A single-ended chopper-stabilized ISFET amplifier for continuous pH measurement applications

This paper introduces a novel low-power Ion-Sensitive Field Effect Transistor (ISFET) readout configuration compatible with standard CMOS technology that utilizes chopping technique to reduce the 1/f noise and the offset of the readout circuitry. In addition, the proposed scheme tackles the well-known non-idealities of the ISFET such as the trapped charge and the long-term drift by using a resetting switch, while suppressing the imperfections of the resetting switch with the proposed chopping amplifier. The readout circuitry can be applied to both continuous time or difference pH measurements. Simulation results using standard 0.35µm CMOS technology shows 20 dB reduction in the output noise while the ISFET readout circuit including the integrator consumes 950nW.