Showing papers by "Diego P. Morales published in 2011"

Flexible ECG acquisition system based on analog and digital reconfigurable devices

Abstract: This paper presents an electrocardiogram (ECG) acquisition system based on reconfigurable devices. This system allows redesigning the analog conditioning stage thanks to the use of a Field Programmable Analog Array (FPAA) device, which may be adapted to the requirements of the signal shape and/or medical specifications. Simulated and real ECG signals have been acquired using this system in a three-lead configuration. A detailed study of its technical features has been carried out, showing good suitability for ECG acquisition. Further digital ECG signal processing is performed on a Field Programmable Gate Array (FPGA) device, which has allowed different digital configurations to be tested, including FIR and wavelet filtering and identification of wave features such as the QRS complex. In addition, the FPGA device is in charge of FPAA reconfiguration. Thus, the pairing of FPAA and FPGA devices conforms a compact and versatile bio-signal acquisition platform. This platform has shown very good performance with different types of electrodes, and has also demonstrated the dynamic reconfiguration capabilities of these devices, which enable, for example, the tuning of gain and bandwidth as required by different input conditions and ECG application requirements. The analyzed performance parameters provide values such as 102 dB CMRR (Common-Mode Rejection Ratio), 14-bit ADC resolution, and 75 dB SNR (signal-to-noise ratio), among others, thus satisfying the minimum requirements for clinical use.

Thermal drift reduction with multiple bias current for MOSFET dosimeters

Abstract: New thermal compensation methods suitable for p-channel MOSFET (pMOS) dosimeters with the usual dose readout procedure based on a constant drain current are presented. Measuring the source–drain voltage shifts for two or three different drain currents and knowing the value of the zero-temperature coefficient drain current, IZTC, the thermal drift of source–drain or threshold voltages can be significantly reduced. Analytical expressions for the thermal compensation have been theoretically deduced on the basis of a linear dependence on temperature of the parameters involved. The proposed thermal modelling has been experimentally proven. These methods have been applied to a group of ten commercial pMOS transistors (3N163). The thermal coefficients of the source–drain voltage and the threshold voltage were reduced from −3.0 mV °C−1, in the worst case, down to −70 µV °C−1. This means a thermal drift of −2.4 mGy °C−1 for the dosimeter. When analysing the thermal drifts of all the studied transistors, in the temperature range from 19 to 36 °C, uncertainty was obtained in the threshold voltage due to a thermal drift of ±9mGy (2 SD), a commonly acceptable value in most radiotherapy treatments. The procedures described herein provide thermal drift reduction comparable to that of other technological or numerical strategies, but can be used in a very simple and low-cost dosimetry sensor.

Wavelets for full reconfigurable ECG acquisition system

Abstract: This paper presents the use of wavelet cores for a full reconfigurable electrocardiogram signal (ECG) acquisition system. The system is compound by two reconfigurable devices, a FPGA and a FPAA. The FPAA is in charge of the ECG signal acquisition, since this device is a versatile and reconfigurable analog front-end for biosignals. The FPGA is in charge of FPAA configuration, digital signal processing and information extraction such as heart beat rate and others. Wavelet analysis has become a powerful tool for ECG signal processing since it perfectly fits ECG signal shape. The use of these cores has been integrated in the LabVIEW FPGA module development tool that makes possible to employ VHDL cores within the usual LabVIEW graphical programming environment, thus freeing the designer from tedious and time consuming design of communication interfaces. This enables rapid test and graphical representation of results.

An Imaging Method for Electrical Capacitance Tomography Based on Projections Multiplication

Abstract: In this work, a novel method for the formation of Electrical Capacitance Tomography (ECT) images is presented. This method is based on the modification of the classical algebraic superposition of sensitivity maps, weighted with the inter-electrode capacitance measurements, which is the basis of most of the existing image reconstruction algorithms. The proposed approach replaces this superposition with the scalar multiplication of partial images generated considering only the data corresponding to fixed source electrodes. Results obtained with this proposed method show that the quality of the images can be improved without any image post-processing, which is very interesting especially for real-time applications.