An 11 \mu w, two-electrode transimpedance biosignal amplifier with active current feedback stabilization

• Published in: IEEE transactions on biomedical circuits and systems 2010-04, Vol.4 (2), p.93-100
• Main Authors: Inan, O.T., Kovacs, G.T.A.
• Format: Article
• Language: English
• Subjects: Bandwidth; Biosignal amplifier; electrocardiogram; Electrocardiography; Energy consumption; Feedback circuits; Force feedback; Immune system; Operational amplifiers; portable physiological monitoring; Power measurement; Rail to rail amplifiers; Voltage
• ISSN: 1932-4545; 1940-9990
• DOI: 10.1109/TBCAS.2009.2032096

A novel two-electrode biosignal amplifier circuit is demonstrated by using a composite transimpedance amplifier input stage with active current feedback. Micropower, low gain-bandwidth product operational amplifiers can be used, leading to the lowest reported overall power consumption in the literature for a design implemented with off-the-shelf commercial integrated circuits (11 μW). Active current feedback forces the common-mode input voltage to stay within the supply rails, reducing baseline drift and amplifier saturation problems that can be present in two-electrode systems. The bandwidth of the amplifier extends from 0.05-200 Hz and the midband voltage gain (assuming an electrode-to-skin resistance of 100 kΩ) is 48 dB. The measured output noise level is 1.2 mV pp , corresponding to a voltage signal-to-noise ratio approaching 50 dB for a typical electrocardiogram (ECG) level input of 1 mV pp . Recordings were taken from a subject by using the proposed two-electrode circuit and, simultaneously, a three-electrode standard ECG circuit. The residual of the normalized ensemble averages for both measurements was computed, and the power of this residual was 0.54% of the power of the standard ECG measurement output. While this paper primarily focuses on ECG applications, the circuit can also be used for amplifying other biosignals, such as the electroencephalogram.