A Total-CMRR-Boosting Technique Using Common-Mode Signal Replication for Biopotential Recording

The common-mode rejection ratio (CMRR) is a crucial specification for biosignal acquisition systems to capture small biosignals in the presence of large common-mode signals. In electrode-based biopotential recording, simply achieving a high CMRR of the readout front-end is not sufficient. Instead, the total CMRR (TCMRR) (Fig. 1 (top)) should be considered as a more realistic specification [1–4]. The TCMRR includes not only the CMRR of the readout circuit itself but also the nonidealities of the entire recording system, including electrode impedance mismatches. The mismatches in the electrodes and front-end inputs convert the incoming common-mode interference (CMI) to a differential interference signal. This effect can be quantified with a parameter called common-mode-to-differential-mode gain (Acm, dm). The larger $\mathrm{A}_{\mathrm{cm}, \mathrm{dm}}$ is, the more TCMRR degrades.