DIGITAL TIME BASE CORRECTORS FOR TELEVISION EQUIPMENT

摘要

A digital time base correction system for television receivers is based upon analogue to digital conversion followed by memory storage. A digital to analogue converter is then used to operate on the memory output. The main feature of the system relates to the method used for controlling a triggered oscillator that is linked with the analogue-to-digital converter. The oscillator consists of an amplifier with a feedback loop with a time constant determined by an R-C network. Depending upon the state of an FET the oscillator operational period may be controlled. When the output of the picture synchronisation circuit goes low a bistable becomes zero and the FET opens allowing the oscillator to run. The oscillator output changes the state of a counter until a predetermined count is reached.