Charge Coupled Device Readout Research Articles

Spectroscopic flat-fields can be used for precision CCD gain and noise tests

Abstract One of the basic parameters of a charge coupled device (CCD) camera is its gain, that is, the number of detected electrons per output Analogue to Digital Unit (ADU). This is normally determined by finding the statistical variances from a series of flat-field exposures with nearly constant levels over substantial areas, and making use of the fact that photon (Poisson) noise has variance equal to the mean. However, when a CCD has been installed in a spectroscopic instrument fed by numerous optical fibres, or with an echelle format, it is no longer possible to obtain illumination that is constant over large areas. Instead of making do with selected small areas, it is shown here that the wide variation of signal level in a spectroscopic ‘flat-field’ can be used to obtain accurate values of the CCD gain, needing only a matched pair of exposures (that differ in their realisation of the noise). Once the gain is known, the CCD readout noise (in electrons) is easily found from a pair of bias frames. Spatial stability of the image in the two flat-fields is important, although correction of minor shifts is shown to be possible, at the expense of further analysis.

Design and Characterizations of the Radiation-Hardened XCR4C ASIC for X-Ray CCDs for Space Astronomical Applications

Correlated double sampling (CDS) circuits are essential to processing the X-ray charge-coupled devices (CCDs) that have been widely used in the modern X-ray astronomical field. For timing observations, both energy resolution and timing resolution are of great importance. We are developing the XCR4C application-specific integrated circuit (ASIC), which is a fully customized four-channel radiation-hardened CDS ASIC targeting the readout of X-ray CCDs, for future space astronomical missions. The ASIC is implemented in a differential switched-capacitor architecture, making it highly linear, low power, immune to common-mode noise and interferences, as well as easily configurable. To combat the harsh low-earth-orbit space environment, some radiation-hardening techniques are applied, including the process hardening method, even-finger double-side bulk butting, and pseudo-double guard ring layout techniques. The XCR4C ASIC was fabricated with 0.35- $\mu \text{m}$ 2P4M CMOS technology with an epitaxial layer. The ASIC achieves a maximum 23-ppm integral nonlinearity and 5.8 e− rms equivalent noise charge under a typical 1-MHz pixel rate and only consumes 50 mW approximately from a single 3.3-V supply voltage. The results from radiation hardness assurance testing show that the ASIC has at least a total ionizing dose tolerance of 300 krad(Si), and no single-event latchup has been found up to a linear energy transfer of $81.35~\text {MeV}\cdot \text {cm}^{2}$ /mg with a total fluence up to $1.68\times 10^{7}$ ions/cm2.

High-Throughput Cell Imaging and Classification by Narrowband and Low-Spectral-Resolution Raman Microscopy.

We investigated the use of narrowband Raman spectra for rapid label-free molecular imaging aimed at cell classification using principal component regression and linear discriminant analysis. In the classification of breast nontumorigenic epithelial and cancer cell lines, the classification accuracies using a spectral range of 100 cm-1 were equivalent to or better than that with using the fingerprint and high-wavenumber regions. Narrowing the Raman spectral range for analysis allows reduction of the charge-coupled device (CCD) pixels required for spectrum detection, resulting in the improvement of image acquisition speed with adequate classification accuracy. Our measurements revealed that the wavenumber region at 1397-1501 cm-1 can provide molecular information sufficient for cell classification without causing notable errors in the baseline-correction. A spectral resolution of ∼9 cm-1 was found to be sufficient to provide high accuracy in cell classification, which allowed us to apply pixel binning at the CCD readout for further acceleration of the imaging speed. As a result, the acquisition time for a 1200 × 1500 pixels Raman hyperspectral image at 1397-1501 cm-1 was reduced to 21 min. Under this condition, different cell lines were classified at accuracies higher than 90%. The presented approach will improve throughput of cell and tissue analysis and classification using Raman spectroscopy and extend practical uses of Raman imaging in biology and medicine.

Importance of charge capture in interphase regions during readout of charge-coupled devices

The current understanding of charge transfer dynamics in charge-coupled devices (CCDs) is that charge is moved so quickly from one phase to the next in a clocking sequence and with a density so low that trapping of charge in the interphase regions is negligible. However, simulation capabilities developed at the Centre for Electronic Imaging, which includes direct input of electron density simulations, have made it possible to investigate this assumption further. As part of the radiation testing campaign of the Euclid CCD273 devices, data have been obtained using the trap pumping method, a method that can be used to identify and characterize single defects within CCDs. Combining these data with simulations, we find that trapping during the transfer of charge among phases is indeed necessary to explain the results of the data analysis. This result could influence not only trap pumping theory and how trap pumping should be performed but also how a radiation-damaged CCD is readout in the most optimal way.

C2D8: An eight channel CCD readout electronics dedicated to low energy neutron detection

Position-sensitive detectors for cold and ultra-cold neutrons (UCN) are in use in fundamental research. In particular, measuring the properties of the quantum states of bouncing neutrons requires micro-metric spatial resolution. To this end, a Charge Coupled Device (CCD) coated with a thin conversion layer that allows a real time detection of neutron hits is under development at LPSC. In this paper, we present the design and performance of a dedicated electronic board designed to read-out eight CCDs simultaneously and operating under vacuum.

A Fully Integrated 0.055% INL X-ray CCD Readout ASIC with Incremental <inline-formula> <tex-math notation="LaTeX">$\Delta \Sigma {\text{ADC}}$</tex-math> </inline-formula>

A fully integrated 100 kHz X-ray charge coupled device (CCD) readout application specific integrated circuit (ASIC) employing delta sigma ( $\Delta \Sigma $ ) digitization is presented. To achieve high linearity with small chip size and low power consumption, the correlated double sampling (CDS) is realized by the $\Sigma \Delta{\rm ADC}$ instead of the analog front end (AFE) as in conventional CCD readout circuits. Besides, the proposed decimation filter features simple structure and eases the integration. The chip is fabricated in $0.35 \upmu\hbox{m}$ CMOS technology and the measured integral nonlinearity (INL) throughout the input dynamic range of ASIC is 0.055% with $35.1 \pm 0.3 \upmu\hbox{V}$ input referred noise. A CCD detection system is built and tested with the sensitivity of CCD being $4 \upmu\hbox{V}/\hbox{e}^-$ . The integration test results show that the readout noise is $11.8 \hbox{e}^ {-} $ at 100 kHz readout pixel rate and the achieved energy spectrum resolution is $168 \hbox{eV} \pm 4.7 \hbox{eV}$ (Full Width at Half Maximum: FWHM) at 5.9 keV.

Optimal CCD readout by digital correlated double sampling

Digital correlated double sampling (DCDS), a readout technique for charge-coupled devices (CCD), is gaining popularity in astronomical applications. By using an oversampling ADC and a digital filter, a DCDS system can achieve a better performance than traditional analogue readout techniques at the expense of a more complex system analysis. Several attempts to analyse and optimize a DCDS system have been reported, but most of the work presented in the literature has been experimental. Some approximate analytical tools have been presented for independent parameters of the system, but the overall performance and trade-offs have not been yet modelled. Furthermore, there is disagreement among experimental results that cannot be explained by the analytical tools available. In this work, a theoretical analysis of a generic DCDS readout system is presented, including key aspects such as the signal conditioning stage, the ADC resolution, the sampling frequency and the digital filter implementation. By using a time-domain noise model, the effect of the digital filter is properly modelled as a discrete-time process, thus avoiding the imprecision of continuous-time approximations that have been used so far. As a result, an accurate, closed-form expression for the signal-to-noise ratio at the output of the readout system is reached. This expression can be easily optimized in order to meet a set of specifications for a given CCD, thus providing a systematic design methodology for an optimal readout system. Simulated results are presented to validate the theory, obtained with both time- and frequency-domain noise generation models for completeness.

CCD image sensor induced error in PIV applications

The readout procedure of charge-coupled device (CCD) cameras is known to generate some image degradation in different scientific imaging fields, especially in astrophysics. In the particular field of particle image velocimetry (PIV), widely extended in the scientific community, the readout procedure of the interline CCD sensor induces a bias in the registered position of particle images. This work proposes simple procedures to predict the magnitude of the associated measurement error. Generally, there are differences in the position bias for the different images of a certain particle at each PIV frame. This leads to a substantial bias error in the PIV velocity measurement (∼0.1 pixels). This is the order of magnitude that other typical PIV errors such as peak-locking may reach. Based on modern CCD technology and architecture, this work offers a description of the readout phenomenon and proposes a modeling for the CCD readout bias error magnitude. This bias, in turn, generates a velocity measurement bias error when there is an illumination difference between two successive PIV exposures. The model predictions match the experiments performed with two 12-bit-depth interline CCD cameras (MegaPlus ES 4.0/E incorporating the Kodak KAI-4000M CCD sensor with 4 megapixels). For different cameras, only two constant values are needed to fit the proposed calibration model and predict the error from the readout procedure. Tests by different researchers using different cameras would allow verification of the model, that can be used to optimize acquisition setups. Simple procedures to obtain these two calibration values are also described.

Novel fast-arrayed CCD X-ray detector using interline transfer-type CCD for time-resolved X-ray diffraction measurements

A novel fast-arrayed fiber-optic taper (FOT) coupled with a charge-coupled device (CCD) X-ray detector was developed. The interline transfer-type CCDs are used as image sensor. The detector was developed for the simultaneous time-resolved small- and wide-angle X-ray diffraction measurement at SPring-8 BL45XU. The detector consists of an array of two identical units, each comprising a phosphor, a demagnifying FOT, and a large format interline transfer-type CCD as an image sensor. The image stored in the CCD can be read out through the dual readout channels with 12 bits ADC within 220 ms (4.5 fps) without binning and within 65 ms (15 fps) with 8×8 binning. Moreover, this detector does not need to stop the incoming X-rays during the CCD readout and can simultaneously execute both exposure and readout on the CCD with a small dead time of ∼1 μs so that a duty-cycle ratio of almost 100% is achieved. Therefore, it allows the continuous rotation method. The basic performance characteristics of the detector are described.

A 3 × 6 arrayed CCD X-ray detector for continuous rotation method in macromolecular crystallography

A 3 x 6 arrayed charge-coupled device (CCD) X-ray detector has been developed for the continuous-rotation method in macromolecular crystallography at the Photon Factory. The detector has an area of 235.9 mm x 235.9 mm and a readout time of 1.9 s. The detector is made of a 3 x 6 array of identical modules, each module consisting of a fiber-optic taper (FOT), a CCD sensor and a readout circuit. The outputs from 18 CCDs are read out in parallel and are then digitized by 16-bit analog-to-digital converters. The advantage of this detector over conventional FOT-coupled CCD detectors is the unique CCD readout scheme (frame transfer) which enables successive X-ray exposures to be recorded without interruption of the sample crystal rotation. A full data set of a lysozyme crystal was continuously collected within 360 s (180 degrees rotation, 3 s/1.5 degrees frame). The duty-cycle ratio of the X-ray exposure to the data collection time was almost 100%. The combination of this detector and synchrotron radiation is well suited to rapid and continuous data collection in macromolecular crystallography.

Plane-grating flat-field soft x-ray spectrometer

We describe a soft x-ray spectrometer covering the 120–800 eV range. It is intended for resonant inelastic x-ray scattering experiments performed at third generation synchrotron radiation (SR) facilities and has been developed with SOLEIL, the future French national SR source in mind. The Hettrick–Underwood principle is at the heart of the design using a combination of varied line-spacing plane grating and spherical-mirror to provide a flat-field image. It is slitless for optimum acceptance. This means the source size determines the resolving power. A spot size of ⩽5μm is planned at SOLEIL which, according to simulations, should ensure a resolving power ⩾1000 over the whole energy range. A 1024×1024 pixel charge-coupled device (CCD) with a 13μm×13μm pixel size is used. This is an improvement on the use of microchannel-plate detectors, both as concerns efficiency and spatial resolution. Additionally spectral line curvature is avoided by the use of a horizontal focusing mirror concentrating the beam in the nondispersing direction. It allows for readout using a binning mode to reduce the intrinsically large CCD readout noise. Preliminary results taken at beamlines at Elettra (Trieste) and at BESSY (Berlin) are presented.

The effect of protons on E2V Technologies L3Vision CCDs

The effect of different 10 MeV equivalent proton fluences on the performance of E2V Technologies (formerly Marconi applied technologies, formerly EEV) L3Vision Charge Coupled Devices (CCDs) was investigated. The first experimental radiation damage results of the L3Vision device are presented, with emphasis given to the analysis of damage to the gain register of the device. Changes in dark current and generation of bright pixels in the CCD image, store, readout register and gain register as a result of proton irradiation are reported and viewed in light of the potential use of the device in space-based applications.

A fast CCD vertex detector for the future linear collider: some recent developments

Experiments at a future e +e − linear collider will require a high-performance vertex detector to identify heavy quarks in multi-jet final states. The SLD experiment at SLAC has successfully demonstrated that charge-coupled devices (CCDs) are ideal candidates for this role, offering excellent two-dimensional spatial resolution with extremely low mass.This paper discusses recent R&D studies aimed at further reducing the vertex detector material budget and significantly increasing the CCD readout speed, in order to extend the physics reach of the future linear collider. A radical new CCD architecture is described, which would enable a CCD-based vertex detector to be used in the extremely challenging environment of the superconducting TESLA collider.

A Wide‐Field Spectral Imager

ABSTRACTA spectroscopic imager was designed and constructed to provide a new capability for measuring the spectrum of the sky across wide fields of view. The instrument uses a high‐speed optical system to form an image on the entrance slit of a matching stigmatic spectrograph, which then disperses a spectrum of a strip of the sky onto a charge‐coupled device (CCD). A separate direct imaging system controls pointing and tracking, and both instruments share in tandem a computer‐controlled mounting which permits automated data acquisition. The demonstrated optical performance is a 4 Å × 11′′ single‐pixel resolution in a 4000 Å × 3 .°2 field. Absolute calibration on Vega gives a response at 6563 Å that is 7 times the CCD readout noise at an integrated exposure of 1 photon cm−2 Å−1. Sample airglow, nebular, stellar, and cometary spectra illustrate the detection of extended emission features with fluxes from 5 to 2000 R. A measurement of zenith brightness for Na and Hg emission lines from urban artificial lighting is tabulated.

Exploration of X-ray and charged-particle spectroscopy with CCDs and PSDs

Two alternative detector types have been studied for use in the Eindhoven Scanning Ion Microprobe set-up. First, the applicability of a Charge Coupled Device (CCD) system for X-ray spectroscopy has been explored. Second, some properties of the SiTek type 1L30 Position Sensitive Detector (PSD) for charged-particle spectroscopy have been studied. A literature survey shows that excellent X-ray spectroscopy with a CCD system is feasible, particularly with a deep-depletion backside-illuminated CCD and low speed read-out. If, however, high-speed CCD read-out is required, such as for scanning microprobe experiments, a CCD system cannot be used for spectroscopy due to excess read-out noise. For the PSD, noise theory calculations are presented, which result in a noise shaping time for optimal energy and position resolution. In practice, however, a much longer time is needed to obtain sufficient energy and position linearity. Characterization measurements of the PSD using our 4 MeV He + microprobe are also described. A position resolution of 0.47 mm and a position linearity of better than 0.15% detector length are found. In addition, an energy linearity better than 0.3% and an energy resolution of 36 keV are measured. The latter will have to be improved, to make the PSD suitable for charged-particle spectroscopy applications.

Design and performance of the SLD vertex detector: a 307 Mpixel tracking system

This paper describes the design, construction, and initial operation of SLD's upgraded vertex detector which comprises 96 two-dimensional charge-coupled devices (CCDs) with a total of 307 Mpixel. Each pixel functions as an independent particle detecting element, providing space point measurements of charged particle tracks with a typical precision of 4 μm in each co-ordinate. The CCDs are arranged in three concentric cylinders just outside the beam-pipe which surrounds the e +e − collision point of the SLAC Linear Collider (SLC). The detector is a powerful tool for distinguishing displaced vertex tracks, produced by decay in flight of heavy flavour hadrons or tau leptons, from tracks produced at the primary event vertex. The requirements for this detector include a very low mass structure (to minimize multiple scattering) both for mechanical support and to provide signal paths for the CCDs; operation at low temperature with a high degree of mechanical stability; and high speed CCD readout, signal processing, and data sparsification. The lessons learned in achieving these goals should be useful for the construction of large arrays of CCDs or active pixel devices in the future in a number of areas of science and technology.

Visible spectroscopy in the DIII–D divertor

Spectroscopy measurements in the DIII–D divertor have been carried out with a survey spectrometer that provides simultaneous registration of the visible spectrum over the region 400–900 nm with a resolution of 0.25 nm. Broad spectral coverage is achieved through the use of a fiberoptic transformer assembly to map the curved focal plane of a fast (f/3) Rowland-circle spectrograph [Tugarinov et al., Rev. Sci. Instrum. 66, 603 (1995)] into a rastered format on the rectangular sensor area of a two-dimensional charge-coupled device (CCD) camera. Vertical grouping of pixels during CCD readout integrates the signal intensity over the height of each spectral segment in the rastered image, minimizing readout time. For the full visible spectrum, readout time is 50 ms. Faster response time (<10 ms) may be obtained by selecting for readout just a small number of the 20 spectral segments in the image on the CCD. Simultaneous recording of low charge states of carbon, oxygen, and injected impurities has yielded information about gas recycling and impurity behavior at the divertor strike points. Transport of lithium to the divertor region during lithium pellet injection has been studied, as well as cumulative deposition of lithium on the divertor targets from pellet injection over many successive discharges.

Focal Plane Array Sensor for Imaging Infrared Seeker of Antitank Guided Missile

Technological issues and Processes for fabrication of mercury cadmium telluride detector arrays, charge coupled device readout arrays and integration of these into a focal plane array sensor have been discussed. Mini arrays of 16 X 16 size have been realised and tested to prove the technology and process schedule with a view to scaling up this for larger arrays to be used in the antitank guided missile.

High‐resolution interline image sensors using two‐phase CCD technology

AbstractTwo interline, 30 frames/second, high‐resolution image sensors are described that use two‐phase charge coupled device (CCD) technology. One is a two‐megapixel, interlaced high‐definition television, sensor, and the other is a 1‐megapixel, progressive‐scan sensor for machine vision applications. These sensors include features such as dual‐horizontal CCD readout, antiblooming protection, electronic shutter capability, low smear, and no lag.©1994 John Wiley & Sons Inc

Characteristics of a freely programmable ICCD detector for multichord particle influx measurements on the ASDEX-Upgrade tokamak

The characteristics of a compact space and wavelength-resolving spectrometer-detector arrangement are described which is used to measure spectral line shapes simultaneously along several viewing chords. The system is based upon a freely programmable slow-scan charge-coupled device (CCD) camera gated by an image intensifier tube. Visible and near-UV light emitted near the plasma boundary is collected from up to 12 viewing chords and transmitted to the spectrograph by quartz fibers. Spectra can be recorded with a temporal resolution of 20 ms by means of multiple pixel binning during CCD readout. Integration of the spectral line profiles yield particle fluxes of various low-Z species for ohmically heated helium discharges. The calibration, sensitivity, and signal-to-noise ratio of the system are reconstructed considering each individual element, allowing an easy prediction of the performance of similar applications.