Abstract: A low noise capacitively-coupled chopper instrumentation amplifier which is able to measure small signals is proposed． In this design，chopper is adopted which can make the input common-mode voltage achieve a rail-to-rail range and also has a low power consumption． A two stage folded-cascode opamp is employed to boost the open-loop gain effectively． Furthermore，a ripple reduction loop is used to suppress the chopping ripple at the output of the CCIA ( Capacitively-Coupled Chopper Instrumentation Amplifier ) ． A tunable positive feedback loop based on the MOS capacitors is adopted to boost the input impedance of the CCIA opamp． At last，a DC( Direct Current) cancellation loop is introduced to suppress the electrode offset and to facilitate the weak signal sensing． The CCIA is implemented in a standard 0． 18 μm CMOS ( Complementary Metal Oxide Semiconductor) process． Simulation results show that the gain inaccuracy of proposed CCIA is 0． 11% and the input referred noise is 6． 98 nV at 100 Hz．

Key words: instrumentation amplifier, chopper, low noise, high gain accuracy, ripple reduction, positive feedback loop