GB1357684A - Colour television convergence correction - Google Patents

Abstract

1357684 Cathode-ray tube circuits SINGER CO 11 April 1972 [29 April 1971] 16583/72 Heading H4T In a dynamic convergence connection system for a three-gun colour display tube the correction-signals supplied to the convergence coils are developed from the outputs of sensing means responsive to the scanning deflection currents. Thus the correction is dependent only on the instantaneous positions of the beam shot and is independent of the size, shape or manner of scanning the raster. As shown, sensing means such as resistors in the deflection coils 35 (Fig. 4) provide voltages VNC and VHC proportional to the vertical and horizontal deflection currents, such voltages being squared in amplifiers 37 and 39 and then combined via adjustable attenuators 40 and 43 in summing amplifiers 42 and 45 with the outputs of further attenuators 41, and 43 supplied with the voltages VNC and VHC respectively. Because the Red and Green rasters are oppositely distorted the VHC input to the Green attenuator 43 is inverted in inverting amplifiers 46 and a corner correction is added to the Green and Red scanning amplifiers 45 from an output of a multiplier 47 which multiplies the outputs of multipliers 37, 39 by an appropriate constant. The outputs of the amplifiers 42 and 45 are then supplied to scanning and current drive circuits 51 together with D.C. bias inputs from sources 53 the outputs of the drive circuits providing the correction currents for the convergence coils 55. An additional summer and current drive circuit 51, D.C. bias 53 and convergence coil 55 supplied directly with the VHC voltage is provided for lateral shift of the Blue beam. The invention is stated to be particularly useful in displays used with simulators but is also useful in commercial TV in areas where frequent main voltage changes may cause convergence problems.