A High‐Input‐Impedance Chopper‐Stabilized Current‐Feedback Instrumentation Amplifier for High‐Precision Multimeter Front Ends

Instrumentation amplifiers are essential front‐end circuits in high‐precision digital multimeters, since their noise, offset, common‐mode rejection, and input impedance directly determine measurement accuracy. Current‐feedback instrumentation amplifiers (CFIAs) offer high precision and high common‐mode rejection, but chopping, although effective in suppressing low‐frequency noise and offset, introduces dynamic charge transfer through the input switches and reduces the effective input impedance. This paper presents a high‐input‐impedance chopper‐stabilized CFIA based on synchronous chopping and port swapping (SCPS). By synchronizing chopping with port swapping between the input and feedback paths, the proposed scheme reduces the average input charge transfer. A common‐mode differential amplifier (CMDA) matches the input and feedback common‐mode voltages, and an AC‐coupled ripple‐cancelation loop (ARCL) suppresses chopping ripple. The amplifier is designed and verified by post‐layout simulation in SMIC 0.18‐μm BCDE process. Post‐layout simulation results show that the input impedance increases from 1.75 MΩ to 2.7 GΩ, with 81‐dB ripple suppression, 5‐nV/√Hz input‐referred noise over 10 Hz to 1 kHz, less than 15‐μV input offset, and 130‐dB worst‐case CMRR at 100 Hz.