Conversion circuit for removing line-by-line phase alternation

摘要

The present invention includes a delay line for memorizing the chrominance composite signal for one horizontal time period of a phase alternating input signal and a switch alternatingly applying a first phase composite signal for one line and then the delayed first phase composite signal (from the output of the delay line) at its output based upon the application of the control signal. In one embodiment, the control signal is obtained by detecting the phase of the phase alternating signal, and more specifically by detecting the phase of the color burst. This is accomplished by first isolating the color burst signal by a switch triggered by the burst gate pulse, then passing the color burst to a phase discriminator to determine whether the phase alternating composite signal for a give line is in phase or out-of-phase with a reference signal. The output of the phase discriminator is applied to the set input of a flip-flop. The flip-flop is clocked by the horizontal sync signal and the output of the flip-flop controls the switch outputting an unalternating phase signal as either a first phase of the phase alternating signal or a delayed first phase signal thereof. The invention can be incorporated in an appratus for converting phase-alternating-line (PAL) signals to unalternating phase signals for processing on equipment adapted to handle NTSC signals.