Design of a biopotential amplifier with large tolerance to CMI and total-CMRR

Abstract

In this thesis, the specications of the previous biopotential ampliers are reviewed in terms ofmaximizing the SNR. Based on the analysis, it is found out that the most important requirementfor maximizing the SNR is the robustness to common-mode interference. In order to enhanceboth tolerance to CMI and T-CMRR simultaneously, a common-mode charge-pump(CMCP)and adaptive CMI cancelling loop are proposed, where CMCP absorbs displacement currentfrom the CMI source and adaptive CMI cancelling loop minimize the CMI shown at the amplieroutput, respectively. A prototype chip fabricated in 180nm CMOS shows that the proposedtechniques preserves the benet of CMCP such as tolerance to CMI, while the T-CMRR isincreased from 66dB to more than 110dB. In addition, the demonstration with two-electrodeECG proves the robustness of the amplier to a large common-mode interference.