Apparatus and method for operating an ISFET at multiple drain currents and gate-source voltages allowing for diagnostics and control of isopotential points

摘要

An apparatus for measuring ion concentration of a solution includes an ion sensitive field effect transistor (ISFET), a reference device, an ISFET control circuit, a memory, a measurement circuit and a diagnostic circuit. The ISFET has a drain, a source, an ion sensitive gate region and a plurality of device characteristics. The reference device is separated from the gate region by a sample solution. The ISFET control circuit is coupled to the ISFET and operates the ISFET at a drain-source voltage VDS and at n successive drain currents IDi and corresponding gate-source voltages VGSi, wherein i is an integer from 1 to n and n is an integer greater than 1. The memory stores the plurality of device characteristics and the n successive drain currents IDi and gate-source voltages VGSi. The measurement circuit measures ion concentration of the solution as a function of at least one of the n successive drain currents IDi and gate-source voltages VGSi and the plurality of device characteristics stored in the memory. The diagnostic circuit measures at least one of the device characteristics of the ISFET as a function of the n successive drain currents IDi and gate-source voltages VGSi.