Non-invasive and ambulatory monitoring of body parameters is receiving much interest from the medical, sports and entertainment world. Possible applications are the monitoring of brain waves to detect epilepsy, monitoring of muscle activity during an athlete's training, and monitoring of heart rate during gaming. The idea is to develop small, low-power, autonomous biomedical monitoring systems that collect and process data from human body sensors and wirelessly transmit the data to a central monitoring system.
For clinical applications, electroencephalogram (EEG, brain signals), electrocardiogram (ECG, heart signals), and electromyogram (EMG, muscle signals) are common bio-potential signals that are monitored routinely. Patients are typically connected to a bulky, mains-powered device through cables that reduce their mobility and create discomfort.
Recently, researchers in Eindhoven, The Netherlands (IMEC-NL) developed a flexible and stretchable ECG patch to monitor heart activity. All of the components are embedded in a flexible electronic patch that is covered with textile and standard ECG electrodes are used to attach it to the body. Wearable, wirefree and easy to set-up, the system removes the disturbances and discomfort caused by current cardiac monitoring systems. The ECG patch can fit any body curves and allows optimal, personalized placement of the electrodes. It can, therefore, be used to monitor cardiac activity "on-the-move" in daily-life conditions. Placed on the arm or on the leg, the same system can also be used to monitor muscle activity (EMG).
The core of the wireless ECG patch is a miniaturized wireless sensor node integrated on a flexible, polyimide substrate. A unique asset of the sensor node is the ultra-low-power bio-potential ASIC for monitoring the ECG signal. It is a generic programmable readout ASIC which can extract different bio-potential signals (EEG, ECG and EMG). It efficiently deals with the interference and noise problems correlated with these types of signals, and it exhibits very low power consumption, necessary to enable longterm power autonomy. The bio-potential ASIC consists of an analog readout front-end, an analog-to-digital converter (ADC), and a digital signal processing (DSP) unit. The analog readout frontend is responsible for signal conditioning such as amplification and filtering, and it is the most important building block in terms of signal quality. The ADC converts the output of the analog readout front-end into digital domain, so that the DSP unit can perform the signal analysis.