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A wideband current source for System-on-Chip Bio-Impedance Spectroscopy using a CCII drive and Pseudo-Resistor feedback

In this paper, a wideband Current Source (CS) for System on Chip (SoC) Bio-Impedance Spectroscopy (BIS) application is presented. The circuit consists of a load-in loop inverting amplifier current source back-end with a PMOS Pseudo-Resistor (PR) feedback, and a Norton current source front-end drive in the form of a Second Generation Current Conveyor (CCII). The load-in-loop structure allows a differential interface to the Sample Under Study (SUT) permitting the four-point probe interface. The use of a PR array results in the creation of a high impedance feedback while consuming small chip area. The CCII drive increases the output impedance of the CS towards the MHz range. Comparison of 6 load-in-loop CS (LL-CS) structures confirm the performance of our design in terms of output impedance, and excitation current precision over a wide frequency range covering the beta-dispersion range of BIS (~10MHz). The LL-CS structures are realized using TSMC 0.35um CMOS 2P4M Mixed Mode Technology.