<s>
A	O
charge-coupled	B-Algorithm
device	I-Algorithm
(	O
CCD	O
)	O
is	O
an	O
integrated	O
circuit	O
containing	O
an	O
array	O
of	O
linked	O
,	O
or	O
coupled	O
,	O
capacitors	O
.	O
</s>
<s>
CCD	B-Algorithm
sensors	I-Algorithm
are	O
a	O
major	O
technology	O
used	O
in	O
digital	B-Algorithm
imaging	I-Algorithm
.	O
</s>
<s>
In	O
a	O
CCD	O
image	B-Algorithm
sensor	I-Algorithm
,	O
pixels	B-Algorithm
are	O
represented	O
by	O
p-doped	B-Algorithm
metal	B-Architecture
–	I-Architecture
oxide	I-Architecture
–	I-Architecture
semiconductor	I-Architecture
(	O
MOS	O
)	O
capacitors	O
.	O
</s>
<s>
These	O
MOS	O
capacitors	O
,	O
the	O
basic	O
building	O
blocks	O
of	O
a	O
CCD	O
,	O
are	O
biased	O
above	O
the	O
threshold	O
for	O
inversion	O
when	O
image	O
acquisition	O
begins	O
,	O
allowing	O
the	O
conversion	O
of	O
incoming	O
photons	B-Application
into	O
electron	O
charges	O
at	O
the	O
semiconductor-oxide	O
interface	O
;	O
the	O
CCD	O
is	O
then	O
used	O
to	O
read	O
out	O
these	O
charges	O
.	O
</s>
<s>
Although	O
CCDs	O
are	O
not	O
the	O
only	O
technology	O
to	O
allow	O
for	O
light	O
detection	O
,	O
CCD	O
image	B-Algorithm
sensors	I-Algorithm
are	O
widely	O
used	O
in	O
professional	O
,	O
medical	O
,	O
and	O
scientific	O
applications	O
where	O
high-quality	O
image	O
data	O
are	O
required	O
.	O
</s>
<s>
In	O
applications	O
with	O
less	O
exacting	O
quality	O
demands	O
,	O
such	O
as	O
consumer	O
and	O
professional	O
digital	B-Device
cameras	I-Device
,	O
active	B-Architecture
pixel	I-Architecture
sensors	I-Architecture
,	O
also	O
known	O
as	O
CMOS	B-Architecture
sensors	I-Architecture
(	O
complementary	O
MOS	O
sensors	O
)	O
,	O
are	O
generally	O
used	O
.	O
</s>
<s>
However	O
,	O
the	O
large	O
quality	O
advantage	O
CCDs	O
enjoyed	O
early	O
on	O
has	O
narrowed	O
over	O
time	O
and	O
since	O
the	O
late	O
2010s	O
CMOS	B-Architecture
sensors	I-Architecture
are	O
the	O
dominant	O
technology	O
,	O
having	O
largely	O
if	O
not	O
completely	O
replaced	O
CCD	O
image	B-Algorithm
sensors	I-Algorithm
.	O
</s>
<s>
The	O
basis	O
for	O
the	O
CCD	O
is	O
the	O
metal	B-Architecture
–	I-Architecture
oxide	I-Architecture
–	I-Architecture
semiconductor	I-Architecture
(	O
MOS	O
)	O
structure	O
,	O
with	O
MOS	O
capacitors	O
being	O
the	O
basic	O
building	O
blocks	O
of	O
a	O
CCD	O
,	O
and	O
a	O
depleted	B-Algorithm
MOS	O
structure	O
used	O
as	O
the	O
photodetector	O
in	O
early	O
CCD	O
devices	O
.	O
</s>
<s>
In	O
the	O
late	O
1960s	O
,	O
Willard	O
Boyle	O
and	O
George	O
E	O
.	O
Smith	O
at	O
Bell	O
Labs	O
were	O
researching	O
MOS	B-Architecture
technology	I-Architecture
while	O
working	O
on	O
semiconductor	O
bubble	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
As	O
it	O
was	O
fairly	O
straightforward	O
to	O
fabricate	B-Architecture
a	O
series	O
of	O
MOS	O
capacitors	O
in	O
a	O
row	O
,	O
they	O
connected	O
a	O
suitable	O
voltage	O
to	O
them	O
so	O
that	O
the	O
charge	O
could	O
be	O
stepped	O
along	O
from	O
one	O
to	O
the	O
next	O
.	O
</s>
<s>
This	O
led	O
to	O
the	O
invention	O
of	O
the	O
charge-coupled	B-Algorithm
device	I-Algorithm
by	O
Boyle	O
and	O
Smith	O
in	O
1969	O
.	O
</s>
<s>
The	O
initial	O
paper	O
describing	O
the	O
concept	O
in	O
April	O
1970	O
listed	O
possible	O
uses	O
as	O
memory	B-General_Concept
,	O
a	O
delay	O
line	O
,	O
and	O
an	O
imaging	O
device	O
.	O
</s>
<s>
The	O
device	O
could	O
also	O
be	O
used	O
as	O
a	O
shift	B-General_Concept
register	I-General_Concept
.	O
</s>
<s>
The	O
first	O
experimental	O
device	O
demonstrating	O
the	O
principle	O
was	O
a	O
row	O
of	O
closely	O
spaced	O
metal	O
squares	O
on	O
an	O
oxidized	B-Algorithm
silicon	O
surface	O
electrically	O
accessed	O
by	O
wire	O
bonds	O
.	O
</s>
<s>
This	O
was	O
the	O
first	O
experimental	O
application	O
of	O
the	O
CCD	O
in	O
image	B-Algorithm
sensor	I-Algorithm
technology	O
,	O
and	O
used	O
a	O
depleted	B-Algorithm
MOS	O
structure	O
as	O
the	O
photodetector	O
.	O
</s>
<s>
The	O
first	O
working	O
CCD	O
made	O
with	O
integrated	O
circuit	O
technology	O
was	O
a	O
simple	O
8-bit	O
shift	B-General_Concept
register	I-General_Concept
,	O
reported	O
by	O
Tompsett	O
,	O
Amelio	O
and	O
Smith	O
in	O
August	O
1970	O
.	O
</s>
<s>
This	O
device	O
had	O
input	O
and	O
output	O
circuits	O
and	O
was	O
used	O
to	O
demonstrate	O
its	O
use	O
as	O
a	O
shift	B-General_Concept
register	I-General_Concept
and	O
as	O
a	O
crude	O
eight	O
pixel	B-Algorithm
linear	O
imaging	O
device	O
.	O
</s>
<s>
Fairchild	O
's	O
effort	O
,	O
led	O
by	O
ex-Bell	O
researcher	O
Gil	O
Amelio	O
,	O
was	O
the	O
first	O
with	O
commercial	O
devices	O
,	O
and	O
by	O
1974	O
had	O
a	O
linear	O
500-element	O
device	O
and	O
a	O
2D	O
100	O
×	O
100	O
pixel	B-Algorithm
device	O
.	O
</s>
<s>
Steven	O
Sasson	O
,	O
an	O
electrical	O
engineer	O
working	O
for	O
Kodak	O
,	O
invented	O
the	O
first	O
digital	B-Device
still	I-Device
camera	I-Device
using	O
a	O
Fairchild	O
CCD	O
in	O
1975	O
.	O
</s>
<s>
The	O
first	O
KH-11	O
KENNEN	B-Application
reconnaissance	O
satellite	O
equipped	O
with	O
charge-coupled	B-Algorithm
device	I-Algorithm
array	O
(	O
pixels	B-Algorithm
)	O
technology	O
for	O
imaging	O
was	O
launched	O
in	O
December	O
1976	O
.	O
</s>
<s>
Early	O
CCD	B-Algorithm
sensors	I-Algorithm
suffered	O
from	O
shutter	O
lag	O
.	O
</s>
<s>
It	O
was	O
invented	O
by	O
Nobukazu	O
Teranishi	O
,	O
Hiromitsu	O
Shiraki	O
and	O
Yasuo	B-Application
Ishihara	O
at	O
NEC	O
in	O
1980	O
.	O
</s>
<s>
In	O
1987	O
,	O
the	O
PPD	O
began	O
to	O
be	O
incorporated	O
into	O
most	O
CCD	O
devices	O
,	O
becoming	O
a	O
fixture	O
in	O
consumer	O
electronic	O
video	O
cameras	O
and	O
then	O
digital	B-Device
still	I-Device
cameras	I-Device
.	O
</s>
<s>
Since	O
then	O
,	O
the	O
PPD	O
has	O
been	O
used	O
in	O
nearly	O
all	O
CCD	B-Algorithm
sensors	I-Algorithm
and	O
then	O
CMOS	B-Architecture
sensors	I-Architecture
.	O
</s>
<s>
Michael	O
Tompsett	O
was	O
awarded	O
the	O
2010	O
National	O
Medal	O
of	O
Technology	O
and	O
Innovation	O
,	O
for	O
pioneering	O
work	O
and	O
electronic	O
technologies	O
including	O
the	O
design	O
and	O
development	O
of	O
the	O
first	O
CCD	B-Algorithm
imagers	I-Algorithm
.	O
</s>
<s>
He	O
was	O
also	O
awarded	O
the	O
2012	O
IEEE	O
Edison	O
Medal	O
for	O
"	O
pioneering	O
contributions	O
to	O
imaging	O
devices	O
including	O
CCD	B-Algorithm
Imagers	I-Algorithm
,	O
cameras	O
and	O
thermal	O
imagers	B-Algorithm
"	O
.	O
</s>
<s>
In	O
a	O
CCD	O
for	O
capturing	O
images	O
,	O
there	O
is	O
a	O
photoactive	O
region	O
(	O
an	O
epitaxial	O
layer	O
of	O
silicon	O
)	O
,	O
and	O
a	O
transmission	O
region	O
made	O
out	O
of	O
a	O
shift	B-General_Concept
register	I-General_Concept
(	O
the	O
CCD	O
,	O
properly	O
speaking	O
)	O
.	O
</s>
<s>
Once	O
the	O
array	O
has	O
been	O
exposed	O
to	O
the	O
image	O
,	O
a	O
control	O
circuit	O
causes	O
each	O
capacitor	O
to	O
transfer	O
its	O
contents	O
to	O
its	O
neighbor	O
(	O
operating	O
as	O
a	O
shift	B-General_Concept
register	I-General_Concept
)	O
.	O
</s>
<s>
In	O
a	O
digital	O
device	O
,	O
these	O
voltages	O
are	O
then	O
sampled	O
,	O
digitized	O
,	O
and	O
usually	O
stored	O
in	O
memory	B-General_Concept
;	O
in	O
an	O
analog	O
device	O
(	O
such	O
as	O
an	O
analog	O
video	O
camera	O
)	O
,	O
they	O
are	O
processed	O
into	O
a	O
continuous	O
analog	O
signal	O
(	O
e.g.	O
</s>
<s>
Before	O
the	O
MOS	O
capacitors	O
are	O
exposed	O
to	O
light	O
,	O
they	O
are	O
biased	O
into	O
the	O
depletion	O
region	O
;	O
in	O
n-channel	O
CCDs	O
,	O
the	O
silicon	O
under	O
the	O
bias	O
gate	O
is	O
slightly	O
p-doped	B-Algorithm
or	O
intrinsic	O
.	O
</s>
<s>
The	O
gate	O
is	O
then	O
biased	O
at	O
a	O
positive	O
potential	O
,	O
above	O
the	O
threshold	O
for	O
strong	O
inversion	O
,	O
which	O
will	O
eventually	O
result	O
in	O
the	O
creation	O
of	O
an	O
n	O
channel	O
below	O
the	O
gate	O
as	O
in	O
a	O
MOSFET	B-Architecture
.	O
</s>
<s>
The	O
maximum	O
capacity	O
of	O
each	O
well	O
is	O
known	O
as	O
the	O
well	O
depth	O
,	O
typically	O
about	O
105	O
electrons	O
per	O
pixel	B-Algorithm
.	O
</s>
<s>
This	O
thin	O
layer	O
(=	O
0.2	O
–	O
0.3	O
micron	O
)	O
is	O
fully	O
depleted	B-Algorithm
and	O
the	O
accumulated	O
photogenerated	O
charge	O
is	O
kept	O
away	O
from	O
the	O
surface	O
.	O
</s>
<s>
Later	O
in	O
the	O
process	O
,	O
polysilicon	O
gates	O
are	O
deposited	O
by	O
chemical	B-Algorithm
vapor	I-Algorithm
deposition	I-Algorithm
,	O
patterned	O
with	O
photolithography	B-Algorithm
,	O
and	O
etched	O
in	O
such	O
a	O
way	O
that	O
the	O
separately	O
phased	O
gates	O
lie	O
perpendicular	O
to	O
the	O
channels	O
.	O
</s>
<s>
The	O
channels	O
are	O
further	O
defined	O
by	O
utilization	O
of	O
the	O
LOCOS	B-Application
process	O
to	O
produce	O
the	O
channel	B-Algorithm
stop	I-Algorithm
region	O
.	O
</s>
<s>
Channel	B-Algorithm
stops	I-Algorithm
are	O
thermally	O
grown	O
oxides	O
that	O
serve	O
to	O
isolate	O
the	O
charge	O
packets	O
in	O
one	O
column	O
from	O
those	O
in	O
another	O
.	O
</s>
<s>
These	O
channel	B-Algorithm
stops	I-Algorithm
are	O
produced	O
before	O
the	O
polysilicon	O
gates	O
are	O
,	O
as	O
the	O
LOCOS	B-Application
process	O
utilizes	O
a	O
high-temperature	O
step	O
that	O
would	O
destroy	O
the	O
gate	O
material	O
.	O
</s>
<s>
The	O
channel	B-Algorithm
stops	I-Algorithm
are	O
parallel	O
to	O
,	O
and	O
exclusive	O
of	O
,	O
the	O
channel	O
,	O
or	O
"	O
charge	O
carrying	O
"	O
,	O
regions	O
.	O
</s>
<s>
Channel	B-Algorithm
stops	I-Algorithm
often	O
have	O
a	O
p+	O
doped	O
region	O
underlying	O
them	O
,	O
providing	O
a	O
further	O
barrier	O
to	O
the	O
electrons	O
in	O
the	O
charge	O
packets	O
(	O
this	O
discussion	O
of	O
the	O
physics	O
of	O
CCD	O
devices	O
assumes	O
an	O
electron	O
transfer	O
device	O
,	O
though	O
hole	O
transfer	O
is	O
possible	O
)	O
.	O
</s>
<s>
The	O
clocking	O
of	O
the	O
gates	O
,	O
alternately	O
high	O
and	O
low	O
,	O
will	O
forward	O
and	O
reverse	O
bias	O
the	O
diode	O
that	O
is	O
provided	O
by	O
the	O
buried	O
channel	O
(	O
n-doped	O
)	O
and	O
the	O
epitaxial	O
layer	O
(	O
p-doped	B-Algorithm
)	O
.	O
</s>
<s>
The	O
above	O
process	O
describes	O
a	O
frame	B-Algorithm
transfer	I-Algorithm
CCD	I-Algorithm
.	O
</s>
<s>
In	O
a	O
peristaltic	O
charge-coupled	B-Algorithm
device	I-Algorithm
,	O
the	O
charge-packet	O
transfer	O
operation	O
is	O
analogous	O
to	O
the	O
peristaltic	O
contraction	O
and	O
dilation	O
of	O
the	O
digestive	O
system	O
.	O
</s>
<s>
The	O
CCD	O
image	B-Algorithm
sensors	I-Algorithm
can	O
be	O
implemented	O
in	O
several	O
different	O
architectures	O
.	O
</s>
<s>
With	O
a	O
frame-transfer	B-Algorithm
CCD	I-Algorithm
,	O
half	O
of	O
the	O
silicon	O
area	O
is	O
covered	O
by	O
an	O
opaque	O
mask	O
(	O
typically	O
aluminum	O
)	O
.	O
</s>
<s>
The	O
interline	O
architecture	O
extends	O
this	O
concept	O
one	O
step	O
further	O
and	O
masks	O
every	O
other	O
column	O
of	O
the	O
image	B-Algorithm
sensor	I-Algorithm
for	O
storage	O
.	O
</s>
<s>
In	O
this	O
device	O
,	O
only	O
one	O
pixel	B-Algorithm
shift	O
has	O
to	O
occur	O
to	O
transfer	O
from	O
image	O
area	O
to	O
storage	O
area	O
;	O
thus	O
,	O
shutter	O
times	O
can	O
be	O
less	O
than	O
a	O
microsecond	O
and	O
smear	O
is	O
essentially	O
eliminated	O
.	O
</s>
<s>
The	O
advantage	O
is	O
not	O
free	O
,	O
however	O
,	O
as	O
the	O
imaging	O
area	O
is	O
now	O
covered	O
by	O
opaque	O
strips	O
dropping	O
the	O
fill	B-Algorithm
factor	I-Algorithm
to	O
approximately	O
50	O
percent	O
and	O
the	O
effective	O
quantum	O
efficiency	O
by	O
an	O
equivalent	O
amount	O
.	O
</s>
<s>
Microlenses	O
can	O
bring	O
the	O
fill	B-Algorithm
factor	I-Algorithm
back	O
up	O
to	O
90	O
percent	O
or	O
more	O
depending	O
on	O
pixel	B-Algorithm
size	O
and	O
the	O
overall	O
system	O
's	O
optical	O
design	O
.	O
</s>
<s>
CCDs	O
containing	O
grids	O
of	O
pixels	B-Algorithm
are	O
used	O
in	O
digital	B-Device
cameras	I-Device
,	O
optical	B-Application
scanners	I-Application
,	O
and	O
video	O
cameras	O
as	O
light-sensing	O
devices	O
.	O
</s>
<s>
Most	O
common	O
types	O
of	O
CCDs	O
are	O
sensitive	O
to	O
near-infrared	O
light	O
,	O
which	O
allows	O
infrared	O
photography	O
,	O
night-vision	O
devices	O
,	O
and	O
zero	O
lux	B-Application
(	O
or	O
near	O
zero	O
lux	B-Application
)	O
video-recording/photography	O
.	O
</s>
<s>
One	O
other	O
consequence	O
of	O
their	O
sensitivity	O
to	O
infrared	O
is	O
that	O
infrared	O
from	O
remote	B-Protocol
controls	I-Protocol
often	O
appears	O
on	O
CCD-based	O
digital	B-Device
cameras	I-Device
or	O
camcorders	O
if	O
they	O
do	O
not	O
have	O
infrared	O
blockers	O
.	O
</s>
<s>
Cooling	O
reduces	O
the	O
array	O
's	O
dark	O
current	O
,	O
improving	O
the	O
sensitivity	O
of	O
the	O
CCD	O
to	O
low	O
light	O
intensities	O
,	O
even	O
for	O
ultraviolet	B-Application
and	O
visible	O
wavelengths	O
.	O
</s>
<s>
The	O
frame	B-Algorithm
transfer	I-Algorithm
CCD	I-Algorithm
imager	B-Algorithm
was	O
the	O
first	O
imaging	O
structure	O
proposed	O
for	O
CCD	B-Algorithm
Imaging	I-Algorithm
by	O
Michael	O
Tompsett	O
at	O
Bell	O
Laboratories	O
.	O
</s>
<s>
A	O
frame	B-Algorithm
transfer	I-Algorithm
CCD	I-Algorithm
is	O
a	O
specialized	O
CCD	O
,	O
often	O
used	O
in	O
astronomy	O
and	O
some	O
professional	O
video	O
cameras	O
,	O
designed	O
for	O
high	O
exposure	O
efficiency	O
and	O
correctness	O
.	O
</s>
<s>
During	O
the	O
first	O
phase	O
,	O
the	O
CCD	O
passively	O
collects	O
incoming	O
photons	B-Application
,	O
storing	O
electrons	O
in	O
its	O
cells	O
.	O
</s>
<s>
A	O
frame	B-Algorithm
transfer	I-Algorithm
CCD	I-Algorithm
solves	O
both	O
problems	O
:	O
it	O
has	O
a	O
shielded	O
,	O
not	O
light	O
sensitive	O
,	O
area	O
containing	O
as	O
many	O
cells	O
as	O
the	O
area	O
exposed	O
to	O
light	O
.	O
</s>
<s>
An	O
intensified	O
charge-coupled	B-Algorithm
device	I-Algorithm
(	O
ICCD	B-Algorithm
)	O
is	O
a	O
CCD	O
that	O
is	O
optically	O
connected	O
to	O
an	O
image	O
intensifier	O
that	O
is	O
mounted	O
in	O
front	O
of	O
the	O
CCD	O
.	O
</s>
<s>
The	O
photons	B-Application
which	O
are	O
coming	O
from	O
the	O
light	O
source	O
fall	O
onto	O
the	O
photocathode	O
,	O
thereby	O
generating	O
photoelectrons	O
.	O
</s>
<s>
The	O
phosphor	O
screen	O
finally	O
converts	O
the	O
multiplied	O
electrons	O
back	O
to	O
photons	B-Application
which	O
are	O
guided	O
to	O
the	O
CCD	O
by	O
a	O
fiber	O
optic	O
or	O
a	O
lens	O
.	O
</s>
<s>
The	O
process	O
of	O
reversing	O
the	O
control	O
voltage	O
at	O
the	O
photocathode	O
is	O
called	O
gating	O
and	O
therefore	O
ICCDs	B-Algorithm
are	O
also	O
called	O
gateable	O
CCD	B-Algorithm
cameras	I-Algorithm
.	O
</s>
<s>
Besides	O
the	O
extremely	O
high	O
sensitivity	O
of	O
ICCD	B-Algorithm
cameras	O
,	O
which	O
enable	O
single	O
photon	B-Application
detection	O
,	O
the	O
gateability	O
is	O
one	O
of	O
the	O
major	O
advantages	O
of	O
the	O
ICCD	B-Algorithm
over	O
the	O
EMCCD	B-Algorithm
cameras	O
.	O
</s>
<s>
The	O
highest	O
performing	O
ICCD	B-Algorithm
cameras	O
enable	O
shutter	O
times	O
as	O
short	O
as	O
200	O
picoseconds	O
.	O
</s>
<s>
ICCD	B-Algorithm
cameras	O
are	O
in	O
general	O
somewhat	O
higher	O
in	O
price	O
than	O
EMCCD	B-Algorithm
cameras	O
because	O
they	O
need	O
the	O
expensive	O
image	O
intensifier	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
EMCCD	B-Algorithm
cameras	O
need	O
a	O
cooling	O
system	O
to	O
cool	O
the	O
EMCCD	B-Algorithm
chip	O
down	O
to	O
temperatures	O
around	O
.	O
</s>
<s>
This	O
cooling	O
system	O
adds	O
additional	O
costs	O
to	O
the	O
EMCCD	B-Algorithm
camera	O
and	O
often	O
yields	O
heavy	O
condensation	O
problems	O
in	O
the	O
application	O
.	O
</s>
<s>
ICCDs	B-Algorithm
are	O
used	O
in	O
night	O
vision	O
devices	O
and	O
in	O
various	O
scientific	O
applications	O
.	O
</s>
<s>
An	O
electron-multiplying	B-Algorithm
CCD	I-Algorithm
(	O
EMCCD	B-Algorithm
,	O
also	O
known	O
as	O
an	O
L3Vision	O
CCD	O
,	O
a	O
product	O
commercialized	O
by	O
e2v	O
Ltd.	O
,	O
GB	O
,	O
L3CCD	B-Algorithm
or	O
Impactron	O
CCD	O
,	O
a	O
now-discontinued	O
product	O
offered	O
in	O
the	O
past	O
by	O
Texas	O
Instruments	O
)	O
is	O
a	O
charge-coupled	B-Algorithm
device	I-Algorithm
in	O
which	O
a	O
gain	O
register	O
is	O
placed	O
between	O
the	O
shift	B-General_Concept
register	I-General_Concept
and	O
the	O
output	O
amplifier	O
.	O
</s>
<s>
In	O
an	O
EMCCD	B-Algorithm
,	O
this	O
noise	O
is	O
superimposed	O
on	O
many	O
thousands	O
of	O
electrons	O
rather	O
than	O
a	O
single	O
electron	O
;	O
the	O
devices	O
 '	O
primary	O
advantage	O
is	O
thus	O
their	O
negligible	O
readout	O
noise	O
.	O
</s>
<s>
EMCCDs	B-Algorithm
show	O
a	O
similar	O
sensitivity	O
to	O
intensified	B-Algorithm
CCDs	I-Algorithm
(	O
ICCDs	B-Algorithm
)	O
.	O
</s>
<s>
However	O
,	O
as	O
with	O
ICCDs	B-Algorithm
,	O
the	O
gain	O
that	O
is	O
applied	O
in	O
the	O
gain	O
register	O
is	O
stochastic	O
and	O
the	O
exact	O
gain	O
that	O
has	O
been	O
applied	O
to	O
a	O
pixel	B-Algorithm
's	O
charge	O
is	O
impossible	O
to	O
know	O
.	O
</s>
<s>
However	O
,	O
at	O
very	O
low	O
light	O
levels	O
(	O
where	O
the	O
quantum	O
efficiency	O
is	O
most	O
important	O
)	O
,	O
it	O
can	O
be	O
assumed	O
that	O
a	O
pixel	B-Algorithm
either	O
contains	O
an	O
electron	O
—	O
or	O
not	O
.	O
</s>
<s>
This	O
removes	O
the	O
noise	O
associated	O
with	O
the	O
stochastic	O
multiplication	O
at	O
the	O
risk	O
of	O
counting	O
multiple	O
electrons	O
in	O
the	O
same	O
pixel	B-Algorithm
as	O
a	O
single	O
electron	O
.	O
</s>
<s>
To	O
avoid	O
multiple	O
counts	O
in	O
one	O
pixel	B-Algorithm
due	O
to	O
coincident	O
photons	B-Application
in	O
this	O
mode	O
of	O
operation	O
,	O
high	O
frame	O
rates	O
are	O
essential	O
.	O
</s>
<s>
Because	O
of	O
the	O
lower	O
costs	O
and	O
better	O
resolution	O
,	O
EMCCDs	B-Algorithm
are	O
capable	O
of	O
replacing	O
ICCDs	B-Algorithm
in	O
many	O
applications	O
.	O
</s>
<s>
ICCDs	B-Algorithm
still	O
have	O
the	O
advantage	O
that	O
they	O
can	O
be	O
gated	O
very	O
fast	O
and	O
thus	O
are	O
useful	O
in	O
applications	O
like	O
range-gated	B-Algorithm
imaging	I-Algorithm
.	O
</s>
<s>
EMCCD	B-Algorithm
cameras	O
indispensably	O
need	O
a	O
cooling	O
system	O
—	O
using	O
either	O
thermoelectric	O
cooling	O
or	O
liquid	O
nitrogen	O
—	O
to	O
cool	O
the	O
chip	O
down	O
to	O
temperatures	O
in	O
the	O
range	O
of	O
.	O
</s>
<s>
This	O
cooling	O
system	O
adds	O
additional	O
costs	O
to	O
the	O
EMCCD	B-Algorithm
imaging	O
system	O
and	O
may	O
yield	O
condensation	O
problems	O
in	O
the	O
application	O
.	O
</s>
<s>
However	O
,	O
high-end	O
EMCCD	B-Algorithm
cameras	O
are	O
equipped	O
with	O
a	O
permanent	O
hermetic	O
vacuum	O
system	O
confining	O
the	O
chip	O
to	O
avoid	O
condensation	O
issues	O
.	O
</s>
<s>
The	O
low-light	O
capabilities	O
of	O
EMCCDs	B-Algorithm
find	O
use	O
in	O
astronomy	O
and	O
biomedical	O
research	O
,	O
among	O
other	O
fields	O
.	O
</s>
<s>
In	O
particular	O
,	O
their	O
low	O
noise	O
at	O
high	O
readout	O
speeds	O
makes	O
them	O
very	O
useful	O
for	O
a	O
variety	O
of	O
astronomical	O
applications	O
involving	O
low	O
light	O
sources	O
and	O
transient	O
events	O
such	O
as	O
lucky	O
imaging	O
of	O
faint	O
stars	O
,	O
high	O
speed	O
photon	B-Application
counting	O
photometry	O
,	O
Fabry-Pérot	O
spectroscopy	O
and	O
high-resolution	O
spectroscopy	O
.	O
</s>
<s>
More	O
recently	O
,	O
these	O
types	O
of	O
CCDs	O
have	O
broken	O
into	O
the	O
field	O
of	O
biomedical	O
research	O
in	O
low-light	O
applications	O
including	O
small	O
animal	O
imaging	O
,	O
single-molecule	O
imaging	O
,	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
,	O
super	O
resolution	O
microscopy	O
as	O
well	O
as	O
a	O
wide	O
variety	O
of	O
modern	O
fluorescence	O
microscopy	O
techniques	O
thanks	O
to	O
greater	O
SNR	O
in	O
low-light	O
conditions	O
in	O
comparison	O
with	O
traditional	O
CCDs	O
and	O
ICCDs	B-Algorithm
.	O
</s>
<s>
In	O
terms	O
of	O
noise	O
,	O
commercial	O
EMCCD	B-Algorithm
cameras	O
typically	O
have	O
clock-induced	O
charge	O
(	O
CIC	O
)	O
and	O
dark	O
current	O
(	O
dependent	O
on	O
the	O
extent	O
of	O
cooling	O
)	O
that	O
together	O
lead	O
to	O
an	O
effective	O
readout	O
noise	O
ranging	O
from	O
0.01	O
to	O
1	O
electrons	O
per	O
pixel	B-Algorithm
read	O
.	O
</s>
<s>
However	O
,	O
recent	O
improvements	O
in	O
EMCCD	B-Algorithm
technology	O
have	O
led	O
to	O
a	O
new	O
generation	O
of	O
cameras	O
capable	O
of	O
producing	O
significantly	O
less	O
CIC	O
,	O
higher	O
charge	O
transfer	O
efficiency	O
and	O
an	O
EM	O
gain	O
5	O
times	O
higher	O
than	O
what	O
was	O
previously	O
available	O
.	O
</s>
<s>
These	O
advances	O
in	O
low-light	O
detection	O
lead	O
to	O
an	O
effective	O
total	O
background	O
noise	O
of	O
0.001	O
electrons	O
per	O
pixel	B-Algorithm
read	O
,	O
a	O
noise	O
floor	O
unmatched	O
by	O
any	O
other	O
low-light	O
imaging	O
device	O
.	O
</s>
<s>
Due	O
to	O
the	O
high	O
quantum	O
efficiencies	O
of	O
charge-coupled	B-Algorithm
device	I-Algorithm
(	O
CCD	O
)	O
(	O
the	O
ideal	O
quantum	O
efficiency	O
is	O
100%	O
,	O
one	O
generated	O
electron	O
per	O
incident	O
photon	B-Application
)	O
,	O
linearity	O
of	O
their	O
outputs	O
,	O
ease	O
of	O
use	O
compared	O
to	O
photographic	O
plates	O
,	O
and	O
a	O
variety	O
of	O
other	O
reasons	O
,	O
CCDs	O
were	O
very	O
rapidly	O
adopted	O
by	O
astronomers	O
for	O
nearly	O
all	O
UV-to-infrared	O
applications	O
.	O
</s>
<s>
Thermal	O
noise	O
and	O
cosmic	O
rays	O
may	O
alter	O
the	O
pixels	B-Algorithm
in	O
the	O
CCD	B-Algorithm
array	I-Algorithm
.	O
</s>
<s>
Once	O
developed	O
,	O
the	O
dark	B-Algorithm
frame	I-Algorithm
average	I-Algorithm
image	I-Algorithm
is	I-Algorithm
then	I-Algorithm
subtracted	I-Algorithm
from	O
the	O
open-shutter	O
image	O
to	O
remove	O
the	O
dark	O
current	O
and	O
other	O
systematic	O
defects	O
(	O
dead	B-General_Concept
pixels	I-General_Concept
,	O
hot	O
pixels	B-Algorithm
,	O
etc	O
.	O
)	O
</s>
<s>
Newer	O
Skipper	O
CCDs	O
counter	O
noise	O
by	O
collecting	O
data	O
with	O
the	O
same	O
collected	O
charge	O
multiple	O
times	O
and	O
has	O
applications	O
in	O
precision	O
light	O
Dark	B-Application
Matter	I-Application
searches	O
and	O
neutrino	O
measurements	O
.	O
</s>
<s>
CCD	B-Algorithm
cameras	I-Algorithm
used	O
in	O
astrophotography	O
often	O
require	O
sturdy	O
mounts	O
to	O
cope	O
with	O
vibrations	O
from	O
wind	O
and	O
other	O
sources	O
,	O
along	O
with	O
the	O
tremendous	O
weight	O
of	O
most	O
imaging	O
platforms	O
.	O
</s>
<s>
An	O
unusual	O
astronomical	O
application	O
of	O
CCDs	O
,	O
called	O
drift-scanning	B-Algorithm
,	O
uses	O
a	O
CCD	O
to	O
make	O
a	O
fixed	O
telescope	O
behave	O
like	O
a	O
tracking	O
telescope	O
and	O
follow	O
the	O
motion	O
of	O
the	O
sky	O
.	O
</s>
<s>
In	O
addition	O
to	O
imagers	B-Algorithm
,	O
CCDs	O
are	O
also	O
used	O
in	O
an	O
array	O
of	O
analytical	O
instrumentation	O
including	O
spectrometers	O
and	O
interferometers	O
.	O
</s>
<s>
Digital	O
color	O
cameras	O
generally	O
use	O
a	O
Bayer	B-Algorithm
mask	I-Algorithm
over	O
the	O
CCD	O
.	O
</s>
<s>
Each	O
square	O
of	O
four	O
pixels	B-Algorithm
has	O
one	O
filtered	O
red	O
,	O
one	O
blue	O
,	O
and	O
two	O
green	O
(	O
the	O
human	O
eye	O
is	O
more	O
sensitive	O
to	O
green	O
than	O
either	O
red	O
or	O
blue	O
)	O
.	O
</s>
<s>
The	O
result	O
of	O
this	O
is	O
that	O
luminance	O
information	O
is	O
collected	O
at	O
every	O
pixel	B-Algorithm
,	O
but	O
the	O
color	O
resolution	O
is	O
lower	O
than	O
the	O
luminance	O
resolution	O
.	O
</s>
<s>
Better	O
color	O
separation	O
can	O
be	O
reached	O
by	O
three-CCD	B-Algorithm
devices	O
(	O
3CCD	B-Algorithm
)	O
and	O
a	O
dichroic	O
beam	O
splitter	O
prism	O
,	O
that	O
splits	O
the	O
image	O
into	O
red	O
,	O
green	O
and	O
blue	O
components	O
.	O
</s>
<s>
Many	O
professional	O
video	O
camcorders	O
,	O
and	O
some	O
semi-professional	O
camcorders	O
,	O
use	O
this	O
technique	O
,	O
although	O
developments	O
in	O
competing	O
CMOS	O
technology	O
have	O
made	O
CMOS	B-Architecture
sensors	I-Architecture
,	O
both	O
with	O
beam-splitters	O
and	O
bayer	B-Algorithm
filters	I-Algorithm
,	O
increasingly	O
popular	O
in	O
high-end	O
video	O
and	O
digital	O
cinema	O
cameras	O
.	O
</s>
<s>
Another	O
advantage	O
of	O
3CCD	B-Algorithm
over	O
a	O
Bayer	B-Algorithm
mask	I-Algorithm
device	O
is	O
higher	O
quantum	O
efficiency	O
(	O
higher	O
light	O
sensitivity	O
)	O
,	O
because	O
most	O
of	O
the	O
light	O
from	O
the	O
lens	O
enters	O
one	O
of	O
the	O
silicon	O
sensors	O
,	O
while	O
a	O
Bayer	B-Algorithm
mask	I-Algorithm
absorbs	O
a	O
high	O
proportion	O
(	O
more	O
than	O
2/3	O
)	O
of	O
the	O
light	O
falling	O
on	O
each	O
pixel	B-Algorithm
location	O
.	O
</s>
<s>
For	O
still	O
scenes	O
,	O
for	O
instance	O
in	O
microscopy	O
,	O
the	O
resolution	O
of	O
a	O
Bayer	B-Algorithm
mask	I-Algorithm
device	O
can	O
be	O
enhanced	O
by	O
microscanning	B-Algorithm
technology	O
.	O
</s>
<s>
During	O
the	O
process	O
of	O
color	B-Algorithm
co-site	I-Algorithm
sampling	I-Algorithm
,	O
several	O
frames	O
of	O
the	O
scene	O
are	O
produced	O
.	O
</s>
<s>
Between	O
acquisitions	O
,	O
the	O
sensor	O
is	O
moved	O
in	O
pixel	B-Algorithm
dimensions	O
,	O
so	O
that	O
each	O
point	O
in	O
the	O
visual	O
field	O
is	O
acquired	O
consecutively	O
by	O
elements	O
of	O
the	O
mask	O
that	O
are	O
sensitive	O
to	O
the	O
red	O
,	O
green	O
,	O
and	O
blue	O
components	O
of	O
its	O
color	O
.	O
</s>
<s>
Eventually	O
every	O
pixel	B-Algorithm
in	O
the	O
image	O
has	O
been	O
scanned	O
at	O
least	O
once	O
in	O
each	O
color	O
and	O
the	O
resolution	O
of	O
the	O
three	O
channels	O
become	O
equivalent	O
(	O
the	O
resolutions	O
of	O
red	O
and	O
blue	O
channels	O
are	O
quadrupled	O
while	O
the	O
green	O
channel	O
is	O
doubled	O
)	O
.	O
</s>
<s>
Sensors	O
(	O
CCD	O
/	O
CMOS	O
)	O
come	O
in	O
various	O
sizes	O
,	O
or	O
image	B-Algorithm
sensor	I-Algorithm
formats	O
.	O
</s>
<s>
These	O
sizes	O
are	O
often	O
referred	O
to	O
with	O
an	O
inch	O
fraction	O
designation	O
such	O
as	O
1/1.8	O
″	O
or	O
2/3	O
″	O
called	O
the	O
optical	B-Algorithm
format	I-Algorithm
.	O
</s>
<s>
Some	O
anti-blooming	O
features	O
that	O
can	O
be	O
built	O
into	O
a	O
CCD	O
reduce	O
its	O
sensitivity	O
to	O
light	O
by	O
using	O
some	O
of	O
the	O
pixel	B-Algorithm
area	O
for	O
a	O
drain	O
structure	O
.	O
</s>
