Picture pick-up or display device for successive scanning in opposing direction includes a circuit for assuring vertical symmetry of the video signal being displayed

Claim 1

A picture pick-up or display device for picking up a scene or for displaying a scene image, said device, comprising a line deflection circuit for generating a symmetrical line deflection current through a line deflection coil, a video signal processing circuit having a memory for storing video information and for alternately generating and supplying the video information of a line in one direction and of the subsequent line in the opposite direction, and a clock oscillator for generating a clock signal for reading the video information from the memory, the clock oscillator being incorporated in a control loop which further comprises a counter for counting pulses of the clock signal, and a phase comparison stage and measuring means for receiving a first signal from the line deflection circuit and a second signal from a signal generator which is also incorporated in the control loop for supplying the second signal at measuring instants, the control loop being adapted to cause the first and the second signal to occur substantially simultaneously at the measuring instants, characterized in that the measuring means comprise a maximum value detector for applying the first signal to the phase comparison stage substantially at the instant when the line deflection current has a maximum value, each measuring instant substantially coinciding with one count of the counter during the line blanking interval.

Claim 7

A device as claimed in claim l, characterized in that said device further comprises a comparator for comparing the second signal with a reference signal, said comparator thereby effectively reducing the amplitude of said second signal prior to being applied to said phase comparison stage.