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
  • G09G3/3622—Control of matrices with row and column drivers using a passive matrix
  • G09G3/3625—Control of matrices with row and column drivers using a passive matrix using active addressing
• • 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
• • 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
  • G09G3/3685—Details of drivers for data electrodes
  • G09G3/3692—Details of drivers for data electrodes suitable for passive matrices only
• • 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
  • G09G3/3696—Generation of voltages supplied to electrode drivers
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2230/00—Details of flat display driving waveforms

Definitions

• the present invention relates to a super-twisted nematic liquid crystal display (STN-LCD) driving circuit adopting a multiple line selection method using pulse width modulation using a driving circuit for a voltage driving flat panel display device, and more particularly, to an STN- LCD driving circuit adopting a multiple line selection method using pulse width modulation, which simplifies an LCD panel driving circuit, by applying a voltage whose pulse width, not magnitude, is modulated, to column lines of an STN-LCD panel, using two voltage potentials.
• STN-LCD super-twisted nematic liquid crystal display
• a voltage driving display panel is classified into a thin film transistor liquid crystal display (TFT-LCD) panel using an active matrix addressing method, and an STN-LCD panel using a passive matrix addressing method, both of which display a picture image by intermitting a light source using liquid crystals.
• TFT-LCD thin film transistor liquid crystal display
• STN-LCD passive matrix addressing method
• the TFT-LCD panel controls each pixel by using the active matrix addressing method using a transistor serving as a switch and a storage capacitor for each pixel for the purpose of displaying a picture image on a liquid crystal display panel, which is advantageous in implementing clear picture quality.
• the transistor and capacitor should be implemented on a glass plate of the LCD panel, which costs much.
• FIG. 1 The structure of the STN-LCD panel using the passive matrix addressing method is shown in FIG. 1, in which transparent electrodes 20 and 21 orthogonally crossing with each other are placed between two glass substrate 10 and 11 and orientation films 30 and 31 are coated on the transparent electrodes 20 and 21 to orientate liquid crystals 40.
• the orientation films 30 and 31 fix the liquid crystals 40 unidirectionally between the glass substrates 10 and 11, because it is difficult to orientate the liquid crystals 40 by using only the glass substrates 10 and 11.
• the liquid crystals 40 are in a nematic state, the unit molecular thereof is long and flat, and are aligned horizontally with respect to a major axis.
• the ends of the long molecules form their combination by Van Der Waals' force.
• the light passing through the afore-constructed STN-LCD panel is twisted locally in its optical axis by optical anisometric property, that is, different refractive indexes, as shown in FIGs. 2A and 2B. Then, the light passes through an outer surface of the glass substrate 10 and 11 by an orthogonally fixed polarizing plate 50.
• the light passing through the STN-LCD panel exhibits intrinsic colors by speed difference depending on the light traveling direction in the course of passing the liquid crystals 40. Since such intrinsic colors impede expression of colors on the liquid crystals, the intrinsic colors should be deleted by reducing the speed difference.
• a delay film 60 shown in FIG. 1 is used for correcting the speed difference.
• the liquid crystals are aligned in a direction of electrical fields, as similarly as shown in FIG. 2B, to then shield the light.
• the twisting degree of the liquid crystals in the STN-LCD panel reaches 240 ⁇ 270° , which is larger than that shown in FIG. 2 showing a twisted nematic liquid crystal display (TN-LCD) panel.
• the STN-LCD panel having the aforementioned characteristics can be implemented at low cost, compared to the TFT-LCD panel, since no element is required other than a capacitor component of the liquid crystals themselves. However, since a pixel is positioned at a point where two matrix-typed electrode lines intersect with each other and the liquid crystals operate by the difference in voltages applied to the electrode lines_, there is no element for reducing the effect on ambient pixels, which causes picture quality to be reduced.
• the LCD driver shown in FIG. 3 includes a buffer 80 for storing input data as picture information in the unit of frames, an ROM for a row function 81 for generating a Walsh function so as to operate row lines of an STN-LCD panel 90, a register 82 for storing the Walsh function output from the ROM for a row function 81, an operating portion 83 for receiving tow signals output from the buffer 80 and register 82 and performing an exclusive OR (XOR) operation, a sum logic portion 84 for accumulating values output from the operating portion 83 and outputting a voltage to a voltage source portion 85 so that the voltage is applied to column lines of the STN-LCD panel 90, the voltage source portion 85 having a plurality of voltage potential levels applied to the column lines set therein, for supplying a voltage corresponding to a value input from the sum logic portion 84, and a level shifter 86 for level-shifting the row function output from the register 82 so as to apply the same to the row lines.
• XOR exclusive OR
• the STN-LCD panel 90 includes a plurality of column lines 91 and a plurality of row lines 92 for displaying picture information, and a plurality of pixels 93 formed at the respective intersection points of the column lines 91 and row lines 92.
• the data stored in the buffer 80 expresses information to be displayed by the pixels 93, which is represented by -1 when the pixels 93 operate (ON) and is represented by +1 when the pixels 93 do not operate (OFF) .
• the operational procedure of the STN-LCD panel driver having the aforementioned configuration will now be described.
• the picture information to be displayed on the LCD is stored in the buffer 80 and at the same time a Walsh function, i.e., an orthogonal function, is outputted from the ROM for a row function 81 to be stored in the register 82 for execution of the XOR operation, which is inputted to the level shifter 86 so as to select all row lines of the LCD panel.
• the operating portion 83 performs an XOR operation with respect to the two input values to then output the respective potential values of a column line corresponding to each row line to the sum logic portion 84.
• the sum logic portion 84 accumulatively operates these values to then output the same as values corresponding to the voltage values applied to the column lines.
• the voltage source portion 85 applies the voltage corresponding to the result values to the respective column lines, and at the same time, the Walsh function value input to the level shifter 86 is level-shifted to apply a voltage to the row lines.
• the Walsh function used in the aforementioned driving circuit will be described for reference.
• the Walsh function is shown in FIG. 5, which is an orthogonal function, whose logic values iterate +1 and -1.
• the respective waveforms shown in FIG. 5 (l ⁇ n) are applied to the respective row lines 92 by the ROM for a row function 81. Also, if the respective waveforms (l ⁇ n) are multiplied with one another to be integrated in one period, a result value of logic ' 0' is output.
• the function having such characteristics is used for reducing the effect of the interference between the respective lines by the voltage applied to the row lines while driving the row lines.
• the voltage applied to the respective column lines 91 allows the data signal and Walsh function to be XOR-operated by the operating portion 83. Then, a predetermined voltage potential applied externally by the operation result of the sum logic portion 84 is used.
• the operation result is expressed by D- ( ⁇ t k ) in FIG. 3.
• the value of D, ( ⁇ t. ) is obtained by adding the logic value of the Walsh function applied to the row lines 92 with the number of cases where the logic values of data correspond to each other, which follows a Gaussian distribution statistically. In the case of driving in the conventional manner, when the number of the row lines 92 is 240, the convergence range of D. ( ⁇ t k ) falls within 45 with 120 centered.
• the row lines are driven at once, which is because it is difficult to implement a moving picture in the slowly responsive STN-LCD panel by using the conventional method.
• the number of voltage potentials applied to the column lines 91 in driving the LCD panel in the aforementioned manner is the same as that of convergent ranges of D, ( ⁇ t k ) , which is called an active addressing method.
• FIG. 4 is an enlarged view of a panel portion and a row line portion of the STN-LCD panel shown in FIG. 3. The other parts are the same as those shown in FIG. 3 and thus, an explanation thereof will be omitted.
• the LCD driver shown in FIG. 4 includes an ROM for a row function 100 for providing a Walsh function, level shifters 120 and 130 each connected to a plurality of row line groups, shift register 110 for switching to operate the level shifter connected to a selected row line group from the respective level shifters 120 and 130, and an STN-LCD panel 140 comprised of a plurality of column lines 141, a plurality of row line groups 142 having a predetermined number of groups, and a plurality of pixels 143.
• the operation of the LCD panel driver having the aforementioned configuration is almost the same as that explained with reference to FIG. 3, and is only different in that all row lines are not selected at once but divided row line groups are selectively driven.
• a lot of predetermined voltage potentials are not applied but two voltage potentials are determined previously to then adjust the widths of pulses having the respective voltage potentials according to operated logics, and to adjust a valid voltage value for duration of one frame, thereby compensating for shortcomings of the active addressing method and MLS method.
• an STN- LCD panel driving circuit adopting a multiple line selection (MLS) voltage applying method using pulse width modulation, comprising: a decoder for receiving a value output from an adder for accumulating to-be-displayed data and XOR-operated values of an orthogonal function and decoding the same into a value being in a state where the value is capable of being pulse-width-modulated; a first buffer for sequentially storing a value modulated from the decoder; a second buffer for re-storing values for a to-be-operated column line which are stored in the first buffer at once; a MUX portion for selectively outputting values stored in the second buffer bit by bit; a flipflop portion for turning on a gate corresponding to a column line selected by the MUX portion so
• FIG. 1 is a sectional view showing a conventional STN- LCD panel
• FIG. 2 explains a twist pattern of light passing through a polarizing plate according to liquid crystals in the conventional STN-LCD panel
• FIG. 3 is a block diagram of a LCD driving circuit using a conventional active addressing method
• FIG. 4 is a block diagram showing a row-line selecting portion in the LCD driving circuit using the conventional multiple line selection method
• FIG. 5 is a waveform diagram of an orthogonal function applied to row lines
• FIG. 6 explains a voltage applied to column lines by modulating a pulse width during a temporal interval of ⁇ shown in FIG. 5 ;
• FIG. 7 is a block diagram ⁇ of a LCD driving circuit implemented by the present invention.
• FIG. 8 is a timing diagram showing an output timing of a clock circuit according to the present invention.
• the above-described MLS method (see FIG. 4) is adopted, and a voltage applied to a selected column line is pulse-width-modulated, as shown in
• a Walsh function which is an orthogonal function applied to a selected row line group is divided in a predetermined number of time intervals ⁇ , as shown in FIG. 5.
• Voltages a and c applied to the selected row line group repeatedly take logic values +1 and -1 for duration of ⁇ , and the magnitude thereof is maintained as F and -F (see FIG. 6) .
• a voltage having a magnitude of ' 0' is applied to non- selected row line groups while the Walsh function is being applied thereto.
• the voltage applied to the column line for the time intervals ⁇ takes a value of eF for a predetermined time period by the operation of data and Walsh function applied to the selected row line group, and takes a value of -eF for the other time periods.
• a reference character L represents a value determined so that values up to 2 ⁇ are contained among the operation results of a row line signal having Gaussian distribution and a picture signal
• a reference character b is a value for determining a modulation point of a voltage applied to the column line according to the result of a sum logic operation.
• the remaining row line groups are not driven.
• data signals for the row line groups are operated by an operating portion, data signals for the remaining non-selected row line groups are not taken into consideration while being applied to the column line.
• the STN-LCD panel adopts a passive addressing method, a voltage value irrespective to the data signal of a pixel connected to the non-selected row line group is applied to the pixel,
• the liquid crystals 40 are driven by a valid voltage level applied thereto during the period of one frame.
• the voltage applied to the pixel influences the magnitude of the valid voltage during the period of one frame. Therefore, in order to control the valid voltage applied to the pixel for one frame exactly when using the MLS method, it is important that the magnitude of the voltage applied while no row line group is selected is made as small as possible so that the influence upon the magnitude of the valid voltage for one frame is reduced.
• a voltage whose magnitude is zero is applied to a non-selected row line, so that the valid voltage applied to a pixel for non-selection time becomes eF which is applied to the column line and the influence upon the magnitude of the valid voltage for one frame is reduced by defining the value of e as a value coming between 0 and 1.
• the valid voltage applied to the pixel for one frame is obtained by the following formula:
• N/S where F represents the magnitude of a row line signal, N represents the total number of the row lines, S represents the number of the row line selected at once, eF represents the magnitude of a column line signal, L represents the number of time units in which a voltage applied to a column line for time intervals ⁇ is modulated, and d. represents a data signal for a pixel positioned at an ith row line in a selected row line group.
• the values of the above formula are determined to have the maximum value in the ratio of voltages applied when a pixel operates and when the pixel does not operate.
• the LCD driving circuit implemented by adopting the aforementioned method includes a buffer 201 for storing picture information as input data in the unit of frames, an ROM for a Walsh function 201 for generating a Walsh function so as to operate a row line on an STN-LCD panel 200, a register 203 for storing a Walsh function value output from the ROM for a Walsh function 201, an operating portion 204 for receiving two signals output from the buffer 201 and ROM for a Walsh function 202 and performing an XOR operation with respect to the two signals, an adder 205 for accumulating values output from the operating portion 204 so as to apply a voltage to a column line in liquid crystals, a decoder 206 for pulse-width- modulating a value output from the adder 205 and decoding the same into a value being in the state where the value is capable of being pulse
• the respective signals are input to the operating portion 204 to then be XOR operated and added in the adder 205, which is then input to the decoder 206.
• the value input to the decoder 206 is output in the form of D- ( ⁇ t. ) , as described in the conventional art .
• the decoder 206 receives the value, aligns the received value in the unit of bits and outputs the same. For example, when the output value is 5 and is output in the unit of 10 bits, the value is output in the data form of 0000010000.
• FIG. 8 is a timing diagram showing waveforms when data of 120 column lines are processed at once, in which the clock A (FIG. 8A) represents a basic clock for the 120 column lines, the clock C (FIG. 8(c)) is for generating a Walsh function for performing an operation with respect to a data signal and a row line signal, and the clock D (FIG. 8 (d) ) is a waveform for generating the Walsh function applied to the row line, in which the Walsh function for operation leads that applied to the row line by one clock.
• the result values are stored by using two buffers 207 and 208 for continuously performing the Walsh functional operation and applying a voltage to the LCD panel, thereby preventing the speed from being lowered by the increased operation quantity.
• the result values stored in the second buffer 208 are outputted bit by bit by the MUX portion 209 and allows the corresponding gate among the plurality of second gate portions 215 connected to the voltage source portion 212 via the T-flipflop portion 210 to be turned on.
• a voltage is set externally through the voltage source portion 212 connected to the turned on gate to the column line.
• the Walsh functions generated from the ROM 202 for the Walsh function are sequentially applied to the row line group selected by the selection switch 214 according to the clock applied from the clock circuit 213 so that the pixel intersecting with the column line is displayed.
• the LCD device since a voltage is applied to a column line by modulating the width of its pulse, not the magnitude thereof, for implementing a high-quality moving picture in an STN-LCD panel, the LCD device can be driven by using two voltage potentials, which simplifies hardware configuration.
• the present invention can be applied to a driving circuit for a voltage driving flat panel display device.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Physics & Mathematics (AREA)
• Computer Hardware Design (AREA)
• General Physics & Mathematics (AREA)
• Theoretical Computer Science (AREA)
• Liquid Crystal Display Device Control (AREA)
• Liquid Crystal (AREA)
• Control Of Indicators Other Than Cathode Ray Tubes (AREA)

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Citations (2)

• 1996
  • 1996-05-15 KR KR1019960016092A patent/KR970076456A/ko not_active IP Right Cessation
  • 1996-11-30 WO PCT/KR1996/000228 patent/WO1997043750A1/en active Application Filing
  • 1996-11-30 JP JP9540752A patent/JPH11510622A/ja active Pending

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