A 64 × 64 SPAD-Based Indirect Time-of-Flight Image Sensor With 2-Tap Analog Pulse Counters

Park, Byungchoul; Park, Injun; Park, Chanmin; Choi, Woojun; Na, Yoondeok; Lee, Myungjae; Chae, Youngcheol

doi:10.1109/jssc.2021.3094524

Cited by 11 publications

(8 citation statements)

References 22 publications

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“…Compared to our previous work in [1] this pixel design has a comparable power consumption while extending the counting range of the pixel to 9-bits compared to [2]. It implements a novel timing sequence to allow for a digital DRS readout scheme and makes use of a dynamic comparator and low voltage clocking scheme to save on clock distribution power compared to [6]. Furthermore, compared to [2] the pixel has a completely in-pixel analog feedback line allowing easy scale-up to large resolution arrays without affecting its capacitive load and conversion speed.…”

Section: Discussionmentioning

confidence: 99%

“…It should be noted that any variability between the SPAD and PULSE pulses can cause an error due to different pulse shapes driving the comparator and therefore the analog counters, thus modulating their step size. To resolve this issue a pulse shaper as used in [6] can be implemented with a slight area penalty as the tradeoff.…”

Section: In-pixel Digital Drs Operationmentioning

confidence: 99%

“…As a result there is no increase of the capacitive load when scaling the pixel to higher resolutions. Moreover, compared to [2] and [6], the use of lowswing clocks with a dynamic comparator significantly reduces the clock distribution power compared to full swing CMOS, as given similar driving circuitry the clock distribution losses are proportional to fCV 2 (where f is the clock frequency, C the capacitance of the metal line and V the clock voltage swing). Finally, through our proposed novel timing sequence the pixel benefits from a digital delta reset sampling (DRS) readout which omits the need for sample and hold capacitors in the column circuit.…”

mentioning

confidence: 99%

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An Indirect Time-of-Flight SPAD Pixel With Dynamic Comparator Reuse for a Single-Slope ADC

Buckbee,

Dutton,

Henderson

2022

IEEE Solid-State Circuits Lett.

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This paper presents a 2-bin SPAD-based indirect time-of-flight (ITOF) pixel circuit with low power low-voltage differential clock distribution and a partially in-pixel single-slope ADC. An in-pixel dynamic comparator performs dual functions as a SPAD event-driven low-swing clock sampler and a comparator for self-referenced ADC conversion with digital delta reset sampling (DRS). The pixel achieves a full well capacity of 128 -512 photons (6.83 -8.82 ENOB), a low dynamic power consumption of 13.9-24.5 nW/MHz SPAD rate at a pitch of 7.2 µm in STMicroelectronics' 40nm CMOS and is 3D stacking ready.

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Section: Discussionmentioning

confidence: 99%

Section: In-pixel Digital Drs Operationmentioning

confidence: 99%

mentioning

confidence: 99%

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An Indirect Time-of-Flight SPAD Pixel With Dynamic Comparator Reuse for a Single-Slope ADC

Buckbee,

Dutton,

Henderson

2022

IEEE Solid-State Circuits Lett.

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“…In [6], a 64 × 64 SPAD flash LIDAR sensor in 130 nm HV CMOS with a combination of TDCs and triple integration interpolators is used to reach a timing resolution of 13 ps, corresponding to a depth resolution of 1.95 mm. In [7], a 64 × 64 iTOF SPAD sensor array in a 110 nm technology is presented, using analog pulse counters that achieves a precision of down to 1.35 cm with a fill factor (FF) of 26.3% and a DCR of 100 cps. A modulation frequency of up to 50 MHz is used.…”

Section: Introductionmentioning

confidence: 99%

Highly Sensitive Indirect Time-of-Flight Distance Sensor With Integrated Single-Photon Avalanche Diode in 0.35 μm CMOS

et al. 2022

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This work describes the architecture and measured capabilities of an optical distance sensing application specific integrated circuit (ASIC) manufactured in 0.35 µm CMOS with a nominal supply voltage of 3.3 V for indirect time-of-flight. An integrated single-photon avalanche diode (SPAD) with an active diameter of 38 µm is used as detector with 6.6 V excess bias, active quenching and active resetting circuit. Phase measurement is performed using a digital correlation approach with digital counters. Due to the unmatched sensitivity of SPADs, sub-cm accuracy measurements can be performed with a received signal power in the pW range. Background light ratios up to 24.1 dB still allow sub-cm precision. Depending on the required accuracy and the received optical power, the measurement time can be adjusted freely up to several seconds only limited by digital counter depth. Compared to a pin-photodiode iTOF sensor in the same technology, this chip has a sensitivity improvement of 33.3 dB and 40.7 dB for a distance accuracy of 1 cm and 10 cm, respectively, while reducing the effective measurement time by 75% at the same time. The chip size is 1.4 mm × 1.4 mm including two correlator blocks, for simultaneous acquisition of two phase steps. The number of correlators is scalable allowing parallel measurements of phase correlations.

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“…Illustrating the strength of our system, we experimentally show that the modulator can be used with a standard camera to enable high spatial-resolution ToF imaging. Our approach enables an attractive alternative to complex LiDAR systems relying on optical phased arrays (OPAs) and SLMs 22,[28][29][30][31][32] with thousands of control elements or highly specialized costly image sensors that are difficult to implement with a large number of pixels [33][34][35][36][37] .…”

mentioning

confidence: 99%

Longitudinal piezoelectric resonant photoelastic modulator for efficient intensity modulation at megahertz frequencies

2022

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Intensity modulators are an essential component in optics for controlling free-space beams. Many applications require the intensity of a free-space beam to be modulated at a single frequency, including wide-field lock-in detection for sensitive measurements, mode-locking in lasers, and phase-shift time-of-flight imaging (LiDAR). Here, we report a new type of single frequency intensity modulator that we refer to as a longitudinal piezoelectric resonant photoelastic modulator. The modulator consists of a thin lithium niobate wafer coated with transparent surface electrodes. One of the fundamental acoustic modes of the modulator is excited through the surface electrodes, confining an acoustic standing wave to the electrode region. The modulator is placed between optical polarizers; light propagating through the modulator and polarizers is intensity modulated with a wide acceptance angle and record breaking modulation efficiency in the megahertz frequency regime. As an illustration of the potential of our approach, we show that the proposed modulator can be integrated with a standard image sensor to effectively convert it into a time-of-flight imaging system.

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A 64 × 64 SPAD-Based Indirect Time-of-Flight Image Sensor With 2-Tap Analog Pulse Counters

Cited by 11 publications

References 22 publications

An Indirect Time-of-Flight SPAD Pixel With Dynamic Comparator Reuse for a Single-Slope ADC

An Indirect Time-of-Flight SPAD Pixel With Dynamic Comparator Reuse for a Single-Slope ADC

Highly Sensitive Indirect Time-of-Flight Distance Sensor With Integrated Single-Photon Avalanche Diode in 0.35 μm CMOS

Longitudinal piezoelectric resonant photoelastic modulator for efficient intensity modulation at megahertz frequencies

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