CONVERGENCE CORRECTING DEVICE

摘要

PURPOSE:To correct comatic aberration in a vertical direction on a screen caused by a pole piece by providing a magnetic field generator to cancel a leakage magnetic field caused in the pole piece. CONSTITUTION:The convergence correcting device 1 consists of the pole piece 4 provided to the electronic gun 3 of a cathode ray tube 2 and the convergence yoke of a magnetic core having four projections provided in the vicinity of the pole piece 4. Moreover, a coil 7 generating a 4-pole magnetic field 6 and a coil 10 generating a magnetic field 9 cancelling the magnetic field 12 caused by the vertical deflection coil are provided. A parabolic current is supplied to the coil 7 in the period of horizontal deflection and the mis-convergence of a vertical raster is corrected. The current of sawtooth waveform of a vertical deflection period is supplied to the coil 10 and the magnetic field 12 generated in the pole piece 4 and the magnetic field 9 in the inverted direction are generated by the vertical main winding 8 to correct the coma aberration in up-and-down direction.