JPS6444876A - Ultrasonic switch - Google Patents

Abstract

PURPOSE:To certainly detect the presence of a body in the vicinity of an ultrasonic switch, by applying a signal having a phase inverse to that of the oscillation signal of an oscillation circuit driving the ultrasonic element during a predetermined time immediately after the ultrasonic element is driven. CONSTITUTION:The output from a gate signal oscillating circuit 1 is inputted to a gate circuit 20, an inverse phase gate circuit 22 and an inhibit gate generating circuit 5 and the circuit 5 generates an inhibit gate signal rising simultaneously with the rising of the transmitting gate signal of the circuit 1 and falling a minute time after the falling of said signal. The output of the circuit 22 generating an inverse phase gate signal of a definite time width at the falling time of the transmitting gate signal of the circuit 1 is inputted to one input terminal of an inverter 23 and the high frequency signal of an oscillation circuit 2 is inputted to the other input terminal of said inverter 23 and the output of the circuit 2 is reversely amplified only during the time of the inverse phase gate signal to be inputted to an ultrasonic element 4. As mentioned above, since the inverse phase signal is inputted to the element 4 after the finish of a transmitting gate, reverberation can be attenuated within a short time and the body in the vicinity of an ultrasonic switch can be certainly detected.