Dual-mode CMOS analog front-end (AFE) for electrical impedance spectroscopy (EIS) systems

This paper presents the operation of a dualmode wideband CMOS analog front-end (AFE) for electrical impedance spectroscopy. The chip combines two current-readout (CR) channels and four voltage-readout (VR) channels suitable for both bipolar and tetrapolar EIS analysis. The chip addresses the need for flexible readout units for real-time simultaneous single-cell and large scale tissue/organ analysis. Postlayout simulations show that the VR channel is capable of wideband operation up to 12 MHz with noise floor as low as 16.4 nV/Hz1/2. A 2-bit control allows to select between a high-frequency low-gain channel and a bandwidth-limited high-gain channel. Each VR channel occupies an area of 0.48 mm2. The CR channel is capable of 80 dB of dynamic range, by converting currents between 1 nA to 10μA, while achieving a noise floor of 1.4 pA/Hz1/2. An automatic gain control (AGC) unit can be enabled in order maintain the sensor signal within the ADC dynamic range. Each CR channel occupies an area of 0.21 mm2. The chip consumes between 290 μA and 690 μA per channel and operates from a 1.8 V supply. The chip will be part of a fully flexible and configurable dual-mode EIS systems for impedance sensors and bioimpedance analysis