Patent ID: 7656750

Claim:
An echo detection circuit comprising: an acoustic sensor configured to convert sensed acoustic pressures into a pre-processed analog electrical signal; analog processing circuitry configured to transform the pre-processed analog electrical signal into a post-processed analog electrical signal suitable for providing to an analog-to-digital converter; an analog to digital converter configured to convert the post-processed analog electrical signal into a digital signal; a sine mixer configured to digitally mix the digital signal provided by the analog to digital converter with a sine wave of approximately the same frequency as a carrier wave of a transmitted acoustic signal whose echo is being detected; a cosine mixer configured to digitally mix the digital signal provided by the analog to digital converter with a cosine wave of approximately the same frequency as the carrier wave of the transmitted acoustic signal whose echo is being detected; a vector magnitude detection mechanism that detects a magnitude of the vector represented by at least a derivative of a signal received from the sine mixer, and at least a derivative of a signal received from the cosine mixer; and a threshold detection circuit that compares the magnitude of the vector with one or more thresholds to determine whether or not an echo is detected.