Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
1996-06-28
2003-04-01
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S053000, C345S208000
Reexamination Certificate
active
06542150
ABSTRACT:
FIELD OF THE INVENTION
The present invention is in the field of portable computers, namely laptop, notebook, or similar portable computers with flat panel displays with or without SIMULSCAN™ capability. In particular, the present invention relates to displaying high resolution graphics data on fixed resolution LCD panel displays.
CROSS-REFERENCE TO RELATED APPLICATIONS
The present invention is related to application Docket Number CRUS-0059 entitled “Method and Apparatus for Expanding Graphics Images for Display on LCD Panels” incorporated herein by reference.
BACKGROUND OF THE INVENTION
A primary element of a portable computer system is a display. Since Cathode. Ray Tube (CRT) displays are relatively large and heavy, with high power requirements, other alternatives have actively been sought. Flat panel display technology represents a significant alternative to CRT display technology. Flat panel displays may have several advantages over CRT displays. Flat panel displays include a number of different display types, Liquid Crystal Display (LCD) being most commonly used. LCD displays may have advantages of being compact and relatively flat, consuming little power, and in many cases displaying color. Typical disadvantages of LCD displays may be poor contrast in bright light—especially bright natural light, inconsistent performance in cold temperatures, and display resolutions which may be constrained by a fixed number of row elements and column elements. Among these limitations, fixed resolution may cause significant problems for LCD operation in a multimedia environment. Multimedia users may demand a monitor which can be configured for different display resolutions. Analog CRT displays may be easily configured for different resolutions.
Flat panel displays may typically comprise two glass plates pressed together with active elements sandwiched between. High resolution flat panel displays use matrix addressing to activate pixels. Conductive strips for rows may be embedded on one side of a panel and similar strips for columns are located on the other side. Panels may be activated on a row by row basis in sequence. This process may be described in more detail in a text entitled: “High Resolution Graphics Display Systems”, Peddie 1994 (pp. 191-225), incorporated herein by reference, however the general nature of LCD addressing is known in the art.
LCD flat panel display resolution may be dictated by physical construction of an LCD. CRT displays have a continuous phosphor coating and may be illuminated by an analog signal driving an electron beam. Because of the analog nature of CRT, scaling display resolution is relatively simple. LCD displays have a fixed array of physical pixels which may be turned on or off by applying or removing a charge. While resolution of a CRT may be changed by changing scanning frequency parameters, LCDs are limited by a fixed number of row and column elements. Fixed resolution LCD displays are particularly troublesome in multimedia systems. Such systems may require changes in display resolution to take full advantage of applications displaying high resolution graphics. In addition, for a manufacturer of display controllers to claim full VGA, SVGA, and XGA compatibility limitations of fixed panel resolution must be overcome.
TABLE 1
Vertical scanning frequencies for different graphics
display modes
Typical
Vertical Scan
Panel Type
Resolution
Frequency
VGA Panel
640 × 480
25 MHz
SVGA Panel
800 × 600
40 MHz
XGA Panel
1024 × 768
65 MHz
Like an analog CRT, an LCD panel may be controlled by a horizontal and vertical scanning signal. Data may be displayed in its respective screen position during an interval in time corresponding to when vertical and horizontal scan signals for a particular location coincide. Horizontal and vertical scan signals are set at a frequency proportional to display resolution. Table 1 contains vertical scanning frequencies for popular graphics display modes. Typical vertical scanning frequencies may be 25 MHz for 640 pixels by 480 pixels display, 40 MHz for 800 pixels by 600 pixels, and 65 MHz for 1024 pixels by 768 pixels. New panels comprising 1280 pixels by 960 pixels may: have an even higher vertical scanning frequency. A high resolution display therefore may have a higher scanning frequency than a relatively lower resolution display.
Using the general principal stating high frequency is proportional to high resolution, some downscaling may be achieved by attempting to replicate lower scanning frequencies of low resolution display while maintaining native scanning resolution. On a fixed resolution display of 600 pixels by 800 pixels for example, a 640 pixel by 480 pixel resolution output may be scaled by lowering the frequency at which data is clocked to the display. This type of approach to expansion related problems may be considered synchronous. Synchronous approaches may have disadvantages for expanding certain resolutions.
Because of the relationship between scan frequencies for certain resolutions that need to be expanded, synchronous approaches to expansion may not be desirable. Visual anomalies such as flicker, and related line dropping may cause noticeable and annoying visual artifacts. Also, horizontal flicker may be noticed and is even more annoying as portions of the display shift from side to side. This is due to the inability of the expansion scheme to account for every line generated at one resolution to a corresponding line on a second resolution. Resolutions which divide evenly into each other may be best suited for synchronous approaches.
Asynchronous approaches may be necessary when the ratio of CRT display lines and LCD display lines, based on different desired display resolution and fixed resolution display capability, is non-integral and when it is generally considered desirable to decouple the time base upon which display data is generated from the time base upon which output display resolution is generated. Consider an example when 3 LCD display lines must be displayed for every 2 CRT lines.
Prior art methods use relatively expensive dual path approaches which may replicate hardware for each display sought to be driven. In addition to hardware costs, bandwidth requirements may be approximately doubled and available bandwidth cut by approximately half for a dual path approach. Other disadvantages of a dual path approach may be non-transparency of software. With a dual path approach, display related software may require separate modification to standard register contents, standard addresses or the like in order to operate at each resolution.
For transforming graphics resolutions, fewer problems are inherent in downscaling, when desired display resolution is larger than the panel. Upscaling however may present special problems. When attempting to display lower resolution graphics on a higher resolution, fixed resolution panel display a variety of compensation methods may be used. Compensation features may be made available through use of shadow registers and extension registers. Both compensation method and desired parameters, such as output resolution may be set through use of registers.
Some systems employ a compensation technique known as centering. With centering, a smaller resolution graphic image may be placed within a larger resolution display in the center of the display. One problem associated with centering a 640 pixel by 480 pixel display at full color within, for example, a 1024 pixel by 768 pixel display is limited bandwidth. On a display which supports 640 pixels by 480 pixels in native mode (e.g at native 640 pixel by 480 pixel timing of 25 Mhz), there may be sufficient bandwidth to support 24 or 32 bits per pixel of color. As frequency increases such as on a fixed panel 1024 pixel by 768 pixel display which does not support the native timing for 640 pixels by 480 pixels resolution, bandwidth requirements increase in proportion to increase in frequency between resolutions. Most 32 or 64 bit controller may only support 24 or 32 bit full color at a native resolution of 640 pix
Bril Vlad
Eglit Alexander J.
Kotha Sridhar
Bell Robert P.
Cirrus Logic Inc.
Kumar Srilakshmi K.
Lin Steven
Saras Steven
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