Introduction to Biopotential Acquisition

The biopotential readout circuits have to cope with various problems, while extracting the biopotential signals from the human body. These problems are not only due to the extremely weak characteristics of the biopotential signals but also due to the environment and the apparatus that are being used during the signal acquisition. Therefore, the design of a readout circuit for the biopotential acquisition systems requires a solid understanding of not only the analog circuit design techniques but also the origin and the characteristics of the biopotential signals.

This Chapter gives a brief introduction to the challenges of extracting biopotential signals. Section 2.2 introduces the genesis of the biopotential signals, and presents the frequency and the amplitude characteristics of the EEG, ECG, and EMG signals. Section 2.3 explains the chemistry of the biopotential electrodes, which acts as a transducer between the human body and the readout circuit, and describes the non-ideal characteristics of the biopotential electrodes. Section 2.4 introduces the interference theory, i.e. the theory of the common-mode interference from the mains. This Section also presents the state-of-the-art in IA design, the building block that defines the quality of the extracted signals from the biopotential electrodes. Section 2.5 describes the chopper modulation technique, which is used in the literature to achieve low-noise and high-CMRR IAs. Finally, Sect. 2.6 states the conclusions of this Chapter.