A 130-dB CMRR Instrumentation Amplifier with Common-Mode Replication

Abstract

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- {m} CMOS technology, the measured instrumentation amplifier (IA) exhibits >130-dB CMRR and 50- {G}Omega input CM impedance at 50/60 Hz concurrently. The >110-dB CMRR is achieved with input CM up to 900 mVpp and >102-dB total CMRR (TCMRR) is obtained with 1- {M}Omega | 10-nF mismatch of source impedance. The prototype consumes 1.86{A} from a 1.8-V supply and occupies an active area of 0.227 mm2.