Exploring FPGA‐Based Lock‐In Techniques for Brain  Monitoring Applications

Abstract

Functional near-infrared spectroscopy (fNIRS) systems for e-health applications usually suffer from 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 performance in such circumstances. In this work a digital LIA system, based on a Zynq® field programmable gate array (FPGA) has been designed and implemented, in an attempt to explore if this technique might improve fNIRS system performance. More broadly, FPGA-based solution flexibility has been investigated, with particular emphasis applied to digital filter parameters, needed in the digital LIA, and its impact on the final signal detection and noise rejection capability has been evaluated. The realized architecture was a mixed solution between VHDL hardware modules and software modules, running within a microprocessor. Experimental results have shown the goodness of the proposed solutions and comparative details among different implementations will be detailed. Finally a key aspect taken into account throughout the design was its modularity, allowing an easy increase of the input channels while avoiding the growth of the design cost of the electronics system.

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.…”

SILIA: software implementation of a multi-channel, multi-frequency lock-in amplifier for spectroscopy and imaging applications

“…Early lock-in amplifiers were analog devices, while many modern lock-in amplifiers include digital components or implemented on a field programmable gate array. Digital lock-in amplifiers tend to be simpler than their analog counterparts, while also achieving wider bandwidth, greater adjustability, higher dynamic reserve and improved accuracy [2,3,4,5,6]. Software implementations are readily extended to multiple measurement channels and reference frequencies.…”

“…than their analog counterparts, while also achieving wider bandwidth, greater adjustability, higher dynamic reserve and improved accuracy [2][3][4][5][6]. Software implementations are readily extended to multiple measurement channels and reference frequencies.…”

1.0 V-0.18 µm CMOS Tunable Low Pass Filters with 73 dB DR for On-Chip Sensing Acquisition Systems

“…The Frequency Response Analyzer (FRA-EIS) technique is based on dual (0, 90 • ) synchronous demodulation, that is, it uses a technique known as phase-sensitive detection (PSD) to extract at an excitation frequency f 0 the real and imaginary response. As shown in Figure 1b, the signal is typically amplified by an instrumentation amplifier (IA), then a mixer working at the same frequency f 0 (0, 90 • ) demodulates the signal, and a low pass filter (LPF) extracts the DC components X-Y, proportional to the real and imaginary response, while noisy signals at other frequencies filtered [5][6][7][8][9][10][11]. In this case, the LPF is going to be used as a DC magnitude extractor at th last stage of the FRA-EIS read-out system to recover the signal, and it is required to hav an adjustable value in the order of sub-Hz to Hz (Table 1) to adjust the accuracy-spee trade-off.…”