Patent ID: 7668045

Claim:
A method of measuring a distance using an ultrasonic wave, the method comprising steps of: receiving through an ultrasonic sensor a signal from an ultrasonic transmitter; amplifying the received signal; filtering a high-frequency component from the amplified signal, thereby generating a filtered signal; generating an output signal when the filtered signal satisfies a predetermined condition; and computing a distance based on a period of the output signal, wherein generating the output signal comprises: comparing the filtered signal against an upper threshold and a lower threshold so as to provide the output signal, wherein the output signal has a lower level and an upper level; wherein the output signal transitions from the lower level to the upper level when the filtered signal changes from below the upper threshold to above the upper threshold, and the output signal stays at the upper level when the filtered signal maintains above the lower threshold, and wherein the output signal transitions from the upper level to the lower level when the filtered signal changes from above the lower threshold to below the lower threshold, and the output signal stays at the lower level when the filtered signal maintains below the upper threshold.