ANORDNUNG ZUR PHASENSTARREN STEUERUNG VON OSZILLATOREN

1521971 Automatic frequency control STANDARD TELEPHONES & CABLES Ltd 21 Oct 1975 [29 Oct 1974] 46744/74 Heading H3A An oscillator arrangement, e.g. clock oscillators in a telephone exchange, includes: an array of oscillators, e.g. crystal oscillators 01, 02, 03 all tuned to the same predetermined frequency; meand PC1,A1 PC2,A2 PC3,A3 for phase locking each oscillator to the next, the last oscillator being locked to the first; detection means Q1, Q2, Q3, one associated with each oscillator, for detecting an out of lock condition between pairs of oscillators; and means, e.g. AND gates G1, G2, G3 for identifying a malfunctioning oscillator and preventing it from changing the frequencies of the other oscillators. If for example oscillator 02 goes too far off frequency, then a large correction signal is produced from phase comparators PC2, PC3. This large signal is detected by detectors Q2, Q3 which then produce an output signal from AND gate G3 to cause oscillator 03 to adopt a frequency near the centre of its range, regardless of the signal from phase comparator PC3.