Patent ID: 8290598

Claim:
An implantable system comprising: a first ultrasonic transducer configured to receive an intra-body ultrasonic amplitude-modulated (AM) signal provided by a second implantable ultrasonic transducer and configured to convert the ultrasonic AM signal to a first electrical signal having a first frequency; and an ultrasonic receiver, coupled to the first ultrasonic transducer, configured to receive the first electrical signal and generate a digital output associated with the ultrasonic signal, the ultrasonic receiver including: a local oscillator configured to generate a second electrical signal having a second frequency; a mixer coupled to the local oscillator, configured to mix the received electrical signal and the second electrical signal and generate a demodulated signal; a filter coupled to the mixer, configured to pass a first portion of the demodulated signal having a frequency range with a center frequency equal to the difference between the first frequency and the second frequency; and a detector coupled to the filter and configured to receive the first portion of the demodulated signal, the detector including: a peak detector configured to determine a peak amplitude of the first portion of the demodulated signal received from the filter over a time interval and to determine a noise floor and use the noise floor to dynamically adjust the maximum sensitivity of the detector; a threshold generator to generate a dynamic signal tracking threshold that starts at a value that is proportional to the first portion of the demodulated signal that then exponentially decays over a time interval; and a comparator to compare the peak amplitude and the dynamic signal tracking threshold and generate the digital output based on the difference.