  FIG. 8B  is applied, τ ON  is slow, and it is difficult to display multiple gray scales within 15 ms. 
     In  FIG. 8A  in accordance with the present invention as above, τ ON  is fast in halftones as shown in ( 2 ) and ( 3 ) of  FIG. 9A , so that multiple gray scales can easily be displayed within 15 ms. On the other hand, when the voltage application waveform of a conventional active matrix driving method, which is shown in  FIG. 8B , is applied, change in the transmitted light intensity is small; thus, it is extremely difficult to display multiple gray scales. 
     The above result shows that the voltage application waveform shown in  FIG. 8A  is effective for high-speed response of a liquid crystal display device. 
     Further, from the above result, since higher speed response is achieved with the voltage application waveform using the present invention, it is found that the reproducibility of multiple gray scales within 15 msec can be obtained and the transmitted light intensity characteristics of an impulse type can be obtained by providing a no-voltage application period. Consequently, the voltage application waveform of the present invention is used for a normally black liquid crystal display device having polarizers arranged as parallel nichols; thus, black display can be inserted between each frame period and the next frame period, which can reduce blur of moving images.