LCD addressing system and method - Patent Review 5485173

Claims

What is claimed is:

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

applying a set of first signals to corresponding first electrodes during a frame period that is divided into time intervals, the first signals having amplitudes, and multiple ones of the first signals each causing multiple selections of the corresponding first electrodes, the multiple selections taking place during different ones of the time intervals and being distributed over the frame period;

each of the first signals provides a number of the time intervals over the frame period that is less than an exponential function of the number of first electrodes;

generating second signals and applying them to the second electrodes, each of the second signals being different from any of the first signals, and the second signals having at a particular time interval during the frame period amplitudes determined by both the amplitudes of the first signals causing selections at the particular time interval and the corresponding pixel input data; and

the amplitudes of multiple second signals being determined by contributions of the multiple selections by each one of the first signals in the set that are distributed over the frame period so as to reduce the frame response of the display.

2. The method of claim 1 wherein the amplitude of each one of the second signals is proportional to a sum of products of the amplitudes of the first signals causing selections and the pixel input data of pixels defined by the corresponding first electrodes, and the proportionality constant is about 1/.sqroot.N, where N is the number of first electrodes.

3. The method of claim 1 wherein all of the first signals cause multiple selections of the corresponding first electrodes the multiple selections being distributed over the frame period.

4. The method of claim 1 wherein multiple ones of the first signals have rms values that are normalized to a common value.

5. The method of claim 1 wherein the first signals are orthogonal to one another.

6. A system for addressing an rms-responding display of a type that displays arbitrary information patterns, 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 arbitrary information patterns corresponding to pixel input data, the system comprising:

a first signal generator for generating and applying a set of first signals to corresponding first electrodes during a frame period, the first signals having amplitudes, and each one of the first signals in the set causing multiple selections of its corresponding first electrode, the multiple selections being distributed over the frame period;

storage sites for storing the pixel input data; and

a second signal generator for generating second signals and output connection means for applying the second signals to the second electrodes, the second signal generator including a correlator for correlating the first signals and the stored pixel input data to determine the second signals so that contributions of the multiple selections by each one of the first signals in the set to determinations of amplitudes of multiple second signals are distributed over the frame period, the correlator including data transfer signal means for writing into and reading from the storage sites sets of pixel input data, each of the sets of pixel input data corresponding to pixels defined by a different one of the second electrodes; multiplying means for multiplying the first signals and the sets of pixel input data to derive product signals; and summing means for summing the product signals derived for each set of pixel input data to produce the second signals for delivery to the output connection means.

7. The method of claim 1 wherein the amplitudes of at least some of the first signals include two nonzero signal levels to effect the multiple selections of the corresponding first electrodes.

8. The method of claim 1 wherein each of the first signals is derived from an orthonormal function matrix having a set order of 2.sup.s, where S is a positive integer and the display includes a number of first electrodes which number is greater than 2.sup.s-1 and less than or equal to 2.sup.s.

9. The method of claim 8 wherein the first signals are derived from a set of Walsh functions.

10. The method of claim 9 wherein the set of Walsh functions is sequency ordered.

11. The method of claim 10 wherein the sequency-ordered set of Walsh functions is of the highest sequency.

12. A system for addressing rms-responding information storage elements that store arbitrary information patterns, the system including overlapping first and second electrodes positioned on opposite sides of an rms-responding material to define an array of information storage elements that store arbitrary information patterns corresponding to information input data, the system comprising:

a first signal generator for generating and applying a set of first signals to corresponding first electrodes during a frame period, the first signals having amplitudes, and the amplitude of each one of the first signals in the set including two nonzero signal levels causing multiple selections of its corresponding first electrode, the multiple selections being distributed over the frame period;

storage sites for storing the information input data;

a second signal generator for generating second signals, the second signal generator including a correlator for correlating the first signals and the stored information input data to determine the second signals, and each of the second signals having at a particular time during the frame period an amplitude determined by the amplitudes of more than one of the first signals causing selections at the particular time and by information input data of information storage elements defined by the corresponding first electrodes so that contributions of the multiple selections by each one of the first signals in the set to determinations of amplitudes of multiple second signals are distributed over the frame period and so as to address an arbitrary number of information storage elements; and

output connection means for applying the second signals to the second electrodes.

13. The method of claim 12 wherein an additional vector is added to the set of Pseudo Random Binary Sequence functions, all elements of the additional vector having a value of +1 so that each first signal is orthogonal to the other first signals and that the rms-responding material is free of net dc voltages.

14. The method of claim 1 wherein the second signals applied to the second electrodes are selected from a reduced set of possible signal levels and the amplitudes of the second signals are selected so as to correspond to the nearest one of the levels.

15. The method of claim 14 wherein the reduced set has maximum and minimum levels and the second signals exceeding the maximum or minimum level of the reduced set are clipped.

16. The method of claim 1 wherein the amplitude of each one of the second signals is proportional to a sum of products of the amplitudes of the first signals causing selections and the pixel input data of pixels defined by the corresponding first electrodes.

17. The method of claim 1, further comprising applying to the corresponding first electrodes the multiple ones of the first signals in an arrangement that reduces anomalous display effects.

18. The method of claim 1, further comprising inverting the amplitudes of a certain proportion of the first signals to reduce the maximum amplitudes of the second signals.

19. The method of claim 18 wherein the certain proportion of inverted first signals is between about 40% and 60% of all of the first signals.

20. The method of claim 1 wherein the amplitudes of the first signals the amplitudes of the first signals have in a time order discrete values associated with each of the time intervals, the method further comprising arranging the time order of the amplitude values of the first signals to reduce crosstalk among the pixels in the array.

21. The method of claim 1 wherein there are N number of first electrodes and the frame period is divided into 2.sup.s or fewer time intervals, where 2.sup.s-1 <N.ltoreq.2.sup.s.

22. The method of claim 1 wherein the rms-responding material includes a liquid crystal material.

23. The method of claim 1 wherein the display is of a high information content type.

24. The method of claim 1 wherein the first signals are derived from a set of pseudo random functions.

25. The method of claim 1 wherein the rms-responding display is of a supertwist liquid crystal type.

26. An apparatus for addressing an rms-responding, high information content liquid crystal display in which a first set of electrodes arranged in a first electrode pattern and a second set of electrodes arranged in a second electrode pattern overlapping each other to define an array of pixels that display arbitrary information patterns corresponding to pixel input logic levels, the apparatus comprising:

means for driving the first set of electrodes with first signals, each first signal having an amplitude, including a periodic train of pulses, and having a common frame period; and

means for driving each electrode of the second set of electrodes with a second signal that is proportional to a sum of exclusive-or (XOR) products of the pixel input logic levels and logic levels representative of the amplitudes of the first signals applied to the first electrodes.

whereby the first and second signals establish across each pixel a peak voltage and an rms voltage, and the absolute value of the peak voltage across any pixel is no more than 5 times the rms voltage across the pixel averaged over one frame period.

27. The apparatus of claim 26 wherein the absolute value of the peak voltage across any pixel is no more than 3 times the rms voltage across the pixel averaged over one frame period.

28. The apparatus of claim 26 wherein the periodic train of pulses of each first signal includes two nonzero voltage levels.

29. The apparatus of claim 26 wherein the liquid crystal display is of a supertwist type.

30. A high information content, direct multiplexed, rms-responding display system that displays arbitrary information patterns in successive frame periods, comprising:

a liquid crystal display having first and second substrates, the first substrate having a first electrode pattern on an inner first surface and the second substrate having a second electrode pattern on an inner second surface; the first and second substrates disposed so as to form a narrow gap enclosed by a seal; a low viscosity liquid crystal material disposed in the gap between the first and second surfaces wherein a plurality of fast responding pixels are formed wherever the first and second electrode patterns overlap; the liquid crystal display having an optical switching response time constant of less than 200 ms; and

means for providing an electrical signal to each of the electrode patterns to apply a voltage across and thereby selectively control an optical state of each pixel, where the electrical signals applied to the electrode patterns establish across each pixel peak voltage and rms voltage amplitudes, and the ratio of the absolute value of the peak voltage amplitude to the rms voltage amplitude across each pixel is less than 7:1 averaged over one frame period.

31. The display system of claim 30 wherein the ratio of the absolute value of the peak voltage amplitude to the rms voltage amplitude across each pixel is less than 5:1 averaged over one frame period.

32. The display system of claim 30 wherein the ratio of the absolute value of the peak voltage amplitude to the rms voltage amplitude across each pixel is less than 3:1 averaged over one frame period.

33. The display system of claim 30 wherein the liquid crystal display has a time constant of less than 50 ms.

34. The display system of claim 30 wherein the liquid crystal display is of a supertwist type.

35. A method for addressing an rms-responding, high information content display of a type that displays arbitrary information patterns in successive frame periods, 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 arbitrary information patterns corresponding to pixel input data, the method comprising:

applying a first signal to each first electrode, each of the first signals having an amplitude and a common frame period divided into time intervals, the amplitudes of the first signals having discrete values associated with each of the time intervals, and no more than a certain proportion equal to about 75% of the first signals having substantially the same amplitude for any given time interval; and

generating second signals and applying them to the second electrodes, each of the second signals having at a particular time during the frame period an amplitude determined by the amplitudes of more than one of the first signals at the particular time and by pixel input data of pixels defined by the corresponding first electrodes.

36. The method of claim 35 wherein the certain proportion is equal to about 50% of all of the first signals for any given time interval.

37. The method of claim 35 wherein the amplitude of each one of the second signals is proportional to a sum of products of the amplitudes of the first signals and the pixel input data of pixels defined by the corresponding first electrodes.

38. The method of claim 37 wherein a proportionality constant relates the amplitude of each of the second signals to the sum of products of the amplitudes of the first signals and the pixel input data of pixels defined by the corresponding first electrodes, and the proportionality constant is about 1/.sqroot.N, where N is the number of first electrodes.

39. The method of claim 35 wherein the rms-responding material includes a liquid crystal material.

40. The method of claim 35 wherein the rms-responding display is of a supertwist liquid crystal type.

41. A method for addressing an rms-responding display of a type that displays arbitrary information patterns, 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 arbitrary information patterns corresponding to pixel input data, the method comprising:

applying first signals to corresponding first electrodes during a frame period that is divided into time intervals, the first signals having amplitudes, and multiple ones of the first signals causing multiple selections of the corresponding first electrodes, the multiple selections taking place during different ones of the time intervals and being distributed over the frame period to reduce the frame response of the display;

each of the first signals provides a number of the time intervals over the frame period that is less than an exponential function of the number of first electrodes; and

generating a second signal of changing magnitude and applying it to one of the second electrodes, the second signal having at a particular time interval during the frame period an amplitude determined by both the amplitudes of more than one of the first signals causing selections at the particular time interval and the corresponding pixel input data.

42. The method of claim 41 wherein the amplitude of the second signal is proportional to a sum of products of the amplitudes of the first signals causing selections and the pixel input data of pixels defined by the corresponding first electrodes.

43. The method of claim 42 wherein a proportionality constant relates the amplitude of the second signal to the sum of products of the amplitudes of the first signals causing selections and the pixel input data of pixels defined by the corresponding first electrodes, and the proportionality constant is about 1/.sqroot.N, where N is the number of first electrodes.

44. The method of claim 41 wherein each of the first signals has an rms value that is normalized to a common value.

45. The method of claim 41 wherein the first signals are orthogonal to one another.

46. The method of claim 41 wherein the amplitudes of at least some of the first signals include two nonzero signal levels to effect the multiple selections of the corresponding first electrodes.

47. The method of claim 46 wherein the amplitude of the second signal is proportional to a sum of exclusive-or products of logic levels representative of the two nonzero signal levels of the first signals and logic levels representative of the pixel input data of pixels defined by the corresponding first electrodes.

48. The method of claim 41 wherein each of the first signals is derived from an orthonormal function matrix having a set order of 2.sup.s, where S is a positive integer and the display includes a number of first electrodes which number is greater than 2.sup.s-1 and less than or equal to 2.sup.s.

49. The method of claim 48 wherein the first signals are derived from a set of Walsh functions.

50. The method of claim 41 wherein the first signals are derived from a set of pseudo random functions.

51. The method of claim 41 wherein the first signals are chosen from a set of 2.sup.s -1 maximal length Pseudo Random Binary Sequence functions, where S is a positive integer and the display includes a number of first electrodes which number is greater than 2.sup.s-1.

52. The method of claim 51 wherein an additional vector is added to the set of Pseudo Random Binary Sequence functions, all elements of the additional vector having a value of +1 so that each first signal is orthogonal to the other first signals and that the rms-responding material is free of net dc voltages.

53. The method of claim 41, further comprising applying to the corresponding first electrodes the multiple ones of the first signals in an arrangement that reduces anomalous display effects.

54. The method of claim 41, further comprising inverting the amplitudes of a certain proportion of the first signals to reduce the maximum amplitudes of the second signals.

55. The method of claim 41 wherein all of the first signals cause multiple selections of the corresponding first electrodes, the multiple selections being distributed over the frame period.

56. The method of claim 41 wherein the rms-responding display is of a supertwist liquid crystal type.

57. In an addressing structure of a type that addresses information storage elements that develop arbitrary information patterns corresponding to information input data, the structure including first and second electrodes operatively associated with an addressing material to define an array of information storage elements that develop arbitrary information patterns corresponding to the information input data, a method of addressing the addressing structure, comprising:

applying first signals to the first electrodes during a frame period that is divided into time intervals, the first signals having amplitudes, and multiple ones of the first signals causing multiple selections of the corresponding first electrodes, the multiple selections taking place during different ones of the time intervals and being distributed over the frame period to reduce the frame response of the addressing structure;

each of the first signals provides a number of the time intervals over the frame period that is less than an exponential function of the number of first electrodes; and

generating a second signal of changing magnitude and applying it to one of the second electrodes, the second signal having at a particular time interval during the frame period an amplitude determined by both the amplitudes of more than one of the first signals causing selections at the particular time interval and the corresponding information input data.

58. The method of claim 57 wherein the amplitude of the second signal is proportional to a sum of products of the amplitudes of the first signals causing selections and the information input data of information storage elements defined by the corresponding first electrodes.

59. The method of claim 57 wherein the first signals are normalized to a common value.

60. The method of claim 57 wherein the first signals are orthogonal to one another.

61. The method of claim 57 wherein the amplitudes of at least some of the first signals include two nonzero signal levels to effect the multiple selections of the corresponding first electrodes.

62. The method of claim 61 wherein the amplitude of the second signal is proportional to a sum of exclusive-or products of logic levels representative of the two nonzero signal levels of the first signals and logic levels representative of the information input data of information storage elements defined by the corresponding first electrodes.

63. The method of claim 57 wherein each of the first signals is derived from an orthonormal function matrix having a set order of 2.sup.s, where S is a positive integer and the addressing structure includes a number of first electrodes which number is greater than 2.sup.s-1 and less than or equal to 2.sup.s.

64. The method of claim 63 wherein the first signals are derived from a set of Walsh functions.

65. The method of claim 64 wherein the set of Walsh functions is sequency-ordered.

66. The method of claim 65 wherein the sequency-ordered set of Walsh functions is of the highest sequency.

67. The method of claim 57 wherein the first signals are derived from a set of pseudo random functions.

68. The method of 57 wherein the first signals are chosen from a set of 2.sup.s -1 maximal length Pseudo Random Binary Sequence functions, where S is a positive integer and the addressing structure includes a number of first electrodes which number is greater than 2.sup.s-1.

69. The method of claim 68 wherein an additional vector is added to the set of Pseudo Random Binary Sequence functions, all elements of the additional vector having a value of +1 so that each first signal is orthogonal to the other first signals and that the rms-responding material is free of net dc voltages.

70. The method of claim 57 wherein all of the first signals cause multiple selections of the corresponding first electrodes, the multiple selections being distributed over the frame period.

71. The method of claim 57 wherein the addressing material includes an rms-responding material.

72. The method of claim 57, further comprising applying to the corresponding first electrodes the multiple ones of the first signals in an arrangement that reduces anomalous information storage effects.

73. The method of claim 57, further comprising inverting the amplitudes of a certain proportion of the first signals to reduce the maximum amplitudes of the second signals.

74. The method of claim 73 wherein the proportion of inverted first signals is between about 40% and 60% of all of the first signals.

75. The method of claim 57 wherein the amplitudes of the first signals have in a time order discrete values associated with each of the time intervals, the method further comprising arranging the time order of the amplitude values of the first signals to reduce crosstalk among the information storage elements in the array.

76. The method of claim 57 wherein there are N number of first electrodes and the frame period is divided into 2.sup.s or fewer time intervals, where 2.sup.s-1 <N<2.sup.s.

77. A method for addressing an rms-responding display of a type that displays arbitrary information patterns, 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 arbitrary information patterns corresponding to pixel input data, the method comprising:

applying first signals to corresponding first electrodes during a frame period that is divided into time intervals, the first signals having amplitudes at least some of which include two nonzero signal levels to effect multiple selections of the corresponding first electrodes, and multiple ones of the first signals causing multiple selections of the corresponding first electrodes, the multiple selections taking place during different ones of the time intervals and being distributed over the frame period;

each of the first signals provides a number of the time intervals over the frame period that is less than an exponential function of the number of first electrodes; and

generating second signals and applying them to the second electrodes, each of the second signals being different from any of the first signals, the second signals having at a particular time interval during the frame period amplitudes determined by both the amplitudes of the first signals at the particular time interval and the corresponding pixel input data, and the amplitude of each of the second signals being proportional to a sum of exclusive-or products of logic levels representative of the two nonzero signal levels of the first signals and logic levels representative of the pixel input data of pixels defined by the corresponding first electrodes; and

the amplitudes of multiple second signals being determined by contributions of the multiple selections by each one of the first signals that are distributed over the frame period so as to reduce the frame response of the display.

78. The method of claim 77 wherein each sum of the logic levels representing all first signals for any time interval has a parity value and each sum of the logic levels of the pixel input data for any second electrode has a parity value, the first signals are chosen such that for all time intervals of the frame period the parity values are the same for each sum of the logic levels representing all first signals for any time interval, and the pixel input data of a designated first electrode are chosen such that the parity values are the same for each sum of the logic levels of the pixel input data for any second electrode.

79. The method of claim 78 wherein the display of the designated first electrode is suppressed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to a method and apparatus for addressing liquid crystal devices. More particularly the present invention pertains to a method and apparatus for addressing high information content, direct multiplexed, rms responding liquid crystal displays.

2. Discussion of the Prior Art

Examples of high information content direct multiplexed, rms-responding liquid crystal displays are systems that incorporate twisted nematic (TN), supertwisted nematic (STN), or superhomeotropic (SH) liquid crystal display (LCD) panels. In such panels, a nematic liquid crystal material is disposed between parallel-spaced, opposing glass plates or substrates. In one common embodiment, a matrix of transparent electrodes is applied to the inner surface of each plate, typically arranged in horizontal rows on one plate and vertical columns on the other plate to provide a picture element or "pixel" wherever a row electrode overlaps a column electrode.

High information content displays, such as those used in computer monitors, require large numbers of pixels to portray arbitrary information patterns in the form of text or graphic images. Matrix LCDs having 480 rows and 640 columns forming 307,200 pixels are commonplace, although it is expected that matrix LCDs may soon comprise several million pixels.

The optical state of a pixel, e.g. whether it will appear dark, bright or an intermediate shade, is determined by the orientation of the liquid crystal director within that pixel. In so-called rms responding displays, the direction of orientation can be changed by the application of an electric field across the pixel which field induces a dielectric torque on the director that is proportional to the square of the applied electric field. The applied electric field can be either a dc field or an ac field, and because of the square dependence, the sign of the torque does not change when the electric field changes sign. In the direct multiplexed addressing techniques typically used with matrix LCDs, the pixel sees an ac field which is proportional to the difference in voltages applied to the electrodes on the opposite sides of the pixel. Signals of appropriate frequency, phase and amplitude, determined by the information to be displayed, are applied to the row and column electrodes creating an ac electric field across each pixel which field places it in an optical state representative of the information to be displayed.

Liquid crystal panels have an inherent time constant .tau. which characterizes the time required for the liquid crystal director to return to its equilibrium state after it has been displaced away from it by an external torque. The time constant .tau. is defined by .tau.=.eta.d.sup.2 /K, where .eta. is an average viscosity of the liquid crystal, d is the cell gap spacing or pitch length and K is an average elastic constant of the liquid crystal. For a conventional liquid crystal material in a 7-10 .mu.m cell gap, typical for displays, the time constant .tau. is on the order of 200-400 ms.

If the time constant .tau. is long compared to the longest period of the ac voltage applied across the pixel, then the liquid crystal director is unable to respond to the instantaneous dielectric torques applied to it, and can respond only to a time-averaged torque. Since the instantaneous torque is proportional to the square of the electric field, the time-averaged torque is proportional to the time average of the electric field squared. Under these conditions the optical state of the pixel is determined by the root-mean-square or rms value of the applied voltage. This is the case in typical multiplexed displays where the liquid crystal panel time constant .tau. is 200-400 ms and the information is refreshed at a 60 Hz rate, corresponding to a frame period of 1/60 s or 16.7 ms.

One of the main disadvantages of conventional direct multiplex addressing schemes for high information content LCDs arises when the liquid crystal panel has a time constant approaching that of the frame period. (The frame period is approximately 16.7 ms). Recent technological improvements have decreased liquid crystal panel time constants (.tau.) from approximately 200-400 ms to below 50 ms by making the gap (d) between the substrates thinner and by the synthesis of liquid crystal material which has lower viscosities (.eta.) and higher elastic constants (K). If it is attempted to use conventional addressing methods for high information content displays with these faster-responding liquid crystal panels, display brightness and contrast ratio are degraded and in the case of SH displays, alignment instabilities are also introduced.

The decrease in display brightness and contrast ratio occurs in these faster panels because with conventional multiplexing schemes for high information content LCDs, each pixel is subjected to a short duration "selection" pulse that occurs once per frame period and has a peak amplitude that is typically 7-13 times higher than the rms voltage averaged over the frame period. Because of the shorter time constant .tau., the liquid crystal director instantaneously responds to this high-amplitude selection pulse resulting in a transient change in the pixel brightness, before returning to a quiescent state corresponding to the much lower rms voltage over the remainder of the frame period. Because the human eye tends to average out the brightness transients to a perceived level, the bright state appears darker and the dark state appears brighter. The degradation is referred to as "frame response". As the difference between a bright state and a dark state is reduced, the contrast ratio, the ratio of the transmitted luminance of a bright state to the transmitted luminance of a dark state, is also reduced.

Several approaches have been attempted to reduce frame response. Decreasing the frame period is one approach, but this approach is restricted by the upper frequency limit of the driver circuitry and the filtering effects on the drive waveforms caused by the electrode sheet resistance and the liquid crystal capacitance. Another approach is to decrease the relative amplitude of the selection pulse, i.e., decreasing the bias ratio, but this ultimately reduces the contrast ratio.

Other matrix addressing techniques are known which do not employ high-amplitude row selection pulses and therefore would not be expected to induce frame response in faster-responding panels. However, these techniques are applicable only to low information content LCDs where either there are just a few matrix rows or where the possible information patterns are somehow restricted, such as in allowing only one "off" pixel per column.

One advantage of the faster responding liquid crystal panels is that it makes video rate, high information content LCDs feasible for flat, "hang on the wall" TV screens. However, this advantage cannot be fully exploited with conventional direct multiplexing addressing schemes because of the degradation of brightness and contrast ratio and the introduction of alignment instabilities in these panels caused by frame response.

SUMMARY OF THE INVENTION

In accordance with the present invention, a novel addressing method and several preferred embodiments of an apparatus for addressing faster-responding, high-information content LCD panels are provided. The present addressing method and preferred embodiments provide a bright, high contrast, high information content, video rate display that is also free of alignment instabilities.

In the method of the present invention, the row electrodes of the matrix are continuously driven with row signals each comprising a train of pulses. The row signals are periodic in time and have a common period T which corresponds to the frame period. The row signals are independent of the information or data to be displayed and are preferably orthogonal and normalized, i.e., orthonormal. The term normalized denotes that all the row signals have the same rms amplitude integrated over the frame period while the term orthogonal denotes that if the amplitude of a signal applied to one row electrode is multiplied by the amplitude of a signal applied to another row electrode, then the integral of this product over the frame period is zero.

During each frame period T, multiple column signals are generated from the collective information state of the pixels in the columns. The pixels display arbitrary information patterns that correspond to pixel input data. The column voltage at any time t during frame period T is proportional to the sum obtained by considering each pixel in the column and adding the voltage of that pixel's row at time t to the sum if the pixel is to be "off" and subtracting the voltage of the row of that pixel at time t from the sum if the pixel is to be "on". If the orthonormal row functions switch between only two voltage levels, the above sum may be represented as the sum of the exclusive-or (XOR) products of the logic level of each row signal at time t times the logic level of the information state of the pixel corresponding to that row.

When LCDs are addressed in the method of the present invention, frame response is drastically reduced because the ratio of the peak amplitude to the rms amplitude seen by each pixel is in the range of 2-5 which is much lower than with conventional multiplexing addressing schemes for high information content LCDs. For LCD panels that have time constants on the order of 50 ms, the pixels are perceived as having brighter bright states and darker dark states, and hence a higher contrast ratio. Alignment instabilities that are introduced by high peak amplitude signals are also eliminated.

Hardware implementation of the addressing method of the present invention comprises an external video source, a controller that receives and formats video data and timing information, a storage means for storing the display data, a row signal generator, a column signal generator, and at least one LCD panel.

The addressing method of the present invention may be extended to provide gray scale shading, where the information state of each pixel is no longer simply "on" or "off" but a multi-bit representation corresponding to the shade of the pixel. In this method each bit is used to generate a separate column signal, and the final optical state of the pixel is determined from a weighted average of the effect of each bit of the information state of the pixel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagramatic view representing row and column addressing signals being applied to a LCD matrix in a display system according to this invention.

FIG. 2 is a partial cross-sectional view of the LCD matrix taken along line 2--2.

FIG. 3 is an example of a 32.times.32 Walsh function matrix utilized in connection with the invention of FIG. 1.

FIG. 4 represents Walsh function waveforms corresponding to the Walsh function matrix of FIG. 3.

FIG. 5 is a generalized form of the Walsh function matrix of FIG. 3.

FIG. 6 is a generalized representation of one embodiment of a circuit used to generate a pseudo-random binary sequence in accordance with the present invention.

FIG. 7 shows a voltage waveform across a pixel for several frame periods according to the addressing method of the present invention.

FIG. 8 represents the optical response of a pixel to the voltage waveform of FIG. 7.

FIG. 9 is a graph depicting the number of occurrences of D matches between the information vector and the Swift matrix vectors corresponding to one frame period for a 240 row display of this invention.

FIG. 10 is a block diagram of the apparatus of the present invention.

FIG. 11 is a flowchart of the basic operation of one embodiment of the apparatus of the present invention.

FIG. 12 is a block diagram of one embodiment of the present invention for addressing an LCD display system.

FIG. 13 is a block diagram of a row driver IC shown in FIG. 12.

FIG. 14 is a more detailed block diagram of the integrated column driver IC shown in FIG. 12.

FIG. 15 is a block diagram of one embodiment of the XOR sum generator shown in FIG. 14.

FIG. 16 is a block diagram of a second embodiment of the XOR sum generator.

FIG. 17 is a block diagram of the integrated driver of FIG. 14 with a third embodiment of the XOR sum generator.

FIG. 18 is a block diagram of a second embodiment of the present invention for addressing an LCD display system.

FIG. 19 is a block diagram showing the column signal computer of FIG. 18.

FIG. 20 is a block diagram showing an embodiment of the present invention of FIG. 14 incorporating gray shading.

FIG. 21 is a block diagram showing an embodiment of the present invention of FIG. 17 incorporating gray shading.

FIG. 22 is a block diagram showing an embodiment of the present invention of FIG. 19 incorporating gray shading.

FIG. 23 is a block diagram of one embodiment of the Swift function generator shown in FIG. 18.

FIG. 24 is a block diagram of a second embodiment of the Swift function gener