Television – Video display – Color sequential
Reexamination Certificate
1998-07-31
2001-07-24
Lee, Michael (Department: 2614)
Television
Video display
Color sequential
C353S084000
Reexamination Certificate
active
06266105
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to color projection systems, and more particularly relates to such projection systems incorporating a single electro-optical light modulator.
Color projection display systems are known in which a white light source is separated into red, blue and green sub-beams for separate modulation by corresponding color components of an incoming display signal, and then the modulated subbeams are recombined into a full color display for projection onto a viewing screen. Modulation of the subbeams is commonly carried out using three separate electro-optical light modulators such as liquid crystal display (LCD) panels, one for each of the three subbeams.
However, in one type of color projection system, described for example in U.S. Pat. No. 5,532,763, the three subbeams are all modulated by a single LCD panel. This is accomplished by shaping the subbeams into band-shaped cross-sections, and scrolling the bands sequentially across the LCD panel, while synchronously addressing those portions of the panel which are illuminated by the bands with the corresponding display signal information. Such projection systems are referred to herein as single panel scrolling raster (SPSR) projectors.
The simultaneous use of a substantial portion of the available red, blue and green light through a single light valve panel provides optical efficiencies comparable to that of three-panel systems employing the same types of light-valve panels. Using only a single panel eliminates the need to mechanically converge different color images, formed on different panels, and reduces system cost.
Various scrolling means for such SPSR systems are disclosed in U.S. Pat. No. 5,548,347. A system employing single-prism scrolling means is simple and compact, while multiple-prism (either separated or physically joined) scrolling means offer better scroll-speed uniformity (for the different color light bands) and scroll-speed linearity (for each light band) than the single-prism system. A system employing three physically separate prisms located in separate light paths, as shown in FIG. 16 of the patent, offers better optical efficiency than a system employing three physically joined prisms, but is less compact.
A disadvantage of all such SPSR systems is the requirement for a relatively large LCD (having at least an approximately 1.3 inch diagonal for current lamp technology), in order to accept the light from the three separate primary color beams. Such large LCDs are expensive, and require the use of comparatively large, expensive optical components.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved SPSR color projection system.
It is another object of the invention to provide such an improved system having only one moving part to accomplish scrolling.
It is another object of the invention to provide such an improved system in which the illumination beam is not separated into separate color beams prior to scrolling.
It is yet another object of the invention to provide such an improved system in which the optical architecture is simple and compact.
In accordance with the invention, a SPSR color projection system includes a single rotationally-symmetric element with reflective surface portions having different color reflection bands, and a single electro-optical light modulator.
In operation, the element rotates about its axis while white light from a source is incident on the reflecting surface, and is separated into color components by the surface portions which reflect the desired color bands into a relay lens which images a prescribed portion of the surface of the element onto the light modulator panel. The color bands reflected from the element are scrolled across the panel by virtue of its rotation.
Driver electronics synchronously address the panel with the corresponding color components of the display information during scrolling.
The use of such a reflective element as the scrolling means in a SPSR system eliminates the need to separate the white light into sub-beams prior to scrolling, and thereby enables a smaller (less than 1.3 inch) light modulator panel, and correspondingly smaller optical components. Thus, a simple and compact optical architecture is possible, leading to a compact projector with a small component count.
In accordance with a preferred embodiment of the invention, the rotationally-symmetric element has a cylindrical surface, and the reflective portions comprise dichroic filters having a cylindrical curvature matching that of the element's surface. Such curvature enables retro-reflection to take place when the incident light beam is directed normal to the surface of the element, insuring minimal color shifts due to the angular sensitivity of the cut-off wavelengths of the dichroic filters, as well as insuring minimal aberrations in the imaging of the surface onto the panel.
Moreover, such a reflective element, eg., a drum, employed in the retro-reflective mode as described above, can be of small cross-section (eg., less than 40 mm diameter), which further reduces size and cost.
REFERENCES:
patent: 5371543 (1994-12-01), Anderson
patent: 5532763 (1996-07-01), Janssen et al.
patent: 5548347 (1996-08-01), Melnik et al.
patent: 5863125 (1999-01-01), Doany
Lee Michael
Philips Electornics North America Corporation
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