Determining arrival time of sound pulse for distance measurement - stimulating EM transducer by pulse-modulated signal, supplying signal caused by reflected received pulse to PLL and detecting locked state

摘要

Determining the arrival time of a sound pulse, transmitted by an e.m. transducer (W) and received back from an object, involves stimulating the transducer with a pulse modulated oscillating signal during a defined transmission period. The transducer signal produced during reception of the reflected sound pulse is fed to a phase-locked-loop tuned to the carrier frequency and whose locked state is detected. The pulse edge of the pulse modulated signal is detected and the arrival time of the reflected sound pulse defined by the detected edge when PLL locking has occurred within a defined time of the edge being detected.