Abstract

Circuit for measuring the relative change in conductivity between two cells which include a test biorigion and a control biorigion as the test cell biorigion conductivity changes as a result of analyte modecules binding to receptor sites in the test cell biorigion. The invention includes circuitry for driving a current through each of the cells and for measuring the voltage drops across the test and control cells as a function of time. A novel two-stage ac analog-to-digital convertion circuit in which the initial conductivities are measured via a successive approximation process, while the relative conductivities are monitored during a test interval via a tracking technique is included. The circuitry is controlled by a digital controller which can vary the parameters of the measurement processes so as to make the circuit adaptable to the measurement of a wide variety of substances using different cell configurations and/or electrolytes.