CMOS transimpedance amplifier for biosensor signal acquisition

We present a 1-GΩ CMOS transimpedance amplifier (TIA) suitable for processing sub-nA-level currents in electrochemical biosensor signal-acquisition circuits. Use of a two-stage active transconductor provides resistive feedback in place of a single large-area linear resistor. We engineer the TIA feedback loop to suppress output offset caused by dc input leakage currents of ±0.9 nA. We also implement a mechanism to tune the low-frequency cutoff of the TIA from 0.7 Hz to 500 Hz which permits operation under variable environmental conditions. We report simulated and experimental results from our custom TIA fabricated in a 3.3-V 0.35-μm CMOS process.