A TDC-based front-end for rapid impedance spectroscopy

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 paper presents an IS front-end 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° phase error. The front-end consumes 28mW total power and occupies 0.4mm² area.