| 摘要 |
PURPOSE:To easily cover the entire required lock range by dividing a frequency lock range into plural ranges, shifting the center frequency of an AFC loop at every input of a sweep control signal and making the frequency coincident with the center frequency for the corresponding division range. CONSTITUTION:The center frequencies of an AFC loop are selected such as f1-fs so as to cover the frequency lock ranges fL--fH of a carrier recovery circuit. Every time a sweep control signal from a synchronizing discrimination device 4 is inputted, a sweep signal generator 51 sends a sweep voltage to an adder 52 so that the center frequency of the AFC loop is a corresponding center frequency in the center frequencies f1-f5. When the frequency difference from the input signal is within the frequency lock range in the AFC loop, the frequency difference is 0 in average and the synchronizing discrimination device 4 interrupts the transmission of the sweep control signal. When the frequency difference is out side of the frequency lock range, the sweep control signal is sent again and the center frequency of the AFC loop is shifted and the same operation as above is repeated. |
