BIOSIGNAL ACQUISITION DEVICE
A Novel Topology for Wearable Signal Acquisition Devices
Luca Maggi, Luca Piccini, Sergio Parini, Giuseppe Andreoni
Dipartimento di Bioingegneria of Politecnico di Milano - Milan, Italy
Guido Panfili
SXT – Sistemi per telemedicina srl. – Lecco, Italy
Keywords: Wearable device, Brain Computer Interface, Amplifier, Signal Conditioning, Offset Recovery, Low Voltage
Amplifier, Band Pass Filtering, ECG amplifier, EEG amplifier.
Abstract: The here presented work illustrates a novel circuit topology for the conditioning of biomedical signals. The
system is composed of an amplification chain and relies on a double feedback path which assures the
stability of the system, regardless of the amplification block gain and the order of the low-pass filter
settings. During the normal operation, the offset recovery circuit has a linear transfer function, when it
detects a saturation of the amplifier, it automatically switches to the fast recovery mode and restores the
baseline in few milliseconds. The proposed configuration has been developed in order to make wearable
biosignal acquisition devices more robust, simpler and smaller. Thanks to the used AC coupling method,
very low high-pass cut-off frequencies, can be achieved even using small valued passive components with
advantages in terms of circuit bulkiness. The noise rejection filter between the pre-amplification and the
amplification stages eliminates the out-of-band noise before the amplification reducing the possibility of
having clipping noise and minimizing the dynamic power consumption. The presented topology is currently
used in a prototypal EEG acquisition device in a Brain Computer Interface (BCI) system, and in a
commercial polygraph which will be soon certificated for clinical use.
1 INTRODUCTION
Wearable systems ought to be totally unobtrusive
devices that allow physicians to overcome the
limitations of standard ambulatory technology,
aiming at providing a response to the need for
monitoring individuals over weeks or even months
without or limiting their usual behaviour. Such a
systems typically rely on wireless, miniature sensors
embedded in patches, bandages, or in items that can
be worn, such as a ring or a shirt. They take
advantage of hand-held units to temporarily store
physiological data, which can be uploaded
periodically to a database server through a wireless
LAN or different gateways that allow Internet
connection. The data sets recorded using these
systems are then processed to detect events able to
indicate a possible worsening of the patient’s clinical
situation or providing information explored to assess
the impact of clinical interventions (Park, 2003).
Wearable devices are usually battery powered:
low voltage supply and low power consumption are
mandatory features for this kind of devices, in order
to provide a good battery life to dimension ratio. In
the last 10 years many garments with embedded
sensors have been developed: the intrinsic
characteristics of such electrodes and the possible
instability of the contact make the design of
wearable acquisition devices more difficult
(Webster, 1991). The main aspects we have to take
into account in the design of a wearable surface
biopotential amplifier (e.g. Electrocardiogram-ECG,
Electroencephalogram–EEG and Electromiogram-
EMG) are:
• Dynamic reserve;
• Max offset rejection;
• Fast recovery from artefacts.
Although the operational amplifiers production
technology has developed several low power and
low cost devices, the development of dedicated
397
Maggi L., Piccini L., Parini S., Andreoni G. and Panfili G. (2008).
BIOSIGNAL ACQUISITION DEVICE - A Novel Topology for Wearable Signal Acquisition Devices.
In Proceedings of the First International Conference on Bio-inspired Systems and Signal Processing, pages 397-402
DOI: 10.5220/0001059703970402
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