Typical Pixel Research Articles

A comparative analysis of different spatial sampling schemes: Modelling of SSRB data

Low spatial resolution satellite sensors provide information over relatively large targets with typical pixel resolutions of hundreds of km2. However, the spatial scales of ground measurements are usually much smaller. Such differences in spatial scales makes the interpretation of comparisons between quantities derived from low resolution sensors and ground measurements particularly difficult. It also highlights the importance of developing appropriate sampling strategies when designing ground campaigns for validation studies of low resolution sensors. We make use of statistical modelling of high resolution surface shortwave radiation budget (SSRB) data to look into this problem. A spatial model that describes the SSRB over a selected region is proposed, and the impact of different sampling schemes in the performance of the model is analysed. Both systematic and random sampling schemes can efficiently represent the full observations set. **Current affiliation: Meteorological Office, Hadley Centre for Climate Prediction and Research, UK

SPICE Models of Fluorine-Ion-Irradiated CMOS Devices

CMOS image sensors are attractive for space applications due to their low-power and system-on-chip features. The typical active pixel sensor (APS) is composed of a photodiode and several transistors. Using Fluorine +7 ions with an energy of 17 MeV, the effects of radiation are investigated on photodiodes and transistors manufactured using a standard 0.35-mum CMOS process. Simulation results show that the range of these ions overlaps with the active region of the device. Thus, the proximity effect of the ions on the performance of the device can be important. The tested photodiode showed a leakage current increase after it was irradiated with fluorine ions. The ideality factor of recombination current is observed to increase up to 4. Moreover, an increase in leakage current and absolute threshold voltage was observed in fluorine-ion-irradiated nMOS and pMOS transistors. In this paper, behavioral SPICE models are developed to analyze the contribution of these components to an overall increase in dark current of a CMOS APS.

Data- and Gate-Line-Sharing Pixel Structure and Driving Method for Low-Cost Polycrystalline Silicon Thin Film Transistor Liquid Crystal Displays

In this paper, we propose a cost-effective pixel structure and its driving method for polycrystalline silicon (poly-Si) thin film transistor liquid crystal displays (TFT-LCDs). That reduces the number of data and gate lines to half that of a TFT-LCD panel with a typical pixel structure. This leads to a reduction in the cost of the panel because the number of driver ICs is halved. Using only P-channel TFTs reduces the process cost, because fewer masks are needed than for pixel structures with both P- and N-channel TFTs. Provided that the inversion polarity of the two pixels sharing a data line is the same, the driving power consumption is reduced because the dynamic voltage swing range is decreased and the number of necessary data and gate lines is reduced. Finally, the proposed pixel structure can minimize the ΔVp, the kickback voltage at the pixel electrode with respect to the gate-drain parasitic capacitance, variation of the four pixels that share one data line and one gate line. This results in high image quality. The proposed data- and gate-line-sharing pixel structure is suitable for the fabrication of TFT-LCD panels in mobile applications at a low cost, with low power consumption and high image quality.

Study of Animal Bio-Ceramic Implants with 3D High Resolution CT

Animal implants experiments are obligatory when developing human artificial hard tissues, such as bio-ceramics. Optical microscope is often used to inspect implant slices but may destroy original status when slicing up. We tried 3D high resolution CT to nondestructively study biocompatibility and degradation of bio-ceramics implants. 3D CT provides 3D structure information. Typical pixel size of 3D high resolution CT is 50 microns. Generally, implants differs with tissues in density and structure, on basis of which we can identify details with CT slice. Experiments of bio-ceramic implanted into rabbit hip are also showed. Interaction could be identified at interface between implant and tissue.

Three-dimensional optical modeling and optimizations of color filter liquid-crystal-on-silicon microdisplays

We have developed a three-dimensional (3D) optical modeling of small color pixels in color filter liquid-crystal-on-silicon (CF-LCOS) microdisplays. The 3D optical modeling includes a LC electromechanical analysis of color LC cells, a calculation of optical reflectance using the extended Jones matrix, and a standard RGB (sRGB) representation of the optical reflectance in the pixel array. The simulated optical reflectance agreed well with the experiments. With this 3D optical analysis as a tool, the relation of the lateral color fringing field with pixel size and thickness of color filter were studied. Minimizations of the fringing field in the CF-LCOS microdisplays were obtained by pixel arrangement, rubbing direction, and LC mode. The color purity of the CF-LCOS microdisplays could attain 63% National Television System Committee (NTSC) level for a typical pixel size of 15μm. With an optimized LC mode, the color purity could still be maintained at 54% NTSC level even when the pixel size was reduced to 9μm. This enabled the feasibility of the CF-LCOS microdisplays for very high-resolution display applications.

High-Performance Planar pH Fluorosensor for Two-Dimensional pH Measurements in Marine Sediment and Water

A new plate fluorosensor foil was developed for two-dimensional pH measurement in marine sediments and overlying waters. The fluorescent dye 8-hydroxy-1,3,6-pyrenetrisulfonic acid trisodium salt (HPTS) was covalently linked onto a transparent poly(vinyl alcohol) membrane backed by polyester sheet. Both excitation and emission bands of the immobilized HPTS showed large red shifts in comparison to HPTS in free solution. The ratio of fluorescence emission intensities at 540 nm following successive excitation at 506 and 428 nm was pH-sensitive and correlated with pH changes from 5.5 to 8.6. These properties are robust and insensitive to factors such as intensity of light source, temperature, and oxygen concentration. The plate sensor responded rapidly (< 2 min), reversibly, and with high precision to pH changes in solution and in sediment. The stability of the sensor was also tested by continually changing the pH between 6 and 8. Performance of the sensor did not vary after > 200 pH cycles. Furthermore, the sensor foil retained its original properties after continuous exposure to natural marine sedimentfor 2 months. The plate optode has been successfully used to measure two-dimensional pH distributions in intertidal flat and subtidal sediment. Images are readily obtained with inexpensive light-emitting diode (LED) excitation and commercial-grade digital cameras with typical pixel resolution of approximately 50 x 50 microm over areas > 150 cm2.

Estimating combustion of large downed woody debris from residual white ash

The production of residual white ash patches within wildfires represents near-complete combustion of the available fuel and releases a considerable quantity of gases to the atmosphere. These patches are generally produced from combustion of large downed woody debris (LDWD) such as fallen trees and snags. However, LDWD are generally ignored in calculations of fuel combusted within environments where surface fires dominate (e.g. southern African savannas). To assess the potential of fractional white ash cover as a remotely sensed measure of LDWD combustion, both the proportion of the surface covered by white ash and the combustion completeness required to produce white ash must be quantified. An aerial photograph of woodland savanna fires in north-western Zimbabwe was analysed to estimate the proportion of white ash cover within a typical satellite sensor pixel. The proportion loss on ignition (LOI) of wood samples from the study area was measured and combined with previous estimates of mean tree biomass. The proportion of white ash within the aerial photographs was 0.2% (± 0.06), which corresponded to an additional 67 320 kg ha−1 of biomass combusted above that typically recorded as combusted from a surface fire in this environment (~7000 kg ha−1). This analysis should be repeated in other savannas and forests, where pre-fire fuel loads and post-fire fractional white ash cover may be higher.

Antenna-coupled infrared detectors for imaging applications

Infrared focal plane arrays (IRFPAs) are a critical component in advanced infrared imaging systems. IRFPAs are made up of two parts, a detector array and a readout integrated circuit (ROIC) multiplexer. Current ROIC technology has typical pitch sizes of 20/spl times/20 to 50/spl times/50 /spl mu/m/sup 2/. In order to make antenna-coupled detectors suited for infrared imaging systems, two-dimensional (2-D) arrays have been fabricated that cover a whole pixel area with the penalty of increasing the noise figure of the detector and, therefore, reducing its performance. By coupling a Fresnel zone plate lens to a single element antenna-coupled detector, infrared radiation can be collected over a typical pixel area and still keep low-noise levels. A Fresnel zone plate lens coupled to a single-element square-spiral-coupled infrared detector has been fabricated and its performance compared to single element antenna-coupled detectors and 2-D arrays of antenna coupled detectors. Measurements made at 10.6 /spl mu/m showed a two-order-of-magnitude increase in SNR and a /spl sim/3/spl times/ increase in D/sup */ as compared to 2-D arrays of antenna-coupled detectors.

Antenna-coupled infrared focal plane array

Uncooled bolometric detectors used in infrared-imaging systems have slow time constants (∼15 ms), which makes them impractical for fast-frame-rate applications. Antenna-coupled microbolometers are fast uncooled detectors with good sensitivity and directivity, and they can be polarization and wavelength selective. These detectors have collection areas in the order of 10 μm2, which are too small for infrared imaging systems where a typical pixel area ranges from 20 × 20 μm2 to 50 × 50 μm2. To solve this problem, 2D arrays of antenna-coupled detectors, which can be used as pixels in infrared-imaging systems, are fabricated. In this paper, antenna-coupled pixels are fabricated on a commercial readout integrated circuit (ROIC), resulting in the first antenna-coupled infrared focal plane array (IR-FPA). Measurements made on this antenna-coupled infrared focal plane array show that the integration of antenna-coupled detectors to a commercial ROIC is possible. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 165–166, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21294

High Fill-Factor Imagers for Neuromorphic Processing Enabled by Floating-Gate Circuits

In neuromorphic modeling of the retina, it would be very nice to have processing capabilities at the focal plane while retaining the density of typical active pixel sensor (APS) imager designs. Unfortunately, these two goals have been mostly incompatible. We introduce our transform imager technology and basic architecture that uses analog floating-gate devices to make it possible to have computational imagers with high pixel densities. This imager approach allows programmable focal-plane processing that can perform retinal and higher-level bioinspired computation. The processing is performed continuously on the image via programmable matrix operations that can operate on the entire image or blocks within the image. The resulting dataflow architecture can directly perform computation of spatial transforms, motion computations, and stereo computations. The core imager performs computations at the pixel plane, but still holds a fill factor greater than 40 percent—comparable to the high fill factors of APS imagers. Each pixel is composed of a photodiode sensor element and a multiplier. We present experimental results from several imager arrays built in 0.5 m process (up to in an area of 4 millimeter squared).

Two Dimensional Array of Antenna-Coupled Microbolometers

Antenna-coupled microbolometers are known for having short time constants and high responsivity, but their small dimensions make them unsuitable for imaging applications where a typical pixel area is generally greater than 20 × 20 μm2. In this paper a two dimensional array of antenna-coupled microbolometers is demonstrated as an area receiver. Using the response of microbolometers to visible frequencies a two-dimensional diagnostic scan in the visible was performed on these arrays which allowed measurement of their homogeneity. Frequency response measurements gave time constants around 130 nsec, similar to the ones obtained for single element microbolometers which indicates that a detector of virtually any size can be fabricated without sacrificing time response. Response and noise measurements show lower noise and higher responsivity compared to single element microbolometers. These results make two-dimensional arrays of antenna-coupled microbolometers a promising option for development of pixels in infrared focal plane arrays.

Detective quantum efficiency of a direct-detection active matrix flat panel imager at megavoltage energies.

The use of an amorphous selenium (a-Se) based direct-detection active matrix flat-panel imager (AMFPI) is studied for megavoltage imaging. The detector consists of a 1.2 mm copper front plate and 200 microm a-Se layer, and has a 85 microm pixel pitch. The Modulation Transfer Function (MTF), Noise Power Spectrum (NPS), and Detective Quantum Efficiency (DQE) are measured for 6 and 15 MV photon beams. A theoretical expression for the DQE is derived using a recently developed formalism for nonelementary cascade stages. A comparison of theory with experiment is good for the 6 and 15 MV beams. The model is used to explore the DQE for more typical pixel sizes. The results indicate that with proper modifications, such as a larger a-Se thickness, a direct flat-panel AMFPI is a very promising detector for megavoltage imaging.

A 640×512 CMOS image sensor with ultrawide dynamic range floating-point pixel-level ADC

Analysis results demonstrate that multiple sampling can achieve consistently higher signal-to-noise ratio at equal or higher dynamic range than using other image sensor dynamic range enhancement schemes such as well capacity adjusting. Implementing multiple sampling, however, requires much higher readout speeds than can be achieved using typical CMOS active pixel sensor (APS). This paper demonstrates, using a 640/spl times/512 CMOS image sensor with 8-b bit-serial Nyquist rate analog-to-digital converter (ADC) per 4 pixels, that pixel-level ADC enables a highly flexible and efficient implementation of multiple sampling to enhance dynamic range. Since pixel values are available to the ADC's at all times, the number and timing of the samples as well as the number of bits obtained from each sample can be freely selected and read out at fast SRAM speeds. By sampling at exponentially increasing exposure times, pixel values with binary floating-point resolution can be obtained. The 640/spl times/512 sensor is implemented in 0.35-/spl mu/m CMOS technology and achieves 10.5/spl times/10.5 /spl mu/m pixel size at 29% fill factor. Characterization techniques and measured quantum efficiency, sensitivity, ADC transfer curve, and fixed pattern noise are presented. A scene with measured dynamic range exceeding 10000:1 is sampled nine times to obtain an image with dynamic range of 65536:1. Limits on achievable dynamic range using multiple sampling are presented.

Arterial phase carotid and vertebral artery imaging in 3D contrast‐enhanced MR angiography by combining fluoroscopic triggering with an elliptical centric acquisition order

Arterial-phase three-dimensional (3D) contrast-enhanced MR angiograms of the carotid and vertebral arteries from their origins through the carotid bifurcations were obtained in 20 patients using acquisition times over 30 sec by using an MR fluoroscopy-triggered pulse sequence with elliptical centric view order. The typical pixel size was 0.8 mm (x) x 1.6 mm (y) x 1.5 mm (z), and 32-48 coronal slices were acquired. The fluoroscopic monitoring of bolus arrival was effective in 18 of the 20 cases; two failures were attributed directly to a poor choice of RF coil. To exploit peak arterial-to-venous contrast, the central 3D views were acquired first in the most compact time period possible for the given TR. For the 18 successfully triggered cases, arterial-phase 3D images were obtained with excellent venous suppression as demonstrated by an average internal jugular vein to common carotid signal enhancement ratio of only 0.05 +/- 0.04.

Characterization of a 64 channel PET detector using photodiodes for crystal identification

The authors present performance results for a prototype PET detector module consisting of 64 LSO scintillator crystals (3/spl times/3/spl times/20 mm) coupled on one end to a single photomultiplier tube and on the opposite end to a 64 pixel array of 3 mm square silicon photodiodes (typical pixel parameters are 5 pF capacitance, 300 pA dark current, and 73% quantum efficiency at 415 nm). The photomultiplier tube (PMT) provides an accurate timing pulse and energy threshold for all crystals in the module, the silicon photodiodes (PD) identify the crystal of interaction, the sum (PD+PMT) provides a total energy signal, and the PD/(PD+PMT) ratio determines the depth of interaction. With 32 of the channels instrumented, the detector module correctly identifies the crystal of interaction (where correct includes the adjacent 4 crystals) 79/spl plusmn/4% of the time with high detection efficiency. The timing resolution for a single LSO detector module is 750 ps fwhm, while its pulse height resolution at 511 keV is 24/spl plusmn/3% fwhm. The depth of interaction measurement resolution is 8/spl plusmn/1 mm fwhm.

New Technique of the X-Ray Efficiency Measurement of a Charge-Coupled Device with a Subpixel Resolution

We report the use of a new technique to measure the X-ray detection efficiency of a charge-coupled device (CCD) with subpixel resolution. The new technique makes use of a parallel X-ray beam and metal mesh placed just in front of the CCD. The CCD camera we used is a conventional system using the TC213 (Texas Instrument Japan (TIJ)) whose pixel size is 12 µ m ×12 µ m with one million pixels. The mesh has 4 µm diameter holes spaced at 12 µm intervals. We produced an efficiency map within a typical pixel showing the gate structure in detail: a virtual gate, a clock gate and an antiblooming gate. The gate structure we measured is consistent with the manufacturer's design value. By selecting single pixel events, we detected a pixel boundary. Additional plans for application will also be discussed.

3D: The next generation near-infrared imaging spectrometer

The new MPE near infrared imaging spectrometer 3D represents a new generation of astronomical instrumentation. It is based on a 2562 NICMOS-3 Rockwell array and can simultaneously obtain 256 H - or K -band spectra at R = 1100 or 2100 from a square 16×16 pixel field on the sky. Typical pixel scales are 0.3″/pixel or 0.5″/pixel. 3D is a combination of a novel image slicer and a liquid nitrogen cooled long slit spectrometer. It includes high definition on-axis lens optics, a high efficiency directly ruled KRS-5 grism as well as a cold closed-loop piezo-driven tilt mirror allowing full spectral sampling. The instrument efficiency including detector is 15%. Combining the advantages of imaging and spectroscopy increases the observing efficiency on key astronomical objects (e.g. galactic nuclei) by such a large factor over existing grating or Fabry-Perot spectrometers that subarcsecond near-IR spectroscopy of faint Seyferts, starbursts, quasars, or distant galaxy clusters becomes feasible for the first time with 4m-class telescopes. As a portable instrument 3D has already been successfully deployed on several 2 and 4m-class telescopes.

Picture quality of different pixel arrangements for large‐sized matrix displays

AbstractThe image information theory is introduced to the study of pixel arrangement for flat displays which has been based mainly on subjective evaluation tests. the objective is to make a theoretical elucidation of the relations between different pixel arrangements‐particularly pixel arrangements of light‐emissive elements for large‐sized matrix displays‐and picture quality.First, the factors determining picture quality are identified using a picture model incorporating the sampling of the original picture. As a result, the Nyquist limits are shown to be essential.Second, the Nyquist limits of different pixel arrangements are evaluated. the areas surrounded by the Nyquist limits are shown to consist of colored and discolored regions. This observation is used to relate the Nyquist limits to visual limits and picture quality.Third, the picture quality of typical pixel arrangements for large‐sized matrix displays is examined. the quality of still and motion pictures displayed by the RGB‐trio and RGGB‐mosaic arrangements are compared by means of subjective evaluation tests and three‐dimensional spectrum analysis. the comparative analysis gives the following conclusions: In displaying still pictures, the RGGB‐mosaic arrangement has the effective number of pixels about twice the real number of pixels because of the overlaps of adjacent pixels, but the RGB‐trio does not have this effect. In displaying motion pictures, the RGGB‐mosaic arrangement provides better picture quality than in the case of still pictures but the RGB‐trio arrangement does not.

Estimating errors in fractional cloud cover obtained with infrared threshold methods

Differences between spatial coherence and infrared threshold derived cloud cover were used to estimate errors in cloud cover that arise through the application of thresholds to imagery data. The differences indicated that threshold errors could be predicted by assuming that the cloud cover at the scale of a typical satellite imagery pixel (4–8 km) is uniformly distributed between some small value δ (δ &lt; 0.2) and 1 − δ. In this study, results were obtained for single‐layered cloud systems from four oceanic regions. Cloud cover was analyzed for both (60 km)2 and (250 km)2 regions. Three distinct infrared thresholds were used: (1) a “cloud‐free threshold” for which the threshold was set slightly below the radiance observed for cloud‐free pixels in the region; (2) an “overcast threshold” for which the threshold was set just above the radiance observed for pixels that were overcast in the region, and (3) a “midpoint threshold” for which the threshold was set midway between the radiances observed for cloud‐free and overcast pixels. For the cloud‐free threshold, cloud cover was overestimated; for the overcast threshold, cloud cover was underestimated, and for the midpoint threshold there was relatively little difference between the threshold and spatial coherence derived cloud cover. Mean differences in cloud cover were as large as 0.25 for (60 km)2 regions and 0.18 for (250 km)2 regions. Mean and rms differences reached maximum values when the regional cloud cover was 0.5. The fraction of 4‐ to 8‐km imager pixels that were neither cloud free nor overcast was approximately 0.5. Furthermore, when the regional cloud cover (60–250 km) was small, the cloud cover in partially covered imager pixels was also small; likewise, when the regional cloud cover was large, the cloud cover in partially covered imager pixels was also large. This connection between regional scale cloud cover and 4‐ to 8‐km pixel scale cloud cover suggests a link between large‐scale fields which govern the regional cloud cover and the small‐scale disturbances to the large‐scale fields, which must govern the pixel scale cloud fraction.

An experimental 10 MHz low power CMOS analog front-end for pixel detectors

The specifications for a true 2-dimensional pixel detector for use in elementary particle physics are discussed. A design of integrated front-end electronics for such a pixel detector with a typical pixel capacitance of 20 fF is described. It comprises a charge amplifier, a latched comparator and a local memory cell. Power dissipation per pixel element is only 30 μW.