Compact Low-Power Impedance-to-Digital Converter for Sensor Array Microsystems

With the rapid progress in CMOS compatible microfabrication of biosensors, there is an emerging need to miniaturize biosensor arrays onto the surface of silicon chips that acquire and process sensor data, permitting improved sensitivity, cost and throughput. In this paper, a low power circuit that extracts and digitizes sensor impedance information is presented. Composed of a novel multiplying integrator and a unique bidirectional counter/shifter, the circuit shares resources for impedance extraction and digitization to maximize hardware efficiency. The extremely compact size of the circuit enables the implementation of sensor array microsystems with simultaneous multi-channel readout. Fabricated in 0.5 mum CMOS, the circuit consumes 6 muW at 3 V and occupies only 0.06 mm², permitting over 100 readout channels within a 3 times 3 mm die. Circuit performance has been verified with a biosensor for gramicidin ion channel embedded in a tethered bilayer lipid membrane.