Sinusoidal Current Source for Bioimpedance Applications Based on a Nonlinear Discrete Time Closed Loop Control Algorithm

Résumé 0

Sinusoidal current sources are fundamental components of electronic equipment used in bioimpedance analysis and in electrical impedance tomography. Currently, these sources are mostly implemented as analog electronic systems. The aim of this paper is to present a new approach to current sources design based on discrete-time closed loop control systems. The experimental results are obtained by implementing the current source in a system of analog and digital programmable blocks, and using as a controller a nonlinear difference equation proposed by the authors. This controller guarantees the convergence of the amplitude of the current flowing through the load, towards a user-desired level. This new control law does not require any parametric adjustment nor knowledge of the load . The developed device is able to produce a sinusoidal current signal of a frequency ranging from 100 Hz to 120 kHz and currents from 500 to 2 mA. The amplitude error of the current signal remained below 1 % for tests performed with resistive-capacitive loads (Cole's type loads). The output impedance is frequency dependent and ranges from 410 kΩ to 966 kΩ. The total harmonic distortion is less than 5 %. All the proposed system is embedded in the mixed signal device PSOC 5LP, a shunt resistance being the only external component.