Circuit arrangement for extracting a field synchronizing signal from a television synchronizing signal

Claim 1

A circuit arrangement having binary clock pulse controlled stages for extracting a field synchronizing signal from a television synchronizing signal having at least line and field synchronizing pulses the amplitude of which extends between a black level and a peak level, said circuit arrangement comprising: a source of said binary clock pulses, means connected to said source of clock pulses for providing said television synchronizing signal, a detector connected to said source of clock pulses, and a time measuring element connected to said source of clock pulses, said means for providing said television synchronizing signal connected to said detector for applying said television synchronizing signal thereto, said detector being periodically made operative by a clock signal from said source of clock pulses for producing a first test signal when said television synchronizing signal substantially reaches said peak level, said first test signal starting said time measuring element which produces a switching signal when said time measuring element reaches a preset value before it is reset, said detector producing a second test signal when said black level is substantially reached, said second test signal resetting said time measuring element when the preset value has not yet been reached by said time measuring element, the period of said clock signal being significantly shorter than the duration of a line synchronizing pulse.