IMPROVING METHOD OF DEFICIENCY OF CONTRAST IN VIDEO CIRCUIT

摘要

PURPOSE:To superimpose a DC component on a video signal, and to obtain sufficient contrasts to drive a CRT, by producing a video signal fed from a video amplifying circuit without DC component and passing through the signal into a DC reproducing circuit. CONSTITUTION:A video signal S3 which is almost AC component only is outputted from a video amplifying circuit 10, and the signal S3 is inputted to a DC reproducing circuit 20. The signal S3 is applied to a base of an NPNTR22 and a collector of an NPN transistor TR21 via a coupling capacitor C21 of the circuit 20. A period signal S0 is inputted to the base of the TR21, a DC potential E0 is applied to an emitter and it is given to the collector via a resistor R21. The emitter of the TR22 is grounded via a resistor 22, the collector is connected to the emitter and a drive voltage +B, which is connected to the base via a resistor 24. A DC component is superimposed on the signal S3 and the resultant is applied to a cathode ray tube 40 via a video output circuit 30 to produce a picture with sufficient contrast.