Silicon Photomultipliers Signals Research Articles

A wide dynamic range front-end electronics for SiPMs using high-speed operational and integration amplifiers

Silicon photomultipliers (SiPM) have gained popularity in particle physics due to their inherent advantages in terms of compactness, low power consumption, and high photon detection efficiency. Moreover, we have to deal with signals ranging from a few photoelectrons (PE), where we need to reconstruct the exact shape, up to thousands of PEs in short time intervals.The design of this amplifier was conceived to handle the SiPMs signal in both cases, combining together a high-speed amplifier for precisely reconstruct the shape of the signals of a few PEs and an integrated one in which the output voltage level is directly proportional to the number of the input PEs.

Novel method to study saturation of silicon photomultiplier in scintillation detector

Signal saturation in the Silicon PhotoMultiplier (SiPM) often causes a serious problem in using a detector equipped with SiPMs for scintillator readout. Conventionally, SiPM signal saturation is measured through direct injection of visible light pulses to the SiPM. However, the method works poorly with the scintillation detector because the effects of the time constant of the emission of scintillation light are not included. Here, we present a novel method to measure the precise degree of SiPM signal saturation in scintillation detectors. The key difference from the conventional method is to use UV light pulses, as opposed to visible light ones, to inject and excite scintillation light in the detector. It allows us to directly measure the degree of saturation in situ taking into account all the major effects in the detector, such as the time constant of the scintillation emission. We also develop a new model for SiPM signal saturation and validate it with the measured degree of saturation with the above-mentioned new method.

Optimization With Simulated Annealing and Experimental Study of a Discretized Position Circuit (DPC) Network Using an Array of SiPMs

Arrays of tens or even hundreds of Silicon Photomultipliers (SiPMs) coupled to scintillators to build compact and robust position sensitive radiation detectors are becoming ubiquitous in nuclear medicine devices. In order to reduce the number of read-out electronic channels, and still be able to keep position information, multiplexing the SiPM signals with 2D resistor networks is fairly common. Good results are obtained with the DPC (Discretized Positioning Circuit) configuration. Even though it is a simple topology with a minimum number of discrete components, it yields good peak/valley ratios. However, it has the disadvantage that the network is asymmetric in X and Y directions, leading to different paths for the signal to reach the output depending on the position of the event. This causes the pulse shape to be also dependent on the position of the interaction in the detector, and creates a distortion (pincushion or barrel) of the position determined with center of energy algorithms. This effect can be partially remedied by a non-homogeneous choice of resistors in the network, but finding the best resistor values, in the case of large SiPM aggregations is very time consuming. We have developed a framework to optimize resistor values in DPC configurations to minimize position distortion and then impose that every SiPMs see an impedance to ground as similar as possible. We solved the DPC circuit and employed a simulated annealing algorithm to explore thousands of resistor combinations. The best combinations found in the computer were implemented in the laboratory confirming the results of the simulated annealing algorithm. In addition, we have verified that the optimized DPC network preserves the pulse shape to the extent that pulse shape discrimination makes it possible to disentangle two different scintillator layers (phoswich) of LYSO and GSO.

Photon-Counting Computed Tomography and Scintillator-Based Detectors: A Simulation Analysis With Scintillating and Reflecting Materials Currently on the Market

During the last decade, Photon-Counting Computed Tomography (PCCT) has been quickly developing and it is expected to revolutionize the X-ray imaging field. Rapid development has also been ongoing in the scintillator and photosensor fields: fast inorganic scintillators have become available on the market and the silicon photomultiplier (SiPM) technology has made substantial progress. Therefore, SiPM-based scintillator detectors may soon be successfully applied in challenging applications like PCCT. In this work, a simulation framework is developed to evaluate detectors composed of scintillators coupled to SiPMs. The idea is to combine Monte Carlo simulations and a library to generate SiPM signals. Focus is given to six fast inorganic scintillators currently on the market (Ce:LYSO, Ce:LuAP, Pr:LuAG, Ce:LuAG, Ce:GGAG (ceramic), Ce:GAGG (single crystal)) and different TiO2-epoxy mixtures. The main properties of scintillating and reflecting materials to be defined in the simulation database are characterised experimentally. Using a virtual model created within this framework, an analysis of the performance in PCCT of a SiPM-based scintillator detector composed of the considered materials is performed. Simulated pulses are processed to report on the count-rate capability. Among the studied crystals, Ce:LYSO would enable sustaining the highest rate of interacting X-ray (2.5 Mcps/pixel with 30% of pile-up). Ce:GAGG could also handle a rate ~ 1 Mcps/pixel with identical pile-up conditions. Other materials show a slow decay time in their scintillation kinetics, implicating a < 1 Mcps/pixel count rate. A qualitative evaluation of the energy binning efficiency is also accomplished, by defining this parameter as a quality metric for multiclass classification. Scintillators with high light yield and good energy resolution (Ce:LYSO, Ce:GAGG and Ce:GGAG) present the best energy binning performance, as expected. The dependence of this aspect is explored as a function of the pulse processing method used, the crystals size and the pile-up probability. Resulting trends respect predictions, even though for a more quantitative analysis a more in-depth study is required.

Next-generation SOlar Neutron TRACking (SONTRAC) instrument

The SOlar Neutron TRACking (SONTRAC) instrument is a novel neutron spectrometer based on proton tracking. The instrument is composed of orthogonally-stacked 1 mm scintillating plastic fibers that are read out by commercially available high-resolution, fine-grain silicon photomultipliers (SiPMs). The fiber pitch is matched to the off-the-shelf 1.36 mm pitch of 8 × 8 arrays of 1 mm SiPMs from Broadcom. SiPM signals are readout by a 32-channel CAEN DT5550W readout system with the A55PET4 with front-end application-specific integrated circuits (ASICs; four Petiroc2 ASICs). The compact, low-power nature of the SiPM interface and ASIC readout translates to a realistic volume, power, and mass budget for a future SmallSAT or probe-class mission. The instrument prototype has been tested with laboratory radiation sources, ground-level muons, and a neutron/proton accelerator beam. We report on the instrument design and performance.

Inter-crystal scattering event identification using a novel silicon photomultiplier signal multiplexing method

Objective. Identifying the inter-crystal scatter (ICS) events and recovering the first interaction position enables the accurate determination of the line-of-response in positron emission tomography (PET). However, conventional silicon photomultiplier (SiPM) signal multiplexing methods based on two-dimensional (2D) charge-division circuits do not allow the detection of multiple gamma-ray interaction positions in a scintillation array coupled with a SiPM array. In this study, we propose a novel multiplexing method that can restore all the individual channel data from a smaller number of multiplexed channels using high-pass filters and neural networks. Approach. The number of output channels is reduced by summing the SiPM signals that have passed through high-pass filters with different time constants. Then, the signal amplitude of each SiPM channel is restored from the combined signal using an artificial neural network. This study explains the principle of this method in detail and demonstrates the results using 4:1 multiplexing as an example. The usefulness of this method was also demonstrated by its application in the identification of ICS events in 1-to-1 coupled LSO-SiPM PET detectors. Main results. The artificial neural network enabled accurate energy estimation for each SiPM channel. One of the high-pass filter sets with the lowest Cramér–Rao lower bound provided the best results, yielding R 2 value of 0.99 between the true and estimated signals. The energy and flood histograms generated using the best-estimated signals were in good agreement with the ground truth. Additionally, the proposed method accurately estimated 2D energy deposit distribution in the LSO crystal array, allowing ICS event identification. Significance. The proposed method is potentially useful for ICS event recovery with a reduced number of array signal readout channels from a SiPM array.

The single-layer readout electronics design and development for CEPC scintillator analog hadronic calorimeter prototype

With the progress in modern high-energy physics, the Standard Model is constantly being refined. As the last brick of the Standard Model, the Higgs boson was confirmed to be discovered in the Large Hadron Collider (LHC) in 2012. For the further exploration of the Higgs boson, the Circular Electron Positron Collider (CEPC) is proposed. The baseline detector concept of CEPC is guided by the particle flow principle. The Particle Flow Algorithm (PFA) reconstructs a list of low-level particles and associates every detector hit with these particles. The high granularity hadronic calorimeter (HCAL) represents an essential component of PFA-based detectors. This paper mainly presents the single-layer electronics design and development for the scintillator analog hadronic calorimeter prototype (AHCAL). The single-layer readout electronics consists of front-end electronics board (FEB) and data interface (DIF) board. The FEB carries the silicon photomultipliers (SiPM), plastic scintillators, and the SiPM signal readout circuit. A single SiPM coupled with a scintillator constitute the basic detection unit. The size of scintillator used here is 4 cm×4 cm. A sensitive area of 72×72 cm2 can be covered by the design presented here. 324 SiPMs coupled with scintillators are mounted on each FEB. Besides the huge sensitive area, The AHCAL prototype must also meet strict requirements on the integration and robustness of the electronics. This paper develops a complete single-layer readout electronics design that meets the requirements for use in the AHCAL. The results of beam test shows that the peak of the minimum ionizing particle (MIP) is separated from the pedestal evidently and the signal-to-noise ratio (SNR) is better than 20. The volume required for the electronics is less than 4 cm3 per channel. In addition, the FEB is sufficiently robust to avoid damage during intercontinental transportation. The development of the single-layer electronics represents significant progress in the design of a prototype device that meets the requirement for use in the CEPC.

Characterisation of the MUSIC ASIC for large-area silicon photomultipliers for gamma-ray astronomy

Large-area silicon photomultipliers (SiPMs) are desired in many applications where large surfaces have to be covered. For instance, a large area SiPM has been developed by Hamamatsu Photonics in collaboration with the University of Geneva, to equip gamma-ray cameras employed in imaging atmospheric Cherenkov telescopes.The sensor being about 1 cm2, a suitable preamplification electronics has been investigated in this work, which can deal with long pulses induced by the large capacitance of the sensor. The so-called Multiple Use SiPM Integrated Circuit (MUSIC), developed by the ICCUB (University of Barcelona), is investigated as a potential front-end ASIC, suitable to cover large area photodetection planes of gamma-ray telescopes.The ASIC offers an interesting pole-zero cancellation (PZC) that allows dealing with long SiPM signals, the feature of active summation of up to 8 input channels into a single differential output and it can offer a solution for reducing power consumption compared to discrete solutions. Measurements and simulations of MUSIC coupled to two SiPMs developed by Hamamatsu are considered and the ASIC response is characterized.

A Comprehensive Study on the Timing Limits of the TOFPET2 ASIC and on Approaches for Improvements

Novel electronic readout schemes of analog silicon photomultipliers (SiPMs) have shown impressive timing performance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula> -detectors in positron emission tomography (PET). However, transferring these novel concepts to the system level is a key to exploit the improved coincidence time resolution (CTR) in (pre-)clinical imaging. In this study, the commercially available TOFPET2 application-specific integrated circuits (ASICs) from PETsys Electronics S.A. is tested in terms of the best achievable CTR. The measurable CTR limits will be obtained by state-of-the-art high-frequency (HF) readout, minimizing the impact of the electronic front end on the time resolution. We achieved (73 ± 1) ps with the HF readout and (134 ± 10) ps with the TOFPET2 ASIC for a Ce-, and Ca-doped lutetium-oxyorthosilcate (LYSO) crystal of 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 3 mm2 size. We show that SiPM signal amplification and an effectively reduced TOFPET2 input stage impedance boost the CTR of a 20-mm high LYSO:Ce crystal to 187 ± 8 ps. Our studies also lead to the observation of side peaks in the coincidence time difference spectrum. These peaks are studied in depth and a conclusion on the ASIC for 100-ps PET applications is drawn.

Performance evaluation of three silicon photomultiplier detector modules within the MAGIC telescopes PMT-based camera

MAGIC is a system of two imaging atmospheric Cherenkov telescopes (IACTs) located on the Canary island of La Palma. Each telescope’s imaging camera consists of 1039 photomultiplier tubes (PMTs). We developed three detector modules based on silicon photomultipliers (SiPMs) of seven pixels each that are mechanically and electronically compatible with those used in the MAGIC camera. These prototype modules are installed next to the PMTs in the imaging camera and are operated in parallel. To achieve a similar active area per pixel we used seven to nine SiPMs for producing a composite pixel. The SiPM signals within one such pixel are actively summed up for retaining the fast signal pulse shapes. Two different PCB designs are tested for thermal performance. We present our simulations of Cherenkov and light of the night sky (LoNS) responses. Based on those we calculate the signal-to-noise ratio (SNR) for this imaging application. We compare our expectations with the measurements of one of the SiPM-based detector modules.

Gamma-Ray Imaging Using Coincident Detection of Cherenkov Photons for Medical Applications

A novel detection concept for high-energy gamma rays for medical applications has been tested using the coincident detection of the Cherenkov photons from Compton-electrons in an optically transparent radiator material. Such detection capability would facilitate imaging of the distribution of certain targeted alpha-emitter therapies and also could be applicable in range verification for proton therapy, which are both connected to prompt gamma emission. To prove the concept, a demonstrator experiment at energies below the MeV scale was conducted: measurements with a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22</sup> Na gamma source emitting two 511-keV photons were performed and the Cherenkov light from Compton and photo electrons in UV transparent polymethyl metacrylate (PMMA) was detected in coincidence. Using a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times 8$ </tex-math></inline-formula> silicon photomultiplier (SiPM) array and fast FPGA-based read-out electronics, efficiency in the order of 0.1 % was achieved. A strong increase up to about 3 % for higher gamma energies up to 1.5 MeV is indicated by the Monte-Carlo simulations. The number of detected Cherenkov photons per event and per channel was counted using the time over threshold (TOT) of the SiPM signal. The measured number of photons and their distribution from accumulated events are in good agreement with simulations, and the measured patterns of photon hits indicate spatial sensitivity. The ability to detect 511-keV photons with the Cherenkov light was demonstrated successfully.

A 4π time-of-flight detector for the ND280/T2K upgrade

ND280 is a near detector of the T2K experiment which is located in the J-PARC accelerator complex in Japan. After a decade of fruitful data-taking, ND280 is scheduled for upgrade. The time-of-flight (ToF) detector, which is described in this article, is one of three new detectors that will be installed in the basket of ND280. The ToF detector has a modular structure. Each module represents an array of 20 plastic scintillator bars which are stacked in a plane of 2.4 × 2.2 m2 area. Six modules of similar construction will be assembled in a cube, thus providing an almost 4π enclosure for an active neutrino target and two TPCs. The light emitted by scintillator is absorbed by arrays of large-area silicon photo-multipliers (SiPMs) which are attached to both ends of every bar. The readout of SiPMs, shaping and analog sum of individual SiPM signals within the array are performed by a discrete circuit amplifier. An average time resolution of about 0.14 ns is achieved for a single bar when measured with cosmic muons. The detector will be installed in the basket of ND280, where it will be used to veto particle originating outside the neutrino target, improve the particle identification and provide a cosmic trigger for calibration of detectors which are enclosed inside it.

Pulse shape analysis of signals from SiPM-based CsI(Tl) detectors for low-energy protons: Saturation correction and particle identification

CsI(Tl) scintillation detectors based on a silicon photomultiplier (SiPM) were tested for low-energy proton detection. Pulse shape analysis of the SiPM signals with a transimpedance amplifier was conducted to investigate the saturation effect due to the recovery time of a pixel and to evaluate particle identification capability. To recover energy linearity, a saturation correction method based on a non-paralyzable dead time model was proposed. The setup using the SiPM with a 25 μm pixel pitch well separated protons and deuterons at energies from 3 to 12 MeV. Additionally, a readout circuit without an amplifier was tested to investigate another type of saturation due to the voltage drop effect.

SiPM signal readout for inter-crystal scatter event identification in PET detectors

In positron emission tomography (PET) with pixelated detectors, a significant number of annihilation photons interact with scintillation crystals through single or multiple Compton scattering events. When these partial energy depositions occur across multiple crystal elements, we call them inter-crystal scatter (ICS) events. ICS events lead to incorrect localization of the annihilation photons, thereby degrading the PET image contrast, spatial resolution, and lesion detectability. The accurate identification of ICS events is the first essential step to improve the quality of PET images by rejecting ICS events or recovering ICS events without losing PET sensitivity. In this study, we propose a novel silicon photomultiplier (SiPM) readout method to identify ICS events in one-to-one coupled PET detectors with a reduced number of data acquisition channels. For concept verification, we assembled a PET detector that consists of a 16-channel SiPM array and 4 4 lutetium oxyorthosilicate (LSO) array with a 3.2 mm crystal pitch. The proposed SiPM readout scheme serializes the 16 SiPM anode signals into four pulse train outputs encoded with four increasing time-delays in steps of 250 ns intervals. A Sum signal of the 16 SiPM anodes provides the timing information for time-of-flight measurement and a trigger signal for coincidence detection. A time-over-threshold (TOT) method was applied for obtaining the energy information followed by a subsequent TOT-to-energy calibration. We successfully identified the ICS events and determined their interacted positions and deposited energies by analyzing the digital pulses from the four pulse train output channels. The occurrence rate of ICS events was 10.85% for the 4 × 4 PET detector module with 3.2 mm-pitch LSO crystals. The PET detector yielded an energy resolution of 10.9 0.6% and coincidence timing resolution of 285 12 ps FWHM. We expect that the proposed method can be a useful solution for alleviating the readout burden of SiPM-based PET scanners with ICS event identification capability.

Highly efficient photon detection systems for noble liquid detectors based on perovskite quantum dots

Wavelength shifting photon detection systems (PDS) are the critical functioning components in noble liquid detectors used for high energy physics (HEP) experiments and dark matter search. The vacuum ultraviolet (VUV) scintillation light emitted by these Liquid argon (LAr) and liquid Xenon (LXe) detectors are shifted to higher wavelengths resulting in its efficient detection using the state-of-the-art photodetectors such as silicon photomultipliers (SiPM). The currently used organic wavelength shifting materials [such as 1,1,4,4 Tetraphenyl Butadiene (TPB)] have several disadvantages and are unreliable for longterm use. In this study, we demonstrate the application of the inorganic perovskite cesium lead bromide (CsPbBr3) quantum dots (QDs) as highly efficient wavelength shifters. The absolute photoluminescence quantum yield of the PDS fabricated using these QDs exceeds 70%. CsPbBr3-based PDS demonstrated an enhancement in the SiPM signal enhancement by up to 3 times when compared to a 3 µm-thick TPB-based PDS. The emission spectrum from the QDs was optimized to match the highest quantum efficiency region of the SiPMs. In addition, we have demonstrated the deposition of the QD-based wavelength shifting material on a large area PDS substrate using low capital cost and widely scalable solution-based techniques providing a pathway appropriate for meter-scale PDS fabrication and widespread use for other wavelength shifting applications.

Over 10 attenuation length gigabits per second underwater wireless optical communication using a silicon photomultiplier (SiPM) based receiver.

Underwater wireless optical communication (UWOC) will play an important role in the underwater environment exploration and marine resource development due to its advantages of high data rate and good mobility. However, the significant signal power attenuation in the underwater channel limits the transmission distance of UWOC. Attenuation length (AL) is widely used as an indicator for evaluating the UWOC system's long-distance transmission capability. At present, Gbps UWOC is limited within 7AL. Using a SiPM based receiver can dramatically increase the AL that UWOC can support. In this paper, a novel UWOC receiver built from an off-the-shelf SiPM has been demonstrated. The finite pulse width and limited bandwidth of SiPM limit the SiPM based UWOC system's data rate. To boost the system's data rate, an optimum method to process the SiPM's signal has therefore been investigated. Based on these methods, the communication capabilities of the SiPM based UWOC have been investigated experimentally. Results show that the SiPM based receiver can support 11.6AL without turbulence and 9.28AL within weak turbulence (scintillation index = 0.0447) at 1 Gbps.

Measurement of liquid argon scintillation light properties by means of an alpha source placed inside the CERN 10-PMT LAr detection system

A particle detection system that exploits the scintillation light produced by ionizing particles in liquid argon (LAr) has been assembled at CERN. The system is based on 10 large-area photomultiplier tubes (PMT) immersed in a 1500-liter dewar filled with liquid argon and equipped with an extendible feed-through and mechanical support for an alpha source (241Am). The position of the source can be changed with respect to the PMT plane in vertical and horizontal directions. Arrays of silicon photomultiplier (SiPM) photodetectors, integrated in the source support, are used for the data acquisition trigger and to define the t0 of the light generation. PMT and SiPM signals can be recorded at different distances and different positions allowing the measurement of some of the LAr scintillation light properties. The system was studied and characterized in detail, and physics results on LAr scintillation properties are expected soon.

Characterisation of SiPM radiation hardness for application in hadron calorimeters at FAIR, CERN and NICA

Silicon PhotoMultipliers (SiPM) are an excellent choice for the scintillator light readout at hadron calorimeters due to their insensitivity to magnetic fields, low operating voltages, low cost, compactness and mechanical endurance. They are already successfully utilized in Projectile Spectator Detector (PSD) of NA61 at CERN, and will be utilized soon in PSD of CBM at FAIR and Forward Hadron CALorimeters (FHCAL) of BM@N at NICA heavy-ion collision experiments. The main issue of SiPM application is their degradation due to high neutron fluence that can reach up to 2×1011 neq/cm2 per year of the experiment operation. Multiple irradiation tests of SiPMs produced by Ketek, Zecotek, Hamamatsu and Sensl manufacturers were conducted at the cyclotron of NPI Řež with a broad neutron spectrum and total fluences in the wide range of 5×1010–6×1012 neq/cm2. Detailed characterisation of all SiPMs was performed based on dependencies of dark current on voltage, capacitance on voltage and frequency, and response to LED light on voltage. SiPM's breakdown voltage, quenching resistance, pixel capacitance, gain and signal to noise ratio were extracted from these measurements. Those parameters' dependence on neutron fluence and their variability are discussed. Performance of the PSD calorimeter module equipped with irradiated SiPMs in CERN during the beam scan with 2–80 GeV/c protons is briefly overviewed.

Characterization of a mixed-sinusoid multiplexing scheme with silicon photomultipliers and an inorganic scintillator

Use of silicon photomultipliers (SiPMs) in radiation detection and imaging systems has been dramatically growing, and, because of their small size, the ability to effectively readout multiple SiPMs in a single channel is a critical objective to developing multichannel SiPM-based systems. Therefore, we have developed a relatively simple multiplexing method for SiPMs based on adding a specific sinusoid to the SiPM signal waveform prior to digitization, where the sinusoid serves as the tagging signal. This method has been previously successfully tested with organic scintillators, and this work characterizes its applicability to inorganic scintillators, specifically LYSO crystals with two different SiPMs. The energy and timing resolution is found to be largely unperturbed by this method for appropriate sinusoids, and excellent signal origin reconstruction is obtained. The ideal tagging sinusoids for adding have frequencies greater than 5 MHz and smaller peak-to-peak amplitudes of approximately 50 mV. The potential to use this method with detection systems comprised of both organic and inorganic scintillators is also demonstrated and discussed in detail.

Wearable, Fiber-less, Multi-Channel System for Continuous Wave Functional Near Infrared Spectroscopy Based on Silicon Photomultipliers Detectors and Lock-In Amplification.

Development and in-vivo validation of a Continuous Wave (CW) functional Near Infrared Spectroscopy (fNIRS) system is presented. The system is wearable, fiber-less, multi-channel (16×16, 256 channels) and expandable and it relies on silicon photomultipliers (SiPMs) for light detection. SiPMs are inexpensive, low voltage and resilient semiconductor light detectors, whose performances are analogous to photomultiplier tubes (PMTs). The advantage of SiPMs with respect to PMTs is that they allow direct contact with the scalp and avoidance of optical fibers. In fact, the coupling of SiPMs and light emitting diodes (LEDs) allows the transfer of the analog signals to and from the scalp through thin electric cables that greatly increase the system flexibility. Moreover, the optical probes, mechanically resembling electroencephalographic electrodes, are robust against motion artifacts. In order to increase the signal-to-noise-ratio (SNR) of the fNIRS acquisition and to decrease ambient noise contamination, a digital lock-in technique was implemented through LEDs modulation and SiPMs signal processing chain. In-vivo validation proved the system capabilities of detecting functional brain activity in the sensorimotor cortices. When compared to other state-of-the-art wearable fNIRS systems, the single photon sensitivity and dynamic range of SiPMs can exploit the long and variable interoptode distances needed for estimation of brain functional hemodynamics using CW-fNIRS.