System for processing bursted amplitude modulated signals using an impedance sensor

Abstract

A low power processing system for processing bursted amplitude modulated signals performing impedance-related measurements across a load including injecting current pulses of constant amplitude across the load using at least a first electrode and a second electrode, the current pulses including bursts of a plurality of pulses at a pulse frequency at which the current pulses are repeated, the bursts transmitted at a burst frequency; detecting voltages across at least a third electrode and a fourth electrode; high pass filtering the voltages to produce filtered voltages; amplifying the filtered voltages to produce amplified voltage signals; bandpass filtering the amplified voltage signals with a bandpass filter with a center frequency equal to approximately the pulse frequency to generate first filtered signals; rectifying the first filtered signals to produce rectified signals; integrating the rectified signals to produce integrated signals; sampling-and-holding the integrated signals after each burst to capture an integrated pulse value for each burst, creating a plurality of discrete integrated pulse values; and bandpass filtering the plurality of discrete integrated pulse values using a filter including an upper cutoff frequency less than the burst frequency to produce the output related to the time-varying impedance of the load. In one application, the first electrode is positioned near to an apex of a right ventricle, the second electrode is outside of the right ventricle, the third electrode and fourth electrode are located within the right ventricle and wherein the output is related to the time-varying impedance of the right ventricle during systole and diastole.