Active matrix liquid crystal display with reduced flicker

Abstract: In a liquid crystal display which includes liquid crystal display pixels, thin film diodes that are connected respectively to the liquid crystal display pixels, a plurality of rows of scan lines connected to the liquid crystal display pixels, data lines connected to the liquid crystal display pixels via the thin film diodes, and means for supplying a signal voltage between the scan line and the data line that changes its polarity for each frame, the applied signal voltage has an absolute value that is different for the different polarities. In this way the asymmetry that exists in the thin film diode can be compensated.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an active matrix liquid crystal display, and more particularly to an active matrix liquid crystal display using a nonlinear resistance element. Description of the Related Art In recent years, applications of liquid crystal displays (LCDs) centered around those of twisted nematic (TN) type have become wide spread, with a large quantity of them being utilized in the fields of wrist watches and hand calculators. On top of it, matrix type displays that can handle arbitrary display of such items as characters and graphics have also been finding their ways into industrial applications. In order to expand the application field for the matrix type LCDs, it is necessary to increase their display capacity. However, the rise of the curve for the voltage versus transmissivity characteristic is not steep enough so that, if the number of scanning lines for multiplexed drive is increased in order to enhance the display capacity, the ratio of the effective voltages that are applied respectively to a selected pixel and a nonselected pixel is reduced which gives rise to a crosstalk of an increase in the transmissivity of the selected pixel and a decrease in the transmissivity of the nonselected pixel. As a result, there is created a marked decrease in the display contrast, and the angle of visibility for which a reasonable contrast can be obtained becomes narrowed down conspicuously. For this reason, a limit of about 60 lines for the scanning lines existed in the conventional LCDs. The conventional LCD of the above kind will be referred to as a simple matrix LCD. Now, in order to sharply increase the display capacity of a matrix type LCDs, there has been disclosed an active matrix LCD in which a switching element is arranged in series to each pixel of the LCD. As the switching element of the experimental models of active matrix LCDs announced so far, use has mostly been made of a thin film transistor (TFT) having amorphous silicon or polycrystalline silicon as the semiconductor material. On the other hand, active matrix LCDs which make use of a thin film diode (referred to as TFD hereinafter) are also drawing attention for the reason that there can be expected a simplification of the manufacturing process, an improvement in the yield and a reduction in the cost due to relatively simple manufacturing method and device structure. Out of such thin film two-terminal element type active matrix LCD (abbreviated as TFD-LCD hereinafter), the LCD which is considered to be the closest to the practical use is that which uses a metal-insulator-metal element (abbreviated as MIM hereinafter) as the TFD. Besides MIM, a diode ring in which two amorphous pin diodes are connected in parallel with their polarities reversed to each other and a back-to-back diode in which two pin diodes are connected in series with their polarities reversed, are known as TFDs. All of the TFDs mentioned in the above are nonlinear resistance elements in which the current increases rapidly in nonlinear fashion as the voltage applied across the ends of the element is increased. By connecting such a TFD to a liquid crystal body in series, the rise of the curve for the voltage versus transmissivity characteristic becomes steep, which makes it possible to increase the number of scanning lines. Prior examples of LCDs that make use of such MIMs are described representatively in D.R. Baraff et al., "The Optimization of Metal-Insulator-Metal Nonlinear Devices for Use in Multiplexed Liquid Crystal Displays," IEEE Trans. Electron Devices, Vol. ED-28, pp. 736 - 739 (1981) and in Shinji Morozumi et al., "250 x 240 Element LCD Addressed by Lateral MIM," Technical Report of Television Society (IPD 83-8), pp. 39 - 44, (issued in December, 1983). In addition, in patent publication gazette, they are disclosed representatively in Japanese Patent Laid Open, Gazette No. 52-149090 and Japanese Patent Laid Open, Gazette No. 55-161273 with details on the principle of operation. In MIMs, the oxide or nitride of tantalum (Ta) or silicon is mainly used as the material for the insulator layer. Further, although almost any metal can be used as the metal in MIMs, chromium or tantalum is mainly made use of. Out of various analytical expressions that can be employed to represent the current versus voltage (I-V) characteristic of a nonlinear resistance element, the following is known as a representative formula: I = A·V α In the above expression, I is the current, V, the voltage, α , a nonlinear coefficient and A is a proportionality constant. In the MIMs mentioned earlier, the value of α is 6 or greater. Referring to Fig. 1 and Fig. 2, in a TFD-LCD, a salient electrode that is connected to a lead electrode 3 is provided on a lower glass substrate 1, an insulator film 4 is provided on the salient electrode 11, an upper electrode 5 is provided on the insulator film 4, where the upper electrode 5 is connected to a lower transparent electrode 6 which is to become a pixel. On the opposite side of the lower glass substrate 1 there is disposed an upper glass substrate 7, an upper transparent electrode 9 is provided thereon, and a liquid crystal layer 10 is inserted between the lower glass substrate 1 and the upper glass substrate 7. A TFD is formed by the salient electrode 11, the insulator film 4 and the upper electrode 5. Referring to Fig. 3, the lower transparent electrodes 6 are arranged in a lattice form, and the lower transparent electrodes 6 are joined vertically by the lead electrode 3. The upper transparent electrode 9 is provided so as to join the pixels horizontally and a pixel is formed where a lower transparent electrode 6 and an upper transparent electrode 9 are overlapped. Normally, the upper transparent electrode 9 is used as a scan signal line while the lead electrode 3 is used as a data signal line, but there may be found cases where their roles are interchanged. An equivalent circuit for one pixel of a TFD-LCD panel may be represented in the form as shown in Fig. 4 in which a TFD 13 and a liquid crystal element 14 are connected in series, and a data signal line 15 and a scan signal line 16 are connected on both ends. A data signal and a scan signal are applied to the data signal line 15 and the scan signal line 16, respectively, and the difference between these signal voltages becomes a voltage to be applied to the pixel. A specified row is selected by the scan signal, and only a pixel in that row to which is applied a selection signal becomes a displayable state. Fig. 5 shows a case in which the pixel under discussion is a selected pixel, and drive signals where selected pixels and nonselected pixels exist alternately on the data signal line 15. The scan signal (a) and the data signal (b) take on the values as shown in Table 1 below in each of the positive and negative frames. Here, the reason for inverting the polarity of the voltage applied to the liquid crystal between a negative and a positive values for each frame is for preventing deterioration of the liquid crystal layer. Further, the reason for applying a scan signal (V P - V D ) is for making the voltage applied to the selected pixel to be V P . One picture is scanned by each one of negative and positive frame, and the display contents are written in. The addressing period T AD is the writing interval, and the nonaddressing period T NA is the charge-holding interval. The ratio V D /V P of V D to V P is called the bias ratio which normally takes on a constant value. A voltage (c) applied to a pixel (or pixel-applied voltage) is (data signal) minus (scan signal) which takes on the value shown in Table 2. The liquid crystal voltage (d) varies corresponding to the values of the voltage signal (c), generating a display contrast. Note that what is meant by the liquid crystal voltage is the voltage applied across the ends of the liquid crystal element. It should be noted that all the values for the nonaddressed period in Table 2 are given within square brackets. The meaning for this is that the voltage applied to the pixel takes on the value within the brackets depending upon whether the content of the data signal is selected or nonselected. The I-V characteristic of a nonlinear element should ideally be symmetric with respect to the positive and negative signs of the voltage. In an actual MIM, however, asymmetry is fairly significant as can be seen from Fig. 6. Namely, there are many cases in which the value A⁺ of A in Eq. (1) for V > 0 and the value A⁻ of A for V < 0 are different, although α remains the same. When A⁻ > A⁺ holds, the absolute value of the voltage applied to the liquid crystal layer is larger for the negative frame than for the positive frame. Since the liquid crystal contrast is determined by the effective value of the liquid crystal voltage (d), flicker of the screen becomes more noticeable in such a case. United Kingdom Patent Application GB-A-2 134 300 describes an early TFT active matrix display, in which the polarity of the applied voltage is inverted more frequently than at the frame rate, e.g. on successive rows or groups of rows. A preferred active matrix liquid crystal display device embodying the present invention is described in more detail below and includes a plurality of lower electrodes arranged in a matrix form, thin film diodes that are respectively connected to the lower electrodes, a plurality of columns of lead electrodes connected respectively to the lower electrodes of each columns via the thin film diodes, a plurality of rows of upper electrodes provided respectively over each rows of lower electrodes separated with a predetermined space from the lower electrodes, a liquid crystal layer inserted between the lower electrodes and the upper electrodes, and means for applying signals with different polarities for every predetermined number of scanning lines and with different absolute values for every polarity, between the lead electrodes and the upper electrodes where one of the lead electrode and the upper electrode is used as a scanning line. Even when there exists asymmetry in a TFD with respect to the positive and negative polarities, by applying signals, with different absolute values for the positive and the negative polarities so as to cancel the asymmetry, between the leads electrodes and the upper electrodes, it becomes possible to symmetrize the voltages applied to the liquid crystal layer for the positive and the negative polarities, and hence to eliminate flickers. The polarity of the signal voltage applied between the lead electrode and the upper electrode is normally inverted for every frame. The drive signals in the case where the polarity is inverted for every frame are shown in Fig. 7. It is basically the same as the method shown in Fig. 5, only difference being that the absolute value of the pixel-applied voltage (c) which is the difference between the scan signal (a) and the data signal (b) is modified. Namely, the value of V P is modified to V P and V P ′ for the positive and negative frames, respectively, and the value of V D is similarly modified to V D and V D ′. Then, assuming that A⁻ > A⁺ holds, it becomes possible to equalize the absolute values of the liquid crystal voltage (d) between the positive and the negative frames by setting V P > V P ′ and V D > V D ′. The values of the liquid crystal voltage (d) are summarized in Table 3 below. Normally, the bias ratio is set equal for the positive and the negative frames (V D /V P = V D ′/V P ′), but this is not essential. By adjusting the ratios of the absolute value of the pixel-applied voltage for the positive and the negative frames, V P /V P ′ and (V P -2V D )/(V P ′-2V D ′), it is possible to find out ratios for which flickers can be eliminated. This ratio will be referred to as the optimum ratio for display. When the bias ratio is constant, one only needs to set V P /V P ′ as the optimum ratio for display. The pixel-applied voltage (c) is defined as (data signal) - (scan signal) which is summarized in Table 4 below. Further, when the driving voltage is raised to increase the pixel-applied voltage in the adjustment to set the optimum ratio for display, the liquid crystal molecules are raised sufficiently well and cause flickers to tend less easily recognized, with a result that setting to the optimum ratio for display being made more difficult. In such a case, adjustment needs be performed in the region where the rise of the liquid crystal molecules is not sufficient yet so that the flickers are observable most violently by reducing the driving voltage to some extent. According to this method, assuming that the bias ratio is constant, it is easy to find out an optimum ratio for display with no flickers by adjusting the ratio of the absolute values of the pixel-applied voltage for the positive and the negative frames. Although the magnitude of flickers can readily be judged visually, to be more exact one may adopt a method in which light that transmitted through the panel is received by a photodiode, amplified and then analyzed with a spectral analyzer. However, there is not a significant difference between the results by these two methods. Besides the above, there has already been proposed a method of inverting the signal polarity every one or two scanning lines in order to suppress the flickers. This is a method in which the driving voltages shown in Table 1 and Table 5 are alternately applied every one or two lines and the pixel-applied voltage becomes as shown in Table 2 and Table 6, so that the flickers look as if they are cancelled in the area of several pixels. However, the suppression of flickers by this method is incomplete with a certain degree of flickers still persisting. In the case of inverting the polarity every one or two scanning lines, it is also possible to eliminate flickers by changing the absolute value of the signal voltage to be applied between the lead electrode and the upper electrode corresponding to the polarity. The driving method for such a case is similar to the case of changing the polarity every frame shown in Fig. 7, except that the polarity is inverted every one or two scanning lines. That is to say, the driving voltages shown in Table 3 and Table 7 are applied alternately every one or two scanning lines. With the driving voltages of Table 3 and Table 7, the pixel-applied voltages become as shown in Table 4 and Table 8, respectively. BRIEF DESCRIPTION OF THE DRAWINGS The above and the further objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein: Fig. 1 is a sectional diagram for explaining the MIM-LCD panel; Fig. 2 is a plan view for explaining one pixel of the MIM-LCD panel; Fig. 3 is a plan view for explaining the MIM-LCD panel; Fig. 4 is an equivalent circuit diagram for one pixel of the MIM-LCD panel; Fig. 5 is a diagram for explaining the conventional 15 driving method of the MIM-LCD; Fig. 6 is a diagram for explaining the current versus voltage (I-V) characteristic; Fig. 7 is a diagram for explaining the driving method of the MIM-LCD of the present invention; Fig. 8 is a block diagram for explaining the liquid crystal display of a first embodiment of the present invention; Fig. 9 is a circuit diagram for explaining the driving voltage generating part of the first embodiment of the present invention; and Fig. 10 is a circuit diagram for explaining the switching circuit of the power source frame for the first embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) The driving method for this embodiment is substantially the same as the method shown in Fig. 7. However, in the driving method shown in Fig. 7, both of the scan signal (a) and the data signal (b) are swinging with 0V as the center (this voltage will be referred to as the center voltage). Accordingly, there are required both of the positive and negative power supplies which makes the situation complicated. In this case, it is possible to reduce the number of power supplies needed by changing the center voltages of the scan signal and the data signal without changing the liquid crystal voltage in Fig. 7 as a potential difference (the so-called phase difference driving method). An example of such a method is shown in Table 9 that follows. Namely, there are many cases in which the voltage V5 in the table is set to 0V (GND), but it is of course possible to set it to an arbitrary other voltage. In order to realize the driving method shown in Fig. 7 and Table 3, it is only necessary to set V LCD = V P , V LCD ′ = V P ′, V₁′ = V P ′ - V D ′, V₂′ = V P ′ - 2V D ′, V₃ = 2V D , V₄ = V D , and V₅ = 0. Referring to Fig. 8, the liquid crystal display of the present embodiment includes a control part 22, a driving voltage generating part 23, a scan driver part 24, a data driver part 25 and a liquid crystal display panel 26. A main body 21 is, for example, a personal computer or a television circuit. Upon receipt of a display signal from the main body 21, the control part 22 converts the signal to control signals for drivers of TFD-LCD, and sends them to the scan driver part 24 and the data driver part 25. With the signals from the control part 22, the scan driver part 24 and the data driver part 25 apply the voltages V LCD , V′ LCD , V₁, V₂, V₃ and V₄ following the signals from the driving voltage generating part 23 in accordance with Table 9. As shown in Table 9, frame signals are output corresponding to the negative and positive frames to the scan driver part 24 and the data driver part 25 from the control part 22. These signals are logic levels, and L (low level) and H (high level) in Table 3 may of course be interchanged. The driving circuit of the present embodiment is characterized in that the voltages V LCD , V LCD ′, V₁, V₂, V₃ and V₄ from the driving voltage generating part 23 are changed for the positive and the negative frames by the frame signal 27 from the control part 22. Such an operation is realized by a power frame switching circuit 31 in the driving voltage generating part 23 shown in Fig. 9. By the use of driving waveforms as in the above, the absolute value of the pixel-applied voltage which is the difference between the scan signal and the data signal can be set independently for each frame, which makes it possible to keep the effective value of the liquid crystal voltage V L at the same value between the frames. In this way, it becomes possible to obtain a TFD-LCD which is free from flickers. Referring to Fig. 9, the driving voltage generating part 23 obtains voltages V₁, V₂, V₃ and V₄ by dividing the voltage V LCD with resistors R₁, R₂, R₃, R₄, R₅ and R₆ in a voltage dividing circuit 32. These voltage levels are current-amplified in an amplifier circuit 33 to be applied to the scan driver part 24 and the data driver part 25. The voltage V LCD is set to different values for the positive and the negative frames by the frame signal 27 from the control part 22. A circuit which performs such a function is the power frame switching circuit 31. Normally, use is made of R₁, R₂, R₃, R₅ and R₆ that have an equal fixed resistance and R₄ that has a semi-fixed resistance, but it is not necessary to be limited to such an arrangement. As an example, one may take the case where the fixed resistance for resistors R₁ - R₃, R₅ and R₆ is 3 kΩ and the semi-fixed resistance of the resistor R₄ is 50 kΩ. Further, for the amplifier circuit 33 use is made of a voltage follower circuit which employs operational amplifiers, but it does not have be limited to such a choice. The operational amplifier is a differential amplifier with high input impedance and high gain. The power frame switching circuit 31 of the present embodiment is shown in Fig. 10. In the figure, OP₁, OP₂, OP₃ and OP₄ are operational amplifiers, VR₁, VR₂ and VR₃ are semi-fixed or variable resistors, and R₁₁, R₁₂ and R₁₃ are fixed resistors. The voltage V LCD is arranged to take the absolute value of V₁₁ and V₁₂ for the positive and the negative frames, respectively (V₁₁ > V₁₂). A voltage V₂₁ is set by the resistor VR₁. The voltage level V₂₁ is current-amplified by the operational amplifier OP₁ similar to the amplifier circuit 33 shown in Fig. 9. A voltage V₂₂ is set by dividing the voltage V₂₁ with the resistors VR₂ and R₁₁. The voltage V₂₂ is current-amplified with the operational amplifier OP₂. The voltages V₂₁ and V₂₂ are switched by the analog switch 40 according to the frame signal 27. The signal that takes on the voltages V₂₁ and V₂₂ for the respective frames is voltage-amplified by the operational amplifier OP₃, and current-amplified by the operational amplifier OP₄. Representative constants for the various circuits are as follows. Namely, VR₁ = 10 kΩ, VR₂ = 10 kΩ, VR₃ = 50 kΩ, R₁₁ = 4.7 kΩ, R₁₂ = 47 kΩ and R₁₃ = 10 kΩ. For the operational amplifiers OP₁, OP₂, OP₃ and OP₄, use is made of ordinary IC operational amplifiers, but those with high breakdown strength are preferred for the operational amplifiers OP₃ and OP₄. In addition, about 5V is appropriate for the voltage V HH . In Fig. 10, the operational amplifiers OP₃ and OP₄ are not indispensable, but analog switches with high breakdown strength are expensive so that these amplifiers were made use of in the present embodiment. Next, the structure and the method of manufacture of the MIM-LCD panel used in the present embodiment will be described. Referring to Fig. 1, the lower glass substrate 1 is covered with a glass protective film 2 of Ta₂O₅, SiO₂ or the like. The protective film 2 is not indispensable so that it is possible to omit the covering. Next, after forming a lead electrode 3 and a salient electrode 11 on top it, there is formed an insulator layer 4. Silicon nitride of the insulator layer 4 may be formed by various methods, but in the present embodiment, a layer of about 1000 Å thickness was formed by plasma CVD method that makes use a mixed gas of nitrogen gas, silane gas and hydrogen gas. The material for the upper electrode 5 was chosen to be Cr which was formed on the insulator layer 4 by resistive heating method, and patternized by the ordinary photolithography. The lower transparent electrode 6 was chosen to be made of indium oxide-tin oxide (usually called ITO) which was formed on the insulator layer 4 by magnetic sputtering, and patternized by the ordinary photolighography. The film formation on the upper glass substrate 7 and the patterning are almost identical to those of the ordinary simple multiplexed LCD. The upper glass substrate 7 is covered with a glass protective film 8 such as SiO₂, but the protective film 8 is not indispensable. The upper transparent electrode 9 is also made of indium oxide-tin oxide same as for the lower transparent electrode 6, and is formed by magnetic sputtering and patternized by the ordinary photolighography. The lower glass substrate 1 and the upper glass substrate 7 are laminated via a spacer such as glass fiber, and sealed with an ordinary epoxy adhesive. The thickness of the cell was chosen to be 8 µm. Both of the glass substrates 1 and 7 were subjected to an orientation treatment by rubbing. In that case, an orientation treatment film of polyimide or the like is often applied to them, but it is omitted in Fig. 1 since it is not indispensable. A quantity of ZLI-1565 (manufactured by Merck Corp.) which is a twisted nematic liquid crystal was injected to the cell through an injection hole to form a liquid crystal layer 10. By sealing the injection hole with an adhesive a TFD-LCD panel was completed. Fig. 2 shows an element pattern of one pixel on the lower glass substrate 1. As shown, the lower transparent electrode 6 is separated for each pixel. The front face of the electrode 3 is covered with the insulator layer 4 by anodic oxidation, and a small projection is formed extending from the lead electrode corresponding to each pixel. This salient electrode 11 intersects the upper electrode 5, and the intersecting part constitutes a MIM. Fig. 3 shows a portion of the structure of the TFD-LCD panel of the present embodiment. As shown, pixels are arranged in matrix form on the lower glass substrate 1, the lead electrode 3 extends in the vertical direction, and forms a terminal part 12 at its end part. The upper transparent electrode 9 on the upper glass substrate 7 shown in Fig. 1 is formed in the shape of a belt joining the pixels in the horizontal direction as shown in Fig. 3. The shape of the upper transparent electrode 9 is substantially the same as that of the electrode of the simple multiplex-driven LCD. When the voltage application method of Fig. 4 is adapted to the LCD with a structure as shown in Fig. 1 to Fig. 3, the upper transparent electrode 9 becomes a scan signal line and the data electrode 3 becomes a data signal line. When the TFD-LCD used in the present embodiment adopted the driving method indicated in Fig. 5, there was obtained a display with maximum contrast for V P = 19V and bias ratio of 9, but there occurred flickers in the display. It was easy to adjust to eliminate flickers completely by changing V P between the frames (namely, V P and V P ′) as in the driving method shown in Fig. 7 after making flickers to be conspicuous in half-tone display by taking V P in the range of 15 to 17V. At that time, it was found that V P = 14.3V, V P ′ = 17V so that the optimum ratio for display (= V P /V P ′) was 0.842. Here, the bias ratio was a constant value 9 for the positive and the negative frames. In particular, realization of a display with no flickers was especially easy to accomplish when a display is adopted in which the entire screen is covered with selected pixels (that is, it is in the on-state across the board). A high contrast display with contrast ratio greater than 20, no crosstalks and absolutely no flickers was obtained by raising the driving voltages to V P = 16V and V P ′ = 19V while keeping the bias ratio, namely, the ratio of V P to V P ′, constant. (Second Embodiment) The half-tone display was achieved by adopting the method of modulating the time width of the data signal for a selected pixel (namely, the pulse width modulation system). That is, 16 gradations were realized by digitizing a video signal by means of a 4-bit A/D converter, and varying the pulse width in accordance with the contrast curve of the liquid crystal. By further increasing the bit number of the A/D converter, it became possible to obtain higher level of gradation. It should be mentioned that in both cases of the embodiments described in the above, the value of V P /V P ′ was determined by visually adjusting the screen of the liquid crystal display so as to eliminate the flickers. Moreover, it should be noted that examples in which only silicon nitride MIM was used for the nonlinear resistance element were presented in the above embodiments. However, substantially the same display capability as in the above and having no flickers can also be obtained by the use of a MIM with other material, and a diode ring and a back-to-back diode as the nonlinear resistance element.

Claims: A liquid crystal display comprising: a plurality of lower electrodes (11) arranged in a matrix form of rows and columns on a substrate; a plurality of thin film non-linear resistance elements (4) each connected to a respective one of said lower electrodes; a plurality of columns of lead electrodes (3) each connected to said lower electrodes of a respective one of said lower electrode columns via said respective thin film non linear resistance elements; a plurality of rows of upper electrodes (9) each provided over said lower electrodes of a respective one of said lower electrode rows; a liquid crystal layer (10) inserted between said lower electrodes and said upper electrodes; and driving means (22-25) arranged to carry out scanning using either said upper electrode rows or said lead electrode columns as scanning lines, said driving means also being arranged to apply a signal between said lead electrodes and said upper electrodes such that the polarity of said signal is inverted for every predetermined number of scanning lines; characterised by said driving means (22-25) being arranged such that the absolute voltage value of said signal in the positive polarity is different to the absolute voltage value of said signal in the negative polarity, and such that the ratio of said absolute voltage values of said signal is that which causes the absolute value of the voltage that is applied to said liquid crystal layer to be substantially equal for both polarities. A liquid crystal display as claimed in claim 1, wherein said driving means (22-25) are arranged such that said polarity is inverted for each frame, where said frame comprises the carrying out of a scan of all the scanning lines. A liquid crystal display as claimed in claim 1, wherein said driving means (22-25) are arranged such that said polarity is changed every one scanning line. A liquid crystal display as claimed in claim 1, wherein said driving means (22-25) are arranged such that said polarity is changed every two scanning lines. A liquid crystal display as claimed in claim 2, wherein said driving means include: control means (22) for generating a frame signal; a first voltage generating means (31) for generating a first and a second voltage in response to said frame signal, said first voltage and said second voltage being different; a second voltage generating means (32,33) for generating a first and a second scan signal and a first and a second data signal in response to said first voltage, as well as a third and a fourth scan signal and a third and a fourth data signal in response to said second voltage, said first and said third scan signals being signals that select said scanning lines, said second and said fourth scan signals being signals that do not select said scanning lines, said first and said third data signals being signals that select said lower electrodes, said second and said fourth data signals being signals that do not select said lower electrodes, the sign of a first signal voltage obtained by subtracting said first data signal from said first scan signal being opposite to the sign of a second signal voltage obtained by subtracting said third data signal from said third scan signal, and the absolute value of said first signal voltage being different from the absolute value of said second signal voltage; scan signal supplying means (24) for applying said scan signals to said scanning lines in response to said frame signal; and data signal supplying means (25) for applying said data signals to data lines in response to said frame signal, said data lines comprising the either of said upper electrode rows or said lead electrode columns not being used as said scanning lines. A liquid crystal display as claimed in claim 5, wherein said first voltage generating means include: a first power supply (V HH ) for supplying a first supply voltage; a second power supply (Ground) for supplying a second supply voltage; a third voltage generating means (VR1) for generating a third voltage from said first supply voltage and said second supply voltage; a first terminal (OP1) connected to an output terminal of said third voltage generating means for receiving said third voltage; a fourth voltage generating means (VR2,R11) connected between said output terminal of said third voltage generating means and said second power supply (Ground) for generating a fourth voltage which is different from said third voltage; a second terminal (OP2) connected to an output terminal of said fourth voltage generating means for receiving said fourth voltage; and a fifth voltage generating means (40) for switching between said first terminal and second terminal in response to said frame signal and generating said first and said second voltages from said third and said fourth voltages, respectively. A liquid crystal display as claimed in any of claims 1 to 6, wherein said thin film non-linear resistance elements (4) are thin film diodes.

Inventors: HIRAI YOSHIHIKO C O NEC CORPOR, HIRAI, YOSHIHIKO C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1989
Main classification: G09G3
IPC codes: G09G3