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 compares two CMOS technologies, the robust 350nm version and its modern 28nm successor, in terms of time-domain signal processing parameters. The evaluated parameters; propagation delay, delay variation due to process and mismatch fluctuations, sensitivity to noise and area and power usage are crucial especially in measurement devices relying on precise timings, high precision time-to-digital converters, for example. Post-layout simulations show that the modern scaled technology offers superior speed, efficient area usage and low power consumption but suffers from considerable delay mismatch. Therefore applications relying on precise time domain signal processing do not always benefit from technology scaling.

/pdf/cmos-technology-scaling-advantages-in-time-domain-signal-c5c5k1j223.pdf

CMOS technology scaling advantages in time domain signal processing

A multi-channel time-to-digital converter has been realized in 0.35μm CMOS. The 7-channel converter is based on a multiplying delay-locked loop acting as a first and a capacitor-scaled parallel delay line as a second interpolator, and is able to measure the time intervals and pulse widths or rise times of several successive timing signals. The circuit utilizes a 20MHz external crystal as a time base and offers better than 9ps measurement precision and a measurement range of up to ±74μs.

A multi-channel wide range time-to-digital converter with better than 9ps RMS precision for pulsed time-of-flight laser rangefinding

This paper presents the use of a multiplying delay locked loop (MDLL) for delay line-based time interval measurement. The structure is introduced together with the theory behind the performance. Measurement results obtained with a MDLL-based time digitizer designed with 0.35 μm CMOS verify the operation and calculated performance of the device. This MDLL technique with modern CMOS technology makes longrange, high-resolution, linear time interval measurement possible with a small, simple one-level interpolation architecture.

Multiplying delay locked loop (MDLL) in time-to-digital conversion

A laser rangefinder device based on pulsed time-of-flight (TOF) distance measurement techniques was constructed and tested. Key blocks of the system are the integrated receiver channel and the integrated time-to-digital converter (TDC) fabricated in a 0.35-um CMOS technology. The receiver-TDC chip set is capable of measuring the time position, rise time and pulse width of incoming optical pulses with ps precision in the amplitude range of more than 1: 50 000. The timing detection is based on leading edge detection in the receiver channel, and the amplitude-dependent timing error is compensated for by utilizing the multichannel TDC. A measurement distance of 100 m is achieved to a target with a reflectance of about 10% at the signal level of SNR = 6, with an optical output power and receiver aperture of 12 W and 18 mm, respectively.

/pdf/a-cmos-chip-set-for-accurate-pulsed-time-of-flight-laser-2b5c9sha1v.pdf

A CMOS chip set for accurate pulsed time-of-flight laser range finding

A laser diode illuminator for single-photon avalanche diode detection-based pulsed time-of-flight 3D range imaging is presented. The illuminator supports a block-based illumination scheme and consists of a 16-element custom-designed common anode quantum-well laser diode bar working in the enhanced gain switching regime and lasing at ∼810  nm. The laser diode elements are separately addressable and driven with gallium nitride drivers, which produce current pulses with a width of ∼2  ns; the current pulse amplitude was estimated from the supply voltage (90 V) as 5 to 10 A. Cylindrical optics are used to produce a total illumination field-of-view of 40  ×  10  deg2 (full width at half maximum) in 16 separately addressable blocks. With a laser pulsing frequency of 256 kHz and laser pulse energy of ∼8.5  nJ, the average optical illumination power of the transmitter is 2.2 mW.

/pdf/solid-state-block-based-pulsed-laser-illuminator-for-single-5blt4tajvn.pdf

Jussi-Pekka Jansson

Papers

CMOS technology scaling advantages in time domain signal processing

A multi-channel wide range time-to-digital converter with better than 9ps RMS precision for pulsed time-of-flight laser rangefinding

Multiplying delay locked loop (MDLL) in time-to-digital conversion

A CMOS chip set for accurate pulsed time-of-flight laser range finding

Solid-state block-based pulsed laser illuminator for single-photon avalanche diode detection-based time-of-flight 3D range imaging