North American Philips Corporation

Anthony R Bugni

Saiprasad V Naimpally

Larry G Phillips

Ted A Darby

William S Burdick

A circuit for ensuring that the level of the front porch of each line in a color video signal is at a predetermined proper level includes a circuit for detecting the position of the horizontal synchronization pulse in each line, a circuit for generating an artificial front porch signal, and a controllable switch connected to receive the color video signal and the artificial front porch signal. The controllable switch, under the control of the detecting circuit, provides a signal for a subsequent color decoder circuit in which the front porch in each line in the color video signal is replaced by the artificial front porch signal.

Artificial front porch insertion circuit

A T.V. input source identifying circuit for determining whether a video signal is from a videotape player or a broadcast signal by measuring jitter of vertical synchronization pulses and by measuring noise. The video signal includes a plurality of frames with each frame including a plurality of fields. In one embodiment of the present invention, timing data is generated corresponding to the period of at least one selected field in each of a plurality of selected frames. From this timing data, a maximum number is stored that corresponds to the greatest period and a minimum number is stored that corresponds to the least period of the selected fields. The minimum number is subtracted from the maximum number and the difference is compared to a threshold to determine the type of video signal. In an alternate embodiment, numbers corresponding to fields from successive frames are compared by a subtraction and the difference is compared to a threshold in order to make a decision as to the type of video signal. In both of the aforementioned embodiments, the noise level of the video signal is constantly monitored. When the noise is above a threshold, the local signal is generated regardless of the information derived from the timing data.

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Knoxville, TN, United States of America

Anthony R Bugni