Exploring FPGA Based Lock-in Techniques for Brain Monitoring Applications

Abstract

Functional Near Infrared Spectroscopy (fNIRS) systems for e-health applications usually suffer of poor signal detection mainly due to a low end-to-end signal to noise ratio of the electronics chain. Lock-In Amplifiers (LIA) historically represent a powerful technique helping to improve performances in such circumstances. In this work it has been designed and implemented a digital LIA system, based on a Zynq® Field Programmable Gate Array (FPGA), trying to explore if this technique might improve fNIRS system performances. More broadly, FPGA based solution flexibility has been investigated, with particular emphasis applied to digital filter parameters, needed in the digital LIA, and it has been evaluated its impact on the final signal detection and noise rejection capability. The realized architecture was a mixed solution between VHDL hardware modules and software ones, running within a softcore microprocessor. Experimental results have shown the goodness of the proposed solutions and comparative details among different implementation will be detailed. Finally a key aspect taken into account throughout the design was its modularity, allowing an ease increase of the input channels while avoiding the growth of the design cost of the electronics system.

Inquiry-based environments for bio-signal processing training in engineering education

“…This second learning activity involved three graduates in the Master’s in Electronic Engineering and one student (performing the Master’s Thesis work). 33 The workshop was focused on the analysis and the processing of real f -NIRS signals, acquired through an innovative instrumentation, developed at the Laboratory ESDP-LAB (Digital Programmable Electronics Systems Laboratory) of the University of Palermo, 34 in the context of the European research project ASTONISH (Advancing Smart Optical Imaging and Sensing for Health). The Astonish project aimed to provide innovative imaging and sensing technologies for applications monitoring, diagnosis and therapeutic treatment, developing an imaging technology, which expands the field of use of minimally invasive diagnosis, making health monitoring possible for any subject independently from clinical status and age (http://www.astonish-project.eu/).…”

“…The system developed at the ESDP-LAB is based on dual-wavelength LEDs that injects infrared light into the scalp and recovers the light, partially diffused and partially dispersed, from the same surface a few centimetres away from the optical source. 34,35 A high number of pairs of source detectors (called f -NIRS channels) leads to a better spatial resolution over the entire head, providing a complete map of cerebral oxygenation. Because the human scalp has quite considerable attenuation values in the infrared region, the detection system has been implemented by means of very sensitive detectors, reaching a single photon counting performance.…”

“…Details about the Astonish experimental set-up can be found in literature. 34,35 The phases and the results of the IO learning activity. The Hemodynamic Response Function (HRF) is the most interesting component contained in the f-NIRS signal.…”

Spectroscopic Techniques versus Pitot Tube for the Measurement of Flow Velocity in Narrow Ducts

“…Once set the function generator and the laser driver, the procedure of synchronization, acquisition and storage is carried out by the FPGA of the NI cRIO. We wrote a dedicated LabVIEW program for data acquisition and for the implementation of a digital lock-in amplifier, according to well-known principles and routines [ 15 , 16 , 17 ]. The lock-in can operate in single and dual-phase mode.…”

A CMOS Self-Contained Quadrature Signal Generator for SoC Impedance Spectroscopy

“…Recent advances in microsensing techniques are leading to a growing need for on-chip electronic instrumentation, not only providing the required performances but also simultaneously complying with the constraints of low power and compact size, to fully satisfy the emerging market demands and potential applications of portable and wearable sensing devices. New transduction techniques in micro-integrated sensors include resonant detection and complex impedance characterization, as in surface acoustic wave sensors [ 1 ], gas sensors [ 2 , 3 , 4 , 5 ], laser interferometry [ 6 ], brain monitoring [ 7 ], non-invasive light detection [ 8 ] or biological impedance measurement [ 9 , 10 ]. For these transducers, a suitable interrogation approach, which presents advantages compared to other electronic readout techniques due to its characteristics, is synchronous demodulation.…”