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The growing interest toward the improvement of patients' quality of life and the use of medical signals in nonmedical applications such as entertainment, sports, and brain-computerinterfaces, requires the implementation of miniaturized and wireless biopotential acquisition systems with ultralow power dissipation. Therefore, this paper presents the implementation of a complete EEG acquisition ASIC tailored towards the needs of such applications, i.e., high-signal quality, low-power dissipation and ease of use. The presented ASIC includes eight readout front-end channels and an 11-bit analog-to-digital converter (ADC). The key to its high performance and low-power dissipation is the new AC coupled chopper stabilized instrumentation amplifier (ACCIA) implementation that uses a coarse-fine servoloop and reaches more than 120 dB CMRR, consumes only 2.3 muA , and achieves a noise-efficiency factor (NEF) of 4.3. Furthermore, the ease of use of the ASIC is realized by incorporating Calibration and Electrode Impedance Measurement Modes to the ASIC. Therefore, the former can be used to check the functionality of the ASIC, as well as, to calibrate the gain matching of the channels, where as the latter can be used to track the quality of the biopotential electrode. The ASIC is implemented in 0.5 mum CMOS process and the total current consumption is 66 muA from 3 V.
Date of Publication: Dec. 2008