Ultrasonic sensor for vehicle, has circuit driving switches to ON/OFF condition so that each of three capacitors is coupled to/decoupled from piezoelectric vibrator to compensate electric capacity and to adjust reverberation period

摘要

The sensor has a driving circuit (6) to drive switches (3a-3c) to ON/OFF condition based on a switch condition signal from an output signal processing circuit (5). The switches are driven to ON/OFF condition so that each of three capacitors (2a-2c) is coupled to/decoupled from a piezoelectric vibrator (1) to compensate vibrator`s electric capacity and to adjust vibrator`s reverberation period to be shorter than a preset threshold time. The piezoelectric vibrator vibrates to transmit an ultrasonic wave, receives a reflected wave of the transmitted wave and produces the output signal related to the vibration. The output signal processing circuit measures the reverberation period from the output signal and provides the switch condition signal.