Automatic frequency control circuit

Details Automatic frequency control circuit Automatic frequency control circuit

1991-02-04

1992-04-21

Chin, Stephen

Pulse or digital communications

Repeaters

Testing

455256, 455265, H04L 2706

Patent

active

051075229

ABSTRACT:
An AFC circuit stabilizes the frequency of an intermediate frequency signal to be applied to a demodulation circuit. A frequency conversion circuit responds to a local oscillation signal generated from a voltage-controlled oscillation circuit to convert the frequency of a digital modulation signal and applies the converted frequency to the demodulation circuit. A carrier reproduction circuit in the demodulation circuit reproduces the carrier of the intermediate frequency signal to output a synchronizing detection signal. The frequency of the reproduced carrier is frequency-divided by a frequency dividing circuit. A frequency division output thereof is counted by a counter for a definite period. Data is outputted from a microprocessor in response to a count output of the counter and the synchronizing detection signal, and the data is then converted into an AFC voltage by a D/A converter. The converted voltage is supplied as a control voltage to the voltage-controlled oscillation circuit. A stable intermediate frequency signal can be obtained by frequency-dividing the frequency of the carrier and counting the frequency division output thereof.

REFERENCES:
patent: 4641325 (1987-02-01), Hughes
patent: 4696056 (1987-09-01), Morita
patent: 4827488 (1989-05-01), Shibano
patent: 4879728 (1989-11-01), Tarallo
patent: 4947409 (1990-08-01), Raith et al.

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