Instrumentation amplifier input capacitance cancellation for biopotential and bioimpedance measurements

An instrumentation amplifier (IA) with a mechanism that generates negative capacitances at its input is presented. The IA architecture includes two digitally programmable (8-bit) capacitors between the input stage and the current feedback loop of the IA to cancel the input capacitances from the electrode cables and printed circuit board. The negative capacitance generation technique can improve the input impedance from a few mega ohms to above 500 MΩ without significant impact on performance parameters such as the common-mode rejection ratio (CMRR), power supply rejection ratio (PSRR), total harmonic distortion (THD), and noise. A 93.6 μW IA was designed and simulated using IBM 0.13-μm CMOS technology.