GB1051623A - - Google Patents

Abstract

1,051,623. Television. MARCONI CO. Ltd. April 1, 1964, No. 13442/64. Heading H4F. Signals derived from a television camera of the vidicon type are processed in equipment comprising a D.C., restoring circuit comprising a diode connected through a normally conductive switch to a point of reference potential, said diode being fed with said signals through a storage condenser inserted in a channel feeding said signals to a utilization device, and said switch being cut off during the camera tube blanking periods. The arrangement being that the D.C. restoration during said blanking period is at a level determined by that which existed at the end of the immediately preceding operative period of the circuit. The negative going video signals derived from a vidicon camera and including system blanking periods and synchronization pulses, are applied at terminal 1 to the base of emitter follower transistor 2, feeding its output signal to an output transistor 4 via a clamping circuit comprising a large condenser 3 and a diode 6 connected to a potentiometer 9 via a normally conducting transistor 7. During the picture signal period and part of the system blanking period occurring before and after the camera blanking period the most positive peaks of the signal at the base of transistor 4 are clamped to the black level potential determined by the position of the wiper 8 of potentiometer 9. To stop the synchronization pulses from interfering, transistor 7 is switched off by the application of camera blanking pulses to transistor 13 such that the charge on condenser 3 remains constant during the camera blanking pulses and synchronization pulses and equal to that existing at the end of the operative period of the clamping circuit.