Ultra Low Current Input Analog to Digital Converter based Bio-Chemical Sensor and Interfacing Circuit

A study of real time biological phenomenon especially at intra-cellular levels mandates usage of nonobtrusive probing and measurement techniques. It is imperative that the phenomenon being observed should not be disturbed in its dynamics and the sensor dimensions should be small enough not to damage cellular integrity. Usage of micro needle tungsten electrode sensors and amperometry techniques is one of the acceptable methods to design sensors for such measurements. In this paper we present amperometry based sensor circuit for measurement of ultra-low currents. Based upon established theory sensing circuits are analyzed and designed for measuring biochemical phenomenon occurring at rates of >10ms. The currents involved in these analyses fall in the range of a few Pico-amperes. Based upon these requirements we achieved an analog to digital converter with input current resolution of ~100pA and a dynamic range of 100pA-1.5uA. The ADC output is coupled via a RF transmitter to enable walk-in readouts from the sensor. In addition, a potentiostat circuit is also presented. The whole system is integrated in AMI 0.5um process for a single System-On-Chip solution.