Single Photon Counting Mode Research Articles

Charge sharing simulations for new digital algorithms achieving subpixel resolution in hybrid pixel detectors

Hybrid pixel detectors are segmented devices used for particles detection, consisting of a sensor and readout electronics. To improve the resolution of the detector and allow operation with high-intensity photon fluxes, the pixel size is reduced. However, with decreasing pixel size, a charge sharing effect is more significant. To detect a photon irrespectively of charge sharing effect, the total photon energy should be reconstructed from fractional signals. Therefore, the algorithms dealing with charge sharing are developed [1–4]. The resolution of such detectors is limited by the pixel size, which must be large enough to fit all the functionality required by the complex algorithms. However, there are known methods that can improve the spatial resolution of a detector applied for high energy physics [5], or astronomy [6–8], and both photon counting detectors [9–11] and integrating detectors [12–14] are used. An alternative digital solution that can be implemented on-chip dedicated to hybrid pixel detectors working in a single photon counting mode is presented in this work. In this approach, charge sharing becomes the desired effect, since the information on the proportions of charge collected by the pixels can be used to estimate the photon interaction position with subpixel resolution. In the work analytical approach towards detector and readout channel modeling is used to state the requirements for the algorithm. The concept of the new digital on-chip algorithm is presented.

Counting Efficiency and Neutron/Gamma Ratio for KDP: Tl+ and UPS-923A Scintillators in a Single Photone Detection Mode

This research related to registration of the fast neutrons with a detector based on the inorganic KDP: TL+ mono crystal (KH2PO4 potassium dihydrogen phosphate) and plastic UPS-923A. The crystal of the KDP: TL+ detector grown from a water solution by the method of lowering the temperature. The high concentration of hydrogen nuclei in the KDP: TL+ crystal grid makes it possible to detect neutron radiation with an efficiency comparable to polystyrene scintillators. KDP: TL+ crystals have a high radiation resistance (up to 1010 neutrons/cm2), which significantly expands the spectrum of their application in high-energy physics applications, intense neutron fields. In this work, we used a technique for recording the detector response in the photon counting mode and pulse filtering mode. Since the detector operates on the principle of detecting gamma quanta from the reactions (n, n 'γ), (n, n' γ)res, (n, γ)cap and others, this makes it possible (in a filtering mode) to isolate the mechanisms of cascade generation processes in the volume of the detector caused by secondary gamma quanta from excited states of compound nuclei. The gamma quanta of the elastic scattering reaction (n, n' γ) for the KDP: TL+ scintillator nuclei are the start of the cascade process of the discharge of excited isomeric states of the input, intermediate, and final nuclei. Measurements of the detection efficiency of fast neutrons were carried out with a KDP: TL+ crystal of size 18x18x42 mm in spherical geometry. The obtained detector reviews in units of impulse / particle for sources and 239Pu-Be and 137Cs were 3.57 and 1.44. In this case, a broadband path with a speed of 7 ns was used. In addition, the counting efficiency of the narrow-band tract measured simultaneously with a processing time of 1 μs and 6.4 μs. The received response from the KDP: TL+ detector (in units of impulse/particle) for both sources 239Pu-Be and 137Cs was 0.09 and 0.00029. The n/γ ratio coefficient was 310. The given measurements of a polystyrene-based scintillator size of 40×40×40 mm. The received response in a single photon-counting mode from the plastic detector (in units of impulse/particle) for both sources 239Pu-Be and 137Cs was 19.4 and 3.9. The n/γ ratio coefficients for detectors are also given: KDP: TL+ - 2.47 and UPS-923A - 4.97 in the 7 ns mode. The statistical error in measurements of the neutron detection efficiency was about ~ 5%.

Optical fiber-based dispersion for spectral discrimination in fluorescence lifetime imaging systems.

.The excited state lifetime of a fluorophore together with its fluorescence emission spectrum provide information that can yield valuable insights into the nature of a fluorophore and its microenvironment. However, it is difficult to obtain both channels of information in a conventional scheme as detectors are typically configured either for spectral or lifetime detection. We present a fiber-based method to obtain spectral information from a multiphoton fluorescence lifetime imaging (FLIM) system. This is made possible using the time delay introduced in the fluorescence emission path by a dispersive optical fiber coupled to a detector operating in time-correlated single-photon counting mode. This add-on spectral implementation requires only a few simple modifications to any existing FLIM system and is considerably more cost-efficient compared to currently available spectral detectors.

Temporally- and Spatially-Resolved Observations of Current Filament Dynamics in Insulated Gate Bipolar Transistor Chip During Avalanche Breakdown

Two-dimensional imaging of the dynamics of current filaments generated in Insulated Gate Bipolar Transistor (IGBT) chip at room temperature during avalanche breakdown has been performed. The images were obtained by using the Hamamatsu TriPHEMOS equipped with the micro-channel plate (MCP) sensor. The equipment can operate in single photon counting mode. From obtained image series, at the beginning of the avalanche breakdown, the emission intensity at the corners in the edge termination region of the IGBT was found to be high. The pixels with high emission intensity of these corners moved to the center of the four sides of the IGBT shape in the latter half of the avalanche breakdown period. Assuming that these pixels with high emission intensity are attributable to the current filament, it shows that the current filaments are moving at a speed of about 0.9 mm/ $\mu \text{s}$ .

FPGA implementation of 10 G Ethernet-based DAQ systems for pixel detectors

High Energy Photon Source-Test Facility is a project to study and verify the feasibility of the key technologies which will be applied to that of High Energy Photon Source (HEPS). The pixel array detector is one of the most important components of synchrotron radiation detection. In order to meet the requirements of the X-ray detection of HEPS, it was asked to independently develop a pixel array detector prototype with an effective detection area larger than $$8 \times 8\,\text {cm}^{2}$$, a spatial resolution better than 200 $$\upmu $$m, a detectable energy range from 8 to 20 keV, and a frame rate higher than 1 kHz. The readout electronics system using the field-programmable gate array (FPGA) as its core of the digital logic makes the basic functions of the detector prototype feasibility by implementing all the configuration and data readout of the BPIX which is the dedicated pixel readout chip designed for Chinese next generation of synchrotron light source and working in the single-photon counting mode. Considering the large amount of data generated by pixel detectors and the demand for real-time data acquisition at higher frame rates, a firmware based on the TCP/IP protocol was developed in FPGA. The implementation of 1 G/10 G Ethernet hub firmware provides a method of processing multi-ports Gigabit data and improving bandwidth. The key idea is the conversion of the GMII/XGMII bus in 1 G/10 G Ethernet protocol and the Arbitrator module applying Round-Robin algorithms. The firmware converts and gathers TCP/IP frames from Gigabit network to 10-Gigabit network successfully. Through measurement, the bandwidth of the hub can reach 8.57 Gbps. A pixel detector integrated with 1 G/10 G Ethernet hub completes the readout of large flux data on 1.5 mega pixels detector at 1.2 kHz frame rate.

Investigating microchannel plate PMTs with TOFPET2 multichannel picosecond timing electronics

TOFPET2 is the second-generation design of a high-performance multichannel picosecond timing readout electronics ASIC produced by PETsys Electronics SA, Portugal. Originally developed for time-of-flight positron emission tomography using silicon photomultipliers, in this work we describe an experimental programme to evaluate the performance of TOFPET2 with pixelated microchannel plate (MCP) photomultiplier tube (PMT) detectors.Investigations were performed using various signal input methods; injected electronic stim signals, SiPM photodetectors, a single anode MCP photomultiplier detector and finally imaging with a demountable multi-anode MCP detector using a 16 x 16 pixelated multi-layer ceramic readout. The detector utilised an active anode plus image charge configuration to provide the positive signal pulses required by the electronics.Measurements were undertaken using the PETsys Time-of-Flight ASIC evaluation kit (mark2) operating in single photon counting mode. We present performance results for time resolution, cross channel coincidence time resolution and energy resolution using internal pulse amplitude measurement and time-over-threshold signal paths.Photodetector timing performance was evaluated using a 40 ps wide pulsed laser, operating at single photon level using a temperature stabilised setup within a dark enclosure. Amplitude walk correction was applied using the in-built time-over-threshold output from the TOFPET2 system. Single photon timing resolution of better than 110 FWHM was demonstrated. Preliminary results obtained using signal spread over adjacent pixels of a pixellated anode yield a coincidence timing resolution of ∼87 ps rms.

Applying Anisotropy to Lubricant Oil Fluorescence to Evaluate Its Physical and Chemical Properties

The development and improvement of fluorescent methods for controlling the working properties of a lubricant in tribosystems is an urgent matter. A method for measuring the decay kinetics of the lubricant fluorescence anisotropy of lubricating oil on a FL900 CTD high-speed fluorometer (Edinburgh Analytical Instruments) in the single-photon counting mode is described in this work. Measurements of the attenuation time of fluorescence anisotropy of new and mineral-oil working in hydraulic systems were made. A correlation was established between the decay time of the fluorescence anisotropy of oils and the product of the dynamic viscosity of the oil and the volume of the fluorescent complex, which can be used in laboratory analysis of the performance of oils, and also in creating methods and devices for on-line diagnostics of friction units.

A 30-frames/s, $252\times144$ SPAD Flash LiDAR With 1728 Dual-Clock 48.8-ps TDCs, and Pixel-Wise Integrated Histogramming

A 252 × 144 single-photon avalanche diode (SPAD) pixel sensor, called Ocelot, is reported for light detection and ranging (LiDAR). The sensor, fabricated in the 180-nm CMOS technology, features 1728 12-bit time-to-digital converters (TDCs) with 48.8-ps resolution (LSB). Each 126 pixels in a half-column are connected to six TDCs through a collision detection bus, which enables effective sharing of resources, and consequently a fill factor of 28% with a pixel pitch of 28.5 μm. The columnparallel TDCs, based on dual-clock architecture, exhibit a DNL of +0.48/-0.48 LSB and an INL of +0.89/-1.67 LSB; they are dynamically reallocated in a scalable daisy chain approach that enables a maximum of five photon detections per illumination cycle per half-column. The sensor can operate in timecorrelated single-photon counting (TCSPC) and single-photon counting (SPC) modes, while peak detection (PD) and partial histogramming (PH) are included in the operation of the sensor. The PD and PH modes are enabled by the first implementation of integrated histogramming for a full array via 3.32-Mb SRAMbased PH readout (PHR) scheme providing a 14.9-to-1 compression. Telemetry measurements up to 50 m achieve an accuracy of 8.8 cm and worst-case precision of 1.4 mm (σ). A flash LiDAR using direct time of flight (dTOF) and based on Ocelot is demonstrated, achieving depth imaging at short distances with a frame rate of 30 frames/s, employing an ultra-low power laser with an average power of 2 mW and peak power of 0.5 W.

A CMOS SPAD Line Sensor With Per-Pixel Histogramming TDC for Time-Resolved Multispectral Imaging

A 512 $\times $ 16 single photon avalanche diode (SPAD)-based line sensor is designed in a 0.13- $\mu \text{m}$ CMOS image sensor technology for time-resolved multispectral beam scanned imaging. The sensor has 23.78- $\mu \text{m}$ pixel pitch and incorporates one SPAD array with 49.31% fill factor optimized for detection in the blue–green spectral region, and a second array at 15.75% fill factor optimized for the red-near-infrared response spectral region. Each pixel contains a 32-bin histogramming time-to-digital converter (TDC) with a mean time resolution of 51.20 ps. Histogram bin resolutions are adjustable from 51.20 ps to 6.55 ns per bin. The line sensor can operate in single photon counting (SPC) mode (102.1 giga-events/s), time-correlated SPC (TCSPC) mode (192.4 million-events/s) or on-chip histogramming mode (16.5 giga-events/s), increasing the count rate up to 85 times compared to TCSPC mode. Sensor capability is demonstrated through spectral fluorescence lifetime imaging, resolving three fluorophore populations with distinct fluorophore lifetimes.

EDLD-Tool: A real-time GPU-based tool to stream and analyze energy-dispersive Laue diffraction of BIG Data sets collected by a pnCCD

Energy-dispersive Laue diffraction (EDLD) is a tool for the characterization of single-crystalline and polycrystalline materials. Using a two-dimensional energy-dispersive detector, both the angular positions and the diffracting energies of the Laue spots can be analysed without additional information, allowing for fast indexing, determination of the crystal structure and the respective lattice parameters. Running the detector at ≈ 400 Hz, a typical data set (≈ 10 min) taken by the single photon counting mode has a size of ten Gigabytes. Up to now, problems such as data transfer, data storage, data reduction and on time data analysis are drawbacks for wider application of this technique. A fast and effective algorithm for processing of these BIG Data is required to overcome the drawbacks and to allow for quality assessment of the running experiment in real time. This paper presents a GPU based tool for energy-dispersive Laue diffraction (EDLD) experiments, named “EDLD-Tool”, providing the optimization of geometric parameters of the experiment, auto-indexation, online steering, error detection and determination of all crystal parameters considering pnCCD data taken from a single crystal. This tool is exploiting parallel computing technology of the GPU and makes use of many scientific, high performance libraries (i.e. OpenCV, Root-Cern, Eigen and others). As a result, the developed tool allows for data processing in the time frame of few seconds compared to the previous analysis system which requires few hours to process the same amount of data.

The Threshold of Detection of Fission Materials by ZnWO4 and Bi4Ge3O12 Scintillation Detectors

In the present work we found the maximum discovery distance for 239Pu-Be source using the detectors based on ZWO (ZnWO4) and BGO (Bi4Ge3O12) oxide scintillators. Detection distance was defined by using the radiation monitoring system ”PORTAL”. This research gives us data for estimation of the contribution of low-energy cascade gamma quanta CGQ. The CGQ emitted by excited scintillator nuclei defined the effective discovery distance of the fast neutrons source. The maximum detection distance was obtained with PMT in a single-photon counting mode. The maximum discovery distance for a BGO scintillator of size Ø40×40 mm – 38 cm, ZWO scintillator of size Ø52×40 mm – 54 cm, with reliability about 0.001. The results of the experiment on the ZWO scintillator can be explained by the registration of additional gamma quanta from the inelastic scattering reaction and the CGQ arising from resonant neutron capture region. This two mechanisms further lead to increase the sensitivity of the detector and increase the detection distance of the monitoring system. The key features of the monitoring system are: ZWO oxide scintillator, wide band measuring path, utilize PMT in single photon mode. The obtained detection distance was about 1.4 times higher in comparison with the spectrometric recording mode and 1.9 times higher in values of efficiency. Our results demonstrate the advantages of the ZWO scintillator compared to the BGO and demonstrate the possibility of using the resonant capture mechanism by ZWO detector nuclei to increase the fast neutrons sensitivity. The resonance capture mechanism increase sensitivity and maximum detection distance of the monitoring system. The low-energy gamma-quanta, which discharge of compound nuclei, are substantially suppressed in comparison with the classic spectrometric recording mode.

Improvement of TimePix energy resolution correcting threshold variations

The Timepix detector is an important tool in spectroscopic imaging since it allows the determination of the energy of absorbed photons using its time over threshold capability. In this paper, however, we look at the energy resolution using the single photon counting mode combined with threshold scans. The pixel circuit of the TimePix detector involves a discriminator logic, which compares the collected amount of charge in each pixel with a threshold level (THL). The counter is incremented only if the induced signal surpasses this threshold. The THL is typically calibrated w.r.t. energy in the proximity of the noise edge, however, due to gain mismatch of the individual pixels, the threshold levels of pixels deviate if a DAC value far from the calibration point is set. This energy threshold mismatch far from the calibration point was corrected in this paper based on spectrum matching between individual pixels. The derived method is compared to straightforward calibration using multiple monochromatic peaks. To this end a threshold scan was performed using a TimePix Si-1mm detector (utilizing counting priciples) in presence of a Am-241 gamma source. The peak at energy 59.5 keV was fitted for each pixel to determine the actual THL values for all pixels at this energy. Then the full spectrums for all pixels were matched, using one fixed point. The matching process gave us two matrices of correction factors, the first matrix corrects the THL gain and the second its offset. In a second evaluation we measured and fitted the x-ray fluorescence of zirconium and copper during threshold scan in addition to the Am-241 peak. The gain and offset of each pixel were then determined by linear fit of the peak positions. The two calibration methods were evaluated by measuring the full width of half maximum FWHM of two other fluorescence peaks (23.17 keVand 26.2 keV peaks of cadmium). The evaluation shows that linear fit of multiple peaks results in a comparable FWHM (reduction of 21%) over spectrum matching the (reduction of 20%), while, opposite to spectrum matching, necessitating multiple measurement setps and THL scans.

Addressing of imperfection of a hybrid pixel sensor for X-ray detection with a circuit for charge sharing cancellation implemented

A developing trend in the design of event-driven sensors for X-ray detection are hybrid pixel detectors working in the single photon counting mode. The factors limiting detector performance, especially for small pixel sizes, include among others, mismatch of circuit components due to process variations, electronic noise and charge sharing. Charge sharing in a hybrid pixel detector occurs when the charge generated in X-ray photon interaction with a sensor is collected by more than one pixel. Charge sharing effect may significantly impair the detector energy resolution and result in counting extra events or missing some of the events. The impact of the charge sharing increases with a decrease of the pixel sizes. The small pixel size is a desired feature of a novel hybrid X-ray detector, as it allows better spatial resolution and helps to overcome the high count rate limits by accepting more photons per unit area. Therefore, the charge sharing effect must be dealt with by a dedicated readout IC or processed off-chip. Minimization of the analog parameters dispersion in the pixel matrix is crucial for the circuits designed for charge sharing cancellation. The chip's sensitivity to the analog parameters spread and mitigation of the performance achieved with the digital correction blocks are studied. The DC offsets and gains spread can be optimized using correction circuits and dedicated trimming algorithms. Detection efficiency in case of charge sharing for the corrected and uncorrected pixel matrix is addressed. The simulation results as well as pencil beam measurements using synchrotron radiation are presented.

Operation of microchannel plate PMTs with TOFPET multichannel timing electronics

We describe an experimental programme to evaluate TOFPET multichannel timing electronics using microchannel plate PMTs in single photon counting mode. Time resolution measurements were made using: (i) the on-board electronic stim signal; (ii) a Photek PMT210 high speed single anode MCP photomultiplier detector, and; (iii) imaging with a PMT240MA multi-anode MCP detector using a pixelated multi-layer ceramic readout. Experimental measurements using an electronic stim with the ASIC electronics gave a time resolution of 43 ps rms. Detector timing of the PMT210 detector was evaluated using a 40 ps wide pulsed laser with amplitude walk correction using the time over threshold capability of the TOFPET electronics. Single photon timing resolution of better than 100 ps rms was demonstrated. Furthermore, 256 discrete pixel imaging has been demonstrated by coupling a multi-anode pixelated MCP detector to the TOFPET system. • First result for coupling TOFPET electronics to microchannel plate detectors. • 43 picosecond electronic time resolution measured. • Photon-counting with 96 picosecond time resolution. • 256 pixel ultra-fast microchannel plate imaging demonstrated. • Amplitude walk correction improves timing resolution from 225 to 96 picoseconds.

Simulation approach to charge sharing compensation algorithms with experimental cross-check

Hybrid pixel detectors for X-ray imaging, working in a single photon counting mode, find applications in a variety of fields, such as medical imaging, material science or industry. However, charge sharing, which occurs when a photon hits a detector in the area between two or four pixels, becomes more significant with decreasing pixel size. If the charge generated when a photon interacts with a detector is collected by more than one pixel, the photon energy and the event position may be improperly detected. Therefore, algorithms for minimization of the impact of charge sharing on a pixel detector for X-ray detection need to be implemented. Firstly, such algorithms must be assessed on a simulation level. The goal is to implement the simulations in such a way that the simulation accuracy and simulation time are optimized. A model should be flexible enough so that it can be quickly adapted for other uses. We propose behavioral models implemented in the Cadence® Virtuoso® environment. This is a solution that enables fast validation of the system at the higher level of abstraction allowing deep verification. A readout channel of a chip is represented using parameterized behavioral blocks of different functionality, such as, a charge sensitive amplifier, shapers, discriminators, comparators. The inter-pixel connections are taken into account. This approach enables top-down design and optimization of parameters. The model was implemented in particular to test the C8P1 algorithm used in the Chase Jr. chip, however, due to its modular implementation, it can be easily adjusted to further test of the algorithms. The simulation approach is described and the simulation results are presented together with the experimental data obtained during synchrotron measurements for the Chase Jr. chip with the C8P1 algorithm implemented.

Laboratory Setup for Scanning-Free Grazing Emission X-ray Fluorescence.

Grazing incidence and grazing emission X-ray fluorescence spectroscopy (GI/GE-XRF) are techniques that enable nondestructive, quantitative analysis of elemental depth profiles with a resolution in the nanometer regime. A laboratory setup for soft X-ray GEXRF measurements is presented. Reasonable measurement times could be achieved by combining a highly brilliant laser produced plasma (LPP) source with a scanning-free GEXRF setup, providing a large solid angle of detection. The detector, a pnCCD, was operated in a single photon counting mode in order to utilize its energy dispersive properties. GEXRF profiles of the Ni-Lα,β line of a nickel-carbon multilayer sample, which displays a lateral (bi)layer thickness gradient, were recorded at several positions. Simulations of theoretical profiles predicted a prominent intensity minimum at grazing emission angles between 5° and 12°, depending strongly on the bilayer thickness of the sample. This information was used to retrieve the bilayer thickness gradient. The results are in good agreement with values obtained by X-ray reflectometry, conventional X-ray fluorescence and transmission electron microscopy measurements and serve as proof-of-principle for the realized GEXRF setup. The presented work demonstrates the potential of nanometer resolved elemental depth profiling in the soft X-ray range with a laboratory source, opening, for example, the possibility of in-line or even in situ process control in semiconductor industry.

Detailed calibration of the PI-LCX:1300 high performance single photon counting hard x-ray CCD camera**Project supported by the Science Foundation of China Academy of Engineering Physics (Grant Nos. 2013A0103003 and 2012B0102008) and the National High-Tech Inertial Confinement Fusion Committee of China.

X-ray charge-coupled-device (CCD) camera working in single photon counting mode is a type of x-ray spectrometer with high-sensitivity and superior signal-to-noise performance. In this study, two single photon counting CCD cameras with the same mode (model: PI-LCX: 1300) are calibrated with quasi-monochromatic x-rays from radioactive sources and a conventional x-ray tube. The details of the CCD response to x-rays are analyzed by using a computer program of multi-pixel analyzing and event-distinguishing capability. The detection efficiency, energy resolution, fraction of multi-pixel events each as a function of x-ray energy, and consistence of two CCD cameras are obtained. The calibrated detection efficiency is consistent with the detection efficiency from Monte Carlo calculations with XOP program. When the multi-pixel event analysis is applied, the CCDs may be used to measure x-rays up to 60 keV with good energy resolution (E/ΔE ≈ 100 at 60 keV). The difference in detection efficiency between two CCD cameras is small (5.6% at 5.89 keV), but the difference in fraction of the single pixel event between them is much larger (25% at 8.04 keV). The obtained small relative error of detection efficiency (2.4% at 5.89 keV) makes the high accurate measurement of x-ray yield possible in the laser plasma interaction studies. Based on the discrete calibration results, the calculated detection efficiency with XOP can be used for the whole range of 5 keV–30 keV.

HEPS-BPIX, a hybrid pixel detector system for the High Energy Photon Source in China

A hybrid pixel detector with single photon counting mode has been designed for the High Energy Photon Source in China. It features a pixel size of 150 μm × 150 μm and a frame rate up to 1.2 kHz with 20-bit dynamic range. Six modules were assembled as the first prototype system, covering an area of 9 cm × 10 cm with 360k pixels. Images have been taken using X-ray and synchrotron radiation light, and the preliminary detector performance is presented.

HEPS-BPIX, a single photon counting pixel detector with a high frame rate for the HEPS project

China's next generation light source, named the High Energy Photon Source (HEPS), is currently under construction. HEPS-BPIX (HEPS-Beijing PIXel) is a dedicated pixel readout chip that operates in single photon counting mode for X-ray applications in HEPS. Designed using CMOS 0.13µm technology, the chip contains a matrix of 104×72 pixels. Each pixel measures 150µm×150µm and has a counting depth of 20bits. A bump-bonded prototyping detector module with a 300-µm thick silicon sensor was tested in the beamline of Beijing Synchrotron Radiation Facility. A fast stream of X-ray images was demonstrated, and a frame rate of 1.2kHz was proven, with a negligible dead time. The test results showed an equivalent noise charge of 115e−rms after bump bonding and a threshold dispersion of 55e−rms after calibration.

Development of Gated Pinned Avalanche Photodiode Pixels for High-Speed Low-Light Imaging

This work explores the benefits of linear-mode avalanche photodiodes (APDs) in high-speed CMOS imaging as compared to different approaches present in literature. Analysis of APDs biased below their breakdown voltage employed in single-photon counting mode is also discussed, showing a potentially interesting alternative to existing Geiger-mode APDs. An overview of the recently presented gated pinned avalanche photodiode pixel concept is provided, as well as the first experimental results on a 8 × 16 pixel test array. Full feasibility of the proposed pixel concept is not demonstrated; however, informative data is obtained from the sensor operating under −32 V substrate bias and clearly exhibiting wavelength-dependent gain in frontside illumination. The readout of the chip designed in standard 130 nm CMOS technology shows no dependence on the high-voltage bias. Readout noise level of 15 rms, full well capacity of 8000, and the conversion gain of 75 µV are extracted from the photon-transfer measurements. The gain characteristics of the avalanche junction are characterized on separate test diodes showing a multiplication factor of 1.6 for red light in frontside illumination.