An automatic transimpedance gain control circuit for analogue front-ends of drifting amperometric biosensors

When amperometric biosensors drift, their sensitivity drops with time: the same difference in detected concentration value ΔC results in lower sensor output current ΔI as the measurement/monitoring time progresses. This limitation affects the longevity of biosensors. To counterbalance for the drop in sensitivity, manual adjustment of the I-to-V transimpedance gain is usually applied. This paper presents an automatic transimpedance gain control circuit suitable for switched-capacitor-based current analogue front-ends. The circuit has been fabricated in the 0.35μm AMS technology, occupies an area of 0.028mm2 and consumes 14.5μW from a 3.3V supply. Measured results confirm the automatic selection between three values of transimpedance gain, namely 1, 10 and 100GΩ each optimised for sensor current range values of ±1.65nA, ±165pA and ±16.5pA respectively. Though the reported topology has been tailored for glucose/lactate amperometric biosensors of slow temporal dynamics, its parameters can be made to match the conditions of other physiological/physical processes in need of monitoring.