A low power bioimpedance module for wearable systems

• Low power novel architecture for bioimpedance measuring.
• Noise reduction achieved through effective signal processing.
• Breathing measurements: good correlation versus spirometer.
• Cardiac output measurements: good correlation versus Doppler echocardiography.

In the emerging field of wearable systems for remote monitoring of physiological parameters, the measurement of bioimpedance has the potential to provide many useful information. On the other hand, in this scenario, an optimization of power consumption of the circuit is crucial. A low power architecture for the measurement of bioimpedance was identified in this work. It reduces the consumption in the most critical blocks of the system: the current driver, the signal sensing and the demodulator. The device was prototyped and electrically characterized. The compromise between power consumption reduction and the increase in electrical noise was analysed and an effective signal processing technique was developed, showing that it is possible to achieve a signal to noise ratio good enough to enable applications like respiration monitoring (breathing rate and amplitude) or cardiac output estimation. Preliminary tests on healthy subjects showed a good correlation with spirometer, for breathing monitoring, and with Doppler echocardiography, for cardiac output. Thanks to the good functionality and the reduced current consumption (750 μA at 2.8 V power supply was obtained with a discrete-components implementation) the module resulted suitable for the integration in wearable devices for remote monitoring of physiological parameters, or other low power applications.