A Differential Low-Power Voltage-Clamped ISFET Topology for Biomedical Applications

Over the past few years, ion-sensitive field-effect transistors (ISFETs) have played a major role in chemical detection systems. This paper presents an architecture for an ultra-low power CMOS pH sensor suitable for biomedical applications. The design uses a differential ISFET readout circuit operating at 0.9V power supply. The minimum supply voltage and minimum power consumption are achieved by operating the MOSFETs in subthreshold regions. The novelty of this design lies in using different size sensing gate areas in a differential voltage clamping ISFET topology. The ISFET model is derived from experimental measurements. Simulation results of the circuit in a 0.5μm standard CMOS process show that the designed differential ISFET provides an average sensitivity -49mV/pH with ISFET sensing areas of 80μm×80μm and 10μm×10μm over a 1-14pH range with 2.3nW of power.