Technique for Sub-mHz Low-Frequency Corner in Capacitively Coupled Instrumentation Amplifiers

This work introduces a tunable technique to push the low-frequency corner (fL) of capacitively coupled instrumentation amplifiers (CCIAs) to the sub-mHz range for emerging biosensing applications. The proposed approach combines Complementary Transimpedance Boosting (CTB) to limit the DC feedback current and segmented duty-cycled resistors (SDR) for tunable resistance. The CTB-SDR technique achieves a stable effective post-layout pseudo-resistance of 535.8 TΩ, equivalent to fL=660 μHz while occupying 0.062 mm2 in a 180 nm process. According to JESD91 standards, it shows a standard deviation of 0.19 mHz under post-layout Monte Carlo + process analysis, 1.1% spread under voltage variations (±5.56% VDD) and 6.2% under temperature variations (−20 °C, 27 °C, and 60 °C). In addition, duty-cycling calibration can compensate for worst-case process corner variations and mismatch-induced feedback instability.