An Eight-Channel Active Electrode System

Abstract

To fulfill the needs of digitization and continuous EEG recording, this chapter presents a complete eight-channel AE system, including both active electrodes and a back-end analog signal processing unit. Furthermore, the system can also measure electrode-tissue impedance (ETI), i.e., the complex impedance between an electrode and skin. ETI measurement extends an AE system’s functionality by enabling the remote assessment of electrode status and by recording ETI-related motion artifacts. The complete eight-channel AE system consists of nine AEs and one back-end (BE) analog signal processor (ASP). The new AEs, based on a non-inverting chopper IA architecture, provide better performance on input impedance and noise. The BE ASP post-processes and digitizes the AEs’ analog outputs, such that the system can be connected to a generic microcontroller through a serial-to-parallel interface (SPI). At the system level, a common-mode feedforward (CMFF) technique improves the CMRR of a pair of AEs by 25 dB.