| 摘要 |
PURPOSE:To obtain an APC circuit which always secures properly fixed phases and is high in C/N, by providing a broad-band pass filter and narrow-band-pass filter and constituting the APC circuit followable to the frequency variation of input signals even if the variation is large. CONSTITUTION:Input signals 201 are multiplied by the output signal 202 of a VCO 103 by means of a multiplier 101 and, by passing the multiplied output signals 203 through a BPF 104, signals 204 which are frequency-converted to a low frequency f-f0 are obtained. The signals 204 are inputted to another BPF 105 which has a broader passing band width than the BPF 104 has and the phase difference between both ends of the signals is found by a phase comparator 106. The phase difference is smoothed by an LPF 107 and controls the VCO 103 as a control voltage 103a. Because of this PLL, the frequency of the VCO 103 follows the variation of frequency of the input signals 201 even if the input signals fluctuate in frequency and the signals 204 stay in a fixed frequency which can make the phase difference smaller. |
