Method and apparatus for determining a digital phase shift in a signal

Abstract

A method for determining a digital phase in a signal comprises sampling a reference signal for a low going edge. If the low going edge is not detected the reference signal is sampled again. If low going edge is detected ( ) a counter is initialized ( ). The reference signal is again sampled if a high going edge is not detected the reference signal is resampled until the high going edge is detected ( ). When a high going edge is detected ( ) a counter is started ( ). A resulting signal is then sampled if the level of the resulting signal is high the resulting signal is sampled until a low going edge is detected ( ). If a low going edge is not detected sampling of the resulting signal continues. If a low going edge is detected ( ) sampling is continued until a high going edge is detected ( ) at which point the counter is stopped ( ). The counter updates a register ( ). When the resulting signal was sampled for a high level the resulting signal is sampled until a high going edge is determined ( ) at which point the register is stopped and converted to a phase difference ( ). In one embodiment of the invention the reference signal being sampled is a driver for an ultrasonic transmitter ( ) and the resulting signal is an electrical signal ( ) representative of a received ultrasonic signal ( ).