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Design of a Circuit for Measuring the Real an‎d Imaginary Parts of Bio-impedance Using a Switching Output-Stage Technique to Reduce Power Consumption

مهندسي برق

Abstract Bioimpedance is the electrical response of living tissues to the passage of an alternating current; an‎d it is used in applications such as non-invasive health monitoring an‎d wearable systems. In these applications, in addition to accuracy, ultra-low power consumption is essential to increase battery lifetime. With the development of low-power circuits, in many designs power reduction has been mainly focused on amplification, conversion, an‎d processing blocks, while power dissipation in the output stage has received less attention. In this research, a low-power sub-block for bioimpedance measurement an‎d separation of its real an‎d imaginary components is presented an‎d simulated in Cadence using a 180-nm CMOS technology. The core of the proposed architecture is the use of a switching output stage in the excitation path so that, by storing the energy of the injected current in an inductive element an‎d recovering part of it, the dissipated power is reduced. To extract the real an‎d imaginary parts, small-signal AC analysis is performed on the proposed circuit; an‎d then, at each frequency, the amplitude an‎d phase are extracted an‎d the complex impedance is formed. Subsequently, the Cole model parameters are fitted by solving a minimization problem, an‎d the real an‎d imaginary components of the impedance at the injection frequency are reconstructed. Moreover, to reduce power, the effect of changing the dimensions of the power transistors on the total power is investigated an‎d the optimum point is selec‎ted. Simulation results show that the total power consumption of the circuit is 37.2 µW an‎d the dissipated power is 14.67 µW. Accuracy eva‎luation in four sets of experiments based on variations of the Cole model parameters indicates that the reconstruction error of |Z| remains below 2.1%, an‎d an average measurement accuracy of 97.9% is achieved; specifically, the mean |Z| error is in the range of 0.17% to 1.2%, an‎d the maximum |Z| error is reported to be less than 2.1%. Also, in the worst case, the errors of the real an‎d imaginary components at the injection frequency are approximately 1.77% an‎d 1.85%, respectively. Overall, the proposed architecture, while preserving the accuracy of component separation, enables reduction of power consumption an‎d dissipated power, an‎d is suitable for low-power wearable sensors. Keywords: Low-power, Bio-impedance, Impedance measurement, Integrated circuit, Wearable sensor, Impedance spectroscopy (EIS).

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