RESUMEN
Sigma Delta analogue-to-digital converters allow acquiring the full dynamic range of biomedical signals at the electrodes, resulting in less complex hardware and increased measurement robustness. However, the increased data size per sample (typically 24 bits) demands the transmission of extremely large volumes of data across the isolation barrier, thus increasing power consumption on the patient side. This problem is accentuated when a large number of channels is used as in current 128-256 electrodes biopotential acquisition systems, that usually opt for an optic fibre link to the computer. An analogous problem occurs for simpler low-power acquisition platforms that transmit data through a wireless link to a computing platform. In this paper, a low-complexity encoding method is presented to decrease sample data size without losses, while preserving the full DC-coupled signal. The method achieved a 2.3 average compression ratio evaluated over an ECG and EMG signal bank acquired with equipment based on Sigma-Delta converters. It demands a very low processing load: a C language implementation is presented that resulted in an 110 clock cycles average execution on an 8-bit microcontroller.
Asunto(s)
Procesamiento de Señales Asistido por Computador , Electrocardiografía , ElectromiografíaRESUMEN
This article presents the development of a versatile hardware platform for brain computer interfaces (BCI). The aim of this work is to produce a small, autonomous and configurable BCI platform adaptable to the user's needs.
Asunto(s)
Encéfalo/fisiología , Computadores , Interfaz Usuario-Computador , Electroencefalografía , HumanosRESUMEN
Unbalance between electrode-skin impedances is a major problem in biopotential recordings, leading to increased power-line interference. This paper proposes a simple, direct method to measure that unbalance at power-line frequency (50-60 Hz), thus allowing the determination of actual recording conditions for biopotential amplifiers. The method is useful in research, amplifier testing, electrode design and teaching purposes. It has been experimentally validated by using both phantom impedances and real electrode-skin impedances.
Asunto(s)
Amplificadores Electrónicos , Artefactos , Impedancia Eléctrica , Electrodos , Fenómenos Fisiológicos de la Piel , Electricidad , Diseño de Equipo , Análisis de Falla de Equipo , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
In this paper, an analysis of power line interference in two-electrode biopotential measurement amplifiers is presented. A model of the amplifier that includes its input stage and takes into account the effects of the common mode input impedance Z(C) is proposed. This approach is valid for high Z(C) values, and also for some recently proposed low-Z(C) strategies. It is shown that power line interference rejection becomes minimal for extreme Z(C) values (null or infinite), depending on the electrode-skin impedance's unbalance deltaZ(E). For low deltaZ(E) values, minimal interference is achieved by a low Z(C) strategy (Z(C) = 0), while for high deltaZ(E) values a very high Z(C) is required. A critical deltaZ(E) is defined to select the best choice, as a function of the amplifier's Common Mode Rejection Ratio (CMRR) and stray coupling capacitances. Conclusions are verified experimentally using a biopotential amplifier specially designed for this test.