| 摘要 |
PURPOSE:To considerably reduce the energy consumption of a transmitter/receiver by completely cut a power supply voltage in the state of no input signal by using a piezoelectric element for monitoring the input signal. CONSTITUTION:A substrate terminal 18a of a piezoelectric element 18 is grounded, and terminals 18b and 18c are respectively connected through resistors to right and left input lines 12 and 11. The piezoelectric voltage of a terminal 18d is impressed to the gate of an FET 21, and the FET 21 is protected from an over current by a protecting resistor 22. The source of the FET 21 is grounded through a delay circuit 25, the FET 21 keeps an ON state for prescribed time when there is a gate input at the FET 21, and the ON state is held even after the input is extinguished. The drain of the FET 21 is supplied through an amplifier 26 and a potential dividing circuit to a comparator 28. The comparing output is supplied through an inverter to the gate of a transistor 30 and supplied through a hold circuit 31 to the output of a power supply switch 17. Thus, when the piezoelectric voltage exceeds a prescribed value, the switch 17 is turned on for the prescribed time, and the transmitter is operated. When no input signal is supplied, the power supply switch 17 is turned off after the lapse of prescribed hold time, and power is consideravly saved. |
