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

This paper presents an integrated receiver channel and an integrated time-to-digital (TDC) converter fabricated in a 0.35 μm SiGe BiCMOS and in 0.35 μm CMOS technologies, respectively, that give the required performance for a pulsed time-of-flight (TOF) laser radar to be used in a laser scanner in automotive applications. The receiver-TDC chip set is capable to measure the positions and widths of three separate successive timing pulses with sub-ns level precision in a wide dynamic amplitude range of more than 1:10.000.

A Laser Scanner Chip Set for Accurate Perception Systems

A potentially compact 2-D range profiler for noncooperative targets with a distance range of >10 m is demonstrated. A laser diode utilizing enhanced gain switching is used as a transmitter to provide short, high-energy optical pulses (~1 nJ/140 ps). Cylindrical lenses spread the laser beam in one dimension and collimate the beam in the other dimension to illuminate a line shaped field of view of about 45°. A similarly shaped field of view for the detector is realized with a single-photon avalanche diode (SPAD) detector matrix. Compared with a flash 3-D rangefinder, the 2-D rangefinding scheme relaxes the SPAD and time-to-digital converter design requirements, increases the signal irradiance at the detector, can have better tolerance for background illumination, and it can be sufficient or advantageous in some applications. The distance measurement precision to each direction is inherently within a few centimeters (FWHM) since the laser pulse width and SPAD detector jitter both correspond with an optical pulse back-and-forth flight time of about a centimeter. Demonstration measurements show >15 Hz line rate and a lateral resolution of about 5 mrad to noncooperative targets at distances of more than 10 m.

/pdf/on-two-dimensional-rangefinding-using-a-1-nj-100-ps-laser-48btcc20hl.pdf

On Two-Dimensional Rangefinding Using a ̃1 nJ/̃100 ps Laser Diode Transmitter and a CMOS SPAD Matrix

A pulsed TOF laser radar has been implemented and its performance characterized. The transmitter applies a QW double-heterostructure laser diode producing 0.6 nJ/ 100 ps laser pulses at the central wavelength of ∼ 817 nm. The detector is a single-chip IC, manufactured in the standard 0.35 μm HV CMOS process, including a 9×9 SPAD array and a 10-channel TDC circuit. Both the SPAD array and the TDC circuit support a time gating feature allowing photon detection only to occur within a predefined time window. The SPAD array also supports the sub-array selection feature in order to respond to the laser spot wandering effect due to paraxial optics. A sub-array is a 3×3 SPAD array freely chosen within a 9×9 SPAD array. The characteristic measurement results demonstrate the measurement range of tens of meters with a linearity precision +/− 0.5 mm to the 11% target reflectivity and at pulsing frequency of 100 kHz. The distance dependent detection rate varies from 28% to 500%, thus providing a high measurement rate. The single-shot precision is ∼ 20 mm. The deteriorating impact of high-level background radiation conditions on the SNR has been demonstrated as well as a scheme to improve it by detector time gating.

/pdf/a-laser-radar-based-on-a-impulse-like-laser-diode-2hf8zjc9bz.pdf

A laser radar based on a “impulse-like” laser diode transmitter and a 2D SPAD/TDC receiver

A 9x9 Single-Photon Avalanche Photodiode (SPAD) array with a 10-channel time-to-digital converter and an integrated laser diode driver fabricated in 035 µm HV- CMOS technology were used to carry out time domain diffuse optics measurements of optical phantoms The average optical power of 20 µW was achieved by the laser diode transmitter at the repetition rate of 500 kHz with a pulse width of 80 ps The resolution of the TDC and the measured instrument response function (IRF) of the system were ~65 ps and ~190 ps, respectively The power consumption of the proposed system was 180 mW Measurements showed that with the proposed system a perturbation with a different absorption property than in surrounding material at the depth of 15 mm could be recognized In addition, in in vivo measurement with the proposed components, hemodynamic changes in volunteer's arm during a venous occlusion were detected

/pdf/an-integrated-9x9-spad-array-with-a-10-channel-tdc-and-a-1a2z1aoy36.pdf

An integrated 9x9 SPAD array with a 10-channel TDC and a CMOS laser diode driver for a wearable time-domain diffuse optics optode

The timing accuracy of a single-photon avalanche diode (SPAD) based receiver is analyzed as a function of excess bias voltage. The width of the used optical pulse was 100 ps, which matches well with the jitter of the used SPAD receiver fabricated in a 0.35 pm HVCMOS technology. The timing error was measured to be 900 ps within the excess bias voltage range of ∼1.25 V–3.25 V. The single-shot resolution changes from 420 ps to 160 ps (FWHM), respectively.

/pdf/on-the-effects-of-the-excess-bias-of-the-spad-on-the-timing-3pbv3mm2gs.pdf

Jussi-Pekka Jansson

Papers

A Laser Scanner Chip Set for Accurate Perception Systems

On Two-Dimensional Rangefinding Using a ̃1 nJ/̃100 ps Laser Diode Transmitter and a CMOS SPAD Matrix

A laser radar based on a “impulse-like” laser diode transmitter and a 2D SPAD/TDC receiver

An integrated 9x9 SPAD array with a 10-channel TDC and a CMOS laser diode driver for a wearable time-domain diffuse optics optode

On the effects of the excess bias of the SPAD on the timing accuracy in time interval measurement