| 摘要 |
PURPOSE:To provide the FSK demodulation circuit in which cost reduction and miniaturization are attained by using a switched capacitor filter(SCF) for a pre-stage band pass filter. CONSTITUTION:A high group band pass filter 39 and a low group band pass filter 40 are formed respectively by an SCF. A filter input F1 is fed to the filters 39, 40. A clock from a variable frequency divider circuit 47 is fed to each of the filters 39, 40 via AND gates 44, 45 to obtain a band width optimum to each group. Its output F0 is selected by analog switches 41, 42 and the result is outputted from a buffer 43. A band of the CCITT recommendations or the Bell standards is set to each of the filters 39, 40 by providing a clock with a different frequency to the filters 39, 40 provided separately for the high group and the low group through a changeover terminal B/C. |
