A time-based VLSI potentiostat for ion current measurements

A time-based CMOS integrated potentiostatic control circuit has been designed and fabricated. The design maintains a constant bias potential between the reference and working electrodes for an amperometric chemical sensor. A technique of converting input currents into time for amperometric measurements is proposed. This technique eliminates current amplifying circuitry, reduces matching problems, and increases dynamic range while saving on area and power consumption. Redox currents ranging from 1 pA to 200 nA can be measured with a maximum nonlinearity of ±0.1% over this range. The design can be used to generate cyclic voltammograms for an electrochemical reaction by sweeping the voltages across a range specified by the user. Analog inputs are processed and digital outputs are generated without requiring a power-hungry A/D converter. A prototype chip has been fabricated in the 0.5-μm AMI CMOS process. Experimental results are reported showing the performance of the circuit as a chemical sensor.