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.

A 64 $\times$ 64-Pixels Digital Silicon Photomultiplier Direct TOF Sensor With 100-MPhotons/s/pixel Background Rejection and Imaging/Altimeter Mode With 0.14% Precision Up To 6 km for Spacecraft Navigation and Landing

A $192 \times 128$ pixel single photon avalanche diode (SPAD) time-resolved single photon counting (TCSPC) image sensor is implemented in STMicroelectronics 40-nm CMOS technology. The 13% fill factor, $18.4\,\,\mu \text {m} \times 9.2\,\,\mu \text{m}$ pixel contains a 33-ps resolution, 135-ns full scale, 12-bit time-to-digital converter (TDC) with 0.9-LSB differential and 5.64-LSB integral nonlinearity (DNL/INL). The sensor achieves a mean 219-ps full-width half-maximum (FWHM) impulse response function (IRF) and is operable at up to 18.6 kframes/s through 64 parallelized serial outputs. Cylindrical microlenses with a concentration factor of 3.25 increase the fill factor to 42%. The median dark count rate (DCR) is 25 Hz at 1.5-V excess bias. A digital calibration scheme integrated into a column of the imager allows off-chip digital process, voltage, and temperature (PVT) compensation of every frame on the fly. Fluorescence lifetime imaging microscopy (FLIM) results are presented.

/pdf/a-192-times128-time-correlated-spad-image-sensor-in-40-nm-340ntb9acm.pdf

A $192\times128$ Time Correlated SPAD Image Sensor in 40-nm CMOS Technology

VCSEL based sensors can measure distance and velocity in three dimensional space and are already produced in high
quantities for professional and consumer applications. Several physical principles are used:
VCSELs are applied as infrared illumination for surveillance cameras. High power arrays combined with imaging optics
provide a uniform illumination of scenes up to a distance of several hundred meters.
Time-of-flight methods use a pulsed VCSEL as light source, either with strong single pulses at low duty cycle or with
pulse trains. Because of the sensitivity to background light and the strong decrease of the signal with distance several Watts
of laser power are needed at a distance of up to 100m. VCSEL arrays enable power scaling and can provide very short
pulses at higher power density. Applications range from extended functions in a smartphone over industrial sensors up to
automotive LIDAR for driver assistance and autonomous driving.
Self-mixing interference works with coherent laser photons scattered back into the cavity. It is therefore insensitive to
environmental light. The method is used to measure target velocity and distance with very high accuracy at distances up
to one meter. Single-mode VCSELs with integrated photodiode and grating stabilized polarization enable very compact
and cost effective products. Besides the well know application as computer input device new applications with even higher
accuracy or for speed over ground measurement in automobiles and up to 250km/h are investigated.
All measurement methods exploit the known VCSEL properties like robustness, stability over temperature and the
potential for packages with integrated optics and electronics. This makes VCSEL sensors ideally suited for new mass
applications in consumer and automotive markets.

VCSEL based sensors for distance and velocity

A single-chip receiver for pulsed laser direct time-of-flight 3-D imaging applications has been realized in a 0.35- $\mu \text{m}$ HV CMOS technology. The chip includes a $32 \times 128$ single-photon avalanche diode (SPAD) array [35% fill factor (FF)] and 257 time-to-digital converters (TDCs) with a ~78-ps resolution. Two adjacent rows ( $2 \times 128$ SPADs) at a time can be selected for simultaneous measurement, i.e., 16 measurement cycles are needed to cover the whole array. SPADs are capable of operating in a gated mode in order to suppress dark and background light-induced detections. The IC was designed to be used in a solid-state 3-D imaging system with laser illumination concentrated in both time (short sub-ns pulses) and space (targeting only the active rows of the SPAD array). The performance of the receiver IC was characterized in a solid-state 3-D range imager with flood-pulsed illumination from a laser diode (LD)-based transmitter, which produced short [~150-ps full-width at half-maximum (FWHM)] high-energy (~3.8-nJ pulse/~14-W peak power) pulses at a pulsing rate of 250 kHz when operating at a wavelength of 810 nm. Two detector/TDC ICs formed an 8k pixel receiver, targeting a field-of-view of $\sim 42^{\circ } \times 21^{\circ }$ by means of simple optics. Frame rates of up to 20 fps were demonstrated with a centimeter-level precision in the case of Lambertian targets within a range of 3.5 m.

http://jultika.oulu.fi/files/nbnfi-fe2020050825689.pdf

A 32 × 128 SPAD-257 TDC Receiver IC for Pulsed TOF Solid-State 3-D Imaging

The design and characterization of an imaging system is presented for depth information capture of arbitrary three-dimensional (3-D) objects. The core of the system is an array of 32 x 32 rangefinding pixels that independently measure the time-of-flight of a ray of light as it is reflected back from the objects in a scene. A single cone of pulsed laser light illuminates the scene, thus no complex mechanical scanning or expensive optical equipment are needed. Millimetric depth accuracies can be reached thanks to the rangefinder's optical detectors that enable picosecond time discrimination. The detectors, based on a single photon avalanche diode operating in Geiger mode, utilize avalanche multiplication to enhance light detection. On-pixel high-speed electrical amplification can therefore be eliminated, thus greatly simplifying the array and potentially reducing its power dissipation. Optical power requirements on the light source can also be significantly relaxed, due to the array's sensitivity to single photon events. A number of standard performance measurements, conducted on the imager, are discussed in the paper. The 3-D imaging system was also tested on real 3-D subjects, including human facial models, demonstrating the suitability of the approach.

Design and characterization of a CMOS 3-D image sensor based on single photon avalanche diodes

This paper discusses the construction principles and performance of a pulsed time-of-flight (TOF) laser radar based on high-speed (FWHM $\sim$ 100 ps) and high-energy ( $\sim$ 1 nJ) optical transmitter pulses produced with a specific laser diode working in an “enhanced gain-switching” regime and based on single-photon detection in the receiver. It is shown by analysis and experiments that single-shot precision at the level of 2…3 cm is achievable. The effective measurement rate can exceed 10 kHz to a noncooperative target (20% reflectivity) at a distance of $>\ 50\ \hbox{m}$ , with an effective receiver aperture size of $2.5\ \hbox{cm}^{2} $ . The effect of background illumination is analyzed. It is shown that the gating of the SPAD detector is an effective means to avoid the blocking of the receiver in a high-level background illumination case. A brief comparison with pulsed TOF laser radars employing linear detection techniques is also made.

On Laser Ranging Based on High-Speed/Energy Laser Diode Pulses and Single-Photon Detection Techniques

A solid state 3D scanner based on a pulsed laser diode source and narrow time gating of a 2D CMOS single photon avalanche diode (SPAD) detector array is presented. The imager uses an on-chip delay-locked loop to program the time gating of 40 sub-arrays individually. The prototype detector has 80 × 25 pixels with a fill factor of 32 % in the sensor area. The chip has been fabricated in a 0.35 μm high-voltage process and occupies a 5.69 × 5.02 mm2 area. A 3D range image rate of ∼5 frames/second with centimeter level precision is demonstrated to passive targets within a range of ∼1 meter and FOV of 36 × 57 degrees.

/pdf/an-80-25-pixel-cmos-single-photon-range-image-sensor-with-a-2v8ebwptdv.pdf

An 80 × 25 pixel CMOS single-photon range image sensor with a flexible on-chip time gating topology for solid state 3D scanning

Imager topology with sub-ns time gating for 3D distance measurement application and first measurement results of the prototype are presented. The imager has a fully digital operating principle with single-photon avalanche diode detectors and on-chip narrow gating of pixel groups. The prototype detector has 80 × 25 pixels with a fill factor of 34 % in the sensor area. The chip has been fabricated in a 0.35 μm high-voltage process and occupies 5.69 × 5.02 mm2 area.

/pdf/an-80-25-pixel-cmos-single-photon-image-sensor-with-sub-ns-eqqq2n0wys.pdf

Harri Rapakko

Papers

On Laser Ranging Based on High-Speed/Energy Laser Diode Pulses and Single-Photon Detection Techniques

An 80 × 25 pixel CMOS single-photon range image sensor with a flexible on-chip time gating topology for solid state 3D scanning

An 80 × 25 pixel CMOS single-photon image sensor with sub-ns time gating for solid state 3D scanning