SIGNAL PROCESSING SYSTEM USING IMPROVED TRANSCONDUCTANCE CELL

摘要

Impedance-related measurements across a load such as a human heart are made by 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 if 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.