Oscillators – Relaxation oscillators
Patent
1975-12-17
1977-06-21
Griffin, Robert L.
Oscillators
Relaxation oscillators
325420, 325 4, 331 1A, H04B 116
Patent
active
040314715
ABSTRACT:
An automatic frequency control circuit is disclosed which is capable of noise suppression and sufficiently reducing the frequency deviation or offset of an input signal at an output, regardless of the variation of the burst width of the input burst signal in a time-division multiplex communication system. The automatic frequency control circuit comprises a frequency converter for the frequency conversion of an input signal, a band-pass filter connected to the output of said frequency converter, first and second phase comparators of mutually different output characteristics adapted to compare phases of input and output signals of said band-pass filter, first and second holding circuits for holding the maximum voltages of output signals of said first and second phase comparators, respectively, an arithmetic circuit for calculating output signals of said first and second holding circuits, and a voltage-controlled oscillator responsive to an output signal fo said arithmetic circuit and connected to said frequency converter. In this circuit, owing to the fact that an additional phase comparator, two holding circuits and an arithmetic circuit are added to the conventional circuit, the output signals of the holding circuits, which hold maximum voltages corresponding to the maximum and minimum values, respectively, of the input burst signal frequency, are calculated by the arithmetic circuit and then the result of the calculation is applied to the voltage-controlled oscillator (VCO). This input to the VCO is virtually a D.C. control signal to provide a local oscillation having a frequency differing by a fixed frequency from the average frequency of the maximum and minimum frequencies of the input burst signal. Accordingly, regardless of the variation of the burst width of the input burst signal, the output frequency of the VCO is maintained at a frequency having a fixed frequency difference from the average frequency of the maximum and minimum frequencies of the input burst signal.
REFERENCES:
patent: 2915626 (1959-12-01), Freedman
patent: 2988637 (1961-06-01), Vandgraaf
patent: 3238460 (1966-03-01), Enloe
patent: 3479600 (1969-11-01), Miller
patent: 3824474 (1974-07-01), Sakamoto
Chin Tommy P.
Griffin Robert L.
Nippon Electric Co. Ltd.
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