A high-input-impedance, low-noise, capacitively-coupled chopper-stabilized instrumentation amplifier for weak bio-signal acquisition is designed in a 180 nm BCD process. Chopper stabilization technique is utilized to mitigate flicker noise and DC offset. To counteract the input impedance degradation introduced by the chopping scheme, a positive feedback loop and pre-charging technique is employed. A DC servo loop is implemented to reject the electrode DC offset. Furthermore, a multi-rate duty-cycled resistor is adopted as the large-value resistor for the integrator within the DC servo loop, aiming to reduce the noise contribution from the DC servo loop itself. Tailored for applications such as electrocardiography or electroencephalography signal processing, the instrumentation amplifier′s -3 dB bandwidth is set to 2 kHz. Post-layout simulation results demonstrate that the amplifier achieves a DC input impedance of 9 GΩ, an input-referred noise of 0.282 μVrms, and a total current consumption of 4.5 μA, corresponding to noise efficiency factor of only 1.63.