| 摘要 |
There is disclosed a local oscillating device useful for a communication system where frequency conversion is implemented to data signals received in a burst manner, particularly for INMARSAT STC-C (International Maritime Satellite Organization Standard - C) system. This local oscillating device comprises a local oscillating circuit including a quartz-crystal oscillator of which oscillating frequency can be controlled, an A/D converter for converting a received phase modulated signal to a received digital signal by using a sampling clock from the local oscillating circuit, and a demodulation circuit for reproducing a symbol clock serving as reference of demodulation from the received digital signal from the A/D converter to demodulate the received digital signal by using the symbol clock, and to detect information indicative of a phase difference between the symbol clock and the sampling clock, thus to control an oscillating frequency of the quartz-crystal oscillator on the basis of the phase difference information to output a local oscillating signal of a predetermined frequency.
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