Displaying gray shades on display panel implemented with phase-displaced multiple row selections

• US 5,852,429 A
• Filed: 07/19/1996
• Issued: 12/22/1998
• Est. Priority Date: 04/01/1991
• Status: Expired due to Term

• Current Assignee: InFocus Corporation (Lap-Shun Hui, MBA)
• Original Assignee: InFocus Corporation (Lap-Shun Hui, MBA)
• Inventors: Scheffer, Terry J., Clifton, Benjamin R.
• Primary Examiner(s): Mengistu, Amare
• Application Number:
  US08/684,433
• Time in Patent Office: 886 Days
• Field of Search: 345/100, 345/87, 345/89, 345/147
• US Class Current: 345/100
• 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

An addressing method and apparatus addresses faster responding liquid crystal display panels (LCDs) so that video rate, high information content LCDs having time constants on the order of 50 ms or less are perceived as having improved contrast by limiting peak voltage levels across the pixels. In a preferred embodiment, a first set of LCD electrodes is continuously driven with signals each comprising a train of pulses that are periodic in time, have a common period T, are independent of the information to be displayed, and are preferably orthonormal. Plural column signals are generated from the collective information states of the pixels defined by the overlap with a second electrode pattern. Each column signal is proportional to the sum, obtained by considering each pixel in the column, of the exclusive-or (XOR) products of the logic level of the amplitude of each row signal times the logic level of the information state of the pixel corresponding to that row. Hardware implementation comprises an external video source, a controller that receives and formats video data and timing information, a storage device that stores display data, a row signal generator, a column signal generator, and at least one LCD panel. Alternative embodiments provide circuits to reduce the number of column voltage levels required to generate a displayed image.

Claims

1. A method for addressing a display panel to display different gray shades or hues, the display panel 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 that depend on values of rms voltages established across the pixels and correspond to pixel input data, each pixel input datum having first and second logic levels that represent corresponding first and second optical transmission states for the pixel to which the pixel input datum corresponds, 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;

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;

controlling for each pixel a length of time the pixel input datum is in the first logic level and a length of time the pixel input datum of the pixel is in the second logic level; and

generating second signals and applying them to corresponding ones of the second electrodes, the second signals having amplitudes determined by the amplitudes of more than one of the first signals causing selections and by the logic levels of the pixel input data of pixels defined by the corresponding first electrodes, the length of time the pixel input datum associated with a pixel is in the first logic level as compared with the length of time the pixel input datum associated with the pixel is in the second logic level producing for the pixel an intermediate optical transmission state between the first and second optical transmission states and corresponding to an intermediate gray shade.

2. The method of claim 1 in which the controlling for each pixel the lengths of time the pixel input datum is in the first and second logic levels further comprises:

determining binary pixel information states corresponding to multiple frame periods; and

controlling the number of frame periods for which the binary pixel information states produce display information patterns that include at least one intermediate gray shade.

3. The method of claim 2 in which the determining binary pixel information states includes determining binary pixel states corresponding to multiple subintervals of a time interval.

4. The method of claim 3 in which the binary pixel information states associated with a pixel and corresponding to the multiple sub-intervals comprise a multi-bit gray level word for the pixel and in which the amplitude of the second signal at a particular time interval is determined by the amplitudes of more than one of the first signals at the particular time interval and by individual bits of the multi-bit gray level words of pixels defined by the corresponding first electrodes.

5. The method of claim 2 in which the amplitude of the second signal at the particular time interval is proportional to the sum of the products of the bits of the multi-bit gray level word and the amplitudes of the first signals of pixels defined by the corresponding first electrode.

6. The method of claim 4 in which the amplitude of the second signal at the particular time interval is proportional to exclusive-OR products of individual bits from each of the multi-bit gray level words and the amplitudes of the first signals of pixels defined by the corresponding first electrode.

7. The method of claim 1 in which:

a number of the time intervals define a set of time intervals;

a number of the first signals define a group that includes first and second subgroups of first signals, the number of time intervals in the set being equal to the number of first signals in the group and each of the first and second subgroups causing multiple simultaneous selections by amplitude transitions within the set of time intervals; and

the amplitude transitions of the multiple simultaneous selections caused by the first subgroup being phase displaced from the amplitude transitions of the multiple simultaneous selections caused by the second subgroup.

8. The method of claim 7 in which the amplitude transitions of the multiple simultaneous selections caused by the first subgroup are phase displaced by at least one time interval from the amplitude transitions of the multiple simultaneous selections caused by the second subgroup.

9. The method of claim 7 in which the number of time intervals in the set is four.

15. The method of claim 8 in which the multiple simultaneous selections caused by the first subgroup are phase displaced by two time intervals from the amplitude transitions.

10. A system for addressing a display panel to display different gray shades or hues, the display panel 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 that depend on values of rms voltages established across the pixels and correspond to pixel input data, each pixel input datum having first and second logic levels that represent corresponding first and second optical transmission states for the pixel to which the pixel input datum corresponds, the system comprising:

a first signal generator for generating and 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;

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

a second signal generator for generating and applying second signals to the second electrodes, the second signal generator including a correlator and a gray shade controller, the correlator correlating the amplitudes of the first signals and the pixel input data to determine the amplitudes of the second signals and the gray shade controller controlling for each pixel a length of time the pixel input datum is in the first logic level and a length of time the pixel input datum of the pixel is in the second logic level to produce for the pixel an intermediate optical transmission state between the first and second optical transmission states and corresponding to an intermediate gray shade.

11. The system of claim 10 in which the gray shade controller further comprises means for causing a pixel to display an intermediate optical transmission state between the first and second optical transmission states by controlling the length of time the pixel input datum of the pixel is in the first logic level as compared with the length of time the pixel input datum of the pixel is in the second logic level over the duration of a plurality of successive frame periods.

12. The system of claim 10 in which:

a number of the time intervals define a set of time intervals;

a number of the first signals define a group that includes first and second subgroups of first signals, the number of time intervals in the set being equal to the number of first signals in the group and each of the first and second subgroups causing multiple simultaneous selections by amplitude transitions within the set of time intervals; and

the amplitude transitions of the multiple simultaneous selections caused by the first subgroup being phase displaced from the amplitude transitions of the multiple simultaneous selections caused by the second subgroup.

13. The system of claim 12 in which the amplitude transitions of the multiple simultaneous selections caused by the first subgroup are phase displaced by at least one time interval from the amplitude transitions of the multiple simultaneous selections caused by the second subgroup.

14. The system of claim 12 in which the number of time intervals in the set is four.

16. The system of claim 13 in which the multiple simultaneous selections caused by the first subgroup are phase displaced by two time intervals from the amplitude transitions.