Monolithic CMOS ISFET with Built-in Gold Reference Electrode and Readout Circuit with Frequency-adjustable Pulse Output in Bio Detection

ISFET with built-in gold reference electrode and integrated readout circuits with frequency-adjustable pulse output is presented. Sensing membrane is surrounded by gold electrodes, treated as reference electrode and working electrode separately, can be as chemical or bio-molecule detection sensor. The ISFET is one of the input differential transistor pair of an operational amplifier in its readout circuit, which mainly consists of a voltage-to-current converter and a current-controlled oscillator. The output pulse frequency is linearly proportional to the effective gate voltage of the ISFET, which is immersed in the analyzed solution with a stably biasing reference electrode. A current-offset structure is added into the oscillator to shift the transfer characteristic line of the output frequency versus the effective input voltage. The transfer characteristics of the pulse frequency versus pH value are measured by an external Ag/AgCl reference electrode and a built-in gold reference electrode, respectively.