Recovering coded signal sequence from film - digitising signals and eliminating DC component using regulating loop

摘要

Time codes are provided on moving picture film has a series of markings. The signals are read (10) and contain a.c. and d.c. components (A). The signals are passed through a low-pass filter (13) and preamplifier (14) coupled to a Schmitt trigger (11). The trigger level is set such that the d.c. component is reduced to a small value. The output of the Schmitt trigger is fed back via an integrator (15) and error voltage amplifier (16). The resulting output is a square wave pulse sequence (C) corresp. to the original time code. ADVANTAGE - Time code is d.c. voltage free over full sequence.