WO2000028516A1 - Afficheur a cristaux liquides a matrice active utilisant des interrupteurs a diodes et procedes d'amelioration de l'uniformite d'affichage de ces afficheurs - Google Patents

Afficheur a cristaux liquides a matrice active utilisant des interrupteurs a diodes et procedes d'amelioration de l'uniformite d'affichage de ces afficheurs Download PDF

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Publication number
WO2000028516A1
WO2000028516A1 PCT/US1998/023837 US9823837W WO0028516A1 WO 2000028516 A1 WO2000028516 A1 WO 2000028516A1 US 9823837 W US9823837 W US 9823837W WO 0028516 A1 WO0028516 A1 WO 0028516A1
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Prior art keywords
pixel
terminal
capacitor
voltage
array
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PCT/US1998/023837
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English (en)
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Nongqiang Fan
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Nongqiang Fan
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Priority to PCT/US1998/023837 priority Critical patent/WO2000028516A1/fr
Publication of WO2000028516A1 publication Critical patent/WO2000028516A1/fr

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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
    • G09G3/34—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
    • 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
    • G09G2320/0285—Improving the quality of display appearance using tables for spatial correction of display data
    • 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
    • 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

Definitions

  • This invention is related to active matrix Liquid Crystal Displays (AM-LCDs), and specially to a method for making active matrix LCDs based on non-linear diodes and a method of improving the display uniformity of these diode based AM-LCDs by calibrating individual pixels.
  • AM-LCDs active matrix Liquid Crystal Displays
  • A-LCDs Active matrix Liquid Crystal Displays
  • TFT thin film transistors
  • MIM metal-insulator-metal
  • active matrix LCDs based on two-terminal diodes should be cheaper than active matrix LCDs based on three- terminal transistors, especially for large area displays.
  • active matrix LCDs based on two-terminal diodes have not been as successful as active matrix based on three-terminal transistors, because the display quality of LCDs based on two-terminal diodes have not been as good as the display quality of LCDs based on three-terminal transistors.
  • both terminals ofthe capacitor for each pixel are used in synchronize for charging the capacitor to a desired voltage level.
  • Terminal one of the capacitor is connected to two diodes.
  • This terminal ofthe capacitor will effectively connect to the ground with low impedance if the two diodes are switched on with a driving current passing though both of them, and effectively connect to the ground with high impedance if no driving current is passing though them.
  • the second terminal ofthe capacitor will be set to a voltage level by driver electronics, and this voltage is used to charge the capacitor.
  • the uniformity problem ofthe LCD matrix can be easily solved by measuring the reference voltage level ofthe terminal one ofthe capacitor once it is effectively connected to the ground with low impedance, and the voltage level on terminal two is set to equal to the sum of two voltages: the reference voltage ofthe terminal one and the desired charging voltage across the capacitor.
  • This new method provides almost perfectly uniform display properties for active matrix LCDs based on two-terminal diodes regardless the inevitable variations of those diodes.
  • the measured reference voltages level ofthe terminal one of all capacitors can be stored in a calibration memory.
  • the main processor When the main processor want to store a pixel's desired light intensity word to a video memory, it will first fetch the reference voltage of the terminal one of that pixel from the calibration memory, then, calculate what voltage level on terminal two will provide the desired voltage level across the capacitor of that pixel, and finally write the compensated voltage level into the video memory.
  • present disclosed method of improving display uniformity by storing each pixel's display characteristics can also be applied to other driving methods for LCDs.
  • present disclosed method of improving display uniformity can be performed in three steps. In the first step, the display characteristics of all pixel element are measured, and the measured characteristics of all pixel element are stored in a calibration memory.
  • the main processor will send the desired light intensity word to a register of a microprocessor; the microprocessor will then fetch the display characteristics ofthe pixel element from the calibration memory to a register or registers; the microprocessor will calculate the compensated light intensity in real time based on the desired light intensity and the display characteristics ofthe pixel element; the microprocessor finally store the compensated light intensity in a video memory.
  • the compensated light intensities in the video memory are used by the driver electronics to drive the display that can achieve error-free images. Either a stand along special microprocessor or the main microprocessor can be used for the calculation.
  • two non-linear elements are provided to connected to terminal one ofthe capacitor for that pixel; a driving method is provided to switch the impedance of that terminal to the ground between a high value and a low value; a method is provided to measure the reference voltage of terminal one when it is connected to the ground with low impedance; a calibration memory is provided to store the measured reference voltages of all pixels; a microprocessor is provided to use the stored reference voltages in the calibration memory to calculate the correct driving voltage for each pixel; a method is provided to charge the capacitor to the target voltage by setting the terminal two ofthe capacitor to the correct driving voltage which is already compensated for the variations among those non-linear element.
  • a third non-linear element is provided to isolate the terminal two ofthe capacitor when the voltage on the capacitor need to be maintained.
  • a method is provided to measure the display characteristics of every pixel element in the display, a calibration memory is provided to store the measured display characteristic of every pixel element in the display, a microprocessor is provided to use the stored display characteristics of each pixel element in the calibration memory to calculate the correct driving parameters for the corresponding pixel element, and finally driver electronics are provided to use the correct driving parameters to drive the active matrix display.
  • a diode-based active matrix LCD driven by driver electronics using the correct driving parameters will provide images free of intensity distortions caused by each diode's property variations.
  • Figure la shows one ofthe most common embodiment of active matrix LCDs based on two-terminal non-linear element.
  • Figure lb shows the voltage-current characteristic ofthe two-terminal non-linear element at i'th row and j'th column.
  • Figure 2 shows a new method to construct an AM-LCD with two-terminal nonlinear elements, and it also shows how to drive such an AM-LCD.
  • Figure 3a shows the equivalent circuit of a pixel element in Fig. 2 when that pixel element is in charging-on mode.
  • Figure 3b shows the equivalent circuit of a pixel element in Fig. 2 when that pixel element is in charging-off mode.
  • Figure 4 illustrate the principle of creating displays with good uniformity by storing reference voltage V ref (i, j) in a calibration memory and using the calibration memory to calculate the correct driving voltage.
  • Figure 5a shows the driver settings at the preparation stage for measuring the reference voltage V ref (i, j) of each pixel in j'th column.
  • Figure 5b shows the driver settings at the measurement stage for measuring the reference voltage V ref (i,j) of each pixel in j'th column.
  • Figure 6a shows an embodiment based on thin film pn diodes.
  • Figure 6b shows an embodiment based on thin film metal-insulator-mental (M-I- M) diodes.
  • Figure 6c shows an embodiment based on avalanche break down of pn diodes.
  • Figure 7a and 7b show that a microprocessor is used to calculate the correct driving voltages based on the display characteristics stored in a calibration memory.
  • Figure 8a shows a method to measure the threshold voltages of each switching diode in the matrix.
  • Figure 8b shows the wave form of current i(t) and function f(t).
  • Figure 8c shows the definition of N ⁇ (i, j) , V * (i, j) , V(i, ;i, j) and several other related parameters.
  • Figure 9 shows the modified driver electronics that use V(i, ;i, j) to determine the correct voltage applied to the LCD cell at i'th row and j'th column.
  • Figure 10a shows the modified driver electronics that use a current source i 0 to charge each LCD cell and use V(i 0 ;i, j) to determine the correct voltage applied to the LCD cell at i'th row and j'th column.
  • Figure 10b shows the definition of V(i 0 ;i, j) .
  • Figure 1 la shows an arrangement that use one diode to charge a LCD cell to a positive voltage and use another diode to charge a LCD to a negative voltage.
  • Figure 1 lb shows the current-voltage characteristic of diode 5(i,j) and 5'(i,j) and the definition of several parameters.
  • Figure 12 shows that the display characteristics of each pixel is measured in a dark chamber.
  • Figure 13 shows an embodiment of AM-LCD based on two-terminal non-linear elements of modest quality.
  • Figure 14a shows the equivalent circuit of a pixel element in Fig. 13 when that pixel element is in charging-on mode.
  • Figure 14b shows the equivalent circuit of a pixel element in Fig. 13 when that pixel element is in charging-off mode.
  • Figure 15a shows that the display characteristics of a pixel is measured by measuring the light intensity of that pixel under several selected data-voltages.
  • Figure 15b shows one can use linear approximation and measured data points to calculate the correct data- voltage V ⁇ ata ( ) j that will provide the desired light intensity
  • Figure 16a shows that a microprocessor use the look-up table in the calibration memory to find out the correct data-voltage, and store the correct data-voltage into the video memory.
  • Figure 16b shows that the driver electronics fetch uncompensated light intensity from the video memory and use the look-up table in the calibration memory to find out the correct data-voltage.
  • Figure 17a shows that a microprocessor use the partial look-up table in the calibration memory in combination with additional calculation to find out the correct data-voltage, and store the correct data-voltage into the video memory.
  • Figure 17b shows that the driver electronics fetch uncompensated light intensity from the video memory and use the partial look-up table in the calibration memory in combination with additional calculation to find out the correct data-voltage.
  • Figure 18a shows that a microprocessor use the partial look-up table in the calibration memory in combination with linear approximation to calculate the correct data- voltage, and store the correct data-voltage into the video memory.
  • Figure 18b shows that the driver electronics fetch uncompensated light intensity from the video memory and use the partial look-up table in the calibration memory in combination with linear approximation to calculate the correct data-voltage.
  • Figure 18c shows a specific implementation of a display processor which uses linear approximation to calculate the correct data-voltage.
  • Figure 19 shows another embodiment of AM-LCD based on two-terminal nonlinear elements of modest quality.
  • Figure la shows one of the priori art embodiment of active matrix LCDs based on two-terminal non-linear element.
  • the LCD consists of an array of column driving lines 1 l(j) and an array of row driving lines 13(i), and these two arrays of driving lines form a matrix structure.
  • the cross position between each column driving line and each row driving line defines a pixel by connecting a non-linear diode 5(i,j) and a LCD cell 8(i,j) in series at that cross position.
  • Each column driving linel l(j) is connected to a voltage driver 12(j), and each row driving line 13(i) is connected to a voltage driver 14(i).
  • the voltage applied to the serially connected non-linear diode 5(i,j) and LCD cell 8(i,j) is V j - V,.
  • the real voltage applied to the LCD cell 8(i,j) at the i'th row and the j'th column V(i, j) depends on the voltage-current characteristic ofthe non-linear diode at that position.
  • Figure lb shows the voltage-current characteristic ofthe non-linear diode at i'th row and j'th column, and the threshold voltage for forward bias and reverse bias is respectively V ; (i, j) and V ⁇ (i, j) .
  • V target (i, j) if a targeted voltage V target (i, j) is to be applied to the LCD cell
  • V * is the nominal forward threshold voltage for all the non-linear diodes.
  • the first part is how to construct an AM-LCD with non-linear diodes
  • the second part is how to drive such a AM- LCD
  • the third part is how to improve the display uniformity of this AM- LCD.
  • the central idea ofthe current invention is to measure and store in a calibration memory the display characteristics of all pixel elements, and to use the display characteristics stored in the calibration memory to calculate the correct driving parameters for each pixel element. LCDs driven by these correct driving parameters will have almost perfect display uniformity.
  • Figure 2 shows a new method on how to construct an AM-LCD with non-linear diodes. As shown in Fig.
  • the LCD consists of an array of row driving lines 13(i) and two array of column driving lines 1 l(j) and 11 '(j), and row driving lines and column driving lines form a matrix structure.
  • the driving line for the i'th row is 13(i)
  • driving lines for the j 'th column are 11 (j) and 11 '(j).
  • the cross position between the driving line for the i'th row and driving lines for the j'th column defines a pixel element (i,j).
  • each pixel element (i,j) there is a storage capacitor 8(i,j) with terminal one 7(i,j) and terminal two 9(i,j).
  • One terminal of diode 5(i,j) is connected to terminal one 7(i,j) of capacitor 8(i,j), and the other terminal of diode 5(i,j) is connected to the first driving line 110)-
  • One terminal of diode 5'(i,j) is also connected to terminal one 7(i,j) of capacitor 8(i,j), and the other terminal of diode 5(i,j) is connected the second driving line 11 '(j).
  • the terminal two 9(i,j) of capacitor 8(i,j) is connected to the driving line 13(i) for the i'th row.
  • Each column driving line 1 l(j) is connected to a voltage driver 12(j), each column driving line 11 '(j) is connected to a voltage driver 12'(j), and each row driving line 13(i) is connected to a voltage driver 14(i).
  • the purpose of diode 5(i,j) and 5'(i,j) is to effectively connect the terminal one 7(i,j) to the ground with low impedance when that terminal is selected with driving line 1 l(j) and 1 l '(j). and isolate that terminal to the ground with high impedance when that terminal is not selected.
  • Any pixel element can be either in charging-on mode or charging-off mode.
  • the two driving lines for that column controls which of the two modes will be for those pixel elements in that column.
  • the capacitor of that pixel element can be charged by the voltage on the row's driving line connected to that pixel element.
  • the voltage on the capacitor of that pixel element is maintained, and that voltage is hardly influenced by the voltage on the row's driving line connected to that pixel element.
  • Figure 3 a shows the equivalent circuit of a pixel element (i,j) when that pixel element is in charging-on mode.
  • Fig 3a when on-voltages V on and V' on are applied to the terminals of diode 5(i,j) and diode 5'(i,j) respectively to drive both diodes 5(i,j) and 5'(i,j) into the conducting state, the terminal one 7(i,j) of the capacitor 8(i,j) is equivalently connecting to a reference voltage V ref (i, j) though a low impedance
  • Figure 3 b shows the equivalent circuit of a pixel element (i,j) when that pixel element is in charging-off mode.
  • the terminal one 7(i,j) ofthe capacitor 8(i,j) is equivalently connecting to a reference voltage V' ref (i, j) though a very high impedance R off (i, j) , and no mater what voltage V data (i) is set on the terminal two 9(i,j) of capacitor 8(i,j), the voltage across that capacitor 8(i,j) will hardly change at all.
  • Figure 2 also shows how to drive the above described AM-LCD.
  • the driving lines of only one column are set to on-voltages V on and V' on , with V on for the first driving line and V' on for the second, and the driving lines for all remaining columns are set to off-voltages V off and V' off , with V off for the first driving lines and V' off for the second.
  • the driving lines of only one column are set to on-voltages V on and V' on , with V on for the first driving line and V' on for the second
  • the driving lines for all remaining columns are set to off-voltages V off and V' off , with V off for the first driving lines and V' off for the second.
  • a voltage on driving line N data (i) j and a voltage V'(i,j) on capacitor 8(i,j) will set the voltage level on terminal one 7(i,j) to be V data (j . - V'(i, j) .
  • the voltages V on , V' on ' V off and V' off are chosen to satisfy two conditions. Condition one is that no matter what voltage V'(i, j) preexists at capacitor 8(i,j), if pixel element (i,j) is selected for charging-on mode and a data- voltage V data (i) .
  • V(i, j) V data (i) j - V ref (i, j) .
  • condition two is that no matter what voltage V (i, j) preexists at capacitor 8(i,j) and no matter what data-voltage V data (i) ⁇ is set on terminal two 9(i,j), if pixel element (i,j) is not selected, diodes 5(i,j) and 5'(i,j) can remain in the non-conducting state despite the fact that a voltage V data (i) j - V'(i, j) on terminal one 7(i,j) is present.
  • V data (i) j on the driving line for the i'th row when the j'th column is in charging-on mode can be taken from a video memory.
  • V t arget (i, j) is the desired voltage to be charged across capacitor 8(i,j).
  • the reference voltage V ref (i, j) will equal to the middle voltage ( V on + V' on ) 12, which is the same for all pixel elements.
  • V data (i) j V target (i, j) + (V on + V' on ) / 2 into the video memory.
  • the diver electronics will use V data (i) j to drive the display matrix.
  • the reference voltage V ref (i, j) will be differ from (V on + V' on ) / 2 by an amount which depend on the difference between the two diodes. And in this case, the reference voltage V ref (i, j) is different for different pixel elements.
  • Figure 4 illustrate the principle of creating displays with good uniformity by storing reference voltage V ref (i, j) in a calibration memory 70 and using the calibration memory 70 in combination with a video memory 80 to provide the correct driving voltage.
  • the reference voltage V ref (i, j)of the terminal one 7(i,j) of capacitor 8(i,j) of any selected pixel element (i,j) need to be measured at least once, and the measured reference voltages V ref (i, j) need to be stored in calibration memory 70, as shown in Fig. 4.
  • a microprocessor In the operation of a conventional AM-LCD, say, TFT AM-LCD, a microprocessor usually write the light intensity word directly to a video memory, and the driver electronics for a AM-LCD will use that light intensity word to set the voltage on the data line.
  • the voltage on the data line V data (i) j should have certain corrections for each pixel element.
  • the voltage on the data line V data (i) should be equal to the sum of two voltages: the desired voltage V target (i, j) to be set on capacitor 8(i,j) of pixel element (i,j) and the reference voltage V ref (i, j) at the terminal one 7(i,j) of that capacitor 8(i,j) when that terminal is connected to the ground with low impedance.
  • microprocessor 50 will not write the light intensity word directly into video memory 80, but instead, microprocessor 50 will first fetch the reference voltage V ref (i, j) ofthe corresponding pixel element (i,j) from calibration memory 70 and sum up that reference voltage V ref (i, j) with the desired voltage V t arget (i, j) to be charged to capacitor 8(i,j) ofthe corresponding pixel element (i,j); then, microprocessor 50 will write that voltage sum V data (i) .
  • V target (i, j) + V ref (i, j) into video memory 80 V target (i, j) + V ref (i, j) into video memory 80.
  • the driver electronics will use the voltages V data (i) . in video memory 80 to drive the display matrix.
  • V ref (i, j) of all pixel elements we next turn to the disclosure on how to measure V ref (i, j) of all pixel elements.
  • the voltages on driving lines 1 l(j) and 11 '(j) for the column j are set to be equal to the ground and the voltages on the driving lines for all other columns are set to V off or V' off correspondingly to make sure all these other columns are in charging-off mode, the voltage on the i'th row is set to the ground as well.
  • the voltage on capacitor 8(i,j) will start to discharge towards zero, and after a time period long enough, the voltage on capacitor 8(i,j) will reach exponentially to zero.
  • the driving line for the i'th row is set to a high impedance or set to be open to the ground, and the voltage on this driving line is monitored with a voltage detector or amplifier 15(1), as shown in Figure 5b.
  • the voltage on the driving line l l(j) and 11 '(j) for the j'th column are quickly switched to V on and V' on respectively, the same voltages used to set column j in charging-on mode; and at this instant, the voltage on the driving line 13(i) ofthe i'th row is measured again with voltage detector 15(1), and this voltage at this instant is just equal to V ref (i, j) .
  • the reference voltages V ref (i, j) of all pixel elements in the j 'th column can be measured simultaneously. After the reference voltages V ref (i, j) of all pixel elements in one column are measured, the reference voltages V ref (i, j) of all pixel elements ⁇ n next column can be measured. In this way, column by column, the reference voltages V ref (i, j) of all pixel elements in the display matrix can be measured, and all these reference voltages can be stored in calibration memory 70 for later use.
  • the above method on how to construct an AM-LCD with non- linear diodes, how to drive such a AM- LCD, and how to improve the display uniformity of this AM- LCD ⁇ is described in general for any kinds of non-linear diodes, as long as the non-linear diode can be switched between a conducting state and a non-conducting state.
  • the kinds of diodes can be used include, but not limited to, thin film pn junctions, thin film Metal- Insulator-Metal (MIM) junctions, and some combinations of multiple diodes in serial or in parallel.
  • MIM Metal- Insulator-Metal
  • the values of on-voltages ( V on and V' on ) and off-voltages ( V off and V' off ) can be different.
  • Figure 6a shows an embodiment, based on thin film pn diodes, which, uses the forward biased state as the conducting state — driven by a positive on-voltage V on > 0 and another negative on-voltage V' on ⁇ 0, , and uses the reverse biased state as the nonconducting state — driven by a negative off- voltage V off ⁇ 0 and another positive off- voltage V' off > 0.
  • Fig. 1 shows an embodiment, based on thin film pn diodes, which, uses the forward biased state as the conducting state — driven by a positive on-voltage V on > 0 and another negative on-voltage V' on ⁇ 0, , and uses the reverse biased state as the nonconducting state — driven by a negative off- voltage V off ⁇ 0 and another positive off- voltage V' off > 0.
  • diode 5(i,j) is actually constructed from a thin film pn diode 5(i,j)a and a resistor 5(i,j)b, and similarly diode 5'(i,j) from a pn diode 5'(i,j)a and a resistor 5'(i,j)b.
  • Resistor 5(i,j)b and resistor 5'(i,j)b are used to limit the current passing though the diodes.
  • V on can be chosen to be +10V
  • V' on to be
  • V ref (i, j) is uniformly 0V. If we assume that the spread of V ref (i, j) is between -1 V to +1 V, then, a data-voltage in the range between -3V to 3V is needed to set voltages across the capacitors in that range between -2V to 2V.
  • Figure 6b shows an embodiment, based on thin film Metal-Insulator-Mental (M- I-M) diodes, which, uses a positive on-voltage V on and another negative on-voltage V' on to drive the two diodes into the conducting states — with the sum
  • V o ⁇ can be chosen to be +10V, and N on to be -10V.
  • a voltage on terminal one in the range between -5V to 5V can not drive either diode 5(i,j) or diode 5'(i,j) into the conducting state if diode 5(i,j) or diode 5'(i,j) have threshold much larger than 5V.
  • This high level of threshold voltage can be achieved by using multiple m-I-m diodes connected in series. In Fig.
  • one pn diode connected in series with another reversed pn diode can be used to substitute for diodes 5(1 j) or 5'(i,j), provided that reverse break down voltages of the two diodes are properly designed, such that, when the reverse breakdown voltages are used as the threshold voltages, the total voltage applied to the two diodes V on - V' on can drive the two diodes into the conducting states.
  • a new method of constructing active matrix LCDs are disclosed, a new method of driving such kinds of active matrix LCDs are disclosed.
  • a new method of improving the display uniformity of diode based AM-LCDs is also disclosed.
  • the above described method of improving display uniformity of diode-based AM-LCDs can be applied in general to any kinds of diode-based AM-LCDs, since the problem of display uniformity is universal for every kind of diode-based AM-LCDs.
  • Present disclosed method of improving display uniformity by calibrating individual pixels can solve this universal display uniformity problem once for all.
  • present method of improving display uniformity by calibrating individual pixels are applied to another kind of diode-based AM-LCDs, the kind of diode-based AM-LCDs as shown in Fig. la.
  • the matrix structure in Fig. la is a priori art embodiment.
  • Several specific implementation ofthe present method of improving display uniformity of AM- LCD in Fig. 1 a are described, and they are severed as examples for teaching the principles ofthe present method, which generally involves how to measure the display characteristics of each pixel element and how to use those measured display characteristics to provide the correct driving parameters. Based on these examples and teachings, people skilled in the art should be above to apply present method to any kinds of diode-based AM-LCDs.
  • each LCD cell is applied with voltage only in one polarity, say, positive polarity.
  • the positive threshold voltages V j (i, j) of all switching diodes are measured and stored in a calibration memory 70, as shown in Fig. 7a.
  • the column driving voltage - V on is used for selecting the j'th column of LCD cells to write into and is not used to code luminosity information.
  • the luminosity of pixel element (i,j) will be independent ofthe characteristics ofthe nonlinear diode at that position, and therefore LCDs with almost perfect display uniformity can be obtained.
  • the voltage on each LCD cell need to be preset to a certain voltage (e.g. a zero or a negative bias voltage) before the real positive driving voltage is applied.
  • both the positive and negative threshold voltages ( V t jj (i, j) and V t ⁇ (i, j) respectively) of all non-linear diodes are measured and stored in calibration memory 70.
  • microprocessor 50 When a computer want to apply a target voltage V t arget (i, j) to the LCD cell at pixel (i,j), microprocessor 50 will fetch the positive threshold voltages V * (i, j) from calibration memory 70, calculate the correct driving voltage V d + ata (i) . and store the correct driving voltage in video memory
  • VJ; (i, j) and V ⁇ (i, j) respectively) of all non-linear diodes are measured and stored in calibration memory 70.
  • microprocessor 50 will fetch the positive threshold voltage V ; (i, j) from calibration memory 70, calculate the correct positive driving voltage V data (i) j and store the correct positive driving voltage in video memory 80; then, microprocessor 50 will fetch the negative threshold voltage V, ⁇ (i, j) from calibration memory 70, calculate the correct negative driving voltage V d ⁇ ata (i) and store the correct negative driving voltage in video memory 80.
  • Microprocessor 50 can be the main microprocessor for the computer or a special dedicated microprocessor.
  • An alternative method to that described in Fig. 7a is to store the target voltage
  • a square wave current source i(t) is applied to the driving line for the i'th row
  • the driving line for the j'th column is applied with a negative voltage - V on which is negative enough to make the non-linear diodes at the i'th row and j'th column conducting
  • all the rest column driving lines are applied to voltage V off .
  • a voltage preamplifier 21(i) is used to measure the voltage V out (t;i, j) on the driving line for the i'th row.
  • the wave form of i(t) and f(t) are indicated in Fig.8b.
  • V out ( ⁇ I ;i,j)] Im[f( ⁇ 1 )]V(i 1 ;i,j)-Re[f( ⁇ )]i p / ⁇ 1 C(i,j), where V out ( ⁇ , ; i, j) is the Fourier transform of V out (t; i, j) , f ( ⁇ , ) is the Fourier transform of f(t), and C(i, j) is the capacitance ofthe LCD cell ofthe diode at the i'th row and j'th column.
  • V(i,;i,j) is a good approximation of V t (i, j) if 1, is small enough.
  • V(i , ; i, j) can be obtained: ⁇ ... . ⁇ , Re[ V oul ( ⁇ , ; i, j)] - ⁇ 2 Re[ V ou , ( ⁇ 2 ; i, j)] Cl " 1,j ⁇ ,Re[f( ⁇ ,)]- ⁇ 2 Re[f( ⁇ 2 )]
  • V(i , ; i, j) is used to represent Y * h (i, j) approximately, the smaller the i , the better.
  • Another way to improve the accuracy in determining V,Jj (i, j) is to measure V(i 2 ;i, j) at a different driver current i 2 , and use linear approximation to determine
  • V(i 2 ;-, j) V ( ⁇ ,j) — ⁇ 2 1,
  • V * (i, j) is a good approximation of V th " (i, j) .
  • One can also use multiple points on the current-voltage characteristic curve in combination with a device model for the non-linear diode to determine the threshold voltage.
  • FIG. 9 shows the modified driver electronics.
  • the voltage on the driving line for the j'th column is set to a negative voltage - V on to select the LCD cells in the j 'th column, and the row driving electronics are used to set the voltages on each LCD cells in the j'th column.
  • the driving current in each row say, the i'th row, is measured with a current detector 31(1), and the measured driving current i(i,j) is compared with a threshold current i, by using a comparator 34(i).
  • the output ofthe comparator 34(i) is used to control a switch 33(i); and when the driving current is equal to or smaller than the threshold current i, , the driving voltage source 14(i) will be disconnected.
  • V(i, j) V d + ata (i) j + V on - V(i, ;i, j) .
  • V(i, ;i, j) V d + ata (i) J .
  • V(i, ;i,j) can store measured voltage V(i, ;i, j) in calibration memory 70, and using V(i, ;i,j) to calculate the correct driving voltage V d + ata (i) J .
  • the correct driving voltage V d + ata (i) j can be stored in video memory 80.
  • each row driving line say, the i'th row is driven by a constant current source 41(i) with a current output i 0 .
  • i 0 is relatively large and V(i 0 ;i, j) can be significantly larger than the threshold voltage V t (i, j) .
  • the voltage V(i 0 ; i, j) can be measured the same way as previously described and a larger i 0 only makes it easier for the previously described method to be performed.
  • Fig. 10a each row driving line, say, the i'th row is driven by a constant current source 41(i) with a current output i 0 .
  • i 0 is relatively large and V(i 0 ;i, j) can be significantly larger than the threshold voltage V t (i, j) .
  • the voltage V(i 0 ; i, j) can be measured the same way as previously described and a larger i 0 only makes it easier for the previously described method to be performed.
  • the voltage on the row driving line is measured by a voltage comparator 43(i), and the measured voltage (which is equal to V(i, j) + V(i 0 ; i, j) - V on ) is compared with a reference voltage V d + ata (i) j ; the output ofthe voltage comparator 43 (i) is used to control a switch 42(i), and the current source will be turned off if the voltage on the row driving line is equal to or larger than the reference voltage.
  • V(i 0 ;i, j) is measured and stored in calibration memory 70 for each pixel (i,j). For a target voltage V targe .
  • the driving voltage V d + ata (i) J V target (i, j) + V(i 0 ; i, j) - V on is then calculated based on the voltage V(i 0 ; i, j) fetched from calibration memory 70, and the data- voltage V d + ata (i) j is then stored in video memory 80.
  • the target voltage V(i, j) is to be written to the LCD cell at pixel (i,j)
  • data- voltage V d + ata (i) j is fetched from video memory 80 and applied to voltage comparator
  • Figure 1 lb shows the current-voltage characteristic of diode 5(i,j) and 5'(i,j) respectively.
  • driver 14(1) can be calculated, and after that, the correct driver voltages for driver 14(i) will be stored in video memory 80.
  • Driver 14(i) will use the correct driver voltages fetched from video memory 80 to drive the corresponding LCD cells. If driver 14(i) is replaced with driver electronics similar to those depicted in Fig. 9 — with current detector 31 (1), comparator 34(i) and switch 33(i), then, voltages V(i, ;i, j) and V(-i] ; i, j) can be measured and stored in calibration memory 70, and these voltages V(i, ;i, j) and V(-iJ ;i, j) can later on be used to obtain the correct driver voltages.
  • the partial table store the correct driving parameters for selected number of target voltages; if the driver electronics need the correct driving parameter for a target voltage which is not listed, that correct driving parameter can be provided with a microprocessor, which calculate the correct driving parameter based on the parietal table by using linear approximation, parabola approximation, or a specific device model. Similarly, a complete table, which lists the correct driving parameter for any particular light intensity (say, one out of 256 gray levels), can be used to characterize the display characteristics of a pixel; or a partial table, which lists the correct driving parameter for selected light intensities, can be used to characterize the display characteristics of a pixel.
  • non- listed parameters can be provided by a microprocessor which perform the calculation based on the partial table.
  • a microprocessor which performs the calculation based on the partial table.
  • FIG. 12 for a particular AM-LCD 100, to obtain a light-intensity versus driving-parameter table for a pixel 101, be it complete or partial, one can put AM- LCD 100 in a dark chamber 200 and use a photo detector 210 to measure the light intensities with a set of driving parameters for that pixel 101 while all the rest of pixels are completely turned off. And, one need to repeat the same procedure one pixel at a time, until the light-intensity versus driving-parameter tables of all pixels in the AM-LCD are measured.
  • These steps of measuring display characteristics of each pixel in a AM- LCD can be performed in the factory before the AM-LCD is shipped.
  • the measurement may need to be performed with different temperatures in the case that the display characteristics of each pixel is temperature dependent.
  • the measured tables are stored in a permanent memory.
  • the permanent memory can be used as the calibration memory directly, or can be used to transfer those stored tables into a separate calibration memory which usually is a faster RAM.
  • calibration memory 70 By storing more data points into calibration memory 70 to describe the display characteristics of each pixel, it is possible to design more advanced circuitry for each pixel element, and based on these circuitry, it is possible to design an AM-LCD with almost perfect display uniformity even by using modest quality nonlinear elements.
  • I leak (i, j) [V data (i) . - V' ref (i, j)] / R off (i, j) .
  • the voltage changes across capacitor 8(i,j) due to the leakage currant through R off (i, j) can be practically neglected. If there are 1000 columns, and assume the display need to be refreshed 30 times in a second, then, when a pixel element is in charging-on mode, capacitor 8(i,j) need to be charged to the target voltage within a time period smaller than 1/(1000 x 30) of a second.
  • R on (i, j) C 1/(1000 x 30 x 5).
  • T 1/30 second that a frame is refreshed
  • the time period that it is in charging-off mode is 999 times the time period that it is in charging-on mode.
  • the voltage changes due to the leakage current has to be smaller than the voltage differences between two adjacent gray levels, which usually is less than 1/256 volt. If we chose the typical target voltage to be 3 V, and in the worst case scenario, it requires that [ 999 / (1000 x 30) ] x [ 3 V / R off (i, j) ] / C ⁇ 1/256 V.
  • the LCD consists of an array of row driving lines 13(i) and two array of column driving lines 1 l(j) and 1 l'(j).
  • the row driving lines and column driving lines form a matrix structure.
  • the driving line for the i'th row is 13(1)
  • driving lines for the j'th column are 1 l(j) and 11 '(j).
  • the cross position between the driving line for the i'th row and driving lines for the j 'th column defines a pixel element (i,j).
  • each pixel element (i,j) there is a storage capacitor 8(i,j) with terminal one 7(i,j) and terminal two 9(i,j), a first non-linear element consisting of a pn diode 5(i,j)a and a resistor 5(i,j)b, a second non-linear element consisting of a pn diode 5'(i,j)a and a resistor 5'(i,j)b, a third non-linear element 6(i,j)a, and a resistor 6(i,j)b.
  • One terminal of the first non-linear element is connected to terminal one 7(i,j) of capacitor 8(i,j), and the other terminal ofthe first non-linear element is connected to the first column driving line 1 l(j).
  • One terminal ofthe second non-linear element is also connected to terminal one 7(i,j) of capacitor 8(i,j), and the other terminal ofthe second non-linear element is connected to a common voltage, which can be the ground voltage.
  • the terminal two 9(i,j) of capacitor 8(i,j) is connected to one terminal ofthe third non-linear element 6(i,j)a.
  • the terminal two 9(i,j) of capacitor 8(i,j) is also connected to one terminal of resistor 6(i,j)b.
  • each column driving line 1 l(j) is connected to a voltage driver 12(j)
  • each column driving line 11 '(j) is connected to a voltage driver
  • each row driving line 13(1) is connected to a voltage driver 14(i).
  • the purpose ofthe first and second non-linear elements is to effectively connect the terminal one 7(i,j) to the ground with low impedance when that terminal is selected with driving line 1 l(j) and 11 '(j), and isolate that terminal to the ground with high impedance when that terminal is not selected.
  • the purpose ofthe third non-linear element is to effectively connect the terminal two 9(i,j) to row driving line 13(1) when pixel (i,j) is selected, and to effectively isolate the terminal two 9(i,j) from row driving line 13(1) when pixel (i,j) is not selected.
  • Any pixel element can be either in charging-on mode or charging-off mode.
  • the two driving lines for that column controls which of the two modes will be for those pixel elements in that column.
  • the capacitor of that pixel element can be charged by the voltage on the row's driving line connected to that pixel element.
  • the voltage on the capacitor of that pixel element is maintained, and that voltage is hardly influenced by the voltage on the row's driving line connected to that pixel element.
  • Figure 14a shows the equivalent circuit of a pixel element (i,j) when that pixel element is in charging-on mode.
  • Figure 14b shows the equivalent circuit of a pixel element (i,j) when that pixel element is in charging-off mode.
  • the terminal one 7(i,j) ofthe capacitor 8(i,j) is equivalently connecting to a reference voltage V' ref (i, j) though a very high impedance R off (i, j) ; and if at the same time another off-voltage V' off is applied to the second column driving line 11 '(j) to drive the third non-linear element into the non-conducting state to effectively isolate the terminal two 9(i,j) from row driving line 13(1), then, no mater what data voltage V data (i) j is set on the second terminal ofthe third non-linear element 6(i,j)a, the voltage change across that capacitor 8(i,j) is still independent of data voltage V data (i)
  • V ref (i, j) is in the range between +5V to +7V and if the voltage across the capacitor 8(i,j) needs to be between -3V to +3V, then, the voltage applied to the second terminal 9(i,j) ofthe capacitor 8(i,j) need to be in the range between +2V to +10V. If the voltage drop across the third non-linear element while in the conducting state is 0.7V, then, the data-voltage V data (i) j should be in the range from +2.7V to +10.7V. The second on-voltage V' on of the value +12V will be able to drive the third non-linear element 6(i,j)a into the conducting state.
  • the data- voltage V data (i) j When the third non-linear element 6(i,j)a is in the conducting state, the data- voltage V data (i) j will be effectively connected to the second terminal 9(i,j) of capacitor 8(i,j), albeit though an equivalent small-resistor R a (i, j) with a voltage drop ⁇ V(i, j) .
  • an off-voltages V off of - 12V can drive both the first and second non-linear elements into the non-conducting states.
  • the second off- voltage V' off is selected to be -6V, then, the data- voltage V data (i) . in the range from +2.7V to +10.7V can not drive the third non-linear element into the conducting state, and thus, the data- voltage N data (i) j is isolated from the second terminal 9(i,j) of capacitor 8(i,j).
  • the voltage across capacitor 8(i,j) is in the range from - 3 V to +3V and the voltage at the second terminal 9(i,j) of capacitor 8(i,j) is -6V, therefore, the voltage at the first terminal 7(i,j) of capacitor 8(i,j) is in the range between - 9 V to -3V, and this voltage can not drive the first or the second non-linear element into the conducting state.
  • the major advantage ofthe embodiment in Fig. 13 over the embodiment in Fig. 2 is that the display characteristics of pixel (i,j) in Fig. 13 only depend on the data- voltage V data (0 j f° r the pixel (i,j), it do not depend on the data-voltages for other columns.
  • V, (t) V data (i) J for t 0 + G-l)T/M ⁇ t ⁇ t 0 + G)T/M
  • V, (t) V data (i) M for t 0 + (M-l)T/M ⁇ t ⁇ t 0 + T
  • V, (t) V data (i) M for t 0 + (M-l)T/M ⁇ t ⁇ t 0 + T
  • V, (t) V data (i) M for t 0 + (M-l)T/M ⁇ t ⁇ t 0 + T
  • V, (t) V data (i) M for t 0 + (M-l)T/M ⁇ t ⁇ t 0 + T
  • V, (t) V data (i) M for t 0 + (M-l)T/M ⁇ t ⁇ t 0 + T
  • V, (t) V data (i) M for t 0 + (M-l)T/M ⁇ t ⁇ t 0 + T
  • V, (t) V data (i) M for t 0 + (M-
  • V(i, j;t) e- ,/ ⁇ (, ' J) Je ⁇ ⁇ (, - J) V, (t)d ⁇ / ⁇ (i, j) + V(i, j;t 0 + T/ M) .
  • the calibration process can be much simpler.
  • the light intensity of pixel (i,j) do not depend on the voltage V, (t) on the driving line for the i'th row once the voltage across capacitor 8(i,j) is set, and as a consequence, the intensity of pixel (i,j) do not depend on the data- voltage for the other pixels in the i'th row.
  • This curve of the perceived intensity L(i, j) versus the initial voltage V(i, j; 1 0 + T / M) can be considered as the display characteristics ofthe pixel (i,j), and it can be used to calibrate pixel (i,j). But, for the embodiment in Fig. 13, with the equivalent of charging- on mode shown in Fig.
  • the curve of L(i,j) versus V data (i) J can be measured experimentally by using the measurement apparatus illustrated in Fig. 12. As shown in Fig.12, to measure the curve of L(i, j) versus V data (i) j , first, one need to put AM-LCD 100 in dark chamber 200, and use photo detector 210 to measure the light intensities of pixel (i,j), with the data- voltage V data (i) equal to a set of voltage values (such as V L1 , V L2 , V L3 , ...), for an averaging time equal to the multiples ofthe frame period T (e.g. T, 2T, 3T, et. al. ), while all the rest of pixels are completely turned off.
  • T the frame period
  • L(i,j) for W__(i) t V L2 is L e2 (i,j) , ...and
  • V LH is L eH (i,j) , where H is the number of points on the display characteristic curve measured for each pixel. The number of points on the display characteristics need to be measured depend on the non-linearity ofthe display curve and the required display resolution ( e.g.4 bit or 8 bit). These measured numbers are stored in a memory for further processing. If the number of row is N and the number of column is M, then a total of N*M*H numbers are stored in the memory.
  • the correct data- voltage for any desired intensity for any pixels can be calculated. For example, for pixel (i,j) at the i'th row and the j'th column, to calculate the correct data-voltage for a desired intensity L target (i,j) , one first compare the desired intensity L target (i, j) with all the measured intensity L el (i,j), L e2 (i,j), L e3 (i,j), ...,and L eH (i,j).
  • VL 3 [L t ar g e,(i )-Le 2 (i )3 + V L2 [Le 3 (i )-Ltar g e,(i )] data(l)j _ L e3 (i,j)-L e2 (i,j)
  • V data (i) i the correct data-voltage V data (i) j is given by
  • look-up tables need to be calculated only once, and these look-up tables can be stored in a permanent memory, such as ROM, or hard disk. If the look-up tables are stored in a slower permanent memory, say, hard disk, the look-up tables will have to be loaded into a faster RAM from the permanent memory, and use this RAM as the calibration memory.
  • Figure 16a shows in detail the method one mentioned above.
  • the correct data- voltages - V, (i, j) , V 2 (i, j) , V 3 (i, j) , ... , and V ⁇ (i, j) for all gray levels — with corresponding desired intensity L, , L 2 , L 3 ..., and L ⁇ , are calculated by using linear approximation or other previously described methods. More specifically, for 8 gray levels, 8 voltages are calculated for each pixel, and for 256 gray levels, 256 voltages are calculated. These calculated correct data-voltages are used as calibration parameters directly and stored in a calibration memory 70.
  • a computer With a conventional display, if a computer want a pixel to display certain intensity, it will write the intensity word (which is a byte for 8 bit gray levels) ofthe pixel to a location in video memory 80, and the driver electronics will use the intensity words in video memory 80 to drive the display.
  • the intensity word which is a byte for 8 bit gray levels
  • the driver electronics With present newly invented display, however, if a computer want a pixel to display certain desired intensity, it will first use the look-up table ofthe corresponding pixel in calibration memory 70 to find out the correct data- voltage for that desired intensity, write this correct data-voltage to video memory 80, and the driver electronics will use the correct data-voltages in video memory 80 to drive the AM-LCD.
  • the computer can still write the uncompensated intensity word to video memory 80, but, the driver electronics itself will use the look-up tables in calibration memory 70 to find out the correct data-voltage for any gray level of any pixel, and use this correct data-voltage to drive the AM-LCD.
  • Another way to reduce the calibration memory requirement which is the method two mentioned previously, is to use partial look-up tables, instead of complete look-up tables.
  • Figure 17a and 17b show in detail the method two mentioned previously. With method two, for every pixel in the display, the correct data- voltages —V, (i, j) ,
  • These calibration parameters are stored as partial look-up tables in a calibration memory 70 for future use.
  • the microprocessor or driver electronics will use the partial look-up tables in combination with some additional calculation in real time to find the correct data- voltages. Where the number of gray levels K selected are smaller than the number of total gray levels.
  • the next step is to use the partial look-up tables to calculate the correct driver voltages to provide nearly perfect display uniformity for the present disclosed AM-LCDs.
  • the driver electronics will use the correct data-voltages in video memory 80 to drive the AM- LCD.
  • the computer can still write the uncompensated intensity word to video memory 80, but, the driver electronics itself will use the partial look-up table in calibration memory 70 in combination with some calculations to find out the correct data- voltage for any gray level of any pixel, and use this correct driving data- voltage to drive the AM-LCD directly.
  • a microprocessor 50 which can be the main microprocessor or preferably a dedicated display processor.
  • a microprocessor 50 which can be the main microprocessor or preferably a dedicated display processor.
  • Figure 18a illustrates a specific implementations of Fig. 17a based on linear approximations
  • Fig. 18b illustrates that of Fig. 17b.
  • Fig. 18a illustrates a specific implementations of Fig. 17a based on linear approximations
  • Fig. 18b illustrates that of Fig. 17b.
  • the microprocessor 50 or driver electronics 90 first compare the desired intensity L(i, j) with the set of intensity levels (L, , L 2 , L 3 ..., and L ⁇ ) which have pre-calculated correct data-voltages stored in calibration memory 70, the microprocessor find the two numbers (among L, , L 2 , L 3 ..., and L ⁇ ) which are most close to the desired intensity L(i, j) ; the microprocessor 50 or driver electronics 90 will then fetch the driving voltages corresponding to these two numbers from calibration memory 70 and use liner approximation to calculate the correct data- voltage V data (i) .
  • V data (i) J is calculated , if L 2 ⁇ L(i, j) ⁇ L 3 , then
  • driver electronics 90 then use v k (i, j) to calculate the correct data-voltage
  • V data (i), v k+1 (i,j)[L(i,j) - L k ] + v k (i,j)[L k+1 - L(i,j)] , where L k ⁇ L(i,j) ⁇ L k+1 .
  • the microprocessor used to perform the above calculations can be the main microprocessor or a dedicated display processor.
  • Figure 18c illustrates a specific design of display processor 50 based on above linear approximation by using hardware gate elements. To minimize the calibration memory requirement one can store a normalized variation of v k (i, j) .
  • ⁇ k (i, j) v k [1 + S ⁇ k (i, j)] , where S is a scaling factor that is chosen based on the variations of all the v k (i, j) , and v k is the average of v k (i, j) over all pixels
  • the average v, , v 2 , v 3 ..and v ⁇ , and the scaling factor S are also stored in a memory, and these numbers can be loaded into the microprocessor to perform the calculation.
  • the design of a dedicated display processor by using the normalized variation ⁇ k (i, j) is straight forward for the people skilled in the art, and will not be discussed further here.
  • the microprocessor 50 or the driver electronics 90 use liner approximation to calculate the driving voltage V data (i) ⁇ that can achieve the desired intensity L(i, j) .
  • polynomial approximation to calculate the driving voltage V data (i) . that can achieve the desired intensity L(i, j) .
  • One can even use more complicated algorithm such as, the algorithm of using least square fit in combination with a device model to calculate the data voltage V data (i) that can achieve the desired intensity L(i, j) .
  • the algorithm of using least square fit in combination with a device model to calculate the data voltage V data (i) that can achieve the desired intensity L(i, j) the more complicated the algorithm, the more it is required for the processing power ofthe microprocessor 50 or the driver electronics 90.
  • FIG. 13 shows a variation ofthe embodiment of Fig. 13 and Fig. 6c, and display uniformity ofthe AM-LCD in Fig.19 can be improved by the same way as that of Fig.13.
  • the embodiment of Fig. 10 consists of only one array of column driving lines, in contrast to two arrays in Fig. 13.
  • the display characteristics of a pixel in an AM-LCD do not depend on the data-voltages applied to other pixels, one can always measure the display characteristics of that pixel independently, and store into a calibration memory the calibration parameters derived from the measured display characteristics (while in certain cases, the measured display characteristics can be used as the calibration parameters directly); then, one can use the calibration parameters in the calibration memory to find out the correct data- voltages, and use the correct data- voltages to drive the AM-LCD.

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Abstract

L'invention concerne un afficheur à cristaux liquides équipé d'éléments à deux bornes non linéaires servant d'éléments interrupteurs. Ce nouveau genre d'afficheur à cristaux liquides à matrice active comprend une matrice d'éléments pixels, chaque élément pixel comprenant un premier élément à deux bornes non linéaire (5), un second élément à deux bornes non linéaire (5') et un condensateur (8) permettent de maintenir la tension sur la cellule d'afficheur à cristaux liquides. Lorsque les deux éléments (5, 5') sont à l'état conducteur, la tension appliquée sur le condensateur (8) peut varier. Lorsque ces deux éléments sont à l'état non conducteur, la tension appliquée sur le condensateur (8) est stable. Afin d'améliorer l'uniformité de l'affichage de l'afficheur à cristaux liquides à matrice active utilisant des éléments à deux bornes non linéaires, les caractéristiques d'affichage de chaque pixel sont mesurées et mémorisées dans une mémoire d'étalonnage (70) et les paramètres de commande adaptés à chaque pixel sont calculés selon les caractéristiques d'affichage du pixel extrait de la mémoire d'étalonnage (70). Finalement, les paramètres de commande adaptés à chaque pixel sont utilisés pour commander l'afficheur à cristaux liquides à matrice active et peuvent être stockés dans une mémoire vidéo (80).
PCT/US1998/023837 1998-11-08 1998-11-08 Afficheur a cristaux liquides a matrice active utilisant des interrupteurs a diodes et procedes d'amelioration de l'uniformite d'affichage de ces afficheurs WO2000028516A1 (fr)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002082417A1 (fr) * 2001-04-06 2002-10-17 Three-Five Systems, Inc. Charge d'un condensateur de colonne d'affichage a cristaux liquides avec une source de courant
WO2004002170A1 (fr) * 2002-06-24 2003-12-31 Koninklijke Philips Electronics N.V. Procede et dispositif pour corriger une non-uniformite de couleur

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WO2002082417A1 (fr) * 2001-04-06 2002-10-17 Three-Five Systems, Inc. Charge d'un condensateur de colonne d'affichage a cristaux liquides avec une source de courant
WO2004002170A1 (fr) * 2002-06-24 2003-12-31 Koninklijke Philips Electronics N.V. Procede et dispositif pour corriger une non-uniformite de couleur

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