An Electrical Bio-Impedance Analyzer for Implantable Medical Devices

A novel solution of electrical bio-impedance (EBI) analyzers with suppression of errors caused by higher odd harmonics of rectangular wave pulses, is proposed. The solution is based on a special method of shortening the rectangular pulses commonly used in the correlation type or lock-in EBI measurements. Comparison of the proposed method with using of regular square wave pulses is given. The results show that the errors of frequency response measurement of a three element EBI equivalent will become tens of times smaller when shortening the excitation and reference signals by 30deg and 18deg, respectively. Also, much simpler cases, as shortening of only one of the signals (excitation or reference one) by 30deg give acceptable results. Acceptable accuracy of the phasor measurement of EBI makes the method reliable for the most clinical applications. Thank to its simplicity, the method is suitable for on-chip realization in implantable devices