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This paper describes a 64 $\times $ 64-pixel 3-D imager based on single-photon avalanche diodes (SPADs) for long-range applications, such as spacecraft navigation and landing. Each 60- \mu \text{m} pixel includes eight SPADs combined as a digital silicon photomultiplier, a triggering logic for photons temporal correlation, a 250-ps 16-b time-to-digital converter, and an intensity counter, with an overall 26.5% fill factor. The sensor provides time-of-flight and intensity information even with a background intensity up to 100 MPhotons/s/pixel. The sensor can work in imaging (short range, 3-D image) and altimeter (long range, single point) modes, achieving up to 300-m and 6-km maximum distance with <0.2-m and <0.5-m precision, respectively, consuming less than 100 mW. [ABSTRACT FROM AUTHOR]

Cross-talk characterization results of high-fill-factor single-photon avalanche diode (SPAD) arrays in CMOS 150-nm technology are reported and discussed. Three different SPAD structures were designed with two different sizes (15.6 and 25.6  μm pitch) and three guard ring widths (0.6, 1.1, and 1.6  μm). Each SPAD was implemented in an array, composed of 25 (5×5) devices, which can be separately activated. Measurement results show that the average cross-talk probability is well below 1% for the shallow-junction SPAD structure with 15.6  μm pitch and 39.9% fill factor, and 1.45% for the structure with 25.6  μm pitch and 60.6% fill factor. An increase of cross-talk probability with the excess bias voltage is observed. [ABSTRACT FROM AUTHOR]

A single-photon, time-gated, 160 \times 120 pixel imager is presented for its application in fluorescence lifetime imaging microscopy. Exploiting single-photon avalanche diodes and an extremely compact pixel circuitry—only seven MOSFETs and one MOSCAP—the imager is capable of gathering information about photon position, number, and time distribution, enabling cost-effective devices for scientific imaging applications. This is achieved thanks to the photon counting and time-gating capabilities implemented in the analog domain, which in turn enable a 15\;{\upmu}{\text{m}} pixel with a 21% fill-factor. A reconfigurable column circuitry supports both the analog conventional readout and a self-referenced analog-to-digital conversion, able to cancel out the pixel-to-pixel nonuniformities, and speeding up the framerate to 486 fps. The imager, featuring also a delay locked loop to stabilize the internal waveform generation for reliable timing performance, has been implemented in a standard high-voltage 0.35\;{\upmu}{\text{m}}$ CMOS technology. Measurements in a fluorescent lifetime setup have been performed, comparing the results with single-point acquisitions made with commercial time-correlated equipment. [ABSTRACT FROM PUBLISHER]

In this brief, the design and experimental characterization of a compact analog readout circuit for photon counting is presented. A test chip, including a 20 $\times$ 20 counter array, has been manufactured in a standard 0.35- \mu\m CMOS technology. The circuit delivers an output voltage proportional to the input pulse count, with a programmable voltage step. The counting resolution can be set to 7 or 8 bits with a readout noise of 0.15 and 0.3 electrons, respectively, and an output nonuniformity of 4% across the array, which brings a factor 3 improvement with respect to previous analog designs. A worst case integral nonlinearity of \pm$0.6 and \pm$1 LSB and a differential nonlinearity of \pm$0.3 and \pm) is a factor 10 smaller than a digital counter of the same resolution. Due to the compactness and the lower counter power consumption with regard to the former designs, the proposed circuit can be exploited for signal processing in high-spatial resolution single-photon-avalanche-diode-based image sensors. [ABSTRACT FROM PUBLISHER]

An 8\,\times\,16 pixel array based on CMOS small-area silicon photomultipliers (mini-SiPMs) detectors for PET applications is reported. Each pixel is 570 \,\times\,610 \mum ^2 in size and contains four digital mini-SiPMs, for a total of 720 SPADs, resulting in a full chip fill-factor of 35.7%. For each gamma detection, the pixel provides the total detected energy and a timestamp, obtained through two 7-b counters and two 12-b 64-ps TDCs. An adder tree overlaid on top of the pixel array sums the sensor total counts at up to 100 Msamples/s, which are then used for detecting the asynchronous gamma events on-chip, while also being output in real-time. Characterization of gamma detection performance with an 3\,\times\,3\,\times\,5 mm ^3 LYSO scintillator at 20 ^\circC is reported, showing a 511-keV gamma energy resolution of 10.9% and a coincidence timing resolution of 399 ps. [ABSTRACT FROM AUTHOR]

This paper presents the design and electro-optical test of a 160\times120-pixels CMOS sensor specifically conceived for Time-Of-Flight 3D imaging. The in-pixel processing allows the implementation of Indirect Time-Of-Flight technique for distance measurement with reset noise removal through Correlated Double Sampling and embedded fixed-pattern noise reduction, whereas a fast readout operation allows the pixels values to be streamed out at a maximum rate of 10 MSample/s. The imager can operate as a fast 2D camera up to 458 fps, as a 3D camera up to 80 fps, or even coupling both operation modes. The chip has been fabricated using a standard 0.18 \mu\m 1P4M 1.8 V CMOS technology with MIM capacitors. The resulting pixel has a pitch of 29.1 \mu\m with a fill-factor of 34% and includes 66 transistors. Distance measurements up to 4.5 m have been performed with pulsed laser light, achieving a best precision of 10 cm at 1 m in real-time at 55 fps and 175 mA current consumption. [ABSTRACT FROM AUTHOR]

In this paper, we report on an Avalanche Photodiode (APD) fabricated in a standard 0.35-μm CMOS technology. The main electrooptical characteristics of the device are presented, showing a remarkably tow-noise factor if compared to other CMOS APDs. An estimation of the noise properties of a pixel based on the proposed photodiode with charge-amplifier readout is performed, showing that it could have an improved noise performance with respect to a standard photodiode-based pixel. [ABSTRACT FROM AUTHOR]

This letter presents the experimental characterization and noise modeling of a CMOS avalanche photodiode with pwell/n-iso active junction fabricated in a 0.15- \mum standard CMOS process. The device exhibits a remarkably low excess noise factor F=6 at a gain M={50} in the blue spectral region, and F={12}$ at M={50} in the near-infrared. Gain and noise characteristics are accurately predicted using Hayat dead-space model applied to a linearly graded junction doping profile. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, numerical device simulations are used to get insight into the DC and dynamic behavior of a CMOS metal-semiconductor-metal photodetector, to be used as a mixing device for active pixels based on a differential read-out concept. On the basis of simulation results, a simple electrical macromodel of the photosensor has been defined and implemented in the Cadence package using Spectre AHDL. The proposed macromodel is shown to accurately reproduce the numerical device simulation predictions in all the considered operation modes. [Copyright &y& Elsevier]