| 摘要 |
PURPOSE:To obtain a FSK signal demodulation circuit of good temperature characteristic, which does not require a high parts precision, by obtaining a digital outut signal after converting a frequency modulated wave to a low frequency signal of the PLL system. CONSTITUTION:A frequency deviation keying FSK signal A of space 1.8kHz and mark 2kHz is converted to a low frequency signal B by the PLL circuit 2. The first LPF3 outputs a signal C showing the average voltage of the signal B, and the second LPF4 outputs a signal D which has removed a noise contained in the signal B. The comparator 5 compares the signal C and the signal D, and regenerates and outputs a digital output signal E which has demodulated the FSK signal, as the aforeside compared output. |
