WO2000014710A1 - Procedes pour ameliorer l'uniformite d'affichage dans des ecrans minces a tubes cathodiques par etalonnage de cathodes individuelles - Google Patents

Procedes pour ameliorer l'uniformite d'affichage dans des ecrans minces a tubes cathodiques par etalonnage de cathodes individuelles Download PDF

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Publication number
WO2000014710A1
WO2000014710A1 PCT/US1998/018599 US9818599W WO0014710A1 WO 2000014710 A1 WO2000014710 A1 WO 2000014710A1 US 9818599 W US9818599 W US 9818599W WO 0014710 A1 WO0014710 A1 WO 0014710A1
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cathode
memory
calibration
cathodes
video
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PCT/US1998/018599
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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/US1998/018599 priority Critical patent/WO2000014710A1/fr
Publication of WO2000014710A1 publication Critical patent/WO2000014710A1/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
    • G09G3/22—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 using controlled light sources
    • 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

Definitions

  • This invention is related to thin CRT displays, and specially to a method for improving the display uniformity of thin CRT displays.
  • a thin CRT display is a type of flat panel display which uses a matrix of cold cathodes to emit electrons towards an anode faceplate coated with phosphors.
  • the most promising type of thin CRT displays use Spindt field emission cathodes, and they are often called Field Emission Displays (FED).
  • FED Field Emission Displays
  • Another promising type of thin CRT displays use Surface Conducting Electron (SCE) cathodes developed by Canon.
  • SCE Surface Conducting Electron
  • 10 other kinds of cold cathode which can be used to construct thin CRT displays include MIS cathodes developed by Pioneer Electric Corp.
  • Thin CRT displays have the potential to provide image qualities comparable to conventional CRT displays. But, because the light intensity of each pixel is determined by the electron emission characteristics of one or more cold cathodes behind the phosphors segment of that pixel, it is difficult to make thin CRT displays with uniform display intensity. The variations of the display intensity is due to the variations of the 20 electron emission characteristics of all the cathodes.
  • the applicant present a new method, which the applicant claims to solve the uniformity problem of thin CRT displays once for all.
  • the new method provides almost perfectly uniform display properties for thin CRT displays regardless the inevitable variations of each cathode.
  • the new method disclosed in this document is performed in three steps: First, the emission characteristics of every cathode in the display is measured. Second, the correct driving parameters for each cathode — used as calibration parameters directly ⁇ are calculated and stored in a calibration memory as a complete look-up table, or the calibration parameters for each cathode are calculated and stored in a calibration memory as a partial look-up table.
  • the correct driving parameter for any cathode with any luminosity level can be obtained, and the correct driving parameters are used to drive the thin CRT display.
  • the emission characteristics of all cathodes can be measured by a current detector connected to the anode, or can be measured in a dark chamber by turning on one cathode at a time.
  • linear approximation or other higher order approximation can be used.
  • the third step there are two general embodiments: (1) with embodiment one, all the calculated correct driving parameters are stored in a video memory and driver electronics use these calculated correct driving parameters in the video memory to drive the display; (2) with embodiment two, the desired light intensities are stored in a video memory without any compensation, and using the complete look-up tables or using partial look-up tables in combination with additional calculation, the driver electronics calculate the correct driving parameters by fetching the light intensities from the video memory and use these calculated correct driving parameters to drive the display directly. For both embodiments mentioned above, when partial look-up tables are used, additional calculations are needed to obtain the correct driving parameters, and these calculations can be performed by the main microprocessor or a dedicated display processor.
  • a measurement method is provided to measure the emission characteristics of every cathode in the display
  • a calculation method is provided to obtain the calibration parameters of any given cathode by using the measured emission characteristics of the corresponding cathode as the raw data
  • a calibration memory is provided to store the calibration parameters for any given cathode as a complete look-up table or as a partial look-up table
  • a method is provided to obtain the correct driving parameters for any given cathode for any give light intensity by using the complete look-up table without additional calculation or by using the partial look-up table with additional calculation
  • a driver electronics is provided to drive the display with the correct driving parameters.
  • Figure la shows the principle of an FED display.
  • Figure lb shows a section of the matrix of field emission cold cathodes.
  • Figure lc shows the enlarged symbol and the structure of a field emission cold cathode.
  • Figure 2a shows that, with the same bias voltage, two different cold cathodes give completely different emission current and therefore completely different pixel luminosity.
  • Figure 2b shows that the same bias voltage is applied to two different cold cathodes in the same selected row.
  • Figure 3 illustrates that the emission characteristics of every cold cathode in a selected row is measured one by one in a scan mode, by measuring the emission current of each cold cathode with a current detector.
  • Figure 4a shows that the emission characteristics of a cold cathode is measured by measuring the emission current of the cold cathode under several selected bias voltages.
  • Figure 4b shows one can use linear approximation and measured data points to calculate the correct voltage V(i, j) which will provide the desired emission current targ t (U) -
  • Figure 5a shows that a microprocessor use the look-up table in the calibration memory to find out the correct driving voltage, and store the correct driving voltage into the video memory.
  • Figure 5b shows that the driver electronics fetch uncompensated light intensity from the video memory and use the look-up table in calibration memory to find out the correct driving voltage.
  • Figure 6a shows that a microprocessor use the partial look-up table in the calibration memory in combination with additional calculation to find out the correct driving voltage, and store the correct driving voltage into the video memory.
  • Figure 6b 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 driving voltage.
  • Figure 7a shows that a microprocessor use the partial look-up table in the calibration memory in combination with linear approximation to calculate the correct driving voltage, and store the correct driving voltage into the video memory.
  • Figure 7b 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 driving voltage.
  • Figure 7c shows a specific implementation of a display processor which uses linear approximation to calculate the correct driving voltage.
  • Figure 7d shows that the driver electronics fetch calibration parameters a(ij) and b(i j) from the calibration memory and use Fowler-Nordheim model to calculate the correct driving voltage.
  • Figure 8a shows that a cathode, presumably in a row of a cathode matrix, is selected by one voltage source and the emission current is determined by another driving voltage source.
  • Figure 8b shows that the driving voltage source is turned on for a time period that is determined by the desired luminosity.
  • Figure 8c shows that the luminosity perceived by an user is linearly proportional to the time period that the cathode is turned on.
  • Figure 9a shows that a cathode, presumably in a row of a cathode matrix, is selected by one voltage source and the emission current is determined by another driving current source.
  • Figure 9b shows that the driving current source is turned on for a time period that is determined by the desired luminosity.
  • Figure 9c shows that the luminosity perceived by an user is linearly proportional to the time period that the cathode is turned on.
  • Figure 10a shows that a cathode, presumably in a row of a cathode matrix, is selected by one voltage source and the emission current is determined by another driving current source.
  • Figure 10b shows that the driving current source is turned on for a fixed time period, and the desired luminosity is determined by the current level in the driving current sources.
  • Figure 10c shows that the luminosity perceived by an user is linearly proportional to the current level in the driving current sources.
  • Figure 11a shows that, for linear emission characteristics, a microprocessor uses the calibration parameter stored in the calibration memory to calculate the correct driving parameters, and store the correct driving parameters into the video memory.
  • the calibration parameter of a cathode is simply the inverse of the slope of the line representing the luminosity versus the driving-parameter.
  • Figure l ib shows that, for linear emission characteristics, the driver electronics uses the calibration parameter stored in the calibration memory to calculate the correct driving parameters.
  • the calibration parameter of a cathode is simply the inverse of the slope of the line representing the luminosity versus the driving-parameter.
  • Figure 12 shows that emission characteristics of every cathode is measured by a current detector and by turning on the driving current for only one cathode at a time.
  • Figure 13 shows that emission characteristics of every cathode is measured by a photo detector in a dark chamber by turning on only one cathode at a time.
  • FED technology have been disclosed in many patent documents, and the basic patents describing the technology include US Patents 3,500,102, 4,857,799 and 4.763,187, which are included hereinafter by reference.
  • the basic principle of a FED is quite similar to that of a CRT display-with the modification that the single electron gun for each color in CRT displays is replaced by a matrix of individually addressable filed emission cold cathodes, with one cathode for each pixel.
  • a FED includes a transparent anode plate 1, a matrix of individually addressable filed emission cold cathodes 2 fixed on a back plate 3 (not shown in Fig. la and lb), and a vacuums space 4 between the anode and the cathode matrix 2.
  • Each of the filed emission cold cathodes is represented by a special symbol , and one of the filed emission cathode 10 with an enlarged symbol is illustrated in Fig. lc
  • the side of the anode plate 1 facing the cathode matrix are coated phosphors 5, and the anode plate 1 is kept at a potential typically around 500 volts relative to the common ground.
  • a driver array 6 is connected to a set of driving lines 7, and each driving line T is connected to one end of a cathode array 7" in the cathode matrix 2.
  • a second driver array 8 is connected to a second set of driving lines 9, and each driving line 9' is connected to the other end of a cathode array 9" in the cathode matrix 2.
  • One row (or column) of cathodes 7" is turned on at one time by turning on one driver 6' in the driver array 6, and the number of electrons emitted from each of cathodes in that row (or column) is controlled by the different voltages applied to the different drivers in the second driver array 8.
  • Each row (or column) of cathode is turned on one by one by scanning the on-state driver 6' in the driver array 6 .
  • the electrons emitted from the cathodes are accelerated towards the anode, and impact the phosphors 5 on the anode plate 1; the phosphors 5 excited by the impact electrons will emit light with the light intensity determined by the number of electrons emitted from the corresponding filed emission cathodes.
  • a filed emission cold cathode 10 has a base electrode 12.
  • a matrix of metal or semiconductor sharp tips 14 are constructed on top of the base electrode 12.
  • Each tip 14' in the tip matrix 14 is covered with a gate 16'. All the individual gate 16' connected together form the second electrode 16 of the cold cathode.
  • the gate 16' covers the tip 14' with a hole 15' lined up with the tip 14' in the middle .
  • the size of the tip 14' is usually on the order of sub-microns, and the vertical distance between the tip 14' and the gate 16' is usually on the order of microns.
  • a positive voltage on the order of tens of volts is applied to the gate electrode, the electrons in the tip will be extracted out by filed emission. The emitted electrons shoot out into the vacuum though the center hole 15' on the gate 16'.
  • the number of electrons emitted into the vacuum is the function of the voltage difference applied between the base electrode and the gate electrode.
  • the on-state driver 6' will set the bias voltage, on each of the cathodes in that cathode array 7", close to the threshold voltage V .
  • the amount of electrons emitted from each individual cathode in the cathode array 7" is determined by the voltage on the corresponding driving lines driven by the second array of drivers 8.
  • a line of image is displayed on the anode plate, and by scanning quickly the on-state driver 6' one by one, a complete image is displayed on the anode plate.
  • the on-state driver can either connected to the base electrode of the cathodes or the gate electrode of the cathodes, and correspondingly, the second driver arrays can be connected either to the gate electrode of the cathodes or the base electrode of the cathodes.
  • FIG. 2a shows that, with the same bias voltage, two different cold cathodes give completely different emission current and therefore completely different pixel luminosity, where, V OT is the voltage applied by the on-state driver to select a particular row into emission mode , and V L is the same luminosity voltage applied to cathode A and cathode B as indicated in Fig. 2b. As shown in Fig.
  • the emission current from the two cathodes are different (they are I eA and I eB respectively for cathode A and B), because the emission characteristics (or the curve defined by emission current I e versus driving- voltage V) of the two cathodes are different.
  • These difference in emission current can be compensated, however, if one knows the emission characteristics of the corresponding cold cathodes.
  • the very basic idea of present invention can be summarized by operating thin CRT displays in three steps. First, the emission characteristics of every cathode in the display is measured.
  • the correct driving voltages for each cathode used as calibration parameters directly are calculated and stored in a calibration memory as a complete look-up table — which is called method one, or the calibration parameters for each cathode are determined and stored in a calibration memory as a partial look-up table - which is called method two.
  • the microprocessor when a certain luminosity in a certain pixel is to be displayed, the microprocessor will use the a complete look-up table in the calibration memory to find the correct driving voltage for that luminosity, or, the microprocessor will use the partial look-up table in the calibration memory in combination with additional calculation to find the correct driving voltage for that luminosity, and the correct driving voltage is used by the driver electronics to drive the display.
  • Figure 3 shows how the emission characteristics of all cathodes are measured by a current detector 50 connected between the anode 1 and the anode voltage 30.
  • the gate electrodes ( or alternatively the emitter electrodes) of only one row is biased to the on-voltage V on . All the rows are scanned one by one. But, in contrast to the display mode where luminosity voltage V L of all cathodes in that turned-on row are applied simultaneously, in the calibration mode, only one cathode is applied with luminosity voltage V L and the rest of the cathodes in that row are turned off, which is shown in Fig. 3.
  • the emission characteristics of that one cathode is measured and stored in a memory for further processing.
  • the number of points on the emission characteristics need to be measured depend on the non-linearity of the emission curve and the required display resolution (e.g. 4 bit or 8 bit). If the emission curve is close to linear, which is the case for some of the cathode driving methods to be discussed later (e.g. current-driving method), only one measurement is necessary for each cathode. As shown in Fig. 3, the emission characteristics of all the cathodes in that selected row can be measured one at a time by scanning all the cathodes in that row.
  • the emission characteristics of a cathode at row i and column j is characterized by a set of numbers, I el (i, j) for luminosity voltage V L1 , I e2 (i,j) for luminosity voltage V L2 , I e3 (i,j) for luminosity voltage V L3 , ..., and I eH (i, j) for luminosity voltage V LH , where H is the number of points on the emission curve measured for each cathode.
  • H is the number of points on the emission curve measured for each cathode.
  • the correct driving voltage for any desired emission current for any cathodes can be calculated. For example, for cathode (ij) at i'th row and j'th column, to calculate a desired emission current I tw « (i > J) > one f ⁇ rst compare the desired emission current I target (i, j) with all the measured emission current I e ,(i,j), I,. 2 (i,j), I e3 (i,j)and I eH (i,j).
  • V (i, j) the correct driving voltage V (i, j) is given by
  • aV 2 exp(-b / V) Fowler-Nordheim model
  • I aV 2 exp(-b / V)
  • first use least square fit to determine the model parameters a and b by fitting the model curve with all measured data on the emission curve then, one can calculate the correct driving voltage V(i, j) which can achieve the desired intensity I targe , (i,j) by finding the voltage V(i, j) for equation
  • I target (i, j) - a(i, j)V 2 (i, j)e "b(1,J) V( ' ,J) 0
  • a(i,j) and b(i,j) are calibration parameters which are already known from curve fitting .
  • calibration parameters are calculated and stored as partial look-up tables in a calibration memory for future use; and one will use the partial look-up table in combination with some additional calculation in real time to find the correct driving voltages.
  • the correct driving voltages for selected number of gray levels can be calculated and used as the calibration parameters, or other model-dependent parameters can be calculated and used as the calibration parameters.
  • the above described 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 there are cathode degrading effect, the above described look-up tables need to calculated again at a later time to correct the cathode degrading effect. If the look-up tables are stored in a relatively fast ROM, the ROM can be used directly as the calibration memory. 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 5a shows in detail the method one mentioned above.
  • the correct driving voltages-- V,(i, j) , V 2 (i, j) , V 3 (i, j), ..., and V ⁇ (i, j) --for all gray levels with corresponding desired emission current -- I , , 1 2 , I 3 ..., and I ⁇ — are calculated by using linear approximation or other previously described methods. More specifically, for 8 gray levels, 8 voltages are calculated for each cathode, and for 256 gray levels, 256 voltages are calculated. These calculated correct driving 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 level) of the pixel to a location in the 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 level
  • 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 of the cathode associated with the corresponding pixel in calibration memory 70 to find out the correct driving voltage for that desired intensity, write this correct driving voltage to video memory 80, and the driver electronics will use the correct driving voltages in video memory 80 to drive the field emission display.
  • 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 driving voltage for any gray level of any cathode, and use this correct driving voltage to drive the field emission display.
  • V k ⁇ V k (i, j) is the average driving voltage for gray level k averaged over all cathodes, and 1 ⁇ k ⁇ K..
  • V k ⁇ V k (i, j) is the average driving voltage for gray level k averaged over all cathodes, and 1 ⁇ k ⁇ K..
  • Another way to reduce the calibration memory requirement is to use partial look-up tables, instead of complete look-up tables.
  • Figure 6a and 6b show in detail the method two mentioned previously.
  • the correct driving voltages -- V, (i, j) , V 2 (i, j) , V 3 (i, j) , ... , and V ⁇ (i, j) -for selected number of gray levels with corresponding desired emission current — I, , I 2 , I 3 ..., and I ⁇ — are calculated and used as calibration parameters.
  • These calibration parameters are stored as partial look-up tables in a calibration memory 70 for future use.
  • the driver electronics will use the partial look-up tables in combination with some additional calculation in real time to find the correct driving voltages. Where the number of gray levels K selected are smaller than the number of total gray levels.
  • I 0 is the emission current corresponding to the maximum light intensity.
  • the next step is to use the partial look-up tables to calculate the correct driver voltages to provide nearly perfect display uniformity for a FED.
  • 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 level) of the pixel to a location in a video memory, and the driver electronics will use the intensity words in the video memory to drive the display.
  • the intensity word which is a byte for 8 bit gray level
  • the driver electronics With present newly invented display, however, if a computer want a pixel to display certain desired intensity, it will first fetch the related calibration parameters from the corresponding partial look-up table from calibration memory 70, as shown in Fig. 6a, then, use these calibration parameters along with the intensity word to calculate the correct driving voltage that can achieve the desired intensity for that pixel, write this correct driving voltage to video memory 80, and the driver electronics will use the correct driving voltages in video memory 80 to drive the field emission display.
  • 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 driving voltage for any gray level of any cathode, and use this correct driving voltage to drive the field emission display directly.
  • some calculations are required to obtain the correct driving voltage; these calculation can be performed with a microprocessor 60, which can be the main microprocessor or preferably a dedicated display processor.
  • a microprocessor 60 which can be the main microprocessor or preferably a dedicated display processor.
  • Figure 7a illustrates a specific implementations of Fig. 6a based on linear approximations
  • Fig. 7b illustrates that of Fig. 6b.
  • the microprocessor 60 or driver electronics 90 first compare desired intensity I(i, j) -which is the desired emission current in this case — with the set of intensity levels ( I , , I 2 , I 3 ..., and I ⁇ ) which have pre-calculated driving voltages stored in calibration memory 70, the microprocessor find the two numbers (among I t , I 2 , I 3 ..., and I ⁇ ) which are most close to the desired intensity I(i, j) ); , the microprocessor 60 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 driving voltage V(i, j) which can achieve the desired intensity I(i, j) ; finally, the calculated driving voltage V(i, j) is stored in video
  • V(i,j) v k+1 (i,j)[I(i,j) - I k ] + v k+1 (i,j)[I k+1 - I(i,j)], where I k ⁇ I(i,j) ⁇ I k+1 .
  • the microprocessor used to perform the above calculations can be the main microprocessor or a dedicated display processor.
  • Figure 7c illustrates a specific design of display processor 60 based on above linear approximation by using hardware gate elements.
  • v k (i, j) v k [l + S ⁇ k (i,j)] , where S is a scaling factor which depend on the variations of all the v k (i, j) , and v k is the average of v k (i, j) over all cathodes 1 N,M
  • 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. To demonstrate the feasibility of the current invention, we now estimate the amount of the calibration memory that is required and the processing power of the display processor that is required.
  • the sample architecture of the display processor in Fig.7c indicates that simple pipe line design can be used , and with the pipeline design one calculation can be performed with every clock cycle.
  • a display processor running at 115 MHz is powerful enough for the current invention.
  • a microprocessor running at a clock rate with a fraction of 115MHz is powerful enough for the present application.
  • the microprocessor 60 or the driver electronics 90 first compare desired intensity I(i, j) -which is the desired emission current in this case — with the set of intensity levels (I, , I 2 , I 3 ..., and I ⁇ ) which have pre-calculated driving voltage stored in calibration memory 70, the microprocessor 60 or the driver electronics 90 find the two numbers (among I , , 1 2 , 1 3 ...
  • the microprocessor 60 or the 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 driving voltage V(i, j) which can achieve the desired intensity I(i, j) .
  • liner approximation to calculate the driving voltage V(i, j) which can achieve the desired intensity I(i, j) .
  • polynomial approximation to calculate the driving voltage V(i, j) which can achieve the desired intensity I(i, j) .
  • algorithm such as, least square fit to calculate the driving voltage V(i, j) which can achieve the desired intensity I(i, j) .
  • the more complicated the algorithm the more it is required for the processing power of the microprocessor 60 or the driver electronics 90.
  • the desired intensity I(i, j) is stored in video memory 80
  • a driver electronics 90 calculate the correct driving voltage by fetching I(i, j) from video memory 80 and calibration parameters— a(i j) and b(i j)--from calibration memory 70, then, driver electronics 90 use the correct driving voltage to drive the display.
  • driver electronics 90 use the correct driving voltage to drive the display.
  • the gray level is roughly proportional to the driving parameter.
  • Fig. 8a, 8b and 8c which is called voltage-time method for facilitating discussion.
  • Fig. 9a, 9b and 9c which we is called current-time method.
  • Fig. 10a, 10b and 10c which is called current-driving method.
  • a voltage V on is used to select one row of cold cathodes in a matrix to emit electrons, and for each cold cathode in that selected row, another voltage source V L is applied to make the cathode to emit electrons.
  • the number of voltage sources V L is equal to the number of cold cathodes in each row.
  • the amplitude of voltage V L when applied to a cathode, is always the same constant voltage V 0 , but the time interval t L during which V L is applied will determine the luminosity L perceived by an user. And in fact, luminosity L is linearly proportional to t L , as shown in Fig. 8c .
  • different cathode in the cathodes matrix may have different slope k in the L verses t L curve.
  • the emission characteristics of a cathode can be determined by a single parameter k, which can be measured by a single measurement.
  • a voltage V on is used to select one row of cold cathodes in a matrix to emit electrons, and for each cold cathode in that selected row, another current source I L is applied to make the cathode to emit electrons.
  • the number of current sources I L is equal to the number of cold cathodes in each row.
  • the amplitude of current I L when applied to a cathode, is always the same constant current I 0 , but the time interval t L during which I L is applied will determine the luminosity L perceived by an user. And in fact, luminosity L is linearly proportional to t L , as shown in Fig. 9c.
  • a voltage V on is used to select one row of cold cathodes in a matrix to emit electrons, and for each cold cathode in that selected row, another current source ⁇ L is applied to make the cathode to emit electrons.
  • the number of current sources I L is equal to the number of cold cathodes in each row.
  • the time interval t L during which I L is applied is always the same.
  • the amplitude of the current I L applied to a cathode will determine the luminosity L perceived by an user. And in fact, luminosity L is linearly proportional to I L , as shown in Fig. 1 Oc. Because the manufacture variations, different cathode in the cathode matrix may have different slope k in the L verses I L curve. And the emission characteristics of a cathode can be determined by a single parameter k, which can be measured by a single measurement.
  • L kx to generally represent L versus t L or L versus I L , where x is the driving parameter ( t L or I L ) .
  • the driving parameter x at cathode (i, j) can be determined by the desired luminosity L(i, j) and the slope k(i, j) .
  • a microprocessor 60 will first calculate the correct driving parameter x(i, j) which provides the desired luminosity L(i, j) , then store the correct driving parameter x(i, j) in video memory 80, and the driver electronics will use the correct driving parameter x(i, j) in video memory 80 to drive the display.
  • Fig.l la a microprocessor 60 will first calculate the correct driving parameter x(i, j) which provides the desired luminosity L(i, j) , then store the correct driving parameter x(i, j) in video memory 80, and the driver electronics will use the correct driving parameter x(i, j) in video memory 80 to drive the display.
  • the driver electronics 90 will calculate the correct driving parameter x(i, j) which provides the desired luminosity L(i, j) by fetching L(i, j) from video memory 80 and ⁇ (i, j) from calibration memory 70, and driver electronics 90 will use the correct driving parameter x(i, j) to drive the display directly.
  • microprocessor 60 can be the main microprocessor or a dedicated microprocessor.
  • the emission characteristics of a cathode will not be perfectly linear.
  • the rate of charging up the capacitor of a cathode also depend on the value of the capacitor, which varies from cathode to cathode due to the inevitable manufacture variations, thus, the emission characteristics of a cathode will not only be non-liner but also varies from one cathode to another cathode.
  • Another reason that the emission characteristics of a cathode varies from one cathode to another cathode is that different cathode have different emission coefficient (or the ratio of the emission current to the driving current).
  • the emission characteristics of every cathode is measured; then, correct driving parameters of every cathode are stored as a complete look-up table in a calibration memory or the calibration parameters of every cathode are stored as a partial look-up table in a calibration memory; finally, the correct driving parameters of every cathode are obtained from the complete look-up table without additional calculation, or obtained from the partial look-up table with additional calculation, and correct driving parameters are used to drive the display.
  • the emission characteristics of a cathode in current-driving method is no longer linear, more than one point on the emission characteristics curve have to be measured.
  • one row of cathodes is selected at one time.
  • the emission characteristics of one individual cathode in that row is measured one by one, by measuring one cathode at a time and by setting all the rest of the cathodes in that row to non-emitting state.
  • one point on the emission characteristics curve is measured if the curve is linear, and several points on the emission characteristics curve are measured if the curve is non-liner.
  • the number of points needed to be measured depend on the non-linearity of the curve, the variations of the curve among different cathodes, and the number of gray levels needed to be achieved with the thin CRT display.
  • the emission characteristics of a cathode is measured by measuring the curve of emission current versus driving voltage.
  • the emission characteristics of a cathode can be measured by measuring the curve of emission current versus driving current, as shown in Fig. 12.
  • voltage-time and current-time methods one needs to measure the emission current integrated over the time period during which the driving voltage or current is turned on, and the emission current integrated over that time period is actually the total charge that is emitted onto the anode.
  • the curve of the total charge versus the driving parameter (which can be voltage, current or time) is a faithful representation of the curve of the luminosity versus the driving parameter.
  • the emission characteristics of a cathode is measured by measuring the curve of the total emitted charge versus the time period during which the driving voltage or current is turned on.
  • the emission characteristics of a cathode can also be measured by measuring the curve of the total emitted charge versus the driving voltage
  • the emission characteristics of a cathode can be measured by measuring the curve of the total emitted charge versus the driving current as well.
  • the emission current can be the maximum time period that a cathode can be turned on.
  • the integration time can be the maximum time period that a cathode can be turned on. For gray level less than the maximum luminosity, the actual time period that a cathode is turned on is of course smaller than the maximum time period that a cathode can be turned on, and the integration over the maximum time period is the same as the integration over the actual time period.
  • the curve of the total charge versus the driving parameter is a faithful representation of the emission characteristics of a cathode.
  • Another way of measuring of the emission characteristics of every cathode in a display is to perform all the measurement in a dark chamber. As shown in Fig. 13, for a particular thin CRT 100, to obtain a light-intensity versus driving-parameter table for a pixel 101, be it complete or partial, one can put thin CRT 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.
  • the process of compensating non-uniformity of a thin CRT display consists of the stage of measuring the emission characteristics of every cathode, the stage of determining the calibration parameters from the measured emission characteristics, and the stage of using the calibration parameters of every cathode to calculate the correct driving parameters which will give desired luminosity levels.
  • the stage of measuring the emission characteristics of every cathodes one can measure those emission characteristics only once, calculate the correct driving parameters and store them as complete look-up tables in a permanent memory, or calculate the calibration parameters and store them as partial look-up tables in a permanent memory. Later on, one can always use those stored complete or partial look-up tables to obtain the correct driving parameters, provided the emission characteristics of those cathodes do not change over time. If the emission characteristics of those cathodes changes or degrade over time, one has to measure the emission characteristics periodically, say, once every month, and how often that need to be re-measured depend on the rate of changes of those emission characteristics.
  • the stage of using the calibration parameters of every cathode to calculate the correct driving parameters one can use specially designed display processor to perform the calculation or use a software programmed general purpose microprocessor, which can even be the main CPU.
  • a software programmed general purpose microprocessor which can even be the main CPU.
  • the selecting of the calibration parameters we listed several examples in the above presentation, such as, using the correct driving parameters for all gray levels of a cathode as the calibration parameters, using the correct driving parameters for selected gray levels of a cathode as the calibration parameters, using the fitting parameters of the measured emission characteristics based on a device model as the calibration parameters, and using the slope of the measured emission characteristics as the calibration parameters. Based on above teaching, people skilled in the art can chose other kinds of parameters as the calibration parameters.
  • present invention is applicable to any kinds of thin CRT displays based on matrix of cold cathodes, in any kind of driving arrangement, provided that any one of the individual cold cathode can be addressed independently.
  • One example is Canon's surface conducting electron display (SED).
  • SED surface conducting electron display
  • present invention of improving display uniformity is applicable to all those designs and driving schemes.
  • present invention is applicable to all the disclosed designs and driving schemes disclosed in U.S. patent No. 5,627,436 and the references cited therein.
  • any kinds of thin CRT displays based on matrix of cold cathodes of any kinds in any kind of driving arrangement. If any one of the individual cold cathode in the matrix can be addressed independently, then, the emission characteristics of any cold cathode can be measured independently. Once the measured emission characteristics of all cold cathodes are measured, the correct driving parameters of all cathodes can be calculated and stored as complete look-up tables, or the calibration parameters of all cathodes can be calculated and stored as partial look-up tables in a calibration memory.
  • a microprocessor can use the stored complete or partial look-up tables to obtain nearly perfect display uniformity based on the algorithm and methods disclosed in the present invention.
  • the emission characteristics of a cathode in the cathode matrix can be measured with a current detector connected to the anode.
  • the emission characteristics of a cathode can be measured by using the current detector to measure the total emitted charges (or simply emission current in some cases), for one or several values of driving parameters -such as voltage, current or time.
  • the emission characteristics of a cathode in the cathode matrix can also be measured in a dark chamber.
  • the kind of cold cathodes mentioned above include, but not limited to, Spindt field emission cathodes, Surface Conducting Electron (SCE) cathodes, MIS cathodes, Silicon avalanche cathodes, diamond cathodes, MIM cathodes, pn junction cathodes and Schottky junction cathodes.
  • SCE Surface Conducting Electron
  • the kind of driving schemes mentioned above include, but not limited to, any amplitude modulation schemes with examples of voltage- driving method or current-diving method, any pulse width modulation schemes with examples of voltage-time or current-time method, and any combination schemes of amplitude modulation and pulse width modulation with which the luminosity of a pixel is changed by changing both the amplitude and the pulse width of the driving parameter such as voltage or current.

Abstract

L'invention concerne des procédés pour améliorer l'uniformité d'affichage des écrans minces à tubes cathodiques. Ces procédés permettent d'obtenir une uniformité d'affichage quasi parfaite pour un écran mince à tubes cathodiques, et ce malgré le fait que les caractéristiques d'émission de ces cathodes faisant partie d'un écran mince à tubes cathodiques sont par définition non uniformes vu les inévitables écarts de fabrication. Afin d'améliorer l'uniformité d'affichage d'un écran mince à tubes cathodiques, on mesure les caractéristiques d'émission de toutes les cathodes et l'on obtient les paramètres d'étalonnage pour chaque cathode à partir des caractéristiques d'émission mesurées de la cathode correspondante. Les paramètres d'étalonnage de chaque cathode sont stockés dans une mémoire d'étalonnage (70) sous la forme d'une table de consultation complète ou partielle. Dans le cas d'une table de consultation complète, lorsque l'U.C. veut afficher un pixel possédant une luminosité désirée, elle utilise la table de consultation complète de la cathode correspondante pour trouver les paramètres de pilotage corrects. Dans le cas d'une table de consultation partielle, lorsque l'U.C. veut afficher un pixel possédant une luminosité désirée, elle utilise la table de consultation partielle de la cathode correspondante en combinaison avec des calculs supplémentaires pour trouver les paramètres de pilotage corrects. Ces calculs peuvent être effectués par l'U.C. principale ou par un processeur d'affichage spécialisé.
PCT/US1998/018599 1998-09-04 1998-09-04 Procedes pour ameliorer l'uniformite d'affichage dans des ecrans minces a tubes cathodiques par etalonnage de cathodes individuelles WO2000014710A1 (fr)

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PCT/US1998/018599 WO2000014710A1 (fr) 1998-09-04 1998-09-04 Procedes pour ameliorer l'uniformite d'affichage dans des ecrans minces a tubes cathodiques par etalonnage de cathodes individuelles

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2683365A1 (fr) * 1991-10-31 1993-05-07 Raytheon Co Dispositif d'affichage a panneau plat a emission de champ et circuit de compensation d'irregulatites utilisable dans un tel dispositif d'affichage.
EP0661726A1 (fr) * 1993-12-22 1995-07-05 Canon Kabushiki Kaisha Dispositif générateur d'un faisceau d'électrons appareil d'affichage d'image, et méthode de leur commande
EP0686993A1 (fr) * 1994-06-08 1995-12-13 Canon Kabushiki Kaisha Dispositif générateur de faisceau d'électrons comprenant une pluralité d'éléments à cathode froide, procédé de commande du dispositif et appareil de formation d'images
EP0755042A1 (fr) * 1995-07-20 1997-01-22 STMicroelectronics S.r.l. Méthode et dispositif pour uniformiser la luminosité et pour réduire la dégradation de la matière fluorescente dans un dispositif d'affichage plat à émission de champ
EP0803892A2 (fr) * 1996-02-23 1997-10-29 Canon Kabushiki Kaisha Dispositif générateur d'électrons, dispositif de formation d'images, procédé de fabrication et procédé de réglage de ses caractéristiques

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2683365A1 (fr) * 1991-10-31 1993-05-07 Raytheon Co Dispositif d'affichage a panneau plat a emission de champ et circuit de compensation d'irregulatites utilisable dans un tel dispositif d'affichage.
EP0661726A1 (fr) * 1993-12-22 1995-07-05 Canon Kabushiki Kaisha Dispositif générateur d'un faisceau d'électrons appareil d'affichage d'image, et méthode de leur commande
EP0686993A1 (fr) * 1994-06-08 1995-12-13 Canon Kabushiki Kaisha Dispositif générateur de faisceau d'électrons comprenant une pluralité d'éléments à cathode froide, procédé de commande du dispositif et appareil de formation d'images
EP0755042A1 (fr) * 1995-07-20 1997-01-22 STMicroelectronics S.r.l. Méthode et dispositif pour uniformiser la luminosité et pour réduire la dégradation de la matière fluorescente dans un dispositif d'affichage plat à émission de champ
EP0803892A2 (fr) * 1996-02-23 1997-10-29 Canon Kabushiki Kaisha Dispositif générateur d'électrons, dispositif de formation d'images, procédé de fabrication et procédé de réglage de ses caractéristiques

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