A New Approach to the DC-Restoration Problem

This report begins with a brief discussion of the problems encountered when an attempt is made to utilize fully the dc component of the television signal in a typical receiver. The past compromise solution of using only a fractional part of the dc component is discussed and the resultant disadvantages are described. A new approach, involving the new concept of the dc/ac coupling, is then presented. It is shown that good black-level stabilization is most important for scenes of low average brightness; this is fortunate because it allows compromise with high-brightness scenes to avoid overload of the high-voltage power supply. The new coupling circuit is simple and provides a combination of dc and ac coupling, dc coupling for low-brightness scenes, and ac coupling, with its accompanying protection against overload, for high-brightness scenes.