Improvement of Lock-in Electrical Bio-Impedance Analyzer for Implantable Medical Devices

A novel solution for improving lock-in electrical bio-impedance (EBI) analyzers by suppressing errors caused by higher odd harmonics of rectangular wave pulses is proposed. The solution is based on a newly developed method of shortening the rectangular full duty cycle pulses, which are commonly used in correlation-type lock-in EBI measurements. Comparison of the proposed method to a common method of regular rectangular waveforms is given. The results show that the measurement errors of the three-element EBI equivalent become several tens of times smaller when shortening the excitation and reference signals separately by different values, for example, by 30 deg and 18deg. Shortening of only a single signal (either excitation or reference) can also give significant progress. Improved accuracy of the EBI phasor measurement makes the proposed method reliable for most clinical applications. Due to its simplicity, the method is appropriate for on-chip realization in implantable devices