Design of A CMOS closed-loop system useful for bio-impedance measurements

This paper proposes a method for impedance measurements based on a closed-loop implementation of CMOS circuits. The proposed system has been conceived for alternate current excited systems, performing simultaneously driving and measuring functions thanks to feedback. The system delivers magnitude and phase signals independently, which can be optimized separately. The method can be applied to any kind of load (resistive and capacitive). Design specifications for CMOS circuit blocks and tradeoffs for accuracy and loop stability have been derived. Simulation results for several loads agree with the theory, enabling its application to any impedance measurement problem, in special, to bio-setups including electrodes.