A circuit for supplying a current to a dynamic convergence coil on a color cathode ray tube for dynamically correcting misconvergence of electron beams in the tube, which comprises current producing means to cause a parabolic current having a period of the line interval to flow through the dynamic convergence coil in response to a horizontal pulse train, modulating means for modulating in amplitude the parabolic current by means of a parabolic voltage having a period of the field interval supplied thereto and voltage supplying means for supplying the parabolic voltage to the dynamic convergence coil further to modulate in amplitude the modulated parabolic current flowing therethrough by the parabolic voltage, whereby a current having a waveform required for properly correcting the misconvergence is easily supplied to the dynamic convergence coil.
A convergence correction apparatus comprises a pair of horizontal deflecting coils and a pair of vertical deflecting coils constituting a deflection yoke of a self-convergence system color picture tube, saturable reactors for correcting convergence error in horizontal lines by varying a distribution of a horizontal deflection magnetic field with time, auxiliary control coils coupled to the vertical deflecting coils and wound of the saturable reactors for varying inductances of coils of the saturable reactors by auxiliary control magnetic fields generated by the auxiliary control coils, and a correcting circuit for supplying to the auxiliary control coils a current which has a waveform other than a sawtooth waveform and has a period equal to the vertical deflection period, and for non-linearly varying magnitudes of the auxiliary magnetic fields generated thereby.
The beam forming means and static convergence correcting means in a color cathode ray tube are arranged to provide for proper convergence of the beams at regions remote from the center of the screen and closer to the corners. The resulting misconvergence at the center of the screen is then corrected by dynamic convergence correcting means which produces less beam distortion then if it had to correct misconvergence at the corners.
Dynamic focus circuitry for a CRT data display terminal provides high resolution even in the corners of the screen by means of a dynamic focus voltage which is the product of parabolic waveforms at horizontal line rate and vertical frame rate. The non-linear characteristic of a diode provides the product function at minimum expense.
