Impedance Spectroscopy Systems Suitable for Biomedical Cell Impedance Measurement

Abstract

Impedance spectroscopy (IS) is an important technique for monitoring and detection of biomaterials. In order to enable point-of-care systems, low-cost IS systems capable of rapidly measuring a wide range of biomaterials are required. This thesis presents two IS systems, one in Printed Circuit Board level and the other in Integrated Circuit level.

The board level system is built for preliminary experimental data collection; it is capable of measuring impedance from 1KHz to 100KHz with 200mV signal injection into cell sample. Experimental results show that magnitude and phase error are less than 6.6% and 2.2%, respectively.

An IC level IS front-end is also proposed which utilizes a time-to-digital converter (TDC) and a peak detector circuit (PDC) for quick measurement of both impedance phase and magnitude, respectively. Designed in a 0.18μm CMOS process, the front-end is capable of performing impedance measurements in 6μs at frequencies ranging from 100Hz-10MHz and with a 100Ω-1MΩ dynamic range. Simulation results with cell impedance models show that the system achieves <2.5% magnitude and <2.2 degree phase error. The front-end consumes 28mW total power and occupies 0.4mm^2 area.