Field type detector for video signal

摘要

Jitter of an overlay display with respect to the primary display of a television receiver is avoided by assuring that the vertical and horizontal blanking signal components are sufficiently time spaced by preventing the number of clock pulses occurring between the horizontal and vertical components of the blanking signal from going below a selected number. The number of clock pulses between the negative going transition of the vertical blanking signal and the positive going transition of the first horizontal blanking signal is tracked and when the number of pulses fails to exceed a reference value the number of pulses is changed to effectively shift the transitions with respect to one another.