CMOS impedance spectroscopy sensor array with synchronous voltage-to-frequency converters

We present a four-channel 48-electrode CMOS sensor array for use in impedance-based cellular assays. Each channel contains a 2 × 6 surface working electrode array and a synchronous voltage-to-frequency converter (SVFC) which implements frequency response analysis to perform electrochemical impedance spectroscopy. The SVFC is composed of a simple circuit architecture which measures the charge transferred over half an input period to extract the real and imaginary components of the input ac current. An input offset correction circuit in each channel mitigates the effect of device mismatch in the SVFC integrator. We report experimental results from electronic characterization of a 1.8×1.5mm² sensor array chip fabricated in a standard mixed-signal 1.8-V 0.18-μm CMOS process.