Image Number 4 for United States Patent #4004235.
Apparatus, in a receiver, for detecting the mid-pulse phase reversal of an nput signal s(t) = a(t).sub.BLT cos (.omega..sub.c t + .theta.). The signal a(t).sub.BLT is a modulating signal a(t), having a phase-reversal at its midpoint, after band-limiting by a transmitter, and cos (.omega..sub.c t + .theta.) relates to a carrier having a frequency f.sub.c and arbitrary phase angle .theta.. The apparatus comprises a hard-limiter and amplifier, a phase-lock loop circuit, a multiplier circuit, a low-pass filter, a comparator, serving the function of a threshold detector, a delay timing logic circuit, and a comparator, serving as a zero crossing detector, whose input is connected to the output of the low-pass filter, which detects the mid-pulse zero-crossing of a(t).sub.BLTR.sub.' and therefore of a(t). The apparatus further includes an AND gate, whose input comprises a positive-going pulse whose trailing edge represents the mid-pulse of a (t).sub.BLTR ; and a one-shot, whose output is a sharp pulse representing the mid-pulse of a(t).