LAUSR

High common-mode rejection ratio (CMRR) of an analog front end (AFE) requires high intrinsic CMRR of the front-end amplifier with high input common-mode (CM) impedance. This article presents a common-mode replication (CM-REP) technique, which replicates the input CM voltage over the front-end amplifier. By eliminating the CM current flow and its mismatch effect, CM-REP improves CMRR and input CM impedance simultaneously. Implementation considerations regarding the input CM range, on-chip, and off-chip parasitics have been discussed with practical techniques incorporated with the proposed CM-REP. Fabricated in a 0.18- $\mu \text{m}$ CMOS technology, the measured instrumentation amplifier (IA) exhibits >130-dB CMRR and 50- $\text{G}\Omega $ input CM impedance at 50/60 Hz concurrently. The >110-dB CMRR is achieved with input CM up to 900 mV_pp and >102-dB total CMRR (TCMRR) is obtained with 1- $\text{M}\Omega \|$ 10-nF mismatch of source impedance. The prototype consumes $1.86~\mu \text{A}$ from a 1.8-V supply and occupies an active area of 0.227 mm².