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Digital convergence image
| Details |
Inventors: George, John Barrett;
Assignee: Thomson Licensing SA (Boulogne Cedex, FR)
Primary Examiner: Hsia; Sherrie
Assistant Examiner:
Attorney, Agent or Firm: Tripoli; Joseph S., Fried; Harvey D., Davenport; Francis A.
An apparatus for convergence correction in a TV receiver with a CRT display comprises a display screen with photo sensors positioned adjacent to screen edges. A cathode ray tube generates a raster for illuminating the display screen and the photo sensors. A signal generator generates a video signal having a first part for convergence alignment and a second part having sufficient video signal amplitude to cause an average level of beam current loading corresponding to an average level that can occur during broadcast video reception. The video signal being coupled to the cathode ray tube for illuminating the display screen and sensors. The video signal facilitating convergence alignment with the average level of beam current loading to ensure that convergence alignment is maintained during broadcast video reception. |
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DETAILED DESCRIPTION FIG.
1 illustrates an exemplary display screen 101 of a video signal display apparatus employing convergence alignment by means of photo sensors located at the screen periphery.
The display screen 101 is positioned within a frame which permits area 100 to be viewed and obscures part of the raster scanned area 105 extending beyond area 100.
The exemplary photo sensors S1-S8 are located within the scanned but obscured viewing area.
An alignment signal image block M is shown close to sensor S8 and, as depicted by the crossed arrows, may be positioned within the raster to illuminate any of photo sensors S1-S8 to facilitate convergence alignment by detection and measurement of the edges of image block M.
With perfect convergence, the block position required for sensor illumination is known.
However the actual displayed block position is subject to mis-convergence errors which may be measured by determining when the sensor detects the block edge.
Thus a convergence error is represented by the difference between the theoretical converged position and actual detected position.
An exemplary projection display apparatus with the display screen of FIG.
1 is depicted, in part, in FIG.
2.
Three cathode ray tubes, RCRT, GCRT, BCRT form raster scanned images responsive to scanning signals generated by horizontal deflection amplifier 600 and vertical deflection amplifier 650.
Cathode ray tube GCRT is illustrated with horizontal convergence coil 615 and vertical convergence coil 665 each of which are driven with corrective currents GHC and GVC generated by amplifiers 610 and 660 respectively.
Convergence drive amplifiers 610 and 660 are each coupled to convergence correction signals formed by digital to analog converters 311 and 312 respectively, in response to digital control values derived from memory 305.
An electronically erasable programmable read only memory PROM 550 is employed to save set up values which are loaded in to memory MEM305 during operation of the display.
A video signal VL is connected to exemplary cathode ray tube GCRT to modulate the magnitude of electron beam current lb to form an intensity or brightness modulated image on the CRT face plate, representative of an electrical analog of an image
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LCD 
