EP0619572B1 - Method of driving a liquid crystal display panel - Google Patents
Method of driving a liquid crystal display panel Download PDFInfo
- Publication number
- EP0619572B1 EP0619572B1 EP19930302765 EP93302765A EP0619572B1 EP 0619572 B1 EP0619572 B1 EP 0619572B1 EP 19930302765 EP19930302765 EP 19930302765 EP 93302765 A EP93302765 A EP 93302765A EP 0619572 B1 EP0619572 B1 EP 0619572B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- positive
- negative
- liquid crystal
- side field
- crystal display
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
- G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
- G09G3/3611—Control of matrices with row and column drivers
- G09G3/367—Control of matrices with row and column drivers with a nonlinear element in series with the liquid crystal cell, e.g. a diode, or M.I.M. element
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/02—Improving the quality of display appearance
- G09G2320/0204—Compensation of DC component across the pixels in flat panels
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/2007—Display of intermediate tones
- G09G3/2011—Display of intermediate tones by amplitude modulation
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/2007—Display of intermediate tones
- G09G3/2014—Display of intermediate tones by modulation of the duration of a single pulse during which the logic level remains constant
Definitions
- the present invention relates to a liquid crystal display panel of the active matrix type which uses non-linear resistance elements as switching elements.
- the invention relates to a liquid crystal display panel having non-linear resistance elements that exhibit asymmetric non-linear characteristics depending upon the polarity of a voltage applied to the elements.
- liquid crystal display panels are becoming large, and the liquid crystal display panels of a simple matrix constitution which employ multiplex drive systems have a problem of a decrease in contrast with an increase in the rate of time division, making it difficult to obtain a sufficient degree of contrast in the case when they have 200 or more scanning lines.
- a liquid crystal display panel of the active matrix type in which the individual liquid crystal pixels are provided with a switching element.
- the liquid crystal display panels of the active matrix type can roughly be divided into those of the three-terminal type which use thin-film transistors and those of the two-terminal type which use non-linear resistance elements. From the standpoint of construction and fabrication, however, the panels of the two-terminal type are superior.
- the panels of the two-terminal type include those of the diode type, varistor type, MIM (metal-insulator-metal) type and the like types. Among them, however, the panel of the MIM type is particularly simple in construction and can be fabricated using a reduced number of steps.
- Fig. 10 shows a constitution of a liquid crystal display panel which employs non-linear resistance elements.
- Scanning electrodes S1 to SN and signal electrodes D1 to DN are provided on the opposing surfaces of two pieces of glass substrate.
- a display pixel consisting of a non-linear resistance element 41 and a liquid crystal pixel 42 is formed at each intersecting portion of the scanning electrode and the signal electrode.
- the non-linear resistance element exhibits a small resistance and the liquid crystal pixel is turned on with a small time constant.
- the drive voltage is turned off, the non-linear resistance element exhibits a large resistance and the electric discharge takes place with a large time constant.
- the result therefore is an increase in the ratio of effective values of voltages applied to the liquid crystals when they are to be turned on and off, making it possible to carry out the multiplex driving while maintaining a high pixel density.
- Non-linear resistance elements exhibit asymmetric non-linear characteristics depending upon the polarity of the applied voltage. That is, referring to Fig. 2 which shows the transmission factor with respect to the write voltage, the positive-side characteristics and the negative-side characteristics are asymmetrical to each other due to the asymmetric characteristics of the non-linear resistance element.
- the positive side stands for the case where a positive voltage is applied to the non-linear resistance element when the display pixel is regarded to be an equivalent circuit in which the non-linear resistance element and the liquid crystal pixel are connected in series
- the negative side stands for the case where a negative voltage is applied thereto.
- Fig. 11 shows voltage-current characteristics wherein large asymmetric characteristics are exhibited with respect to the polarity of the applied voltage.
- the curve A represents element characteristics of the positive side and the curve B represents element characteristics of the negative side.
- the voltage applied to the liquid crystal pixel is inverted for every field (period from a given scan to a next scan of the same line) or is inverted for every lien by the AC driving method.
- the voltage applied to the liquid crystal pixel under the condition where the non-linear resistance element exhibits asymmetric non-linear characteristics depending on the positive side and the negative side as described above, different voltages are eventually applied to the liquid crystal pixel since different voltages are applied to the non-linear resistance element depending on the positive side and the negative side.
- Japanese Patent Application No. 181229/1989 discloses a method of enhancing the quality of display by compensating asymmetric non-linear characteristics.
- the driving method disclosed in application No. 181229/1989 will now be described with reference to Figs. 12 and 11.
- the feature of this driving method resides in that different offset voltages, i.e., Voff 3 and Voff 2 are applied to the scanning electrode depending upon writing and nonwriting.
- the offset voltages are set as described below.
- an element turn-on current during writing determined from the drive voltage and an element turn-off current during the non-writing are drawn on the diagram of voltage-current characteristics of a non-linear resistance element of Fig. 11.
- a voltage is found that corresponds to an intermediate point P1 of the voltage corresponding to the turn-on current between the positive side and the negative side, and is denoted as Voff 3.
- a voltage is found that corresponds to an intermediate point P2 of the voltage corresponding to the turn-off current between the positive side and the negative side, and is denoted as Voff 2.
- the offset voltage is not simply applied but the offset voltages are independently set depending on the writing and the non-writing voltages, in order to realize the drive voltage that correctly corresponds to the voltage-current characteristics of the positive side and negative side of the non-linear resistance element.
- the above-mentioned method of adjusting the offset voltage of the scanning signal is capable of preventing the quality of the display from deteriorating due to the asymmetric characteristics of the non-linear resistance element, but is not sufficient since the amplitude of the data signal remains constant and the transmission factor modulation range of the liquid crystal pixel for the write voltage is different depending on the positive side and the negative side.
- Fig. 13 shows waveforms of data signals in the case when the gradation is displayed using pulse width modulation.
- the ratio of a period f in which the voltage is Vd1 to a period e in which the voltage is Vd2 is changed depending upon the gradation.
- the object of the present invention is to provide a method of driving a liquid crystal display panel based on a pulse-width-modulation writing system of a high display quality which is free from problems caused by the pulse waveforms applied to the signal electrodes.
- European patent application EP-A-0360523 discloses a system in which the amplitude of the data signal is varied between positive and negative frames to avoid flicker; however, the pulse width ratio is set to the same value irrespective of whether it is in a positive frame or a negative frame.
- European patent application EP-A-0508628 discloses a liquid crystal display device capable of a gradational display, including a plurality of scanning electrodes and a plurality of signal electrodes; a matrix of display elements corresponding to points of intersection of the scanning electrodes and the signal electrodes, each of the display elements having both a liquid crystal pixel and a non-linear resistance element that exhibits asymmetric non-linear characteristics, depending on the polarity of the applied voltage, so as to exhibit asymmetric electro-optical characteristics; means for supplying scanning signals to the scanning electrodes; and means for supplying a data signal which comprises gradational information to the signal electrodes.
- the present invention is characterised over the disclosure of EP-A-0508628 in that said data signal is in the form of a bipolar pulse in which the ratio of the width of the positive portion to the width of the negative portion is determined by the gradation to be displayed, said ratio being set independently for the positive-side field and for the negative-side field, according to the asymmetric electro-optical characteristics of the display elements, so as to converge the display intensity at the maximum, minimum and intermediate values of the gradation during the positive-side field and negative-side field.
- the liquid crystal display panel used in this embodiment has the constitution of Fig. 10 that is used by the conventional driving method. Moreover, the non-linear resistance element exhibits the same characteristics as those employed by the conventional driving method, and its voltage-current characteristics are as shown in Fig. 11. According to an example useful for understanding the invention but not forming an embodiment of the invention, the liquid crystal display panel is driven by an application voltage, that is, by applying a scanning voltage shown in Fig. 1 to the scanning electrode and by applying a data signal voltage of Fig. 1 and the like to the signal electrode. The waveforms of these signals will now be described in detail.
- the voltages c and d of scanning signals during the non-writing period are those obtained by adding the offset voltage Voff2 of Fig. 12 to the bias voltages Vbias 1 and Vbias 2. It has been known that the drivability increases when the bias voltage is applied, and the asymmetric characteristics of the element during the non-writing are relatively compensated when the offset voltage is applied.
- Fig. 2 is a diagram showing application voltage characteristics for the transmission factor during the writing when the data signal voltage is set to OV and the application voltages during the writing onto the pixel in the two fields are so found that the transmission factor is the same between the positive-side field and the negative-side field during the writing.
- the modulation range of the transmission factor is set to be from T1 to T2
- the corresponding application modulation voltage during writing is a2 in the positive-side field and is b2 in the negative-side field.
- the transmission factor is modulated by the method of modulating the pulse amplitude from the signal electrode; as shown in Fig.
- This offset voltage can be optimized for the pulse amplitude modulation and creates a special case of offset voltage from the standpoint of prior art.
- the maximum amplitude of the data signal is set to be the voltage that corresponds to the modulation range T1 to T2 of transmission factor of Fig. 2 and the amplitude thereof is controlled corresponding to the gradation. That is, the voltage a2 is applied in the positive-side field and the voltage b2 is applied in the negative-side field.
- the transmission factor is modulated by the method of modulating the width of the pulse from the signal electrode.
- the difference of the transmission is as shown in Fig. 4 during the intermediate gradation.
- Ta and Td correspond to T2 and T1 of Fig. 2
- Tb and Tc are intermediate transmission factors.
- the pulse amplitudes of data signals corresponding to T2 and T1 are the same as that of Fig. 2.
- the ratio of the widths f and e of the data signals is set to be constant in the positive-side field and the negative-side field in the pulse width modulation method for the gradation display.
- a problem as shown in Fig. 4 arises in the intermediate gradation when a liquid crystal display panel is driven. Therefore, for the above problem, as shown in Fig.
- the pulse amplitudes a2'(a2''), b2'(b2") of the data signals in the intermediate gradation is corrected to be a2'(a2"), b2'(b2'') in the positive-side field and the negative-side field respectively, so that the transmission factor becomes constant for each of the gradations.
- transmission range T1 to T2 desired to modulate is determined in Fig. 2.
- the pulse amplitudes of data signals are set to be equal to each other in the positive-side field and the negative-side, while the difference at both ends of the pulse width occurs in the prior art as shown in Fig. 14.
- al, bl, b0 in Fig. 8 are set to make the difference as small as possible, when the pulse widths are set to be equal to each other in the positive-side field and the negative-side field to drive the liquid crystal display panel, the difference of the transmission factor exists for each of gradations as shown in Fig. 14. Therefore the pulse width is corrected to e ⁇ e', if e ⁇ g (Fig.
- the applied voltages from the signal electrode are four levels, that is, there are a2/2, -a2/2 in the positive-field and b2/2, -b2/2 in the negative-field.
- Fig. 9 shows an example of thereof.
- the offset voltage during the writing Voffl is set to be al-b3.
- This offset voltage can be optimized for the pulse width modulation in this way and creates a special case of offset voltage from the standpoint of prior art.
- the driving method of this embodiment makes it possible to apply the same voltage to the liquid crystal layer in the positive-side field and in the negative-side field. As a result, no DC component is applied, and the display is realized without flickering and scorching of the image.
- the signal levels of the data signals are changed depending upon the characteristics of the non-linear resistance element, and the liquid crystal pixels are impressed with a write voltage that corresponds more correctly to the positive-side and negative-side transmission factor modulating ranges, making it possible to obtain a display with little flickering and scorching.
- the pulse width is adjusted depending upon the non-linear characteristics. Therefore, an equal voltage is applied to the liquid crystal layer on the positive side and on the negative side, making it possible to realize the gradation display with less flickering and scorching.
- the data signals may be formed in the three levels to provide a reasonable circuit construction of a voltage supplying source and to drive the liquid crystal display panel with high accuracy.
Description
Claims (6)
- A liquid crystal display device capable of a gradational display, including a plurality of scanning electrodes (S1 to SN) and a plurality of signal electrodes (D1 to DN); a matrix of display elements corresponding to points of intersection of the scanning electrodes and the signal electrodes, each of the display elements having both a liquid crystal pixel (42) and a non-linear resistance element (41) that exhibits asymmetric non-linear characteristics, depending on the polarity of the applied voltage, so as to exhibit asymmetric electro-optical characteristics; means for supplying scanning signals to the scanning electrodes; and means for supplying a data signal which comprises gradational information (Ta, Tb, Tc, Td) to the signal electrodes, characterised in that:
said data signal is in the form of a bipolar pulse (a2, b2) in which the ratio of the width (f) of the positive portion to the width (e) of the negative portion is determined by the gradation to be displayed, said ratio being set independently for the positive-side field and for the negative-side field, according to the asymmetric electro-optical characteristics of the display elements, so as to converge the display intensity at the maximum (Ta), minimum (Td) and intermediate values (Tb, Tc) of the gradation during the positive-side field and negative-side field. - A liquid crystal display device according to claim 1 wherein the amplitude (a2, b2) of said bipolar pulse is different in the positive-side field (a2) and the negative-side field (b2).
- A liquid crystal display device according to claim 1 wherein the amplitude of said bipolar pulse is the same in the positive-side field and the negative-side field.
- A liquid crystal display device according to claim 1, wherein the amplitude of said bipolar pulse is set independently for the positive-side field and for the negative-side field, according to the asymmetric electro-optical characteristics of the display elements, so as to converge the display intensity at the maximum, minimum and intermediate values of the gradation during the positive-side field and negative-side field.
- A liquid crystal display device according to any preceding claim wherein the bipolar pulse has equal positive and negative excursions.
- A liquid crystal display device according to any preceding claim, wherein the scanning signal comprises a component which has one form during positive-side fields and a polarity inverted form during negative-side fields, and a bias component selected to provide, in conjunction with the data signal, equal display intensity at both extremes of the displayed gradation for both positive-side fields and negative-side fields.
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE1993622154 DE69322154T2 (en) | 1993-04-08 | 1993-04-08 | Method for controlling a liquid crystal display panel |
EP19930302765 EP0619572B1 (en) | 1993-04-08 | 1993-04-08 | Method of driving a liquid crystal display panel |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP19930302765 EP0619572B1 (en) | 1993-04-08 | 1993-04-08 | Method of driving a liquid crystal display panel |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0619572A1 EP0619572A1 (en) | 1994-10-12 |
EP0619572B1 true EP0619572B1 (en) | 1998-11-18 |
Family
ID=8214379
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19930302765 Expired - Lifetime EP0619572B1 (en) | 1993-04-08 | 1993-04-08 | Method of driving a liquid crystal display panel |
Country Status (2)
Country | Link |
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EP (1) | EP0619572B1 (en) |
DE (1) | DE69322154T2 (en) |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB9704149D0 (en) * | 1996-08-16 | 1997-04-16 | Philips Electronics Nv | Active matrix display devices and methods of driving such |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5117298A (en) * | 1988-09-20 | 1992-05-26 | Nec Corporation | Active matrix liquid crystal display with reduced flickers |
EP0376233B1 (en) * | 1988-12-29 | 1996-03-20 | Seiko Instruments Inc. | Driving system for a display device |
TW200572B (en) * | 1991-03-20 | 1993-02-21 | Seiko Epson Corp |
-
1993
- 1993-04-08 DE DE1993622154 patent/DE69322154T2/en not_active Expired - Fee Related
- 1993-04-08 EP EP19930302765 patent/EP0619572B1/en not_active Expired - Lifetime
Also Published As
Publication number | Publication date |
---|---|
DE69322154D1 (en) | 1998-12-24 |
DE69322154T2 (en) | 1999-07-01 |
EP0619572A1 (en) | 1994-10-12 |
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