ASTM E2642-09(2015)

Standard Terminology for Scientific Charge-Coupled Device (CCD) Detectors

SIGNIFICANCE AND USE
3.1 This terminology was drafted to exclude any commercial relevance to any one vendor by using only general terms that are acknowledged by all vendors and should be revised as charge-coupled device (CCD) technology matures. This terminology uses standard explanations, symbols, and abbreviations.
SCOPE
1.1 This terminology brings together and clarifies the basic terms and definitions used with scientific grade cooled charge-coupled device (CCD) detectors, thus allowing end users and vendors to use common documented terminology when evaluating or discussing these instruments. CCD detectors are sensitive to light in the region from 200 to 1100 nm and the terminology outlined in the document is based on the detection technology developed around CCDs for this range of the spectrum.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

General Information

• Status: Historical
• Publication Date: 30-Apr-2015
• ICS: 01.040.37 - Image technology (Vocabularies)
• ICS: 37.020 - Optical equipment
• Technical Committee: E13 - Molecular Spectroscopy and Separation Science
• Drafting Committee: E13.08 - Raman Spectroscopy

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:E2642 −09 (Reapproved 2015)
Standard Terminology for
Scientific Charge-Coupled Device (CCD) Detectors
This standard is issued under the fixed designation E2642; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope values, which are specified in terms of bits that can be
manipulated by the computer.
1.1 This terminology brings together and clarifies the basic
terms and definitions used with scientific grade cooled charge-
anti-blooming structure, n—a structure built into the pixel to
coupled device (CCD) detectors, thus allowing end users and
prevent signal charge above full-well capacity from bloom-
vendors to use common documented terminology when evalu-
ing into adjacent pixels.
ating or discussing these instruments. CCD detectors are
DISCUSSION—Anti-blooming structures bleed off any excess charge
sensitive to light in the region from 200 to 1100 nm and the
before they can overflow the pixel and thereby stop blooming. These
terminologyoutlinedinthedocumentisbasedonthedetection structures can reduce the effective quantum efficiency and introduce
nonlinearity into the sensor.
technology developed around CCDs for this range of the
spectrum.
antireflective (AR) coating, n—a coating applied to either the
1.2 The values stated in SI units are to be regarded as
frontsurfaceoftheCCDorthevacuumwindowsurfaces,to
standard. No other units of measurement are included in this
minimizetheamountofreflectedenergy(orelectromagnetic
standard.
radiation) so as to maximize the amount of transmitted
energy.
2. Referenced Documents
back-illuminated CCD (BI CCD), n—a type of CCD that has
2.1 ASTM Standards:
been uniformly reduced in thickness on the side away from
E131Terminology Relating to Molecular Spectroscopy
the gate structure (see Fig. 1b) and positioned such that the
photons are detected on that side.
3. Significance and Use
DISCUSSION—A BI CCD leads to an improvement in sensitivity to
3.1 This terminology was drafted to exclude any commer-
incoming photons from the soft X-ray to the near-infrared (NIR)
cial relevance to any one vendor by using only general terms
regions of the spectrum with the highest response in the visible region.
that are acknowledged by all vendors and should be revised as
However, compared to a front-illuminated CCD, it suffers from higher
dark currents and interference fringe formation (etaloning) usually in
charge-coupled device (CCD) technology matures.This termi-
the NIR region. Also called back-thinned CCD.
nologyusesstandardexplanations,symbols,andabbreviations.
binning, n—the process of combining charge from adjacent
4. Terminology
pixels in a CCD prior to read out.
4.1 Definitions:
DISCUSSION—There are two main types of binning: (1) vertical
advanced inverted mode operation (AIMO), n—a commer-
binningand (2)horizontalbinning(seeFig.2).Summingchargeonthe
cial tradename given to a method of reducing the rate of CCD and doing a single readout results in better noise performance
thanreadingoutseveralpixelsandthensummingtheminthecomputer
generation of dark current. Also known as multi-pinned
memory. This is because each act of reading out contributes to noise
phase operation.
(see noise).
analog-to-digital (A/D) converter, n—an electronic circuitry
CCD bias, n—the minimum analog offset added to the signal
in a CCD detector that converts an analog signal into digital
before the A/D converter to ensure a positive digital output
each time a signal is read out.
This terminology is under the jurisdiction of ASTM Committee E13 on DISCUSSION—The CCD bias is set at the time of manufacture and
Molecular Spectroscopy and Separation Science and is the direct responsibility of
remains set over the lifetime of the camera.
Subcommittee E13.08 on Raman Spectroscopy.
Current edition approved May 1, 2015. Published June 2015. Originally
charge, n—measure of number of electrons that are contained
approved in 2008. Last previous edition approved in 2009 as E2642–09. DOI:
in a pixel potential well.
10.1520/E2642-09R15.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
charge-coupled device (CCD), n—a silicon-based semicon-
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
ductor chip consisting of a two-dimensional matrix of photo
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. sensors or pixels (see Fig. 3).
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2642−09 (2015)
FIG. 1 Cross Sections of Front-Illuminated (a) and Back-Illuminated (b) CCDs
FIG. 2 Example of a 2×2 Vertical and Horizontal Binning Methodology
DISCUSSION—The matrix is usually referred to as the image area. dimension unit of a square pixel is typically given in square microns
Electronic charge is accumulated on the image area and transferred out (for example, a pixel of dimension 26×26 µm is specified as 26×26
by the application of electrical potentials to shielded electrodes. The µm ).
size of pixels in the sensor is typically 26×26 µm; however, sensors
charge transfer, n—the process by which a CCD moves
can be manufactured in a variety of different pixel sizes ranging from
6×6 µm to 50×50 µm. Although mathematically incorrect, the electrons or charge from one pixel to the next.
E2642−09 (2015)
FIG. 3 Typical 1024×256 (26×26 µm pixel) Element CCD Sensor Used for Spectroscopy
charge transfer efficiency (CTE), n—measureoftheabilityof each pixel has its own charge-to-voltage conversion circuit,
the CCD to transfer charge from the point of generation to and the sensor often also includes amplifiers, noise-
the device output.
correction, and digitization circuits. Due to the additional
DISCUSSION—Itisdefinedasthefractionofthechargeinitiallystored
components associated with each pixel, the sensitivity to
in a CCD element that is transferred to an adjacent element by a single
light is lower than with a CCD, the signal is noisier, and the
clock cycle. The value for CTE is not constant but varies with signal
uniformity is lower. But the sensor can be built to require
size, temperature, and clock frequency.
less off-chip circuitry for basic operation (see Fig. 4).
column, n—a line of pixels in the CCD’s image area that is
perpendicular to the horizontal register. correlated double sampling, n—areadoutsamplingtechnique
used to achieve higher precision in CCD readout.
complementary metal oxide semiconductor (CMOS),
n—technology widely used to manufacture electronic de-
vicesandimagesensorssimilartoCCDs.InaCMOSsensor,
FIG. 4 Typical Architectures of CCD and CMOS Sensors
E2642−09 (2015)
DISCUSSION—Thesamplingcircuitissettoapredeterminedreference DISCUSSION—A true 16-bit detector will have a dynamic range of
level and then the actual pixel voltage is sampled in order to find the 65535:1.
difference between the two. The resulting correlation minimizes read
electron-multiplying CCD (EMCCD), n—type of CCD that
noise, especially in ultra-low-noise CCD detectors.
has a two-way readout register, that is, the shift register and
cosmic event, n—a spurious signal caused by a cosmic ray or
the gain register, each with its own output amplifier. When
particle hitting the CCD sensor. It is typically observed to
the charge is read out through the shift register, the detector
resultinahighintensitysignalcomingfromasinglepixelor
works like a standard CCD detector, and when the charge is
small group of pixels.
read out through the gain register, it undergoes charge
amplification as a result of a different electrode structure
dark current, n—a current that occurs naturally through the
embedded underneath the pixels of this register (see Fig. 6).
thermally generated electrons in the semiconductor material
DISCUSSION—Passing charge through the gain register allows the
of the CCD. It is intrinsic to semiconductors and is indepen-
signal to be amplified before readout noise is added at the readout
dent of incident photons.
amplifier, thus improving the signal-to-noise ratios making the camera
DISCUSSION—DarkcurrentisdependantontheCCD’stemperature.It
highly sensitive in the low-light regime.
is expressed in electrons/pixel/unit time.
etaloning, n—a phenomenon by which constructive and de-
dark noise, n—the shot noise associated with the dark current
structive interference fringes are produced in a back-
for the given exposure time, and is approximately equal to
illuminated CCD caused by internal reflections between the
the square root of the dark current times the exposure time
two parallel surfaces of the CCD. Typically BI CCDs
used.Itisusuallyexpressedintermsofnumberofelectrons.
experience etaloning effects when subjected to NIR signals
(see Fig. 5).
deep depletion CCD, n—a CCD that has been designed with
DISCUSSION—This effect causes the device to become transparent to
a thicker active area to provide enhanced sensitivity in the
incoming photons in the NIR region.
NIR and hard X-ray regimes.
DISCUSSION—Both front-illuminated and back-illuminated CCDs can
exposure time, n—the length of time for which a CCD
be manufactured with a deep depletion process to enhance the NIR
accumulated charge.
response; however, such devices cannot be operated in AIMO and are
frame, n—one full image that is read out of a CCD.
also more susceptible to cosmic rays. A back-illuminated deep deple-
tion CCD will have reduced etaloning effects that are typically
frame-transfer CCD, n—a type of CCD whose active image
observed in back-illuminated devices exposed to NIR signals (see Fig.
area is divided into two sections, that is, image area and the
5).
storagearea.Theimageareaisthelightsensitiveareaofthe
dynamic range, n—the ratio of the full well saturation charge
CCDandthestorageareaismaskedtomakeitinsensitiveto
to the system noise level. It represents the ratio of the
light (see Fig. 7).
brightest and darkest signals a detector can measure in a
DISCUSSION—During operation the charge accumulated in the image
single measurement. section is rapidly transferred to the storage section at the end of the
FIG. 5 Cross-Sections of Back-Illuminated (a) and Back-Illuminated Deep Depletion (b) Devices
E2642−09 (2015)
FIG. 6 Typical Sketch of Full-Frame EMCCD Sensor
FIG. 7 Typical Sketch of a Frame-Transfer CCD
exposure time. The storage area is then readout as the image section
full well capacity, n—the maximum number of photoelectrons
accumulateschargeforthenextexposure.ThistypeofCCDreducesor
thatcanbecollectedonasinglepixelintheimageareaorin
eliminatestheneedforashutter,dependingonthespeedofthetransfer
the horizontal register of a CCD. It is typically specified in
from image to storage.
terms of number of electrons.
front-illuminated CCD (FI CCD), n—a type of CCD in
gate structure, n—apolysiliconarrangementofelectrodesthat
which the photons are detected through the gate structure
create pixels and move charge.
located in front of the silicon material of the semiconductor
(see Fig. 1a).
horizontal binning, n—the process that allows charge from a
DISCUSSION—ThistypeofCCDhasmoderatequantumefficiency(see
row of pixels to be combined on the CCD chip prior to
Fig. 8) over the spectral range it covers and it is also free from any
readout (See Fig. 2). Horizontal binning is commonly used
etaloning effects that occur in the back-illuminated CCD when sub-
in spectroscopy to increase the signal level of a data point,
jected to NIR signals. These devices are relatively less expensive to
when less horizontal (or wavelength) resolution is not of
manufacture than the back-illuminated type.
concern.
full-frame CCD, n—a type of CCD that uses the entire silicon
active area for photon detection. A shutter is required to horizontal register, n—a row of light insensitive pixels that is
eliminate image smear (see Fig. 3). located below the CCD’s image acquisition area into which
E2642−09 (2015)
NOTE 1—Image used courtesy of E2V Technologies, 106 Waterhouse Lane, Chelmsford, Essex CM1 2QU, England, http://www.e2v.com.
FIG. 8 Typical QE Curves for FI and BI CCD Sensors
GenIIandGenIII.Themaindifferencebetweenthemisinthematerial
charge from the pixel columns is clocked and subsequently
used in the photocathode. The Gen III models are a more advanced
passed on to the output node to be read out.Also called the
design and they provide higher quantum efficiencies than the Gen II
serial register or readout register.
models.
indium tin oxide (ITO), n—a transparent conductive material
interline transfer CCD, n—a type of CCD designed with
used in some CCD designs to provide an increase in
columns of pixels alternated with masked storage registers
quantum efficiency (QE) in the blue-green region of the
spectrum. soastoincreasetherateofacquisition.Thestorageregisters
occupy a portion of the pixel area reducing the fill factor of
intensified CCD (ICCD), n—a type of CCD camera that has
the diodes under the pixels, and hence, such a CCD
an intensifier block attached in front of it.An ICCD is used
architecture has typically lower quantum efficiencies that
to amplify the incoming signal without varying the image
other types of CCDs (see Fig. 10).
size so as to provide single-photon sensitivity and it can be
electronicallygateddowntonanosecondranges(seeFig.9).
linear array CCD, n—a type of CCD that is comprised of a
DISCUSSION—Intensifiers were initially designed for the military for
single row of pixels that are used as the active area for
night-vision ability and are now being widely used in applications that
capturing incident photons.
need nanosecond gate widths or single-photon sensitivity or both. The
intensifierconsistsofaphotocathode,multichannelplateandphosphor.
multi-pinned phase (MPP), n—mode of operation in CCDs
Alargepotentialdifferenceisappliedacrosstheendsofthemultichan-
nelplatetoamplifythesignal.Therearetwomaintypesofintensifiers: that reduces dark charge.
FIG. 9 Schematic of a Typical Intensifier Fiber Optically Coupled to a CCD Sensor
E2642−09 (2015)
FIG. 10 Typical Sketch of an Interline CCD Sensor
DISCUSSION—Also known as advanced inverted mode operation
outgassing, v—gradual release of gaseous molecules in a
(AIMO).
vacuum chamber that degrades long-term vacuum perfor-
mance.
noise, n—unwantedrandomvariationsofoutput
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E2642 − 09 E2642 − 09 (Reapproved 2015)
Standard Terminology for
Scientific Charge-Coupled Device (CCD) Detectors
This standard is issued under the fixed designation E2642; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This terminology brings together and clarifies the basic terms and definitions used with scientific grade cooled
charge-coupled device (CCD) detectors, thus allowing end users and vendors to use common documented terminology when
evaluating or discussing these instruments. CCD detectors are sensitive to light in the region from 200 to 1100 nm and the
terminology outlined in the document is based on the detection technology developed around CCDs for this range of the spectrum.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
2. Referenced Documents
2.1 ASTM Standards:
E131 Terminology Relating to Molecular Spectroscopy
3. Significance and Use
3.1 This terminology was drafted to exclude any commercial relevance to any one vendor by using only general terms that are
acknowledged by all vendors and should be revised as charge-coupled device (CCD) technology matures. This terminology uses
standard explanations, symbols, and abbreviations.
4. Terminology
4.1 Definitions:
advanced inverted mode operation (AIMO), n—a commercial tradename given to a method of reducing the rate of generation
of dark current. Also known as multi-pinned phase operation.
analog-to-digital (A/D) converter, n—an electronic circuitry in a CCD detector that converts an analog signal into digital values,
which are specified in terms of bits that can be manipulated by the computer.
anti-blooming structure, n—a structure built into the pixel to prevent signal charge above full-well capacity from blooming into
adjacent pixels.
This terminology is under the jurisdiction of ASTM Committee E13 on Molecular Spectroscopy and Separation Science and is the direct responsibility of Subcommittee
E13.08 on Raman Spectroscopy.
Current edition approved April 15, 2009May 1, 2015. Published May 2009June 2015. Originally approved in 2008. Last previous edition approved in 20082009 as
E2642 – 08.E2642 – 09. DOI: 10.1520/E2642-09.10.1520/E2642-09R15.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
DISCUSSION—
Anti-blooming structures bleed off any excess charge before they can overflow the pixel and thereby stop blooming. These structures can reduce the
effective quantum efficiency and introduce nonlinearity into the sensor.
antireflective (AR) coating, n—a coating applied to either the front surface of the CCD or the vacuum window surfaces, to
minimize the amount of reflected energy (or electromagnetic radiation) so as to maximize the amount of transmitted energy.
back-illuminated CCD (BI CCD), n—a type of CCD that has been uniformly reduced in thickness on the side away from the gate
structure (see Fig. 1b) and positioned such that the photons are detected on that side.
DISCUSSION—
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2642 − 09 (2015)
FIG. 1 Cross Sections of Front-Illuminated (a) and Back-Illuminated (b) CCDs
A BI CCD leads to an improvement in sensitivity to incoming photons from the soft X-ray to the near-infrared (NIR) regions of the spectrum with
the highest response in the visible region. However, compared to a front-illuminated CCD, it suffers from higher dark currents and interference fringe
formation (etaloning) usually in the NIR region. Also called back-thinned CCD.
binning, n—the process of combining charge from adjacent pixels in a CCD prior to read out.
DISCUSSION—
FIG. 2 Example of a 2 × 2 Vertical and Horizontal Binning Methodology
E2642 − 09 (2015)
There are two main types of binning: (1) vertical binning and (2) horizontal binning (see Fig. 2). Summing charge on the CCD and doing a single
readout results in better noise performance than reading out several pixels and then summing them in the computer memory. This is because each act
of reading out contributes to noise (see noise).
CCD bias, n—the minimum analog offset added to the signal before the A/D converter to ensure a positive digital output each time
a signal is read out.
DISCUSSION—
The CCD bias is set at the time of manufacture and remains set over the lifetime of the camera.
charge, n—measure of number of electrons that are contained in a pixel potential well.
charge-coupled device (CCD), n—a silicon-based semiconductor chip consisting of a two-dimensional matrix of photo sensors
or pixels (see Fig. 3).
DISCUSSION—
The matrix is usually referred to as the image area. Electronic charge is accumulated on the image area and transferred out by the application of
electrical potentials to shielded electrodes. The size of pixels in the sensor is typically 26 μm × 26 26 × 26 μm; however, sensors can be manufactured
in a variety of different pixel sizes ranging from 6 μm × 6 μ m to 50 μm × 50 6 × 6 μm to 50 × 50 μm. Although mathematically incorrect, the dimension
unit of a square pixel is typically given in square microns (for example, a pixel of dimension 26 μm × 26 μ m 26 × 26 μm is specified as 26 × 26 μm ).
charge transfer, n—the process by which a CCD moves electrons or charge from one pixel to the next.
charge transfer efficiency (CTE), n—measure of the ability of the CCD to transfer charge from the point of generation to the
device output.
DISCUSSION—
It is defined as the fraction of the charge initially stored in a CCD element that is transferred to an adjacent element by a single clock cycle. The value
for CTE is not constant but varies with signal size, temperature, and clock frequency.
column, n—a line of pixels in the CCD’s image area that is perpendicular to the horizontal register.
complementary metal oxide semiconductor (CMOS), n—technology widely used to manufacture electronic devices and image
sensors similar to CCDs. In a CMOS sensor, each pixel has its own charge-to-voltage conversion circuit, and the sensor often
also includes amplifiers, noise-correction, and digitization circuits. Due to the additional components associated with each pixel,
FIG. 3 Typical 1024 × 256 (26 × 26 μm pixel) Element CCD Sensor Used for Spectroscopy
E2642 − 09 (2015)
the sensitivity to light is lower than with a CCD, the signal is noisier, and the uniformity is lower. But the sensor can be built
to require less off-chip circuitry for basic operation (see Fig. 4).
correlated double sampling, n—a readout sampling technique used to achieve higher precision in CCD readout.
DISCUSSION—
The sampling circuit is set to a predetermined reference level and then the actual pixel voltage is sampled in order to find the difference between the
two. The resulting correlation minimizes read noise, especially in ultra-low-noise CCD detectors.
cosmic event, n—a spurious signal caused by a cosmic ray or particle hitting the CCD sensor. It is typically observed to result in
a high intensity signal coming from a single pixel or small group of pixels.
dark current, n—a current that occurs naturally through the thermally generated electrons in the semiconductor material of the
CCD. It is intrinsic to semiconductors and is independent of incident photons.
DISCUSSION—
Dark current is dependant on the CCD’s temperature. It is expressed in electrons/pixel/unit time.
dark noise, n—the shot noise associated with the dark current for the given exposure time, and is approximately equal to the square
root of the dark current times the exposure time used. It is usually expressed in terms of number of electrons.
deep depletion CCD, n—a CCD that has been designed with a thicker active area to provide enhanced sensitivity in the NIR and
hard X-ray regimes.
DISCUSSION—
Both front-illuminated and back-illuminated CCDs can be manufactured with a deep depletion process to enhance the NIR response; however, such
devices cannot be operated in AIMO and are also more susceptible to cosmic rays. A back-illuminated deep depletion CCD will have reduced etaloning
effects that are typically observed in back-illuminated devices exposed to NIR signals (see Fig. 5).
dynamic range, n—the ratio of the full well saturation charge to the system noise level. It represents the ratio of the brightest and
darkest signals a detector can measure in a single measurement.
DISCUSSION—
A true 16-bit detector will have a dynamic range of 65 535:1.
electron-multiplying CCD (EMCCD), n—type of CCD that has a two-way readout register, that is, the shift register and the gain
register, each with its own output amplifier. When the charge is read out through the shift register, the detector works like a
standard CCD detector, and when the charge is read out through the gain register, it undergoes charge amplification as a result
of a different electrode structure embedded underneath the pixels of this register (see Fig. 6).
FIG. 4 Typical Architectures of CCD and CMOS Sensors
E2642 − 09 (2015)
FIG. 5 Cross-Sections of Back-Illuminated (a) and Back-Illuminated Deep Depletion (b) Devices
FIG. 6 Typical Sketch of Full-Frame EMCCD Sensor
DISCUSSION—
Passing charge through the gain register allows the signal to be amplified before readout noise is added at the readout amplifier, thus improving the
signal-to-noise ratios making the camera highly sensitive in the low-light regime.
etaloning, n—a phenomenon by which constructive and destructive interference fringes are produced in a back-illuminated CCD
caused by internal reflections between the two parallel surfaces of the CCD. Typically BI CCDs experience etaloning effects
when subjected to NIR signals (see Fig. 5).
DISCUSSION—
E2642 − 09 (2015)
This effect causes the device to become transparent to incoming photons in the NIR region.
exposure time, n—the length of time for which a CCD accumulated charge.
frame, n—one full image that is read out of a CCD.
frame-transfer CCD, n—a type of CCD whose active image area is divided into two sections, that is, image area and the storage
area. The image area is the light sensitive area of the CCD and the storage area is masked to make it insensitive to light (see
Fig. 7).
DISCUSSION—
During operation the charge accumulated in the image section is rapidly transferred to the storage section at the end of the exposure time. The storage
area is then readout as the image section accumulates charge for the next exposure. This type of CCD reduces or eliminates the need for a shutter,
depending on the speed of the transfer from image to storage.
front-illuminated CCD (FI CCD), n—a type of CCD in which the photons are detected through the gate structure located in front
of the silicon material of the semiconductor (see Fig. 1a).
DISCUSSION—
This type of CCD has moderate quantum efficiency (see Fig. 8) over the spectral range it covers and it is also free from any etaloning effects that occur
in the back-illuminated CCD when subjected to NIR signals. These devices are relatively less expensive to manufacture than the back-illuminated type.
full-frame CCD, n—a type of CCD that uses the entire silicon active area for photon detection. A shutter is required to eliminate
image smear (see Fig. 3).
full well capacity, n—the maximum number of photoelectrons that can be collected on a single pixel in the image area or in the
horizontal register of a CCD. It is typically specified in terms of number of electrons.
gate structure, n—a polysilicon arrangement of electrodes that create pixels and move charge.
horizontal binning, n—the process that allows charge from a row of pixels to be combined on the CCD chip prior to readout (See
Fig. 2). Horizontal binning is commonly used in spectroscopy to increase the signal level of a data point, when less horizontal
(or wavelength) resolution is not of concern.
horizontal register, n—a row of light insensitive pixels that is located below the CCD’s image acquisition area into which charge
from the pixel columns is clocked and subsequently passed on to the output node to be read out. Also called the serial register
or readout register.
indium tin oxide (ITO), n—a transparent conductive material used in some CCD designs to provide an increase in quantum
efficiency (QE) in the blue-green region of the spectrum.
intensified CCD (ICCD), n—a type of CCD camera that has an intensifier block attached in front of it. An ICCD is used to amplify
the incoming signal without varying the image size so as to provide single-photon sensitivity and it can be electronically gated
down to nanosecond ranges (see Fig. 9).
FIG. 7 Typical Sketch of a Frame-Transfer CCD
E2642 − 09 (2015)
NOTE 1—Image used courtesy of E2V Technologies, 106 Waterhouse Lane, Chelmsford, Essex CM1 2QU, England, http://www.e2v.com.
FIG. 8 Typical QE Curves for FI and BI CCD Sensors
FIG. 9 Schematic of a Typical Intensifier Fiber Optically Coupled to a CCD Sensor
DISCUSSION—
Intensifiers were initially designed for the military for night-vision ability and are now being widely used in applications that need nanosecond gate
widths or single-photon sensitivity or both. The intensifier consists of a photocathode, multichannel plate and phosphor. A large potential difference
is applied across the ends of the multichannel plate to amplify the signal. There are two main types of intensifiers: Gen II and Gen III. The main
difference between them is in the material used in the photocathode. The Gen III models are a more advanced design and they provide higher quantum
efficiencies than the Gen II models.
interline transfer CCD, n—a type of CCD designed with columns of pixels alternated with masked storage registers so as to
increase the rate of acquisition. The storage registers occupy a portion of the pixel
...