Gray level addressing for LCDs

• US 5,459,495 A
• Filed: 05/14/1992
• Issued: 10/17/1995
• Est. Priority Date: 05/14/1992
• Status: Expired due to Term

• Current Assignee: InFocus Corporation (Lap-Shun Hui, MBA)
• Original Assignee: InFocus Corporation (Lap-Shun Hui, MBA)
• Inventors: Conner, Arlie R., Scheffer, Terry J., Clifton, Benjamin R.
• Primary Examiner(s): Weldon, Ulysses
• Assistant Examiner(s): Mengistu, Amare
• Application Number:
  US07/883,002
• Time in Patent Office: 1,251 Days
• Field of Search: 340/793, 340/784, 340/805, 340/811, 358/298, 345/63, 345/89, 345/87, 345/12, 345/77, 345/147
• US Class Current: 345/690
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/3622 using a passive matrix G09G3/3674 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3625 using active addressing

Abstract

Method and apparatus for providing gray level addressing for passive liquid crystal display (LCD) panels having overlapping row and column electrodes defining pixels are disclosed. Depending upon whether the rows are being addressed by "standard" or "Swift" addressing, the signals for applying to the column electrodes are determined by different calculations, in all of which modes the amplitudes of the column signals are related to the gray level desired to be displayed by the individual pixels. For a split interval system, column signals of appropriate amplitude and polarity are applied during different subintervals of a characteristic time interval of the display panel depending upon the method of addressing the rows. In the full interval mode, the column signals applied over a full time interval are based on the desired gray level of all the pixels in the column, adjusted to provide the proper rms voltage across all the pixels so that they display the desired gray levels.

Claims

1. A method for addressing a display in which multiple overlapping first and second electrodes positioned on opposite sides of an rms-responding material define an array of pixels that display information in more than two gray levels, the pixels having in a frame period desired gray levels that are represented by pixel information elements having values between a lower limit and an upper limit, the pixels characterized by optical states that depend on values of rms voltages established across the pixels, the method comprising:

generating at least one virtual first signal having an amplitude for at least one virtual first electrode that overlaps the second electrodes and provides a plurality of virtual pixels having desired gray levels represented by virtual pixel information elements;

applying first signals having amplitudes to corresponding first electrodes during the frame period, the first signals selecting pixels defined by the corresponding first electrodes and each of the virtual first signals selecting virtual pixels defined by its corresponding virtual electrode; and

generating second signals of changing magnitudes and applying them to corresponding second electrodes during characteristic time intervals of the frame period, the magnitude of each second signal being selected from more than two available voltages and being proportional to a term related to the square root of a number of first electrodes and to the pixel information element of each selected pixel multiplied by the amplitude of the corresponding first signal or to the virtual pixel information element of each selected virtual pixel multiplied by the amplitude of the corresponding virtual first signal during the time interval.

2. The method of claim 1, in which:

the first signals are pulses of amplitude S;

during each time interval that a first electrode is selected, the magnitude of a second signal G is determined by;

space="preserve" listing-type="equation">G=DI;

where D is a constant term related to the number of first electrodes in the display and to a non-select voltage and I is a value associated with a pixel information element corresponding to the corresponding second electrode and the selected first electrode, and

during each time interval that a virtual electrode is selected, the magnitude of a second signal G is determined by;

space="preserve" listing-type="equation">G=DV

where;

##EQU10## where V_ns is the non-select rms voltage across a pixel, N is the number of first electrodes in the display, I_i are the pixel information elements of the corresponding second electrode and V is the virtual information element of the virtual electrode.

3. A method for addressing a display in which multiple overlapping first and second electrodes positioned on opposite sides of an rms-responding material define an array of pixels that display information in more than two gray levels, each pixel having in a frame period a desired gray level that is represented by a pixel information element having a value between a lower limit and an upper limit, the pixels characterized by optical states that depend on values of rms voltages established across the pixels, the method comprising:

applying first signals to cause selections of corresponding first electrodes, at least some of the first signals causing selections of corresponding first electrodes during more than one characteristic time interval of the frame period;

generating at least one virtual first signal for at least one virtual first electrode that defines a group of virtual pixels, each virtual pixel corresponding to a second electrode and represented by a virtual information element having a value determined from the values of more than one pixel information element representing pixels defined by the corresponding second electrode; and

generating second signals of changing magnitudes and applying them to corresponding second electrodes during characteristic time intervals of the frame period, the magnitude of each second signal during at least some of the characteristic time intervals being proportional to the inverse of the square root of a number of first electrodes and to a sum of first and second quantities, the first quantity being proportional to a sum of the products of the amplitude of each first signal causing a selection of a first electrode at that time interval and the pixel information element of the pixel defined by the corresponding first and second overlapping electrodes and the second quantity representing a sum of one or more quantities derived for the group of virtual pixels defined by each virtual first electrode, each group of virtual pixels contributing to the sum a quantity proportional to the product of the amplitude of the corresponding virtual first signal at the time interval and the virtual information element of the virtual pixel defined by the virtual electrode and the corresponding second electrode.

4. The method of claim 3, in which

the magnitude, G, of each second signal at any given time interval is determined by:

##EQU11## where N is the number of first electrodes, I_i is the pixel information element at a pixel defined by the corresponding second electrode and a particular first electrode, F_i is the amplitude of the first signal applied to the corresponding first electrode during the time interval, V_k is the virtual information element at a virtual pixel defined by the corresponding second electrode and a particular virtual first electrode, and F_k is the amplitude of the first signal associated with the virtual first electrode during the time interval.

5. The method of claim 3 in which during at least one characteristic time interval of the frame period, a second signal is generated and applied when none of the first electrodes is selected.

6. The method of claim 3 in which a single virtual pixel is associated with each second electrode.

7. The method of claim 3 in which multiple virtual pixels are associated with each second electrode.

8. The method of claim 3 in which the second quantity is equal to zero during at least one but not all of the characteristic time intervals of the frame period.

9. The method of claim 3 in which the first quantity is equal to zero during at least one but not all of the characteristic time intervals of the frame period.

10. The method of claim 3 in which the first quantity is non-zero in at least one characteristic time interval, the second quantity is non-zero in at least one characteristic time interval, and in no characteristic time interval are both the first and second quantities non-zero.

11. An apparatus for converting video signals including control and information components into signals for addressing a display in which multiple overlapping first and second electrodes positioned on opposite sides of an rms-responding material define an array of pixels that display information in more than two gray levels, the pixels characterized in a frame period by desired gray levels that are represented by pixel information elements having values between a lower limit and an upper limit, the pixels characterized by optical states that depend on values of rms voltages established across the pixels, the apparatus comprising:

first signal generating means for generating first signals that are block pulse functions independent of the information component of the video signal, the first signal generating means including means for generating at least one virtual first signal for at least one corresponding virtual first electrode overlapping the second electrodes and defining multiple virtual pixels having desired gray levels represented by multiple virtual information elements,

means for applying the first signals to select pixels defined by the corresponding first electrodes and for applying the one or ones of the virtual first signals to select virtual pixels defined by the one or ones of the first virtual electrodes during the frame period,

second signal generating means for generating second signals having magnitudes that are proportional to the pixel information element or the virtual information element of each selected first electrode and virtual first electrode, respectively, during the time interval, and

means for applying the second signals to the second electrodes during the frame period coincidentally with the application of the signals to the first electrodes.

12. An apparatus for converting video signals including control and information components into signals for addressing a display in which multiple overlapping first and second electrodes positioned on opposite sides of an rms-responding material define an array of pixels that display information in more than two gray levels, the pixels having in a frame period desired gray levels that are represented by pixel information elements having values between a lower limit and an upper limit, the pixels characterized by optical states that depend on values of rms voltages established across the pixels, the apparatus comprising:

first signal generating means for generating first signals that are independent of the information component of the video signal and that select pixels defined by each first electrode more than once during the frame period, the frame period being divided into characteristic time intervals, the first signal generating means including means for generating at least one virtual first signal for at least one virtual first electrode overlapping the second electrodes and providing a plurality of virtual pixels having desired gray levels represented by virtual information elements.

means for applying the first signals to corresponding first electrodes during the frame period,

second signal generating means for generating second signals having magnitudes, the magnitude of each second signal during the characteristic time interval being proportional to the inverse of the square root of a number of first electrodes and to the sum of the products of the amplitude of each first signal at that time interval and the pixel information element at the corresponding first and second electrodes and being adjusted by a term that is proportional to the sum of the products of the magnitude of each virtual first signal during the time interval and the virtual information element at the corresponding second electrode and virtual first electrode, and

means for applying the second signals to the second electrodes during the frame period coincidentally with the application of the signals to the first electrodes.

13. Apparatus for converting video signals including control and information components into signals for addressing a display in which multiple overlapping first and second electrodes positioned on opposite sides of an rms-responding material define an array of pixels that display information in more than two gray levels, the pixels characterized by optical states that depend on values of rms voltages established across the pixel, comprising:

first signal generating means for generating first signals that are orthonormal functions independent of the information component of the video signal, the first signals selecting pixels defined by each first electrode more than once during the frame period,

means for applying the first signals to corresponding first electrodes during a frame period;

second signal generating means for generating second signals that represent the information component of said video signals including desired gray levels, the second signals having magnitudes that at any time during the frame period are selected from more than two available voltages related to the desired gray level of at least one of the pixels, and the second signal generating means including dot product generating means for generating a dot product term of each first signal and the corresponding pixel information element, and

means for applying the second signals to the second electrodes during the frame period coincidentally with the application of the signals to the first electrodes.

14. The apparatus of claim 13, in which the second signal generating means includes means for generating a plurality of virtual information elements from at least one virtual first signal applied to at least one virtual first electrode overlapping said second electrodes, and further comprising:

adjustment term generating means for generating an adjustment term that is proportional to the sum of the products of the amplitude of the virtual first signal and the virtual information element at the corresponding virtual first electrode; and

combiner means for combining said dot product term and said adjustment term to provide said second signal.

15. A method for addressing a display in which multiple overlapping first and second electrodes positioned on opposite ends of an rms-responding material define an array of pixels that display information in more than two gray levels, the pixels having in a frame period desired gray levels that are represented by pixel information elements having values between a lower limit and an upper limit, the pixels characterized by optical states that depend on values of rms voltages established across the pixels, and in which multiple virtual information elements are defined by virtual pixels defined by at least one virtual first electrode overlapping the second electrodes, the method comprising:

applying first signals and a virtual first signal to cause selections of the corresponding of the respective first and virtual first electrodes periodically during the frame period; and

generating second signals of changing magnitudes and applying them to corresponding second electrodes during characteristic time intervals of the frame period, the magnitudes of at least some of the second signals during a characteristic time interval being selected from more than two available voltages and being proportional to the information elements or virtual information element of the respective pixels or virtual pixels defined by the overlap of the corresponding second electrodes with the selected one of the respective first and virtual first electrodes.

16. A method for addressing a display in which multiple overlapping first and second electrodes positioned on opposite sides of an rms-responding material define an array of pixels that display information in more than two gray levels, the pixels having in a frame period desired gray levels that are represented by pixel information elements having values between a lower limit and an upper limit, the pixels characterized by optical states that depend on values of rms voltages established across the pixels, and in which multiple virtual information elements are defined by virtual pixels defined by at least one virtual first electrode overlapping the second electrodes, the method comprising:

applying first signals to corresponding first electrodes during the frame period; and

generating second signals of changing magnitudes and applying them to corresponding second electrodes during characteristic time intervals of the frame period, the magnitudes of at least some of the second signals during a characteristic time interval being selected from more than two available voltages related to the gray level values of the information elements or the virtual information elements of the respective pixels or virtual pixels defined by the corresponding second electrodes, the magnitudes of the second signals being proportional to the virtual information elements during time intervals in which no first electrode is selected.

17. A method for addressing a display in which multiple overlapping first and second electrodes positioned on opposite sides of an rms-responding material define an array of pixels that display information in more than two gray levels, the pixels having in a frame period desired gray levels that are represented by pixel information elements having values between a lower limit and an upper limit, the pixels being characterized by optical states that depend on values of rms voltages established across the pixels, the method comprising:

applying first signals to cause selections of corresponding ones of the first electrodes during the frame period; and

generating during the frame period second signals of changing magnitudes and applying them to corresponding second electrodes during characteristic time intervals of the frame period, the magnitudes of at least some of the second signals during at least some of the characteristic time intervals being determined by a sum of first and second quantities, the first quantity being proportional to a sum of products of the value of the information element of each pixel defined by the overlapping of the corresponding second electrode and first electrodes selected during the time interval by corresponding first signals and the amplitude of the corresponding first signal and the second quantity including a term related to the square of the value of at least some of the information elements of the pixels defined by the corresponding second electrode.

18. The method of claim 17 in which multiple ones of the first signals cause multiple selections of the corresponding first electrodes during a frame period.

19. The method of claim 17 in which at least some of the first signals cause no more than one selection of their corresponding first electrodes during a frame period.

20. The method of claim 17 in which the first quantity is equal to zero during at least one but not all of the characteristic time intervals of the frame period.

21. The method of claim 17 in which during at least one characteristic time interval of the frame period, a second signal is generated and applied when none of the first electrodes is selected.

22. The method of claim 17 in which the second quantity is equal to zero during at least one but not all of the characteristic time intervals of the frame period.

24. A method for addressing a display of a type that displays information patterns in more than two gray levels, the display including overlapping first and second electrodes positioned on opposite sides of an rms-responding material to define an array of pixels that display information patterns corresponding to pixel input data, the pixels characterized by optical states that depend on values of rms voltages established across the pixels, the method comprising:

applying first signals to corresponding first electrodes during a frame period, the first signals having amplitudes;

generating a second signal of changing magnitude during the frame period and applying the second signal to one of the second electrodes during characteristic time intervals, the second signal having, during at least some characteristic time intervals of the frame period, an amplitude determined by the amplitudes of the first signals causing selections during the characteristic time interval, by pixel input data corresponding to more than two gray levels of pixels defined by the corresponding second electrode, and by a number of first electrodes; and

generating at least one additional second signal and applying it to at least that one of the second electrodes at a time during the frame period when none of the first electrodes is selected, the additional second signal having a magnitude related to the number of first electrodes minus the sum of the squares of pixel input data of multiple pixels defined by the corresponding second electrode and producing across corresponding pixels over the frame period an rms voltage related to the pixel input data.

25. A method for addressing a display in which multiple overlapping first and second electrodes positioned on opposite sides of an rms-responding material define an array of pixels that display information in more than two gray levels, the pixels having in a frame period desired gray levels that are represented by pixel information elements, each element having a value between a lower limit and an upper limit, the pixels characterized by optical states that depend on values of rms voltages established across the pixels, the method comprising:

applying first signals to corresponding first electrodes during the frame period; and

generating second signals of changing magnitudes during the frame period and applying them to corresponding second electrodes during characteristic time intervals of the frame period, the magnitude of at least one of the second signals during at least one of the characteristic time intervals being determined by the value of the information element of each pixel defined by the intersection of the corresponding second electrode and selected ones of the first electrodes and by a term related to the sum of the squares of the values of at least some of the information elements of the pixels defined by the corresponding second electrode.

26. A method for addressing a display in which multiple overlapping first and second electrodes positioned on opposite sides of an rms-responding material define an array of pixels that display information in more than two gray levels, each pixel having in a frame period a desired gray level that is represented by pixel information elements, each element having a value between a lower limit and an upper limit, the pixels characterized by optical states that depend on values of rms voltages established across the pixel, the method comprising:

applying first signals to cause selections of corresponding first electrodes during the frame period; and

generating second signals of changing magnitudes during the frame period and applying them to corresponding second electrodes during characteristic time intervals of the frame period, the magnitude of at least one of the second signals during at least one of the characteristic time intervals being related to the square root of a number of first electrodes minus a sum of the squares of multiple ones of the pixel information elements.

27. A method for addressing a display in which multiple overlapping first and second electrodes positioned on opposite sides of an rms-responding material define an array of pixels that display information in more than two gray levels, the pixels having in a frame period desired gray levels that are represented by pixel information elements having values between a lower limit and an upper limit, and the pixels characterized by optical states that depend on values of rms voltages established across the pixels, the method comprising:

applying first signals to cause selections of corresponding ones of the first electrodes during the frame period;

generating at least one virtual first signal for at least one virtual first electrode that defines a plurality of virtual pixels, each virtual pixel corresponding to a second electrode and represented by a virtual information element having a value determined from the values of more than one pixel information element representing pixels defined by the corresponding second electrode; and

generating second signals of changing magnitudes during the frame period and applying them to corresponding second electrodes during characteristic time intervals of the frame period, the magnitude of at least one of the second signals at any of the characteristic time intervals being proportional to a term related to the square root of a number of first electrodes and to a sum of first and second quantities, the first quantity being proportional to a sum of the products of the amplitude of each first signal causing a selection of a first electrode at that time interval and the pixel information element of the pixel defined by the corresponding first and second overlapping electrodes and the second quantity representing a sum of quantities derived for each of the selected virtual first electrodes, each virtual first electrode contributing to the sum a quantity proportional to the product of the amplitude of the corresponding virtual first signal at the time interval and the virtual information element of the virtual pixel defined by the virtual first electrode and the corresponding second electrode.

28. A method for addressing a display in which multiple overlapping first and second electrodes positioned on opposite sides of an rms-responding material define an array of pixels that display information in more than two gray levels, each pixel having a desired gray level that is represented by a pixel information element having a value during a frame period between a lower limit and an upper limit, the pixels characterized by optical states that depend on values of rms voltages established across the pixels, the method comprising:

applying first signals to cause selections of corresponding first electrodes during characteristic time intervals of the frame period;

generating at least one virtual first signal for at least one virtual first electrode that defines a plurality of virtual pixels, each virtual pixel corresponding to a second electrode and represented by a virtual information element having a value determined from the values of more than one pixel information element representing pixels defined by the corresponding second electrode; and

generating second signals of changing magnitudes and applying them to corresponding second electrodes during characteristic time intervals of the frame period, the magnitude of at least one second signal being related during at least one of the characteristic time intervals of the frame period to a sum of the products of the amplitude of each first signal causing a selection of a first electrode at that time interval and the pixel information element of the pixel defined by the corresponding first and second overlapping electrodes and the magnitude of at least one of the second signals being related during at least one of the characteristic time intervals of the frame period to a product of the amplitude of a virtual first signal during the time interval and the virtual information element of the virtual pixel defined by the corresponding virtual electrode and the corresponding second electrode.

23. The method of claim 28 in which the first quantity is non-zero in at least one characteristic time interval, the second quantity is non-zero in at least one characteristics time interval, and in no characteristic time interval are both the first and second quantities non-zero.

29. The method of claim 28 in which the magnitude of at least one second signal during at least one time interval of the frame period is related to a sum of products of the amplitude of corresponding virtual first signals at the time interval and virtual information elements of virtual pixels defined by the virtual electrode and the corresponding second electrode.

30. The method of claim 28 in which the magnitude of at least one second signal is related during a characteristic time interval of the frame period to a sum of the products of the amplitude of each first signal causing a selection of a first electrode at that time interval and the pixel information element of the pixel defined by the corresponding first and second overlapping electrodes and to a product of the amplitude of a corresponding virtual first signal at the time interval and the virtual information element of the virtual pixel defined by the virtual electrode and the corresponding second electrode.

31. The method of claim 28 in which the magnitude of at least one second signal is related during different characteristic time intervals of the frame period to a sum of the products of the amplitude of each first signal causing a selection of a first electrode at that time interval and the pixel information element of the pixel defined by the corresponding first and second overlapping electrodes or to a product of the amplitude of a corresponding virtual first signal at the time interval and the virtual information element of the virtual pixel defined by the virtual electrode and the corresponding second electrode.

32. A method for addressing a display in which multiple overlapping first and second electrodes positioned on opposite sides of an rms-responding material define an array of pixels that display information in more than two gray levels, the pixels having in a frame period desired gray levels that are represented by pixel information elements having values between a lower limit and an upper limit, and the pixels being characterized by optical states that depend on values of rms voltages established across the pixels, the method comprising:

applying first signals to cause selections of corresponding ones of the first electrodes during the frame period; and

generating second signals of changing magnitudes during the frame period and applying them to corresponding second electrodes during characteristic time intervals of the frame period, the magnitudes of at least some of the second signals during at least one of the characteristic time intervals being related to a number of first electrodes and to a square of the values of at least some of the information elements of the pixels defined by the corresponding second electrode.

33. The method of claim 32 in which at least some of the second signals during at least some of the characteristic time intervals are related to a sum of products of the value of the information element of each pixel defined by the overlapping of the corresponding second electrode and first electrodes selected during the time interval by corresponding first signals and the amplitude of the corresponding first signal.