A convergence correction apparatus for a picture image display device including a picture tube provided with an anode and a convergence coil, for displaying a picture image, a receiver for receiving a composite video signal, a separator for separating a horizontal periodic pulse and a vertical periodic pulse from the composite video signal, a convergence unit responsive to the horizontal periodic pulse for generating a high voltage convergence signal to be applied to the anode of the picture tube, a detector for detecting a fluctuation of the high voltage convergence signal, a ripple signal generator for generating a high voltage ripple signal corresponding to the fluctuation, a correction signal generator for generating a convergence correction signal including at least one of a horizontal periodic sawtooth wave signal, a vertical periodic sawtooth wave signal and a parabolic wave signal based on the horizontal periodic pulse and a vertical periodic pulse, an adjuster for adjusting the convergence correction signal by arithmetically processing the convergence correction signal with the high voltage ripple signal, and a supply unit for supplying the convergence coil of the picture tube with the adjusted convergence correction signal to cancel distortions of a picture image displayed in associated with the picture tube.

A dynamic beam current focussing circuit for providing improved focussing across the screen of a cathode ray video display tube utilizes a tuned voltage step-up transformer to achieve sufficient amplitude of horizontal sweep waveform components of the dynamic focussing voltage. The circuit is useful for high definition television and video display units.

A projection display comprises three cathode ray tubes each having a deflection yoke and convergence yoke and each tube generating a raster for projection. One of the three cathode ray tubes has the convergence yoke coupled for current flow in a direction opposite to that of the other two convergence yokes. An amplifier is respectively coupled to each convergence yoke for convergence correction of each raster. A convergence circuit supplies correction signal values that are coupled to each respective amplifier such that convergence correction by the other two convergence yokes is responsive to a difference between the correction signal value coupled to the one convergence yoke and the correction signal values coupled to the other two convergence yokes.

A projection television receiver has a cathode ray tube with an electron gun for emitting an electron beam incident on a screen, an electromagnetic deflection yoke and an electromagnetic focusing coil. A horizontal deflection driving circuit is coupled to a horizontal deflection coil and provides deflection current to the horizontal deflection coil for scanning the beam repetitively on the screen. The focusing coil is driven from a current step-down transformer having a primary winding coupled in series with the horizontal deflection coil. A secondary winding of the transformer is coupled to the focusing coil for driving the focusing coil with a horizontal rate parabolic current. A capacitor-resistor circuit is coupled in parallel with the focusing coil and with the secondary winding of the transformer for adjusting a phase relationship of the parabolic current relative to the horizontal deflection current and for adjusting the amplitude of the parabolic current.

An autotransformer steps up the output of a high voltage amplifier for applying a drive signal to the focus electrode of a CRT. A parabolic signal is obtained or generated at a deflection frequency such as the horizontal scanning frequency and is applied as an input to the amplifier. The amplifier output is coupled to a center tap of the autotransformer. One winding is serially coupled to the focus electrode and the other winding is AC coupled by a capacitor to ground, in parallel with the amplifier output. The transformer steps up the amplifier output voltage and can reduce the voltage rating required of transistors in the amplifier.