A circuit for detecting changes in the amplitude of a video signal features a sampler for sampling the signal. The sampled signal is then held and delayed by a selected amount. The delayed and undelayed signals are then compared and when the difference exceeds a threshold, an output signal is suppli...http://www.google.fr/patents/US4130835?utm_source=gb-gplus-shareBrevet US4130835 - Electrical waveform analysis
