| 摘要 |
PURPOSE:To detect the lack or attenuation of a sound carrier signal, and to compensate it by providing a switching circuit for introducing the output of a phase locked loop circuit into a demodulator as an artificial sound carrier signal instead of a sound carrier signal when it does not exist. CONSTITUTION:A demodulator 7 demodulates an FM-modulated sound carrier wave and outputs a reproducing sound signal 8. A PLL (phase locked loop) oscillating circuit is constituted of a phase comparator 10, low-pass filter 11, VCO (voltage controlled oscillator, variable voltage control oscillator) 12, and an (n) frequency dividing circuit 14, and it is controlled by an output of an (n) frequency dividing circuit 9. An inputted reproducing sound carrier wave signal is usually inputted to the demodulator 7 through a switch 6, demodulated and goes to the reproducing sound signal 8. When the lack or attenuation being below a prescribed level is detected in the inputted reproducing sound carrier wave, the switch 6 is switched to B from A, and an artificial sound carrier wave by the PLL oscillating circuit is led into the demodulator 7 instead of the reproducing sound carrier wave. |
