PLL for demodulation of specified optical signals - has pilot generator, evaluator circuit and oscillator whose phase is modulated by pilot signal

摘要

The signals are of analogue frequencies, or phase modulated type. The p.l.l. consists of a phase comparator (1), a loop filter (3), and an optical oscillator (5), with electrically controllable frequency. There is also a pilot signal generator (11) and an evaluation circuit (13). In addition to the loop filter output signal, the oscillator is phase modulated by a pilot signal (Sp). The latter frequency (fp) is lower than the smallest frequency of the useful signal band to be transmitted. The output signal of the phase comparator can be evaluated w.r.t. the pilot frequency. The evaluator circuit finally adjusts the oscillator such that the comparator working point is stabilised. USE/ADVANTAGE - Wide band communications, e.g. simultaneous transmission of several TV programmed with p.l.l. continuously holding working point of phase detector constant.