IEEE open journal of solid-state circuits 

About: IEEE open journal of solid-state circuits is an academic journal published by Institute of Electrical and Electronics Engineers. The journal publishes majorly in the area(s): Computer science & Engineering. It has an ISSN identifier of 2644-1349. Over the lifetime, 6 publications have been published receiving 11 citations. The journal is also known as: IOJSBG & Solid-State Circuits Society.

A 240 × 160 3D-Stacked SPAD dToF Image Sensor With Rolling Shutter and In-Pixel Histogram for Mobile Devices

Abstract: A 240 $\times$ 160 single-photon avalanche diode (SPAD) sensor integrated with a 3D-stacked 65nm/65nm CMOS technology is reported for direct time-of-flight (dToF) 3D imaging in mobile devices. The top tier is occupied by backside illuminated SPADs with 16 $\mu {\mathrm{ m}}$ pitch and 49.7% fill-factor. The SPADS consists of multiple 16 $\times$ 16 SPADs top groups, in which each of 8 $\times$ 8 SPADs sub-group shares a 10-bit, 97.65ps and 100ns range time-to-digital converter (TDC) in a quad-partition rolling shutter mode. During the exposure of each rolling stage, partial histogramming readout (PHR) approach is implemented to compress photon events to in-pixel histograms. Since the fine histograms is incomplete, for the first time we propose histogram distortion correction (HDC) algorithm to solve the linearity discontinuity at the coarse bin edges. With this algorithm, depth measurement up to 9.5m achieves an accuracy of 1cm and precision of 9mm in office lighting condition. Outdoor measurement with 10 klux sunlight achieves a maximum distance detection of 4m at 20 fps, using a VCSEL laser with the average power of 90 mW and peak power of 15 W.

A High-Throughput Photon Processing Technique for Range Extension of SPAD-Based LiDAR Receivers

Abstract: There has recently been a keen interest in developing Light Detection and Ranging (LiDAR) systems using Single Photon Avalanche Diode (SPAD) sensors. This has led to a variety of implementations in pixel combining techniques and Time to Digital Converter (TDC) architectures for such sensors. This paper presents a comparison of these approaches and demonstrates a technique capable of extending the range of LiDAR systems with improved resilience to background conditions. A LiDAR system emulator using a reconfigurable SPAD array and FPGA interface is used to compare these different techniques. A Monte Carlo simulation model leveraging synthetic 3D data is presented to visualize the sensor performance on realistic automotive LiDAR scenes.

A 50-GBaud QPSK Optical Receiver With a Phase/Frequency Detector for Energy-Efficient Intra-Data Center Interconnects

Abstract: This paper describes the energy-efficient realization of a QPSK optical receiver (CoRX) for short-reach intra-datacenter interconnects based on analog coherent detection. The CoRX comprises inphase and quadrature channels for each polarization and a high-speed phase-frequency detector (PFD) that provides feedback to stabilize an optical local oscillator (LO) and maintain coherence with the received optical signal. Each receive (RX) channel consists of a transimpedance amplifier (TIA) based on a Cherry-Hooper emitter follower (CHEF). The electronic RX is implemented in a 130-nm SiGe HBT technology ( $f_{T} = 300$ GHz), consumes 534 mW of DC power for a total electrical RX energy efficiency of 5.34 pJ/bit, and occupies 2.8 $mm^{2}$ . Electrical characterization of the CoRX on an FR-4 PCB assembly demonstrates operation up to 60 GBaud with a bit error rate (BER) of less than 10⁻¹². A co-packaged optical/electrical CoRX assembly with a silicon photonic receiver is characterized using a commercial-off-the-shelf quadrature phase-shift keying (QPSK) transmitter for constellations up to 50 GBaud (100 Gbps) at BER below KP4-FEC ( $2.2\times 10^{-4}$ ).

Range-Finding SPAD Array With Smart Laser-Spot Tracking and TDC Sharing for Background Suppression

Abstract: We present the design and experimental characterization of a CMOS sensor based on Single-Photon Avalanche Diodes for direct Time-Of-Flight single-point distance ranging, under high background illumination for short-range applications. The sensing area has a rectangular shape ( $40\,\,\mathbf {\mathrm {\times }}\,\,10$ SPADs) to deal with the backscattered light spot displacement across the detector, dependent on target distance, due to the non-confocal optical setup. Since only few SPADs are illuminated by the laser spot, we implemented a smart laser-spot tracking within the active area, so to define the specific Region-Of-Interest (ROI) with only SPADs hit by signal photons and a smart sharing of the timing electronics, so to significantly improve Signal-to-Noise Ratio (SNR) of TOF measurements and to reduce overall chip area and power consumption. The timing electronics consists of 80 Time-to-Digital Converter (TDC) shared among the 400 SPADs with a self-reconfigurable routing, which dynamically connects the SPADs within the ROI to the available TDCs. The latter have 78 ps resolution and 20 ns Full-Scale Range (FSR), i.e., up to 2 m maximum distance range. An on-chip histogram builder block accumulates TDC conversions so to provide the final TOF histogram. We achieve a precision better than 2.3 mm at 1 m distance and 80% target reflectivity, with 3 klux halogen lamp background illumination and 2 kHz measurement rate. The sensor rejects 10 klux of background light, still with a precision better than 20 mm at 2 m.

Hybrid Time-of-Flight Image Sensors for Middle-Range Outdoor Applications

Abstract: This paper introduces a new series of time-of-flight (TOF) range image sensors that can be used for outdoor middle-range (10m to 100m) applications by employing a small duty-cycle modulated light pulse with a relatively high optical peak power. This set of TOF sensors is referred to here as a hybrid TOF (hTOF) image sensor. The hTOF image sensor is based on the indirect TOF measurement principle but simultaneously uses the direct TOF concept for coarse measurements. Compared to conventional indirect TOF image sensors for outdoor middle-range applications, the hTOF image sensor has a distinct advantage due to the reduction of capturing ambient light charge. To show the potential of the hTOF image sensor for outdoor middle-range operation, a model of estimating distance precision of hTOF image sensors is built and applied it by using possible sensor specifications to estimate the distance precision of the hTOF range camera in 10m, 20m and 40m measurements under the ambient-light condition of 100klux and its feasibility is discussed. In outdoor 10m-range measurements, the advantage of hTOF image sensors compared to the conventional indirect TOF image sensors is discussed by considering the amount of captured ambient-light charge in pixels.