| 摘要 |
PURPOSE:To not only improve the reception sensitivity and S/N but also effectively use the frequency by changing the local oscillation frequency so that the intermediate frequency is fixed and taking out the demodulation output from an LPF through a phase comparing circuit. CONSTITUTION:The reception signal from an antenna 1 has the amplitude limited by a limiter circuit 11 after passing the processings such as tuning, frequency conversion, and amplification, and the output has the frequency divided by a frequency dividing circuit 42 and is inputted to a phase comparing circuit 43. The reference frequency outputted from a reference frequency oscillating circuit 22 has the frequency divided by a frequency divider 44 and is inputted to the other end of the circuit 43. Phases of two frequencies are compared with each other by the circuit 43, and the output proportional to the extent of advance or delay of the output signal or the circuit 42, that is, the output including an audio signal is inputted to an LPF 45. Frequency components on the outside the audio band are eliminated by the LPF 45, and the output is inputted to a local oscillating circuit 8 as the frequency control voltage. In this constitution, the oscillation frequency of the circuit 8 is changed in accordance with the change of the reception signal in the PLL circuit consisting of circuits 8, 11, 42, 43, 45, etc., at the time of input of an FM reception signal. |
