IEEE International Solid-State Circuits Conference

The recent developments in time-domain diffuse optics that rely on physical concepts (e.g., time-gating and null distance) and advanced photonic components (e.g., vertical cavity source-emitting laser as light sources, single photon avalanche diode, and silicon photomultipliers as detectors, fast-gating circuits, and time-to-digital converters for acquisition) are focused. This study shows how these tools could lead on one hand to compact and wearable time-domain devices for point-of-care diagnostics down to the consumer level and on the other hand to powerful systems with exceptional depth penetration and sensitivity.

https://www.spiedigitallibrary.org/journals/Journal-of-Biomedical-Optics/volume-21/issue-9/091310/New-frontiers-in-time-domain-diffuse-optics-a-review/10.1117/1.JBO.21.9.091310.pdf

New frontiers in time-domain diffuse optics, a review

This paper presents a time-to-digital converter (TDC) architecture capable of reaching high-precision and high-linearity with moderate area occupation per measurement channel. The architecture is based on a coarse counter and a couple of two-stage interpolators that exploit the cyclic sliding scale technique in order to improve the conversion linearity. The interpolators are based on a new coarse-fine synchronization circuit and a new single-stage Vernier delay loop fine interpolation. In a standard cost-effective 0.35 μm CMOS technology the TDC reaches a dynamic range of 160 ns, 17.2 ps precision and differential non-linearity better than 0.9% LSB rms. The TDC building block was designed in order to be easily assembled in a multi-channel monolithic TDC chip. Coupled with a SPAD photodetector it is aimed for TCSPC applications (like FLIM, FCS, FRET) and direct ToF 3-D ranging.

A High-Linearity, 17 ps Precision Time-to-Digital Converter Based on a Single-Stage Vernier Delay Loop Fine Interpolation

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 multichannel time-to-digital converter (TDC) implemented with 0.35-μm complementary metal-oxide-semiconductor technology that uses a low-frequency crystal as reference and measures the time intervals with counter and delay line interpolation techniques is described. The multichannel measurement architecture provides information on the time intervals between several timing signals. The circuit can be used for laser time-of-flight distance measurements, e.g., where it can determine time intervals between a transmitted laser pulse and several reflected pulses and also pulsewidths or rise times, to compensate for the timing walk error. This paper shows how several measurement channels can be integrated into one TDC without losing the measurement performance. The circuit offers a measurement precision that is better than 8 ps and a measurement range of up to 74 μs. In terms of laser distance measurement, its performance is equivalent to millimeter-level precision within an 11-km range.

A Multichannel High-Precision CMOS Time-to-Digital Converter for Laser-Scanner-Based Perception Systems

Accurate time-to-digital conversion is typically based on determining the positions of the timing signals within the period of an accurate clock with digital delay-line interpolators. In order to save circuit area and to improve single-shot precision to the picosecond level, multilevel interpolators can be used. Timing signals are generally asynchronous with respect to the main clock, and thus, in order to obtain unambiguous and errorless results, careful attention should be given to the synchronization of the timing signals and various operating blocks and to the generation of the interpolation residue between the interpolators. This paper attempts to describe these problems in detail and suggests some solutions using a time-to-digital converter architecture based on two-level interpolation as a test vehicle, which demonstrates 6-ps rms single-shot precision in a measurement range of 1 ms.

Synchronization in a Multilevel CMOS Time-to-Digital Converter

An integrated receiver–time-to-digital converter (TDC) chip set is developed for pulsed time-of-flight (TOF) laser rangefinding. The receiver detects the current pulse from the optical detector and produces a timing mark for the TDC. The receiver uses time mode walk error compensation scheme achieving $\mu \text{m}$ complementary metal–oxide–semiconductor (CMOS) technology. The functionality of the chip set was demonstrated in a laser radar platform using 12 W and 3-ns optical pulses produced by a laser diode (LD). Measurement accuracy of ~ ±3 mm was achieved with noncooperative targets at a distance range of a few tens of meters within an amplitude range of received echoes of 1:40 000.

/pdf/a-cmos-receiver-tdc-chip-set-for-accurate-pulsed-tof-laser-47u3wggyw1.pdf

A CMOS Receiver–TDC Chip Set for Accurate Pulsed TOF Laser Ranging

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

A single chip receiver for pulsed laser time-of-flight rangefinding applications has been realized in a standard 0.35um HV CMOS technology. It includes a 9×9 SPAD array and a 10-channel time-to-digital converter with 10ps single shot precision. Any of the 3×3 sub-arrays can be selected for simultaneous measurement. The selected SPAD array can be gated to be operative only within a selected time window in order to suppress dark and background light induced counts. Functional tests in a laser radar environment indicate full functionality over a range of nearly 80 metres.

A single chip laser radar receiver with a 9×9 SPAD detector array and a 10-channel TDC

A 3D imaging concept based on pulsed time-of-flight focal plane imaging is presented which can be tailored flexibly in terms of performance parameters such as range, image update rate, field-of-view, 2D resolution, depth accuracy, etc. according to the needs of different applications. The transmitter is based on a laser diode operating in enhanced gain-switching mode with a simple MOS/CMOS-switch current driver and capable of producing short (~100ps FWHM) high energy (up to nJ) pulses at a high pulsing rate. The receiver consists of 2D SPAD and TDC arrays placed on the same die, but in separate arrays. Paraxial optics can be used to illuminate the target field-of-view with the receiver placed at the focal plane of the receiver lens. To validate the concept, a prototype system is presented with a bulk laser diode/MOS driver operating at a wavelength of 870nm with a pulsing rate of 100kHz as the transmitter and a single-chip 9x9 SPAD array with 10-channel TDC as the receiver. The possibility of using this method as a solid-state solution to the task of 3D imaging is discussed in the light of the results derived from this prototype.

Jussi-Pekka Jansson

Papers

Synchronization in a Multilevel CMOS Time-to-Digital Converter

A CMOS Receiver–TDC Chip Set for Accurate Pulsed TOF Laser Ranging

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

A single chip laser radar receiver with a 9×9 SPAD detector array and a 10-channel TDC

Solid-state 3D imaging using a 1nJ/100ps laser diode transmitter and a single photon receiver matrix