公开(公告)号：US3912970A

公开(公告)日：1975-10-14

申请号：US36814273

申请日：1973-06-08

Applicant: ZENITH RADIO CORP

Inventor： CHANDLER JAMES F ,  CHIODI WAYNE R ,  FIGLEWICZ RAYMOND C ,  KARLOVICS STEVEN

IPC: H01J29/70 ,  H01J31/20 ,  H04N9/285 ,  H01J29/56

CPC classification number: H04N9/285 ,  H01J29/702 ,  H01J31/205 ,  H01J2229/5637 ,  H01J2229/5687 ,  H01J2229/7037

Abstract: A color television receiver is of the type which includes a cathode ray tube having an image screen composed of luminescent dot triads distributed in a raster pattern. Each triad has dots individually productive of respective red, green and blue colors. An electron gun produces a delta array of three electron beams to excite respectively assigned ones of the dots on the screen. Two of the electron beams are aligned in the horizontal direction while the third is displaced in the orthogonal direction. The usual yoke assembly is provided on the neck of the cathode ray tube for producing horizontal and vertical scanning fields that deflect the beams over the raster pattern in order to define the image. At the same time, the yoke assembly introduces astigmatic distortion in the electron beam array as the beams are deflected toward edges of the raster. Also included is a system which tends to maintain convergence of the electron beams upon the dot triads throughout action of the deflection means. To compensate the astigmatic distortion, at least the third beam is subjected to a pair of correcting fields that are spaced opposed in the horizontal direction on opposite sides of the third beam and serve mutually to aid movement of that third beam in the orthogonal direction; in most embodiments, the correcting fields also act upon the other two beams. The correcting fields are developed in response to a waveform which includes at least a component that varies parabolically at the rate of change of the horizontal scanning field; ideally, the waveform also includes a parabolic component that varies at the vertical scanning rate. Together, the correcting fields function as a dynamic purity control.