Television – Cathode-ray tube burn-in prevention
Reexamination Certificate
1999-11-29
2002-08-06
Kostak, Victor R. (Department: 2611)
Television
Cathode-ray tube burn-in prevention
C348S556000, C348S558000
Reexamination Certificate
active
06429894
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods and apparatus for use in conjunction with display devices. Most particularly, these inventions relate to methods and apparatus for uniformly aging one or more cathode ray tubes (CRT's) within a display device, such as a television.
RELATED APPLICATION INFORMATION
This application is related to Application Ser. No. 09/450,942, which is expressly incorporated herein by reference and filed on the same date.
BACKGROUND OF THE INVENTION
All televisions utilize one or more cathode ray tubes (CRT's) to transform video information into light rays for display on the television screen. This is typically accomplished by exciting the phosphor material on the CRT with a scanned beam of electrons, causing the phosphor material to output light. Typically, over time, usage of the CRT causes aging or reduction of light output from the CRT phosphor material. When the entire nominal scan area of the CRT phosphor is excited (i.e., the area of the CRT phosphor corresponding to the geometry of the television screen), the CRT phosphor material is uniformly aged, resulting in an unnoticeable uniform reduction of light from the CRT. Under these circumstances, this phenomenon is typically not problematic. When only a portion of the nominal scan area of the CRT phosphor is excited over a period of time, however, the CRT phosphor is non-uniformly aged, resulting in a noticeable non-uniform reduction of light from the CRT.
This problem typically arises when video signals formatted with one aspect ratio are displayed on a television formatted in another different aspect ratio. The aspect ratio of a television picture image is a ratio of horizontal length to vertical length, expressed in relative units. Standard video signals, such as NTSC and PAL video signals, are formatted with a 4:3 aspect ratio (i.e., 1.33 aspect ratio), whereas non-standard video signals, such as HDTV video signals, are formatted with an aspect ratio greater than the standard 4:3 aspect ratio. For example, an HDTV video signal is typically formatted with a 16:9 aspect ratio (i.e., 1.77 aspect ratio). Modern cinematographic theater movies, not made expressly for conventional television, are typically films with aspect ratios greater than 1.33, typically ranging between 1.65 and 2.35.
When standard video signals are displayed on a standard television screen (i.e., a television screen having a 1.33 aspect ratio), the picture image appears on the entire television screen. As long as these standard video signals are displayed on a standard television screen, the associated CRT or CRT's are uniformly illuminated, and thus uniformly aged. When a non-standard video signal, such as an HDTV video signal, is displayed on a standard television screen, the picture image appears on the middle horizontal region of the television screen and black bars appear on the respective top and bottom horizontal regions of the television screen. As a result, a region of the CRT that would normally be illuminated in response to a standard video signal is not illuminated in response to the non-standard video signal.
Thus, without correction, display of a non-standard video signal on a standard television screen over an extended period of time causes the phosphor material disposed on a primary region of the CRT (represented by a middle horizontal region of the nominal CRT scan area) to age more than the phosphor material disposed on a secondary region of the CRT (represented by respective top and bottom horizontal regions of the nominal CRT scan area). When a standard video signal is then displayed on a standard television screen on which non-standard video signals have been displayed over an extended period of time, the top and bottom horizontal regions of the television screen will be distinctly brighter than the middle horizontal region of the television screen. These distinctions will appear as two respective spatial transition lines between the top and middle horizontal regions of the television screen and between the bottom and middle horizontal regions of the television screen. Most viewers will complain about this phenomenon, which may require a service call to replace the CRT or CRT's. If the television is a projection television (PTV), which typically includes three color CRT's, this service call may cost $500 or more.
One method used to reduce this non-uniform CRT phosphor aging problem involves slowly moving the electron scanning angle over time, so that the spatial transition lines are blurred. Another method involves pre-aging the CRT phosphor with white video, which takes advantage of the fact that the problem of non-uniform CRT illumination lessens with time. These methods, however, only reduce the problem of non-uniform CRT illumination, and do not necessarily eliminate the problem. Still another method involves illuminating the respective top and bottom portions of the CRT with gray video when an HDTV video signal is displayed. This method, however, reduces the amount of resolution that is available for display of the actual HDTV video signal. For example, if the entire area of the CRT is provided with a resolution of 1080 interlaced lines, only 810 interlaced lines will be provided for display of the HDTV video signal.
Accordingly, an improved method and apparatus for uniformly aging the phosphor material on a CRT is desired.
SUMMARY OF THE INVENTION
Methods and apparatus are utilized for uniformly aging the phosphor material on a CRT. The CRT may be located in a display device, such as a television, a computer monitor, or any other device that uses a CRT to transform a video signal into light output. The method serves to uniformly age a CRT that has been previously illuminated at a mismatched illumination ratio. This mismatched illumination ratio occurs when the CRT is illuminated in response to a video signal formatted in an aspect ratio different from the aspect ratio of the display screen. By way of non-limiting example, if the display screen has an aspect ratio of 4:3, illumination of the CRT in response to a video signal formatted in a 16:9 aspect ratio, such as an HDTV video signal, will cause a mismatched illumination. In this scenario, a primary region of the CRT corresponding to the middle horizontal region of the television screen is illuminated, and a secondary region of the CRT corresponding to the respective top and bottom horizontal regions of the television screen is non-illuminated.
To facilitate the uniform aging of the CRT, one or more CRT aging indicators, which indicates the extent to which the CRT has been illuminated at the mismatched illumination aspect ratio are obtained. These one or more CRT aging indicators may include, for example, an unequalized CRT burn time, i.e., an amount of time the CRT was illuminated at the mismatched illumination aspect ratio, or a combination of an unequalized CRT burn time and an average CRT luminous intensity level exhibited by the CRT when illuminated at the mismatched illumination aspect ratio. The one or more CRT aging indicators may include a pair of luminous intensity levels measured at the respective primary and secondary CRT regions in response to an internal video signal, preferably a uniform white video signal.
The secondary CRT region is illuminated based upon the one or more CRT aging indicators. In the preferred method, this is accomplished by generating an internal video signal, during a television off-state, which effects illumination of the secondary CRT region at a greater intensity than that of the primary CRT region. This can be accomplished by illuminating the secondary CRT region without illuminating the primary CRT region. In the preferred method, a desired CRT age equalizing time, i.e., the amount of time the secondary CRT region should be illuminated to equalize the CRT aging, is calculated based on the one or more CRT aging indicators. Precalculation of the desired CRT age equalizing time can be accomplished by aging like CRT's, given known sets of CRT aging indicators, and stor
Kostak Victor R.
Lyon & Lyon LLP
Mitsubishi Digital Electronics
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