| 摘要 |
PROBLEM TO BE SOLVED: To always optimally constitute the loop band of a PLL in the carrier recovery circuit of a composite modulated wave signal obtained by frequency modulating a quadrature modulated signal with an SC signal. SOLUTION: An input IF signal Si of this carrier recovery circuit is a composite modulated wave signal. In this carrier recovery circuit, a phase locked loop(PLL) is constituted of multiplier circuits 1 and 2, LPF 3 and 4, amplifier circuits 5 and 6, A/D converters 7 and 8, an identifier 9, an APC signal detector circuit 10, an LPF 13, and a VCO 12. A carrier control information signal S6 from the APC signal detector circuit 10 is amplified by an SC amplifier circuit 14, and frequency-demodulated, and an SC signal Sc is reproduced. The identifier 9 is the identifying circuit of a main signal. An error pulse detecting circuit 15 receives a digital signal Sd from the A/D converter 7 or 8, and controls the band of the LPF 13 according to the BER of an error pulse. An SC level detecting circuit 17 connected with the SC amplifier circuit 14 controls the band of the LPF 13 according to the presence or absence of the SC signal. |
