Gray scales method and circuitry for flat panel graphics display

• US 5,196,839 A
• Filed: 10/15/1990
• Issued: 03/23/1993
• Est. Priority Date: 09/16/1988
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Chips and Technologies, Inc. (Intel Corporation)
• Inventors: Oguchi, Tetsuji, Johary, Arun
• Primary Examiner(s): Oberley, Alvin E.
• Assistant Examiner(s): HJERPE, RICHARD A
• Application Number:
  US07/598,582
• Time in Patent Office: 890 Days
• Field of Search: 340/723, 340/767, 340/793, 340/805, 340/812, 358/240, 358/241, 358/455, 358/456, 358/457, 358/458, 358/459
• US Class Current: 345/691
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• 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 3/2025 the sub-frames having all the same time duration
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers
• CPC Class Codes: H04N 3/127 using liquid crystals

Abstract

A controller for providing O to N gray scales at a monochrome display. The monochrome display is of the type having an array of pixels energized by a display voltage over time to generate the gray scales. The controller generates a baseline time and uses the baseline time to provide gray scales at the display. In particular, each pixel is energized at least the baseline time for any gray scale above level 0 to reduce flicker in the display. In one embodiment, the baseline time corresponds to a point on the intensity response curve for the display at which the display exhibits a linear intensity response for a given display voltage versus time. In one embodiment, the baseline time is used to generate pixel on/off data to provide gray scales at the display. In yet another embodiment, the baseline time information is used to generate weighted clock information to provide gray scales at the display. In another aspect, the controller includes a plurality of programmable gray scale generators which provide pixel on/off data, weighted clock information, and black/white pixel data to provide gray scales at the display. One of the gray scale generators is selected and programmed depending on the identity of the display device.

Claims

1. A controller for controlling a monochrome video display, the monochrome video display comprised of a plurality of pixel elements, the pixel elements having a non-linear response of a first predetermined time period to the application of a predetermined display voltage, the controller providing zero to N gray scale levels of the pixel elements, the controller comprising:

table means for storing zero to N time periods, the N time periods corresponding to the zero to N gray scale levels, wherein the N time periods corresponding to gray scale levels two to N are dependent upon an incremental time period, the incremental time period being determined by the steps of;

determining a minimum baseline time for applying the predetermined display voltage to a pixel element, the minimum baseline time corresponding to the time period necessary to apply the display voltage to charge pixel element to gray scale level one, the minimum baseline time being at least equal to the first predetermined time period during which the pixel has a non-linear response to the predetermined voltage;

determining a maximum time that the display voltage can be applied to a pixel element, the maximum time corresponding to the time period necessary to apply the display voltage to charge the pixel element to the gray scale level N;

subtracting the minimum baseline time from the maximum time;

dividing the result of the subtracting step by N, the maximum gray level, the result being the incremental time; and

means for applying the display voltage to the pixel elements for a time equal to the zero to N time periods, wherein time period one is equal to the minimum baseline time and time periods two through N correspond to the minimum baseline time added to the incremental time period multiplied by two through N, respectively.

2. The controller of claim 1 further comprising means for changing the time periods stored in the table means, wherein the time period in the table means can be changed when a different monochrome video display is coupled to the controller.

3. A method for controlling a monochrome display having a plurality of pixel elements so that the display has N different gray levels, each pixel element being characterized by a first period of time for which the pixel element has a non-linear response to the application of a predefined voltage, the method comprising the steps of:

determining the first period of time for which the pixel element has a non-linear response to the application of the predefined voltage;

subtracting the first period of time from a maximum time that the pixel element may have the predetermined voltage applied to it;

dividing the result of the subtracting step by N, the number of gray levels desired, the result of the dividing being an incremental time period for each gray level; and

storing the incremental time period so that when a pixel must be activated, its gray level can be multiplied by the incremental time, and the product of the gray level multiplied by the incremental time added to the first period of time to provide the length of time that the predetermined voltage is applied to the pixel.

4. The method of claim 3 further comprising the step of programming a programmable table means, to allow different time periods to be in the table means for different monochrome video displays.

5. A controller for generating zero to N gray scales on a monochrome display, said monochrome display having an array of pixels, each pixel element being characterized by a first period of time for which the pixel element has a non-linear response to the application of a predetermined voltage, the predetermined voltage being applied to the pixels for various time intervals to generate the gray scales, the longest time interval being equal to the inverse of the refresh rate of the display, said controller receiving multi-bit color information, horizontal sync information, and clock information from a digital computer, the controller comprising:

table means for storing zero to N time periods, the N time periods corresponding to the zero to N gray scale levels, wherein the N time periods corresponding to gray scale levels two to N are dependent upon an incremental time period, the incremental time period being determined by the steps of;

determining a minimum baseline time for applying the predetermined voltage to a pixel element, the minimum baseline time corresponding to the time period necessary to apply the display voltage to charge pixel element to gray scale level one, the minimum baseline time being at least equal to the predetermined length during which the pixel has a non-linear response to the predetermined voltage;

subtracting the minimum baseline time from the longest time interval, the longest time interval corresponding to the time period necessary to apply the display voltage to charge the pixel element to the gray scale level N; and

dividing the result of the subtracting step by N, the maximum gray level, the result being the incremental time;

converter means for receiving the multi-bit color information, horizontal sync information and clock information within the range of zero to N, the converter means being coupled to the table means and supplying the series of gray scale levels to the table means; and

means for applying the display voltage to the pixels, the means for applying being coupled to the table means, the length of time the voltage is applied for gray scale level one corresponding to the minimum baseline time and the length of time the voltage is applied for gray scale levels two to N corresponding to the minimum baseline time added to the incremental time multiplied by two through N respectively.

6. The controller of claim 5 wherein the means for applying display voltage to the pixels is also coupled to receive the clock information and horizontal sync information from the computer to select the pixels to which the gray scale intensity level should be applied.