Circuit arrangement for producing an unambiguous marker in a television image

Claim 1

A marker circuit for a television system providing line and field frequency synchronization signals and a video signal, said circuit comprising a field pulse generator having an input means for receiving said field synchronizing signal, and an output means for generating pulses of field frequency having an adjustable duration; a field pulse shaper means having an input coupled to said field pulse generator output, and first and second output means for producing first and second pulse trains of field frequency respectively, at least said first train having pulses of varying amplitude; a line pulse generator having an input means for receiving said line synchronizing signals, and an output means for generating line frequency pulses having an adjustable duration; a line pulse shaper means for generating at least a first train of line frequency pulses reoccuring at the field frequency, said line pulse shaper comprising at least first and second serially coupled square wave generators, for generating square wave pulses, each of said square wave generators having an input and an output, means for coupling said first square wave generator input to said line pulse generator output means, means for coupling said first square wave generator output to said second square wave generator input, each of said square wave generators having a control input means coupled to the field pulse shaper first output means for varying the duration of the generated pulses of said square wave generators; means for superimposing pulses from said second square wave generator onto the video signal to produce a marker, said superimposing means having a first input means for receiving said video signal, a second input means coupled to said second square wave generator output, and an output means for providing said video signal with said marker superimposed thereon; and gating means having a first input coupled to said field pulse shaper second output to receive said second pulse train as a gating signal for controlling the occurrence of pulses superimposed on said television signal during a given field interval; and means for coupling said gating means in series with said line pulse generator, said line pulse shaper, and said superimposing means.