Patent Publication Number: US-6342881-B1

Title: Display device, electronic equipment, and driving method

Description:
TECHNICAL FIELD 
     The present invention relates to a display device, to an electronic apparatus using the display device, and to drive method. 
     BACKGROUND ART 
     Recently, liquid crystal displays, which are display devices of one of various kinds, have been widely used as light low-power-consumption display devices for electronic apparatuses such as television sets, electronic notebooks, personal computers and portable telephone sets. With respect to such liquid crystal displays, a further increase in the number of gray scale steps for improvement in the accuracy with which images are displayed is expected. Known techniques for realizing grayshade display with such liquid crystal displays are, for example, pulse height modulation of changing the height of pulses written to liquid crystal elements and pulse width modulation of changing the width of written pulses. 
     Recently, a drive method using a new system has attracted attention, which system is operated in a liquid crystal display using a nonlinear switching element such as a MIM element, a back-to-back diode element, a diode ring element or a varistor element in such a manner that, in a first mode, a first selecting voltage is supplied to a scanning line, and, in a second mode, a precharge voltage is supplied to the scanning line and a second selecting voltage is thereafter supplied to the scanning line. (This kind of method will hereinafter be referred to as a charge-discharge drive method.) For example, Japanese Patent Laid-Open No. 125225/1990 discloses a charge-discharge drive method. As described in this document, it has been considered that the mainstream of this kind of drive method is grayshade display by pulse height modulation. Pulse height modulation, however, entails the problem of difficulty in voltage control for display with a predetermined gray scale and the problem of a high cost of the liquid crystal display. On the other hand, a drive method which has been proposed or put to use before the charge-discharge drive method and which is called a four-value method because of use of a two-value selecting voltage and a two-value data voltage is also known. The idea of pulse width modulation in the four-value drive method, however, cannot be applied directly to the charge-discharge drive method. 
     The present invention has been achieved in consideration of the above-described problems, and an object of the present invention is to provide a display device having improved display characteristics, most suitable for the charge-discharge drive method and capable of grayshade display by pulse width modulation, an electronic apparatus using the display device, and a drive method. 
     DISCLOSURE OF INVENTION 
     To achieve the above-described object, according to the present invention, there is provided a display device including a plurality of scanning lines, a plurality of data lines, and display elements driven with the scanning lines and the data lines, the display device performing grayshade display by pulse width modulation, the display device comprising scanning signal drive means for supplying a first selecting voltage to the scanning lines in a first mode, and for supplying, in a second mode, a precharge voltage opposite in polarity to the first selecting voltage about a middle value of a data voltage applied to the data lines and thereafter supplying a second selecting voltage opposite in polarity to the precharge voltage about the middle value of the data voltage to the scanning lines, and data signal drive means for supplying a pulse-width-modulated data voltage to the data lines, wherein first and second write pulses formed by the first and second selecting voltages and data voltage in the first and second modes and setting the same gray scale value are such that, as the pulse width of one of the first and second write pulses is increased, the pulse width of the other is reduced and the rate of reduction of the pulse width of the other becomes lower. 
     The present invention enables driving of display elements using a so-called charge-discharge drive method. According to the present invention, as the pulse width of one of the first and second write pulses is increased, the pulse width of the other is reduced and the rate of this reduction becomes lower. 
     In this manner, the present invention enables suitable grayshade display using pulse width modulation while preventing application of a DC voltage to each display element over a long time period. 
     In the present invention, the precharge voltage may be positive or negative, and driving using a positive precharge voltage and driving using a negative precharge voltage may be mixedly performed. 
     The present invention also provides a display device including a plurality of scanning lines, a plurality of data lines, and display elements driven with the scanning lines and the data lines, the display device performing grayshade display by pulse width modulation, the display device comprising scanning signal drive means for supplying a first selecting voltage to the scanning lines in a first mode, and for supplying, in a second mode, a precharge voltage opposite in polarity to the first selecting voltage about a middle value of a data voltage applied to the data lines and thereafter supplying a second selecting voltage opposite in polarity to the precharge voltage about the middle value of the data voltage to the scanning lines, and data signal drive means for supplying a pulse-width-modulated data voltage to the data lines, wherein first and second write pulses formed by the first and second selecting voltages and data voltage in the first and second modes and setting the same gray scale value have pulse widths set to such values that voltages applied to each of the display elements immediately after the periods of selecting by the first and second selecting voltages are approximately equal to each other. 
     According to the present invention, the pulse widths of the first and second pulses are set to such values that voltages applied to each of the display elements immediately after the selecting periods (voltages applied at initial stages of holding periods) are approximately equal to each other with respect to the first mode and the second mode, thereby enabling suitable grayshade display using pulse width modulation. 
     The present invention also provides a display device including a plurality of scanning lines, a plurality of data lines, and display elements driven with the scanning lines and the data lines, the display device performing grayshade display by pulse width modulation, the display device comprising scanning signal drive means for supplying a first selecting voltage to the scanning lines in a first mode, and for supplying, in a second mode, a precharge voltage opposite in polarity to the first selecting voltage about a middle value of a data voltage applied to the data lines and thereafter supplying a second selecting voltage opposite in polarity to the precharge voltage about the middle value of the data voltage to the scanning lines, and data signal drive means for supplying a pulse-width-modulated data voltage to the data lines, wherein a DC component of the data voltage in one horizontal scanning period with respect to a middle voltage between an ON voltage and an OFF voltage is made approximately zero independent of the gray scale. 
     According to the present invention, the proportion of data signal formed of the ON voltage and the proportion of data signal portion formed of the OFF voltage in one horizontal scanning period can be made approximately equal to each other regardless of the display pattern, thereby effectively preventing occurrence of a vertical crosstalk or the like. 
     The present invention is also characterized in that the scanning signal drive means supplies, in the first mode, the first selecting voltage in a second period following a first period corresponding to the first half of one horizontal scanning period and equal in length to the first period, and supplies, in the second mode, the precharge voltage in a third period corresponding to the first half of one horizontal scanning period, and the second selecting voltage in a fourth period following the third period and equal in length to the third period, and that the data signal drive means keeps the data voltage at a low level with respect to the middle voltage of the ON and OFF voltages for a period in the first period equal in length to the period in the second period through which the data voltage is kept at a high level with respect to the middle voltage, keeps the data voltage at the high level for a period in the first period equal in length to the period in the second period through which the data voltage is kept at the low level, keeps the data voltage at the low level for a period in the third period equal in length to the period in the fourth period through which the data voltage is kept at the high level, and keeps the data voltage at the high level for a period in the third period equal in length to the period in the fourth period through which the data voltage is kept at the low level. In this manner, the DC component of the data voltage in one horizontal period can be made approximately zero independent of the gray scale, thereby preventing occurrence of a vertical crosstalk or the like. Advantageously, according to the present invention, the data signals in the first and third periods can easily be obtained by inverting the data signals in the second and fourth periods. 
     The present invention also provides an electronic apparatus comprising one of the above-described display devices. Thus, a display device used in an electronic apparatus such as a remote controller, an electronic calculator, a portable telephone set, a projector, or a personal computer can be improved in display characteristics and can be reduced in cost. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a diagram showing an example of drive waveforms of a four-value drive method, and 
     FIG. 2 is a diagram showing an example of drive waveforms of a charge-discharge method. 
     FIG.  3 (A) is a diagram showing an equivalent circuit of a pixel of a liquid crystal panel, and 
     FIG.  3 (B) is a diagram showing an I-V characteristic of a MIM element. 
     FIG. 4 is a diagram for explaining an improvement in display characteristic achieved by the charge-discharge drive method. 
     FIGS.  5 (A) and  5 (B) are diagrams showing other examples of the drive waveforms of the charge-discharge drive method. 
     FIG. 6 is a block diagram common to a first embodiment and a second embodiment, and 
     FIGS.  7 (A) and  7 (B) are diagrams for explaining the principle of the first embodiment. 
     FIGS.  8 (A) and  8 (B) are diagrams for explaining pulse width modulation based on the four-value drive method. 
     FIG. 9 is a diagram showing the result of a measurement of the relationship between gray scale data in a charging mode and gray scale data in a discharging mode. 
     FIG. 10 is a diagram for explaining the principle of the second embodiment. 
     FIGS.  11 (A),  11 (B),  11 (C), and  11 (D) are diagrams for also explaining the principle of the second embodiment. 
     FIGS.  12 (A),  12 (B),  12 (C), and  12 (D) are diagrams for explaining a vertical crosstalk. 
     FIG. 13 is a diagram showing the configuration a liquid crystal display device of a third embodiment, and 
     FIG. 14 is a diagram for explaining the operation of the third embodiment. 
     FIG. 15 is a diagram showing an example of arrangement of a grayshade display fundamental clock generation circuit. 
     FIG. 16 is a diagram showing an example of a remote controller as an electronic apparatus. 
     FIG. 17 is a diagram showing an example of an electronic calculator as an electronic apparatus. 
     FIG. 18 is a diagram showing an example of a portable telephone set as an electronic apparatus. 
     FIG. 19 is a diagram showing the overall configuration of a control circuit of a liquid crystal device incorporated in an electronic apparatus. 
     FIG. 20 is a diagram showing an example of a personal portable information apparatus as an electronic apparatus. 
     FIGS.  21 (A),  21 (B), and  21 (C) are diagrams showing an example of a liquid crystal projector as an electronic apparatus. 
     FIG. 22 is a diagram showing an example of a modification of the drive waveforms. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The embodiments of the present invention will be described below with reference to the drawings. 
     (First Embodiment) 
     A charge-discharge drive method will first be described in detail. 
     FIG. 1 shows an example of drive waveforms of a four-value drive method which is a conventional drive method, and FIG. 2 shows an example of drive waveforms of a charge-discharge drive method. FIG.  3 (A) shows an equivalent circuit relating to one pixel of a liquid crystal panel. A MIM element which is one of nonlinear switching elements, and a liquid crystal element which is one of display elements can be represented by a parallel circuit of a resistor R M  and a capacitor C M  and a parallel circuit of a resistor R L  and a capacitor C L , respectively. FIGS. 1 and 2 illustrate the waveform of a voltage V D  applied to two terminals of a MIM element and a liquid crystal element connected in series, and the waveform of a voltage V LC  applied to two terminals of the liquid crystal element. 
     In the four-value drive method shown in FIG. 1, voltages V A1  and V A2  each applied to one liquid crystal element (or to the pixel electrode) immediately after the end of a selecting period (V LC  at time t 1  or t 2 ) are 
     
       
           V   A1 =( V   S1   +V   H   −V   ON )− K·V   S1   (1) 
       
     
     
       
           V   A2 =−[( V   S1   +V   H   −V   ON )− K·V   S1 ]  (2) 
       
     
     where V S1  is a selecting voltage of a scanning signal, V H  is an ON voltage or OFF voltage of a data signal, and K=C M /(C H  +C L ) . Also, V ON  is V MIM  which is applied to the MIM element immediately before the end of each selecting period. The value of V ON  depends upon the I-V characteristic of the MIM element shown in FIG.  3 (B). In other words, the V ON  is a voltage applied to the MIM element when charging to the liquid crystal element is nearly stopped (when the current through the MIM element becomes about 10 −9  to 10 −8  amperes). 
     If an error occurs in V ON . for example, if the V ON  becomes larger by ΔV ON  as shown in FIG.  3 (B), an error is also caused in V A1  and V A2 , such that, as is apparent from the above equations (1) and (2), the absolute value of each of V A1  and V A2  decreases by ΔV ON . On the other hand, if the V ON  becomes smaller by ΔV ON , the absolute value of each of V A1  and V A2  increases by ΔV ON . If an error ΔK occurs in K, an error not negligibly small is caused in V A1  and V A2 . 
     On the other hand, the charge-discharge drive method has, as shown in FIG. 2, a charging mode (e.g., a first mode) in which a first selecting voltage V S1  is supplied to the scanning line, and a discharging mode in which −V PRE  which is a precharge voltage opposite in polarity to V S1  is supplied and a second selecting voltage V S2  opposite in polarity to −V PRE  is thereafter supplied. A voltage V B1  (V LC  at time t 1 ) applied to the liquid crystal element immediately after the end of the selecting period is the same as that shown above by equation (1). That is, 
     
       
           V   B1 =( V   S1   +V   H   −V   ON )= K·V   S1   (3) 
       
     
     On the other hand, in the discharging mode, after overcharging by the precharge voltage −V PRE  the electric charge is discharged by the second selecting voltage V S2 , and a voltage applied to the liquid crystal element immediately before the selecting period is V S2 −V ON . Therefore, a voltage V B2  (V LC  at time t 2 ) applied to the liquid crystal element immediately after the end of the selecting period is 
     
       
           V   B2 =−[( V   ON   +V   S2 )+ K· ( V   S2   +V   H )]  (4) 
       
     
     As is apparent from the above equations (3) and (4), if, for example, V ON  becomes larger by ΔV ON , the absolute value of V B1  becomes smaller by ΔV ON  and, conversely, the absolute value of V B2  becomes larger by ΔV ON . Further, if an error ΔK occurs in K and if the absolute value of V B1  becomes larger by this error, the absolute value of V B2  becomes smaller. If the absolute value of V B1  becomes smaller by this error, the absolute value of VB 2  becomes larger. 
     According to the charge-discharge drive method, as described above, even if V ON  of the MIM element varies, an error voltage caused in the liquid crystal (pixel electrode) applied voltage in the charging mode can be canceled out, in terms of effective voltage, by an error voltage caused in the liquid crystal applied voltage in the charging mode. Consequently, it is possible to effectively prevent occurrence of a display nonuniformity or the like due to a variation in V ON  of the MIM elements in the liquid crystal panel. FIG. 4 schematically illustrates the above-described effect. Error ΔV ON  occurs in V ON , the absolute value of the liquid crystal applied voltage in the charging mode increases from E to F of FIG. 4, and the effective voltage applied to the liquid crystal element also increases. The transmittance of the liquid crystal element is thereby reduced, so that the display becomes lower in brightness (in the case of normally white display). However, the absolute value of the liquid crystal applied voltage then decreases from G to H of FIG. 4 in the discharging mode, and the effective voltage applied to the liquid crystal element also decreases. The transmittance of the liquid crystal element is thereby increased, so that the display becomes brighter. As a result, the total brightness of the display on one pixel is not substantially changed. Consequently, even if V ON  of the MIM elements varies in the liquid crystal panel, substantially no variation occurs in the brightness of the display, thus preventing a display nonuniformity or the like. According to the charge-discharge drive method, even if a variation in K=C M /(C M +C L ) occurs, a display nonuniformity can be prevented in the same manner. 
     The drive waveforms of the charge-discharge drive method are not limited to those shown in FIG.  2 . Some modifications of the drive waveforms are conceivable. For example, positive precharging may be performed as shown in FIGS.  4  and  5 (A), and precharging both with positive and negative polarities may be performed as shown in FIG.  5 (B). 
     The first embodiment will now be described in detail. 
     FIG. 6 is a block diagram of the first embodiment, which is a block diagram used in common in the following description of the present invention. FIG.  7 (A) shows an example of drive waveforms for explanation of the principle of the present invention. A liquid crystal panel  10  has a plurality of data lines X 1  to Xn and a plurality of scanning lines Y 1  to Yn. MIM elements  12  and liquid crystal elements  14  are electrically connected between the data lines and the scanning lines a shown in FIG. 6, for example. A scanning signal drive circuit  20  supplies the first selecting voltage V S1  to one of the scanning lines as shown in FIG.  7 (A) in the charging mode (e.g., a first mode). In the discharging mode (e.g., a second mode), the scanning signal drive circuit  20  supplies the scanning line with −V PRE , which is a precharge voltage opposite in polarity to the first selecting voltage V S1  about a middle value of a data voltage applied to the data line, and thereafter supplies the scanning line with the second selecting voltage V S2  opposite in polarity to −V PRE  about the middle value of the data voltage applied to the data line. On the other hand, a data signal drive circuit  30  supplies the pulse-width-modulated data voltage to the data line. In the above-described manner, grayshade display using the charge-discharge drive method and using pulse width modulation is performed. 
     FIGS.  8 (A) and  8 (B) show an example of drive waveforms in a case where pulse width modulation is performed with the conventional four-value drive method. In the method of driving a liquid crystal display device, positive drive by supplying a positive voltage and negative drive by supplying a negative voltage are alternately performed with respect to frames in order to prevent application of a DC component to each liquid crystal element over a long time period. In such driving, according to the conventional four-value drive method, if the pulse widths of write pulses  40  and  42  setting the same gray scale value by positive and negative drives are W 1  and W 2 , the pulse widths W 1  and W 2  are equal to each other as shown in FIGS.  8 (A) and  8 (B). 
     In contrast, in the first embodiment shown in FIG.  7 (A), if the pulse widths of first and second write pulses  44  and  46  which are formed by the first and second selecting voltages V S1  and V S2  in the charging and discharging modes and which set the same gray scale value are W C  and W D , the pulse widths W C  and W D  are in the relationship shown in FIG.  7 (B). That is, W D  decreases as W C  increases, and the rate at which W D  decreases becomes lower as W C  increases. In other words, W C  decreases as W D  increases, and the rate at which W C  decreases becomes lower as W D  increases. If the pulse width is set in this manner, suitable grayshade display by pulse width modulation is also possible in the charge-discharge drive method while application of a DC voltage to each liquid crystal element over a long time period can be prevented. If the conception of the pulse width modulation in the conventional four-value drive method is directly applied, W C  and W D  are made equal to each other. In the first embodiment, however, that conception is not applied and, specifically, pulse width setting is performed in such a manner that, when one of W C  and W D  is increased, the other is reduced. Further, the first embodiment has been made upon knowing that not only reducing the other but also reducing the rate of this reduction is required to enable suitable grayshade display. The first embodiment is characterized mainly by this conception. 
     In the case of grayshade display using pulse height modulation in a charge-discharge drive method, e.g., that disclosed in Japanese Patent Laid-Open No. 125225/1990, there is the problem of difficulty in performing voltage control for obtaining the desired gray scale, which results in a high cost of a liquid crystal display device. This problem, however, can be solved according to the first embodiment. 
     FIG. 9 shows the result of a measurement of the relationship between gray scale data in the charging mode and gray scale data in the discharging mode. For this measurement, gray scale data in the charging mode, for example, is first changed. Thereafter, gray scale data in the discharging mode is changed so that the liquid crystal (pixel electrode) applied voltages (V LC  at times t 1  and t 2  in FIG. 2) immediately after the periods of selecting by the first and second selecting voltages V S1  and V S2  are equal to each other. The relationship between the groups of gray scale data in the charging and discharging modes shown in FIG. 9 was obtained in this manner. The magnitude of this gray scale data corresponds to the pulse width of write pulses. 
     As can be understood from FIG. 9, if pulse widths W c  and W D  are set such that the liquid crystal applied voltages immediately after the periods of selecting with the first and second selecting voltages V S1  and V S2  (or at initial stages in the holding periods) are equal to each other, suitable grayshade display can be achieved and application of a DC voltage to each liquid crystal element over a long time period can be prevented. 
     (Second Embodiment) 
     FIG. 10 shows an example of drive waveforms in the second embodiment, and FIGS.  11 (A) and  11 (B) show enlarged diagrams of portions H and I of FIG.  10 . 
     In the second embodiment, in the charging mode, the scanning signal drive circuit  20  shown in FIG. 6 supplies the first selecting voltage V S1  in a second period T 2  following a first period T 1 , which is the first-half period in a 1H period (one horizontal scanning period) (T 1 =T 2 =0.5H). In the discharging mode, the scanning signal drive circuit  20  supplies −V PRE , which is a precharge voltage, in a third period T 3 , which is the first-half period of another IH period, and supplies the second selecting voltage V S2  in a fourth period T 4  following the third period T 3  (T 3 =T 4 =0.5H). 
     In the charging mode, the data signal drive circuit  30  keeps the data voltage at a low level for the same period in the first period T 1  as a period TH 2  in the second period T 2  through which the data voltage is at a high level (with respect to a middle voltage between the ON voltage and the OFF voltage). That is, the data signal drive circuit  30  keeps the data voltage at the low level for a period TL 1  (=TH 2 ). The data signal drive circuit  30  also keeps the data voltage at the high level for the same period in T 1  as a period TL 2  in T 2  through which the data voltage is at the low level. That is, the data signal drive circuit  30  keeps the data voltage at the high level in a period TH 1  (=TL 2 ). 
     On the other hand, in the discharging mode, the data signal drive circuit  30  keeps the data voltage at the low level for the same period in the third period T 3  as a period TH 4  in the fourth period T 4  through which the data voltage is at the high level. That is, the data signal drive circuit  30  keeps the data voltage at the low level for a period TL 3  (=TH 4 ). The data signal drive circuit  30  also keeps the data voltage at the high level for the same period in T 3  as a period TL 4  in T 4  through which the data voltage is at the low level. That is, the data signal drive circuit  30  keeps the data voltage at the high level in a period TH 3  (=TL 4 ). 
     In the above-described manner, the DC component (with respect to the middle voltage between the ON voltage and the OFF voltage) of the data voltage supplied to each data signal line can be made approximately zero independent of the gray scale. That is, as shown in FIGS.  11 (C) and  11 (C), even if the data voltage is at the high or lower level through the entire selecting period H/2, the DC component of the data voltage through the 1H period can be made zero. Thus, the DC component of the data voltage through the 1H period is zero without being influenced by setting of the display gray scale. As a result, occurrence of a so-called vertical crosstalk can be effectively prevented. 
     For example, in a case where OFF display is made on regions R 2 , R 2 , R 3 , and R 4  while ON display is made on a region R 5 , that is, bright display (R 5 ) is made with a dark background (R 1 , R 2 , R 3 , and R 4 ), there is a possibility of occurrence of a vertical crosstalk, such as that shown in FIG. 12 (A), in the regions R 3  and R 4  above and below the region R 5 . Such a vertical crosstalk can be reduced substantially effectively by performing 1H inverting drive (driving by inverting the polarity of the liquid crystal applied voltage with respect to each scanning line). However, if area grayshade display (a grayshade made by changing the ratio of the number of ON pixels and the number of OFF pixels in each of pixel units consisting of a plurality of pixels) or zebra display such as shown in FIG.  12 (B) or  12 (C) is made on the region R 5 , a vertical crosstalk occurs even if 1H inverting drive is performed. According to this embodiment, even in such a situation, the DC component of the data voltage is zero independent of the gray scale, and the ON voltage period and the OFF voltage period in one horizontal scanning period is 1:1 independent of the display pattern, thus preventing occurrence of a vertical crosstalk such as that shown in FIG.  12 (D). 
     As drive waveforms for keeping the DC component of the data voltage zero independent of the gray scale, those shown in FIGS.  10  and  11 (A) to (D) are particularly preferred considering ease of waveform formation and ease of control. However, other various waveforms equivalent to these are also available. 
     (Third Embodiment) 
     The third embodiment relates to details of an example of a liquid crystal display device arranged in accordance with the first and second embodiments. As shown in FIG. 13, this liquid crystal display device includes a liquid crystal panel  110 , a scanning signal drive circuit  120 , and a data signal drive circuit  130 . The data signal drive circuit  130  includes a conversion table circuit  132 , a grayshade display fundamental clock generation circuit  134 , and a drive circuit  136 . 
     The grayshade display fundamental clock generation circuit  134  generates a grayshade display fundamental clock GCLK shown in FIG.  14 . The generated GCLK is output to the drive circuit  136 . As shown in FIG. 13, GCLK is output in accordance with different timings with respect to the charging and discharging modes. GCLK is a signal for determining timing of applying the data voltage to each liquid crystal element according to each value of gray scale data. 
     For example, in the charging mode, the drive circuit  136  is supplied with GCLK by timing indicated at E in FIG.  14 . If the gray scale data is (001), the drive circuit  136  changes the data voltage from VH to −VH by the fall of a pulse  61  of GCLK. Similarly, if the gray scale data is (010), the drive circuit  136  changes the data voltage from VH to −VH by the fall of a pulse  62  of GCLK. 
     On the other hand, in the discharging mode, the drive circuit  136  is supplied with GCLK by timing indicated at F in FIG.  14 . If the gray scale data is (001), the drive circuit  136  changes the data voltage from VH to −VH by the fall of a pulse  71  of GCLK. Similarly, if the gray scale data is (010), the drive circuit  136  changes the data voltage from VH to −VH by the fall of a pulse  72  of GCLK. Thus, grayshade display with different write pulse widths set with respect to the charging and discharging modes can be performed. 
     FIG. 15 shows an example of arrangement of the grayshade display fundamental clock generation circuit  134 . As shown in FIG. 15, this grayshade display fundamental clock generation circuit  134  includes counters  152 - 1 ,  152 - 2 , . . . ,  152 - 8 , decoders  154 - 1 ,  154 - 2 , . . . ,  154 - 8 , and a logical add circuit  160 . The counter  152 - 1  and the decoder  154 - 1  correspond to gray scale data (000), the counter  152 - 2  and the decoder  154 - 2  correspond to gray scale data (010), . . . , and the counter  152 - 8  and the decoder  154 - 8  correspond to gray scale data (111). 
     The counters  152 - 1  to  152 - 8  are supplied with count initial value data from the conversion table circuit  132  shown in FIG. 13, and perform the count-up (or count-down) operation from an initial state corresponding to the count initial value data. The decoders  154 - 1  to  154 - 8  form pulses of GCLK by decoding outputs from the counters  152 - 1  to  152 - 8 . In the charging mode, for example, the decoder  154 - 1  forms pulse  60  shown in FIG. 14, the decoder  154 - 2  forms pulse  61 , . . . , and the decoder  154 - 8  forms pulse  67 . In the discharging mode, the decoder  154 - 1  forms pulse  70 , the decoder  154 - 2  forms pulse  71 , . . . , and the decoder  154 - 8  forms pulse  77 . The logical add circuit  160  logically combines outputs from the decoders  154 - 1  to  1548 , thereby forming GCLK. 
     In this embodiment, the counters  152 - 1  to  152 - 8  are loaded with different groups of count initial value data with respect to the charging and discharging modes. For example, in the charging mode, if the gray scale data is (001), count initial value data for generating pulse  61  by the timing shown in FIG. 14 is loaded from the conversion table circuit  132  into the counter  152 - 2 . On the other hand, in the discharging mode, if the gray scale data is (001), count initial value data for generating pulse  71  by the timing shown in FIG. 14 is loaded from the conversion table circuit  132  into the counter  152 - 2 . 
     The conversion table circuit  132  determines one of the charging and discharging modes according to a mode select signal shown in FIG. 13, and outputs count initial value data corresponding to the determined mode to the grayshade display fundamental clock generation circuit  134 . The conversion table circuit  132  incorporates a conversion table memory in which the above-described count initial data is stored so that the pulse widths W C  and W D  of write pulses in the charging and discharging modes have the relationship shown in FIG.  7 (B). 
     The drive circuit  136  shown in FIG. 13 also has a function of forming data signals in the periods T 1  and T 3  from data signals in the periods T 2  and T 4  shown in FIGS.  11 (A) and  11 (B). This can be achieved by forming signals in the inverted relationship with the data signals in the periods T 2  and T 4  and by outputting the formed signals before outputting the data signals in the periods T 2  and T 4 . 
     The fourth embodiment relates to electronic apparatuses including the liquid crystal display device described above with respect to the first to third embodiments. 
     Various electronic apparatuses will be described with reference to FIGS. 16 to  21 (C). 
     Referring to FIG. 16, a microcomputer is incorporated in a remote controller  9100  for an air controller  9000 . The controller  9100  controls the air controller  9000  and has a liquid crystal display device  9200 , which displays the operating state of the air controller, etc. 
     Referring to FIG. 17, a microcomputer is incorporated in an electronic calculator  9300 , which has input keys  9410  and a liquid crystal display device  9400 . 
     Referring to FIG. 18, a microcomputer is incorporated in a portable telephone set  9500 , which has input keys  9420  and a liquid crystal display device  9600 . 
     The above-described electronic apparatuses are, for example, portable electronic apparatuses using batteries (including solar cells). FIG. 19 schematically shows the overall configuration of a control circuit of a liquid crystal display device incorporated in such electronic apparatuses. 
     A microcomputer  9720  shown in FIG. 19 is incorporated in the controller for the air controller shown in FIG.  16 . However, it can also be applied to electronic apparatuses such as those shown in FIGS. 17 and 18. 
     The microcomputer  9720  shown in FIG. 19 includes a CPU  9610 , an oscillator circuit  9620 , a frequency divider circuit  9630 , an input circuit  9640 , a timer circuit  9645 , a power supply circuit  9650 , a ROM  9670 , a RAM  9680 , an output circuit  9690 , a control circuit  9700 , an infrared output controller  9710 , etc. 
     The input circuit  9640  and the output circuit  9690  are, for example, communication interface circuits interfacing with the input keys  9410  or the like. The control circuit  9700  is a circuit for controlling the liquid crystal display device  9200  and so on to make the displays of various states. The infrared output controller  9710  is a circuit for on/off-drives an infrared emitting diode D 1  through a switching transistor Q 100 . 
     The liquid crystal display device described with respect to the first to third embodiments can also be used in a personal portable information apparatus (personal digital assistance)  1000  such as that shown in FIG.  20 . 
     This information apparatus  1000  has an IC card  1100 , a simultaneous translation system  1200 , a handwriting screen  1300 , TV conference systems  1400   a  and  1400   b,  map information system  1500 , and a data preparation system  1660 . Image displays for these systems are made by the liquid crystal display device of the first to third embodiments. The information apparatus  1000  further has, in an input and output interface unit  1600 , a video camera  1610 , a speaker  1620 , a microphone  1630 , an input pen  1640 , and an earphone  1650 . 
     The liquid crystal display device described with respect to the first to third embodiments can also be applied to a liquid crystal projector  1010 , such as that shown in FIGS.  21 (A),  21 (B), and  21 (C), which is a kind of electronic apparatus. FIG.  21 (A) illustrates a state where a given image is projected from a projection opening  1012  onto a display area set as desired, e.g., a screen  1016 . An infrared emitting portion  1036  is provided in the remote controller  1020  at a front end to transmit an operating signal to the liquid crystal projector  1010 . As shown in FIGS.  21 (B) and  21 (C), infrared receiving portions  1014   a  and  1014   b  are provided in front and rear surfaces of the liquid crystal projector  1010 , thereby enabling an operator to remote-control the liquid crystal projector  1010  on each of the front and rear sides. 
     The present invention is not limited to the above-described first to fourth embodiments. The present invention can be modified in other various ways without departing from the gist of the invention. 
     For example, the first and second embodiments may be combined to provide a liquid crystal device or the like having further improved display characteristic. 
     The drive waveforms in accordance with the present invention are not limited to those described with respect to the first to third embodiments, and can be modified in various ways. For example, FIG. 22 shows an example of the drive waveforms in the case where the selecting period is 1H, different from that shown in FIG.  10 . Also referring to FIG. 22, in comparison with FIG. 10, write pulses  80  and  82  are shifted into the first half of the selecting period. By shifting write pulses into the front half in this manner, gentler gray scale steps can be obtained to enable accurate grayshade representation. In FIGS. 10 and 22, examples of the waveforms for 1H inverting drive are illustrated. However, nH inverting drive (drive of inverting the polarity at every nth scanning lines) may be performed instead of 1H inverting drive. It is also possible to perform only frame inverting drive without performing 1H inverting drive. 
     The drive waveforms of the charge-discharge drive method to which the present invention can be applied are not limited to those such as shown in FIGS. 2,  5 (A), and  5 (B). 
     The arrangement of the display device with which the present invention can be realized is not limited to that shown in FIG. 13, and any other arrangement may also be used. 
     The kind of display device to which the present invention is applied is not limited to a liquid crystal display device, and the display element is not limited to a liquid crystal element. 
     INDUSTRIAL APPLICABILITY 
     The present invention is a drive method most suitably used as a charge-discharge method, and is useful in the case of use as a display device capable of grayshade display by pulse width modulation, and is suitable for use as a display device having an improved display characteristic in an electronic apparatus.