| 摘要 |
PURPOSE:To suppress effectively noise in demodulation by preventing the noise generated when the counted value of a counter fluctuates, by varying the threshold value of the counted value of the counter according to the variation state of the level of the frequency which corresponds to an FSK signal. CONSTITUTION:Read-only memory ROM15 is stored with threshold values B1 and B2 (B1<B2) previously and the differential output of an FSK signal is applied to interruption input part 11; every time an interruption signal is inputted from input part 11, arithmetic part 12 reads the counted value of counter 13 and resets the counter. Then, when the demodulation output is at level L, smaller threshold value B1 of ROM15 is applied to arithmetic part 12 via AND gates 18 and 19 and when at level H, larger threshold value B2 is applied to arithmetic part 12. When the signal changes in frequency from level L to level H and the count value of counter 12 is less than value B1, an H level output is generated and when the signal changes in frequency from H to L and the counter counts above value B2, an L level output is generated to suppress noise in demodulation. |
