| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a digital demodulator, capable of more surely making the frequency of a recovered carrier synchronize with the frequency of a carrier of a modulation signal, in a short time, when there is out-of-synchronism between the frequency of the carrier of the modulation signal and the frequency of the recovered carrier. <P>SOLUTION: A synchronization state monitor section 56 of a frequency correction circuit 50 outputs an out-of-synchronism signal to a timer control section 58, on the basis of an edge pulse resulting from the leading and the trailing of an IQ product signal from an edge detection section 52; and a clock from a crystal oscillator 30, a counter 60 counts the number of pulses of the recovered carrier within a prescribed time set by the timer control section 58, on the basis of the out-of-synchronism signal; and a correction voltage generating section 73 outputs a voltage corresponding to a difference between the frequency depending on the count by the counter 60 and the frequency of the carrier of the modulation signal to a VCO 36 as a correction voltage. <P>COPYRIGHT: (C)2008,JPO&INPIT |
