Horizontal deflection circuit with linearity correction

Abstract

In a television display system, a deflection yoke is placed over the neck of a cathode ray tube to generate a raster by means of simultaneous horizontal and vertical sweep of the electron beams. A picture, derived from information contained in the composite video signal produced by the signal processing circuits, is displayed on the screen of the cathode ray tube. In the horizontal deflection circuit portion of the television display system, a trace capacitor is coupled to a deflection winding. A trace switch, responsive to a deflection rate signal that is synchronized with the composite video signal, periodically applies to the deflection winding the voltage developed across the trace capacitor to generate raster scanning current in the deflection winding during a deflection cycle. The losses incurred during a deflection cycle tend to produce a scanning current waveform that introduces asymmetrical linearity distortion to the picture display. A switched current source is coupled to the deflection winding to develop a DC component that flows in a direction that provides correction for the introduction of the asymmetrical linearity distortion. The DC component is of sufficient magnitude to by itself produce substantially all of the change to the scanning current needed to obtain a picture display that is substantially corrected for the asymmetrical linearity distortion.