| 摘要 |
PURPOSE:To surely detect the periodic pulse by combining Schmitt circuits inverted in response to the periodic pulse and re-inverted by a fixed value of an output level of a charge/discharge circuit. CONSTITUTION:When a periodic pulse S1 comes, a Schmitt circuit 30 comprising transistors (TRs) 5, 10, 13 is inverted by the action of a TR 7 and an output level at an output terminal 22 goes to a logic H level. The TR 7 is reversely biased and turned off, but the Schmitt circuit 30 keeps the state. Thus, the charging of the capacitor 18 is started by the turningon of a TR 16, and when a voltage Vc across the capacitor 18 exceeds the upper comparing limit level of the Schmitt circuit 30, it is inverted again, the capacitor 18 starts discharging through a current source 17, and when the voltage Vc across the capacitor 18 reaches the emitter voltage of a TR 20, it is turned on and the capacitor 18 completes its discharge. Thus, it means that a mask period masking other pulses than the periodic pulse S1 is provided. |
