At the International Solid State Circuit Conference, IMEC presents a complete 200µW 8-channel EEG (electro-encephalogram) acquisition ASIC (application-specific integrated circuit) suitable for miniaturized ambulatory EEG measurement systems. The ASIC meets the requirements for clinical EEG systems. Gain and filtering is programmable making it suitable for a wide range of ambulatory EEG applications.
IMEC’s EEG acquisition ASIC comprises eight programmable readout channels, an 11bit ADC (analog to digital convertor) to digitize the amplified and filtered EEG signals, a square-wave oscillator to generate the 1MHz clock for the ADC and a bias circuit. Besides the acquisition function, it also comprises calibration of the readout channels and enables measurement of the impedance of the bio-potential electrodes.
The ASIC, fabricated in a 0.5µm CMOS process, measures 17.55mm2 and consumes only 200µW. Such low power consumption makes it capable of operating for more than 1 month from a standard coin cell battery like a CR2032, making it ideal for autonomous applications.
EEG signals are µV-range low-frequency signals that suffer from a large amount of common-mode (CM) interference. Furthermore, the bio-potential electrodes that are needed to view the signals generate a non-negligible offset. To achieve signal extraction, the ASIC requires readout front-ends with high common-mode rejection ratio (CMRR), low-noise, and high-pass filter characteristics to filter the differential electrode offset voltage. The implemented front-end is based on AC-coupled chopper-stabilized instrumentation amplifiers with a DC-servo loop outside the choppers for the high-pass filtering. Each channel has adjustable high-pass filtering (cut-off at 0.1Hz) and the gain and bandwidth is electronically selectable. The front-ends achieve the lowest noise-efficiency factor (4.1) and the highest common-mode rejection ratio (CMRR >120dB) ever reported. The large input impedance (>1G) ensures high CMRR even if there is a mismatch between the electrode impedances. Meeting the critical IFCN (International Federation of Clinical Neurophysiology) requirements makes this ASIC applicable for clinical EEG systems.
The EEG ASIC is suitable for miniaturized ambulatory EEG acquisition systems which increase the patient’s autonomy and quality of life. It’s also applicable for sports devices, entertainment, comfort monitoring, and other health and lifestyle products and services. Interested parties can license the ASIC for further product development.
IMEC is a world-leading independent research center in nanoelectronics and nanotechnology. Its research focuses on the next generations of chips and systems, and on the enabling technologies for ambient intelligence. IMEC’s research bridges the gap between fundamental research at universities and technology development in industry. Its unique balance of processing and system know-how, intellectual property portfolio, state-of-the-art infrastructure and its strong network of companies, universities and research institutes worldwide position IMEC as a key partner for shaping technologies for future systems. IMEC vzw is headquartered in Leuven, Belgium, has a sister company in the Netherlands, IMEC-NL, concentrating on wireless autonomous transducer solutions, and has representatives in the US, China and Japan. Its staff of more than 1600 people includes more than 500 industrial residents and guest researchers. In 2007, its revenue (P&L) is estimated at about EUR 235 million.