High-resolution Image Sensors Research Articles

A 12 pJ/Pixel Analog-to-Information Converter Based 816 × 640 Pixel CMOS Image Sensor

Analog-to-information converters (AICs) take advantage of the limited information bandwidth in high-frequency signals to improve the energy efficiency of front-end data converters. High-resolution image sensors often convey limited information due to the spatial redundancy between neighboring pixels. This paper proposes a mixed-signal AIC which compresses each nonoverlapping 4 × 4 pixel block in a 816 × 640 pixel prototype active-pixel sensor (APS) imager. It combines an energy-efficient charge-pump bit-image processor (BIP) with an area-efficient successive-approximation-register-single-slope (SAR-SS) hybrid analog-to-digital converter (ADC) via a charge-transfer-amplifier (CTA). The AIC is fully dynamic and consumes no static power. The ADC's capacitor array doubles as a computational device for parts of the compression algorithm which reduces its sampling rate by a factor of four. The compressed data contains direct edge information and can be decoded by a very simple receiver. The fabricated prototype consumes 12 pJ per pixel at 111 fps in the image compression mode and 48 pJ per pixel at 28.7 fps in raw data mode (9 b per pixel) under the same clock rate. To the best of our knowledge, this is the most energy-efficient compressive CMOS image sensor ever reported in the literature, thanks to the proposed AIC.

Analysis of Satellite Images for the Extraction of Structural Features

ABSTRACTThe development of high-resolution satellite imaging sensors has enhanced the collection of remotely sensed data and offers a cost-effective way to obtain information over large areas. The main structural features that are to be detected through satellite imaging are roads, buildings, and bridges. Detection of clouds and shadows supports the extraction of these features. However, the type of satellite images provided by different imaging sensors varies widely depending on spatial and spectral resolutions, which makes the process of feature extraction more complicated. This paper presents a detailed analysis of different algorithms developed to extract structural features using a variety of satellite images available for a single region. A comparative study of various techniques is done to justify the best method for the extraction of each feature.

Room-temperature bonding of heterogeneous materials for near-infrared image sensor

A room-temperature bonding technique using cone-shaped microbumps with the aid of ultrasonic vibration is applied to the fabrication of a near-infrared (NIR) image sensor. The image sensor is fabricated using the chip-on-chip integration of an InGaAs photodiode array on an InP substrate and a Si CMOS readout IC. The pixel pitch is 25 µm to compose quarter-VGA class (320 × 256 pixels) resolution. A high-quality imaging of a heated object is demonstrated. Bonding of the VGA array with 15 µm pitch is attempted to realize a high-resolution image sensor.

Electrical Properties of Ga2O3:Sn/CIGS Hetero-junction

ABSTRACTThere is an increased need for highly sensitive imaging devices to develop high resolution and high speed image sensors. Incident light intensity per pixel of image sensors is getting lower because the pixel resolution and frame rate of image sensors are becoming higher. We investigated the feasibility of using a photoconductor with tin-doped gallium oxide (Ga2O3:Sn)/Cu(In,Ga)Se2 (CIGS) hetero-junction for visible light image sensors. CIGS chalcopyrite thin films have great potential for improving the sensitivity of image sensors and CIGS chalcopyrite semiconductors have both a high absorption coefficient and high quantum efficiency. Moreover, the band gap can be adjusted for visible light. We applied Ga2O3 as an n-type semiconductor layer and a hole-blocking layer to CIGS thin film to reduce the dark current. The experimental results revealed that dark current was drastically reduced due to the application of Ga2O3 thin film, and an avalanche multiplication phenomenon was observed at an applied voltage of over 6 V. However, non-doped Ga2O3/CIGS hetero-junction only had sensitivity in the ultraviolet light region because their depletion region was almost completely spread throughout the Ga2O3 layer due to the low carrier density of the Ga2O3 layer. Therefore, we used Ga2O3:Sn for the n-type layer to increase carrier density. As a result, the depletion region shifted to the CIGS film and the cells had sensitivity in all visible regions. These results indicate that Ga2O3:Sn/CIGS hetero-junction are feasible for visible light photoconductors.

Three-dimensional imaging using fast micromachined electro-absorptive shutter

A 20-MHz switching high-speed light-modulating device for three-dimensional (3-D) image capturing and its system prototype are presented. For 3-D image capturing, the system utilizes a time-of-flight (TOF) principle by means of a 20-MHz high-speed micromachined electro-absorptive modulator, the so-called optical shutter. The high-speed modulation is obtained by utilizing the electro-absorption mechanism of the multilayer structure, which has an optical resonance cavity and light-absorption epilayers grown by metal organic chemical vapor deposition process. The optical shutter device is specially designed to have small resistor–capacitor–time constant to get the high-speed modulation. The optical shutter is positioned in front of a standard high-resolution complementary metal oxide semiconductor image sensor. The optical shutter modulates the incoming infrared image to acquire the depth image. The suggested novel optical shutter device enables capturing of a full high resolution-depth image, which has been limited to video graphics array (VGA) by previous depth-capturing technologies. The suggested 3-D image sensing device can have a crucial impact on 3-D–related business such as 3-D cameras, gesture recognition, user interfaces, and 3-D displays. This paper presents micro-opto-electro-mechanical systems-based optical shutter design, fabrication, characterization, 3-D camera system prototype, and image evaluation.

A CURRENT SOURCE WITH IMMUNITY FROM IR-DROP FOR HIGH-RESOLUTION CMOS IMAGE SENSORS

A current source circuit for high-resolution CMOS image sensors is introduced in this paper, which can provide a stable current with immunity from IR-drop along the power and ground wires. In the circuit, two pre-charged floating capacitors controlled by two-phase non-overlap clock are connected between the gate and source of a MOS transistor alternately to maintain a constant V GS of the MOS transistor. In this way, the current flowing through the MOS transistor will be stable and has nothing to do with power level. The post simulation results show that the current supplied by the proposed circuit decreases only by 1.6% when the voltage of the power supply decreases by 30%. The simulations have proved that the proposed circuit can improve the performance of high-resolution CMOS image sensors.

Comparison and analysis of point target reference spectrum of FMCW synthetic aperture imaging sensor

Abstract Frequency-modulated continuous-wave (FMCW) synthetic aperture imaging sensor (SAIS) combines FMCW technology and SAIS techniques which makes a lightweight, high-resolution, and cost-effective imaging sensor. FMCW SAIS systems are going to play an important role in airborne and spaceborne earth observation fields. However, the stop-and-go approximation used in conventional pulsed SAIR (e.g., synthetic aperture radar—SAR) is no longer valid due to the long signal duration time or low wave propagation speed. To exploit the potentialities of an accurate signal model under FMCW SAIS circumstances, this article presents the relationship and remarkable differences between the analytical FMCW SAIS point target reference spectrum model and the traditional ones in pulsed SAR and Synthetic Aperture Acoustic imaging system, and validates the significance of the additional range–azimuth coupling term and range walk term in FMCW SAIS spectrum introduced by the variation of slant range during the long pulse durations, and highlight the limitations of other two spectra. Finally, the simulation experiments are carried out to compare the performance of the aforementioned spectrum formulations.

High Definition Image Pre-Processing System for Multi-Stripe Satellites' Image Sensors

High-resolution image sensors play an important role in today's satellites' remote sensing applications. This paper presents an image recombination and processing system for one-dimensional multi-strip complementary metal-oxide semiconductor image sensors (CISs.) The proposed system takes advantage of the satellites' linear moving property to control the exposure time of CIS and provides the real-time ability to generate 11 200× N high-resolution images for satellites' remote sensing. Using hardware accelerators coupled with versatile microprocessors, the architecture is able to offer processing capability as well as long-term maintainability for space-borne platforms. The details of hardware design to meet real-time requirement are presented. The prototype, which contains four strip CISs and field programmable gate array-based prototyping, was implemented to verify functionality and capability of real-time image acquisition and combination. The implementation results show that it is feasible to integrate the proposed system into a single chip.

Segment Optimization and Data-Driven Thresholding for Knowledge-Based Landslide Detection by Object-Based Image Analysis

To detect landslides by object-based image analysis using criteria based on shape, color, texture, and, in particular, contextual information and process knowledge, candidate segments must be delineated properly. This has proved challenging in the past, since segments are mainly created using spectral and size criteria that are not consistent for landslides. This paper presents an approach to select objectively parameters for a region growing segmentation technique to outline landslides as individual segments and also addresses the scale dependence of landslides and false positives occurring in a natural landscape. Multiple scale parameters were determined using a plateau objective function derived from the spatial autocorrelation and intrasegment variance analysis, allowing for differently sized features to be identified. While a high-resolution Resourcesat-1 Linear Imaging and Self Scanning Sensor IV (5.8 m) multispectral image was used to create segments for landslide recognition, terrain curvature derived from a digital terrain model based on Cartosat-1 (2.5 m) data was used to create segments for subsequent landslide classification. Here, optimal segments were used in a knowledge-based classification approach with the thresholds of diagnostic parameters derived from If-means cluster analysis, to detect landslides of five different types, with an overall recognition accuracy of 76.9%. The approach, when tested in a geomorphologically dissimilar area, recognized landslides with an overall accuracy of 77.7%, without modification to the methodology. The multiscale classification-based segment optimization procedure was also able to reduce the error of commission significantly in comparison to a single-optimal-scale approach.

Indoor Positioning by LED Visible Light Communication and Image Sensors

High power white LEDs are expected to replace the existing lighting technologies in near future which are also suggested for visible light communication (VLC). We proposed an algorithm for high precision indoor positioning using lighting LEDs, VLC and image sensors. In the proposed algorithm, four LEDs transmitted their three-dimensional coordinate information which were received and demodulated by two image sensors near the unknown position. The unknown position was then calculated from the geometrical relations of the LED images created on the image sensors. We described the algorithm in details. Simulation of the proposed algorithm was done and presented in this paper. This technique did not require any angular measurement which was needed in contemporary positioning algorithms using LED and image sensor. Simulation results showed that the proposed system could estimate the unknown position within the accuracy of few centimeters. Positioning accuracy could be increased by using high resolution image sensors or by increasing the separation between the image sensors. DOI: http://dx.doi.org/10.11591/ijece.v1i2.165

A fast and effective approach to generate true orthophoto in built‐up area

PurposeOrthophoto suffers from the relief displacement effects magnified by high resolution imaging sensors especially when mapping urban areas. True orthophotos eliminating relief displacement with digital surface model (DSM) are presented to assure reliable interpretability and maintain the high quality of the available data. Previous efforts did not provide accurate and fast ways for generating true othorphoto. The purpose of this paper is to try to solve the problem by analyzing the complexity of algorithm processes and finding the optimum manner to allocate them.Design/methodology/approachIn this paper, an optimum segmentation number for radial sweep is presented to achieve minimum complexity. First, the scan area, number of azimuth lines and visibility judgment area of radial sweep and spiral sweep method have been discussed with rigorous geometric theory, and then algorithm complexities of both methods are estimated with mathematical computation theory. Finally, minimum complexity of the methods is obtained with extreme point theory of differential calculus.FindingsExperiments have demonstrated that the proposed method has the best efficiency, and is efficient to avoid “M‐potion” problem, and false occlusions and false visibilities caused by the rolling area, the incompatibility between the DSM and ground image resolution.Originality/valueThe deduction and experiments indicate that the proposed method is a robust, accurate, fast, and effective approach to generate high quality, true orthophoto at a large‐scale.

14-12 有機撮像デバイスの高解像度化,高効率化に向けた作製プロセスの基礎検討(第14部門情報センシング)

14-12 有機撮像デバイスの高解像度化,高効率化に向けた作製プロセスの基礎検討(第14部門情報センシング)

High speed column-parallel CDS/ADC circuit with nonlinearity compensation for CMOS image sensors

A high speed column-parallel CDS/ADC circuit with nonlinearity compensation is proposed in this paper. The correlated double sampling (CDS) and analog-to-digital converter (ADC) functions are integrated in a three-phase column-parallel circuit based on two floating gate inverters and switched-capacitor network. The conversion rate of traditional single-slope ADC is speeded up by dividing quantization to coarse step and fine step. A storage capacitor is used to store the result of coarse step and locate the section of ramp signal of fine step, which can reduce the clock step from 2 n to 2(n/2+1). The floating gate inverters are implemented to reduce the power consumption. Its induced nonlinear offset is cancelled by introducing a compensation module to the input of inverter, which can equalize the coupling path in three phases of the proposed circuit. This circuit is designed and simulated for CMOS image sensor with 640×480 pixel array using Chartered 0.18 μm process. Simulation results indicate that the resolution can reach 10-bit and the maximum frame rate can reach 200 frames/s with a main clock of 10 MHz. The power consumption of this circuit is less than 36.5 μW with a 3.3 V power supply. The proposed CDS/ADC circuit is suitable for high resolution and high speed image sensors.

2D luminescence imaging of pH in vivo

Luminescence imaging of biological parameters is an emerging field in biomedical sciences. Tools to study 2D pH distribution are needed to gain new insights into complex disease processes, such as wound healing and tumor metabolism. In recent years, luminescence-based methods for pH measurement have been developed. However, for in vivo applications, especially for studies on humans, biocompatibility and reliability under varying conditions have to be ensured. Here, we present a referenced luminescent sensor for 2D high-resolution imaging of pH in vivo. The ratiometric sensing scheme is based on time-domain luminescence imaging of FITC and ruthenium(II)tris-(4,7-diphenyl-1,10-phenanthroline). To create a biocompatible 2D sensor, these dyes were bound to or incorporated into microparticles (aminocellulose and polyacrylonitrile), and particles were immobilized in polyurethane hydrogel on transparent foils. We show sensor precision and validity by conducting in vitro and in vivo experiments, and we show the versatility in imaging pH during physiological and chronic cutaneous wound healing in humans. Implementation of this technique may open vistas in wound healing, tumor biology, and other biomedical fields.

4+1-transistor pixel architecture for high-speed, high-resolution CMOS image sensors

A pixel architecture is introduced which allows a drastic reduction of the column capacitance of a monolithic pixel array. It consists of a classic 4T pixel architecture together with an extra switch added at regular positions in the column array and shared by a group of pixels of the column. In this way, each pixel will see an output capacitance proportional to the number of pixels sharing the extra switch and the total number of extra switches.

Analysis of Low-Dark-Current, High-Sensitivity, Low-Optical-Crosstalk, and Small-Pixel-Size Pinned Photodiode With No-Gap Microlens

A low-dark-current, high-sensitivity, low-optical-crosstalk, and small-pixel-size pinned photodiode with no-gap microlens is designed, fabricated, and measured. Compared with nonpinned photodiodes of the same size, the dark current of a 2μm × 2μm pinned photodiode is reduced about 41.2%, while the photocurrent is reduced less than only 1% at the low reverse biased voltage Vpd=2 V under illumination of the same light source (470 nm, 450 μw/cm2). Due to the use of the pinning layer, the equivalent capacitance of the 2-m pinned photodiode is increased about 1.1 fF. In addition, the no-gap microlens technology has been developed here to improve the photodiode performance. Prototype complementary metal-oxide-semiconductor (CMOS) imagers consisting of a 640 (row) by 480 (column) array of pinned photodiodes with no-gap or conventional microlens have been designed and fabricated based on 0.18-μm CMOS process. The test results show that, compared with the photodiode with a conventional microlens, the sensitivity is increased about 74% and the optical crosstalk is reduced up to 7.2% for the photodiode with a no-gap microlens. Thus, the small-pixel-size pinned photodiode with no-gap microlens shows advantages in applications of high-resolution optical detectors and high-quality CMOS image sensors.

Surface plasmon resonance biosensor for parallelized detection of protein biomarkers in diluted blood plasma

Surface plasmon resonance (SPR) biosensor for high-throughput screening of protein biomarkers in diluted blood plasma is reported. The biosensor combines a high-resolution SPR imaging sensor and a high-density protein array with low-fouling background. The SPR imaging sensor utilizes polarization contrast and advanced referencing and provides a total of 120 sensing areas (each 200 μm × 150 μm). Antibodies are immobilized on the sensing areas via hybridization of antibody–oligonucleotide conjugates to thiolated complementary oligonucleotides microspotted on the sensor surface (DNA-directed immobilization). A low-fouling background is achieved by covalent immobilization of bovine serum albumin to carboxyl-terminated thiols filling the areas among the thiolated oligonucleotides and outside the sensing areas. The biosensor was evaluated for detection of protein biomarkers relevant to cancer diagnostics—human chorionic gonadotropin (hCG) and activated leukocyte cell adhesion molecule (ALCAM) both in buffer and in 10% blood plasma. Limits of detection as low as 45 ng/mL (ALCAM) and 100 ng/mL (hCG) were achieved in blood plasma samples.

Hyperspectral interferometry for single-shot absolute measurement of two-dimensional optical path distributions

We propose a method that we call hyperspectral interferometry (HSI) to resolve the 2π phase unwrapping problem in the analysis of interferograms recorded with a narrow-band light source. By using a broadband light source and a hyperspectral imaging system, a set of interferograms at different wave numbers are recorded simultaneously on a high resolution image sensor. These are then assembled to form a three-dimensional intensity distribution. By Fourier transformation along the wave number axis, an absolute optical path difference is obtained for each pixel independently of the other pixels in the field of view. As a result, interferograms with spatially distinct regions are analysed as easily as continuous ones. The approach is illustrated with a HSI system to measure 3D profiles of optically smooth or rough surfaces. Compared to existing profilometers able to measure absolute path differences, the single-shot nature of the approach provides greater immunity from environmental disturbance.

Analytical performance during ratiometric long-term imaging of pH in bioturbated sediments

In this study, the long-term analytical performance of a high-resolution ratiometric imaging sensor for pH was quantitatively determined. The sensor was applied in an experimental microcosm to illustrate biogeochemical consequences from mining activities by the chemosymbiotic bivalve Thyasira sarsi. Utilizing time-correlated pixel-by-pixel calibration protocols during imaging, close to 90% of the pixels were associated with a precision (S.D.) of <0.05 pH units at the end of an experimental period of 17 days. For comparison, a precision of <0.05 pH units was achieved for less than 50% of the pixels throughout experiments using conventional pre-sample calibration procedures. The average standard deviation of pixels was 0.01 pH units. Image analysis of single pixel derivatives and pH measurements over time suggested that T. sarsi affect pH distributions and general sediment geochemistry more than would be expected based on the small size of the bivalves. A significant decrease of pH in the overlying water suggested a considerable release of reduced compounds from the exhalent stream of the thyasirids. Strong pH gradients were demonstrated not only across the sediment-water interface but, also associated with bioturbation activities immediately adjacent to T. sarsi burrowing tracts, inhalant tubes and pedal tracts in the sediment matrix. Gradients of up to 1.16 pH units per mm were observed.

Hyperspectral interferometry for single-shot absolute measurement of 3-D shape and displacement fields

We propose a method that we call Hyperspectral Interferometry (HSI) to resolve the 2π phase unwrapping problem in the analysis of interferograms recorded with a narrow-band light source. By using a broad-band light source and hyperspectral imaging system, a set of interferograms at different wavenumbers are recorded simultaneously on a high resolution image sensor. These are then assembled to form a three-dimensional intensity distribution. By Fourier transformation along the wavenumber axis, an absolute optical path difference is obtained for each pixel independently of the other pixels in the field of view. As a result, interferograms with spatially distinct regions are analysed as easily as continuous ones. The approach is illustrated with a HSI system to measure 3-D profiles of optically smooth or rough surfaces. Compared to existing profilometers able to measure absolute path differences, the single shot nature of the approach provides greater immunity from environmental disturbance.