A novel approach for the design of fast-settling amplifiers for biosignal detection

E. Alonso, G. Scandurra, C. Ciofi, C. Rodríguez-Morcillo, R. Giannetti

Electronics Vol. 10, nº. 21, pp. 2631-1 - 2631-14

Summary:

The most common method used to pick up biomedical signals is through metallic electrodes coupled to the input of high-gain, low-noise amplifiers. Unfortunately, electrodes, amongst other effects, introduce an undesired contact resistance and a contact potential. The contact potential needs to be rejected since it would otherwise cause the saturation of the input stage of the amplifiers, and this is almost always obtained by inserting a simple RC high-pass filter in the input signal path. The contact resistance needs to be estimated to ensure that it does not impair correct measurements. Methods exist for estimating the contact resistance by dynamically modifying the input network configuration, but because of the presence of the input RC filter, long transients are induced any time a switch occurs between different input configurations, so that the measurement time may become unacceptably long. In this paper, we propose a new topology for a DC removal network at the input of the differential signal amplifier that results in an AC filter whose time constant can be continuously changed by means of a control voltage. As such, we can speed up the recovery from transients by setting very short time constants (during the input resistance estimation process) while maintaining the ability to obtain very low cut-in frequencies by setting a much larger time constant during actual measurements. A prototype of the system was built and tested in order to demonstrate the advantage of the approach we propose in terms of reduced measurement time.

Spanish layman's summary:

En este trabajo presentamos una solución circuital innovadora que permite cambiar la frecuencia de corte inferior de un amplificador diferencial acoplado en AC de forma continua, mediante una tensión de control,  y sin crear transitorios durante el ajuste.

Se ha comprobado la efectividad del sistema en caso de medidas de señales biomédicas.    

English layman's summary:

The article introduces a novel circuit topology to change the cut-in frequency of an AC-coupled differential amplifier by way of an external control voltage. The cut-in frequency can be changed in a smooth way without introducing spurious transients. The system has been tested in a biomedical signal adquisition setup.

Keywords: differential amplifier; DC removal; biological signals; electrode potential

JCR Impact Factor and WoS quartile: 2,690 - Q3 (2021); 2,600 - Q2 (2023)

DOI reference: https://doi.org/10.3390/electronics10212631

Published on paper: November 2021.

Published on-line: October 2021.

Citation:
E. Alonso, G. Scandurra, C. Ciofi, C. Rodríguez-Morcillo, R. Giannetti, A novel approach for the design of fast-settling amplifiers for biosignal detection. Electronics. Vol. 10, nº. 21, pp. 2631-1 - 2631-14, November 2021. [Online: October 2021]