Integrating data converters for picoampere currents from electrochemical transducers

This paper describes a current mode A D converter designed for a maximum input current range of 5nA and a resolution of the order of IPA. The converter is designed for a potentiostat for amperometric chemical sensors and provides a constant polarization voltage for the measuring electrode. A prototype chip using the dual slope conversion method has been fabricated in a 0.7pm CMOS process. Experimental results from this converter are reported. Design problems and limitations of the converter are discussed and a new conversion technique providing a larger dynamic range and easy calibration is proposed.