Multi-standard video option for oscilloscope

摘要

A multi-standard vide option for an oscilloscope detects whether an input video signal has a bi-level or a tri-level horizontal sync pulse from a composite sync signal derived from the input video signal. A ramp signal is generated from the horizontal sync pulse having a slope of one polarity that changes to a slope of the opposite polarity when the horizontal sync pulse is tri-level. For a bi-level horizontal sync pulse the ramp is limited in magnitude and rapidly discharged at the end of the horizontal sync pulse. A digital output signal is generated from the ramp signal and has a width equal to the width of the horizontal sync pulse regardless whether it is bi-level or tri-level. From the type of horizontal sync pulse and the width or the number of lines per frame, a video standard is determined and is subsequently used to determine field identification and to automatically set up the horizontal sweep of the oscilloscope according to a selected video setup.