| 摘要 |
PURPOSE:To discriminate only the time tone signal and so on from other noise to perform tuning without malfunction, by using a switched capacitor filter using the frequency division output and so on as the clock. CONSTITUTION:The previous notice signal of the time tone signal picked up by microphone 7 is applied through amplifying circuit 8 to switched capacitor filter 9, to which the prescribed frequency division-state output from frequency dividing circuit 3 of time counting circuit 1 is applied as a clock to switch the switch, consisting of the MOS transistor, the capacitor, the operational amplifter, and so on. The time tone previous notice signal passes through filter 9 in distinction from other noise, and the time tone previous notice signal pattern is discriminated by crest discriminating circuit 10 and time tone pattern discriminating circuit 11. On basis of this discrimination, count contents of second counter 4 of circuit 1 is automatically corrected to the correct time through circuit 12 reset to zero for every 30 seconds, thus performing auto-tuning without malfunction. |
