| 摘要 |
PURPOSE:To improve the stability of a FSK demodulation circuit on a zero-cross system, by using a clock generator of sufficiently-high frequency stability and a counter. CONSTITUTION:The demodulation circuit is provided crystal oscillator 25 and with counter 26 of sufficiently-high frequency stability, which counts up the frequency of oscillator 25 and is reset by the output pulse of zero-cross detector 10. In the above constitution, FSK signal (a) is converted into output pulse (c) by detector 10. When the oscillation of above-mentioned oscillator 25 is set to a period much shorter than the maximum period of the output pulse of detector 10, counter 26 counts the output pulses of oscillator 25 and generates its output until the discrete value reaches a fixed value, thereby obtaining rectangular wave (e). This output signal becomes demodulated signal (g) by passing through LPF7 and level converter 8. In this way, the demodulator can be obtained which is under no influence of variance of parts and a power voltage. |
