A Novel Multi-Feedback Differential Filter Instrumentation Amplifier for Βiosignals Acquisition Applications

Efficient filtering in biosignals acquisition is challenging. The resistance of the sources exhibits inter- and intra-subject variability or is unknown; thus, using passive filters before the first amplification stage is problematic. Conversely, filtering after amplification does not effectively eliminate the amplified electrical noise, main’s interference, and the artifacts. In this context, the design and utilization of filters in the analog front end of biosensors, in conjunction with the first amplification stage, is not common but offers substantial advantages. In this study, the design of a novel Multi-feedback Differential Filter Instrumentation Amplifier (MFDFIA) is proposed. The design and the equations governing the gain and bandwidth characteristics of the MFDFIA are presented, and relevant topologies are explored. Even though MFDFIA has two op-amps in its first stage, due to its symmetric topology, the analysis can be conducted separately for the differential- and common-mode input signal with a simplified one op-amp equivalent circuit. Notably, MFDFIA’s CMRR is equal and depends only on the CMRR of the second stage. An exemplary simulation for EEG signal acquisition is provided, with a flat band of 1db between 0.7 Hz and 25.4 Hz, a gain of 34.1 db, and an input noise of 70.66 nVrms in the range of 0.1–10 Hz.