Digital counter arrangement, which contains a plurality of counting stages, the entry narrow input pulses of a common input line are fed via gates

摘要

1,049,856. Automatic frequency control systems. PLESSEY-U.K. Ltd. Aug. 23, 1963 [Aug. 31, 1962], No. 33600/62. Heading H3A. [Also in Division G4] Gating devices control the input to a predetermined number counter or frequencydivider to enable instantaneous re-setting. The counters (see Division G4-G6) may be used to control an oscillation generator to fine limits. A standard frequency F s is divided at 2 by K, Fig. 1, while the oscillator frequency F 0 to be controlled is divided at 6 by N, the resultant values being controlled to be equal by frequency comparator 8 and phase comparator 9 acting on the oscillator. The frequency comparator is shown in Fig. 2. Pulses from 2 and 6 are applied to opposite sides of a binary device 13 which controls gates 14, 15. As long as pulses appear alternately on leads 3 and 7 the gates 14, 15 are closed to the passage of pulses on leads 11b, 12b, but when two pulses occur in succession on one or other lead 3 or 7 the second pulse finds its gate 14 or 15 open and passes through to step a counter 17 forwards or backwards and via a reactor set 18 to alter the tuning of the oscillator 4. To prevent errors due to slow operation of gate 14 or 15 due to pulses on leads 3 and 7 being too close, circuits 11, 12 widen the input pulses. If then the widened pulses overlap an inhibit circuit 21 prevents stepping of the counter 17. The phase comparator 10, Fig. 3, provides fine control of the oscillator. When the two inputs from 2 and 6 are in phase a unidirectional voltage of constant level is produced at 53. If the inputs are not in phase a saw-tooth waveform of a frequency proportional to the difference in frequency of the two pulse trains is produced.