<s>
An	O
active-pixel	B-Architecture
sensor	I-Architecture
(	O
APS	O
)	O
is	O
an	O
image	B-Algorithm
sensor	I-Algorithm
,	O
which	O
was	O
invented	O
by	O
Peter	O
J.W.	O
</s>
<s>
Noble	O
in	O
1968	O
,	O
where	O
each	O
pixel	B-Algorithm
sensor	O
unit	O
cell	O
has	O
a	O
photodetector	O
(	O
typically	O
a	O
pinned	O
photodiode	O
)	O
and	O
one	O
or	O
more	O
active	O
transistors	B-Application
.	O
</s>
<s>
In	O
a	O
metal	B-Architecture
–	I-Architecture
oxide	I-Architecture
–	I-Architecture
semiconductor	I-Architecture
(	O
MOS	B-Architecture
)	O
active-pixel	B-Architecture
sensor	I-Architecture
,	O
MOS	B-Architecture
field-effect	I-Architecture
transistors	I-Architecture
(	O
MOSFETs	B-Architecture
)	O
are	O
used	O
as	O
amplifiers	O
.	O
</s>
<s>
There	O
are	O
different	O
types	O
of	O
APS	O
,	O
including	O
the	O
early	O
NMOS	B-Algorithm
APS	O
and	O
the	O
now	O
much	O
more	O
common	O
complementary	O
MOS	B-Architecture
(	O
CMOS	B-Device
)	O
APS	O
,	O
also	O
known	O
as	O
the	O
CMOS	B-Architecture
sensor	I-Architecture
.	O
</s>
<s>
CMOS	B-Architecture
sensors	I-Architecture
are	O
used	O
in	O
digital	B-Device
camera	I-Device
technologies	O
such	O
as	O
cell	O
phone	O
cameras	O
,	O
web	B-Protocol
cameras	I-Protocol
,	O
most	O
modern	O
digital	O
pocket	O
cameras	O
,	O
most	O
digital	B-Device
single-lens	I-Device
reflex	I-Device
cameras	I-Device
(	O
DSLRs	B-Device
)	O
,	O
and	O
mirrorless	B-Device
interchangeable-lens	I-Device
cameras	I-Device
(	O
MILCs	B-Device
)	O
.	O
</s>
<s>
CMOS	B-Architecture
sensors	I-Architecture
emerged	O
as	O
an	O
alternative	O
to	O
charge-coupled	B-Algorithm
device	I-Algorithm
(	O
CCD	O
)	O
image	B-Algorithm
sensors	I-Algorithm
and	O
eventually	O
outsold	O
them	O
by	O
the	O
mid-2000s	O
.	O
</s>
<s>
The	O
term	O
active	B-Architecture
pixel	I-Architecture
sensor	I-Architecture
is	O
also	O
used	O
to	O
refer	O
to	O
the	O
individual	O
pixel	B-Algorithm
sensor	O
itself	O
,	O
as	O
opposed	O
to	O
the	O
image	B-Algorithm
sensor	I-Algorithm
.	O
</s>
<s>
In	O
this	O
case	O
,	O
the	O
image	B-Algorithm
sensor	I-Algorithm
is	O
sometimes	O
called	O
an	O
active	B-Architecture
pixel	I-Architecture
sensor	I-Architecture
imager	B-Algorithm
,	O
or	O
active-pixel	O
image	B-Algorithm
sensor	I-Algorithm
.	O
</s>
<s>
While	O
researching	O
metal	B-Architecture
–	I-Architecture
oxide	I-Architecture
–	I-Architecture
semiconductor	I-Architecture
(	O
MOS	B-Architecture
)	O
technology	O
,	O
Willard	O
Boyle	O
and	O
George	O
E	O
.	O
Smith	O
realized	O
that	O
an	O
electric	O
charge	O
could	O
be	O
stored	O
on	O
a	O
tiny	O
MOS	B-Architecture
capacitor	O
,	O
which	O
became	O
the	O
basic	O
building	O
block	O
of	O
the	O
charge-couple	B-Algorithm
device	I-Algorithm
(	O
CCD	O
)	O
,	O
which	O
they	O
invented	O
in	O
1969	O
.	O
</s>
<s>
Pike	O
and	O
G	O
.	O
Sadasiv	O
in	O
1969	O
proposed	O
a	O
solid-state	O
image	B-Algorithm
sensor	I-Algorithm
with	O
scanning	O
circuits	O
using	O
thin-film	O
transistors	B-Application
(	O
TFTs	O
)	O
,	O
with	O
photoconductive	O
film	O
used	O
for	O
the	O
photodetector	O
.	O
</s>
<s>
A	O
low-resolution	O
"	O
mostly	O
digital	O
"	O
N-channel	B-Algorithm
MOSFET	I-Algorithm
(	O
NMOS	B-Algorithm
)	O
imager	B-Algorithm
with	O
intra-pixel	B-General_Concept
amplification	O
,	O
for	O
an	O
optical	O
mouse	O
application	O
,	O
was	O
demonstrated	O
by	O
Richard	O
F	O
.	O
Lyon	O
in	O
1981	O
.	O
</s>
<s>
Another	O
type	O
of	O
image	B-Algorithm
sensor	I-Algorithm
technology	O
that	O
is	O
related	O
to	O
the	O
APS	O
is	O
the	O
hybrid	O
infrared	O
focal	O
plane	O
array	O
(	O
IRFPA	O
)	O
,	O
designed	O
to	O
operate	O
at	O
cryogenic	O
temperatures	O
in	O
the	O
infrared	O
spectrum	O
.	O
</s>
<s>
A	O
key	O
element	O
of	O
the	O
modern	O
CMOS	B-Architecture
sensor	I-Architecture
is	O
the	O
pinned	O
photodiode	O
(	O
PPD	O
)	O
.	O
</s>
<s>
The	O
pinned	O
photodiode	O
is	O
a	O
photodetector	O
structure	O
with	O
low	O
lag	O
,	O
low	O
noise	B-Algorithm
,	O
high	O
quantum	O
efficiency	O
and	O
low	O
dark	O
current	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	B-Algorithm
sensors	I-Algorithm
,	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>
The	O
precursor	O
to	O
the	O
APS	O
was	O
the	O
passive-pixel	O
sensor	O
(	O
PPS	O
)	O
,	O
a	O
type	O
of	O
photodiode	O
array	O
(	O
PDA	O
)	O
.	O
</s>
<s>
A	O
passive-pixel	O
sensor	O
consists	O
of	O
passive	O
pixels	B-Algorithm
which	O
are	O
read	O
out	O
without	O
amplification	O
,	O
with	O
each	O
pixel	B-Algorithm
consisting	O
of	O
a	O
photodiode	O
and	O
a	O
MOSFET	B-Architecture
switch	O
.	O
</s>
<s>
In	O
a	O
photodiode	O
array	O
,	O
pixels	B-Algorithm
contain	O
a	O
p-n	O
junction	O
,	O
integrated	O
capacitor	O
,	O
and	O
MOSFETs	B-Architecture
as	O
selection	O
transistors	B-Application
.	O
</s>
<s>
This	O
was	O
the	O
basis	O
for	O
the	O
PPS	O
,	O
which	O
had	O
image	B-Algorithm
sensor	I-Algorithm
elements	O
with	O
in-pixel	O
selection	O
transistors	B-Application
,	O
proposed	O
by	O
Peter	O
J.W.	O
</s>
<s>
Passive-pixel	O
sensors	O
were	O
being	O
investigated	O
as	O
a	O
solid-state	O
alternative	O
to	O
vacuum-tube	O
imaging	O
devices	O
.	O
</s>
<s>
The	O
MOS	B-Architecture
passive-pixel	O
sensor	O
used	O
just	O
a	O
simple	O
switch	O
in	O
the	O
pixel	B-Algorithm
to	O
read	O
out	O
the	O
photodiode	O
integrated	O
charge	O
.	O
</s>
<s>
Pixels	B-Algorithm
were	O
arrayed	O
in	O
a	O
two-dimensional	O
structure	O
,	O
with	O
an	O
access	O
enable	O
wire	O
shared	O
by	O
pixels	B-Algorithm
in	O
the	O
same	O
row	O
,	O
and	O
output	O
wire	O
shared	O
by	O
column	O
.	O
</s>
<s>
At	O
the	O
end	O
of	O
each	O
column	O
was	O
a	O
transistor	B-Application
.	O
</s>
<s>
Passive-pixel	O
sensors	O
suffered	O
from	O
many	O
limitations	O
,	O
such	O
as	O
high	O
noise	B-Algorithm
,	O
slow	O
readout	O
,	O
and	O
lack	O
of	O
scalability	B-Architecture
.	O
</s>
<s>
Early	O
(	O
1960s	O
–	O
1970s	O
)	O
photodiode	O
arrays	O
with	O
selection	O
transistors	B-Application
within	O
each	O
pixel	B-Algorithm
,	O
along	O
with	O
on-chip	O
multiplexer	B-Protocol
circuits	O
,	O
were	O
impractically	O
large	O
.	O
</s>
<s>
The	O
noise	B-Algorithm
of	O
photodiode	O
arrays	O
was	O
also	O
a	O
limitation	O
to	O
performance	O
,	O
as	O
the	O
photodiode	O
readout	O
bus	O
capacitance	O
resulted	O
in	O
increased	O
read-noise	O
level	O
.	O
</s>
<s>
Correlated	O
double	O
sampling	O
(	O
CDS	O
)	O
could	O
also	O
not	O
be	O
used	O
with	O
a	O
photodiode	O
array	O
without	O
external	O
memory	B-General_Concept
.	O
</s>
<s>
It	O
was	O
not	O
possible	O
to	O
fabricate	B-Architecture
active-pixel	B-Architecture
sensors	I-Architecture
with	O
a	O
practical	O
pixel	B-Algorithm
size	O
in	O
the	O
1970s	O
,	O
due	O
to	O
limited	O
microlithography	O
technology	O
at	O
the	O
time	O
.	O
</s>
<s>
Because	O
the	O
MOS	B-Architecture
process	O
was	O
so	O
variable	O
and	O
MOS	B-Architecture
transistors	I-Architecture
had	O
characteristics	O
that	O
changed	O
over	O
time	O
(	O
Vth	O
instability	O
)	O
,	O
the	O
CCD	O
's	O
charge-domain	O
operation	O
was	O
more	O
manufacturable	O
and	O
higher	O
performance	O
than	O
MOS	B-Architecture
passive-pixel	O
sensors	O
.	O
</s>
<s>
The	O
active-pixel	B-Architecture
sensor	I-Architecture
consists	O
of	O
active	O
pixels	B-Algorithm
,	O
each	O
containing	O
one	O
or	O
more	O
MOSFET	B-Architecture
amplifiers	O
which	O
convert	O
the	O
photo-generated	O
charge	O
to	O
a	O
voltage	O
,	O
amplify	O
the	O
signal	O
voltage	O
,	O
and	O
reduce	O
noise	B-Algorithm
.	O
</s>
<s>
The	O
concept	O
of	O
an	O
active-pixel	O
device	O
was	O
proposed	O
by	O
Peter	O
Noble	O
in	O
1968	O
.	O
</s>
<s>
He	O
created	O
sensor	O
arrays	O
with	O
active	O
MOS	B-Architecture
readout	O
amplifiers	O
per	O
pixel	B-Algorithm
,	O
in	O
essentially	O
the	O
modern	O
three-transistor	O
configuration	O
:	O
the	O
buried	O
photodiode-structure	O
,	O
selection	O
transistor	B-Application
and	O
MOS	B-Architecture
amplifier	O
.	O
</s>
<s>
The	O
MOS	B-Architecture
active-pixel	O
concept	O
was	O
implemented	O
as	O
the	O
charge	O
modulation	O
device	O
(	O
CMD	O
)	O
by	O
Olympus	O
in	O
Japan	O
during	O
the	O
mid-1980s	O
.	O
</s>
<s>
This	O
was	O
enabled	O
by	O
advances	O
in	O
MOSFET	B-Architecture
semiconductor	B-Architecture
device	I-Architecture
fabrication	I-Architecture
,	O
with	O
MOSFET	B-Architecture
scaling	B-Architecture
reaching	O
smaller	O
micron	B-Algorithm
and	I-Algorithm
then	I-Algorithm
sub-micron	I-Algorithm
levels	O
during	O
the	O
1980s	O
to	O
early	O
1990s	O
.	O
</s>
<s>
The	O
first	O
MOS	B-Architecture
APS	O
was	O
fabricated	O
by	O
Tsutomu	O
Nakamura	O
's	O
team	O
at	O
Olympus	O
in	O
1985	O
.	O
</s>
<s>
The	O
term	O
active	B-Architecture
pixel	I-Architecture
sensor	I-Architecture
(	O
APS	O
)	O
was	O
coined	O
by	O
Nakamura	O
while	O
working	O
on	O
the	O
CMD	O
active-pixel	B-Architecture
sensor	I-Architecture
at	O
Olympus	O
.	O
</s>
<s>
The	O
CMD	O
imager	B-Algorithm
had	O
a	O
vertical	O
APS	O
structure	O
,	O
which	O
increases	O
fill-factor	O
(	O
or	O
reduces	O
pixel	B-Algorithm
size	O
)	O
by	O
storing	O
the	O
signal	O
charge	O
under	O
an	O
output	O
NMOS	B-Architecture
transistor	I-Architecture
.	O
</s>
<s>
Other	O
Japanese	O
semiconductor	O
companies	O
soon	O
followed	O
with	O
their	O
own	O
active	B-Architecture
pixel	I-Architecture
sensors	I-Architecture
during	O
the	O
late	O
1980s	O
to	O
early	O
1990s	O
.	O
</s>
<s>
Between	O
1988	O
and	O
1991	O
,	O
Toshiba	O
developed	O
the	O
"	O
double-gate	B-Algorithm
floating	B-Algorithm
surface	O
transistor	B-Application
"	O
sensor	O
,	O
which	O
had	O
a	O
lateral	O
APS	O
structure	O
,	O
with	O
each	O
pixel	B-Algorithm
containing	O
a	O
buried-channel	O
MOS	B-Architecture
photogate	O
and	O
a	O
PMOS	B-Algorithm
output	O
amplifier	O
.	O
</s>
<s>
Between	O
1989	O
and	O
1992	O
,	O
Canon	O
developed	O
the	O
base-stored	O
image	B-Algorithm
sensor	I-Algorithm
(	O
BASIS	O
)	O
,	O
which	O
used	O
a	O
vertical	O
APS	O
structure	O
similar	O
to	O
the	O
Olympus	O
sensor	O
,	O
but	O
with	O
bipolar	O
transistors	B-Application
rather	O
than	O
MOSFETs	B-Architecture
.	O
</s>
<s>
In	O
the	O
early	O
1990s	O
,	O
American	O
companies	O
began	O
developing	O
practical	O
MOS	B-Architecture
active	B-Architecture
pixel	I-Architecture
sensors	I-Architecture
.	O
</s>
<s>
In	O
1991	O
,	O
Texas	O
Instruments	O
developed	O
the	O
bulk	O
CMD	O
(	O
BCMD	O
)	O
sensor	O
,	O
which	O
was	O
fabricated	O
at	O
the	O
company	O
's	O
Japanese	O
branch	O
and	O
had	O
a	O
vertical	O
APS	O
structure	O
similar	O
to	O
the	O
Olympus	O
CMD	O
sensor	O
,	O
but	O
was	O
more	O
complex	O
and	O
used	O
PMOS	B-Algorithm
rather	O
than	O
NMOS	B-Architecture
transistors	I-Architecture
.	O
</s>
<s>
By	O
the	O
late	O
1980s	O
to	O
early	O
1990s	O
,	O
the	O
CMOS	B-Device
process	O
was	O
well-established	O
as	O
a	O
well-controlled	O
stable	O
semiconductor	B-Architecture
manufacturing	I-Architecture
process	I-Architecture
and	O
was	O
the	O
baseline	O
process	O
for	O
almost	O
all	O
logic	O
and	O
microprocessors	B-Architecture
.	O
</s>
<s>
There	O
was	O
a	O
resurgence	O
in	O
the	O
use	O
of	O
passive-pixel	O
sensors	O
for	O
low-end	O
imaging	O
applications	O
,	O
while	O
active-pixel	B-Architecture
sensors	I-Architecture
began	O
being	O
used	O
for	O
low-resolution	O
high-function	O
applications	O
such	O
as	O
retina	O
simulation	O
and	O
high-energy	O
particle	O
detectors	O
.	O
</s>
<s>
However	O
,	O
CCDs	O
continued	O
to	O
have	O
much	O
lower	O
temporal	O
noise	B-Algorithm
and	O
fixed-pattern	O
noise	B-Algorithm
and	O
were	O
the	O
dominant	O
technology	O
for	O
consumer	O
applications	O
such	O
as	O
camcorders	O
as	O
well	O
as	O
for	O
broadcast	O
cameras	O
,	O
where	O
they	O
were	O
displacing	O
video	O
camera	O
tubes	O
.	O
</s>
<s>
In	O
1993	O
,	O
the	O
first	O
practical	O
APS	O
to	O
be	O
successfully	O
fabricated	O
outside	O
of	O
Japan	O
was	O
developed	O
at	O
NASA	O
's	O
Jet	O
Propulsion	O
Laboratory	O
(	O
JPL	O
)	O
,	O
which	O
fabricated	O
a	O
CMOS	B-Device
compatible	O
APS	O
.	O
</s>
<s>
It	O
had	O
a	O
lateral	O
APS	O
structure	O
similar	O
to	O
the	O
Toshiba	O
sensor	O
,	O
but	O
was	O
fabricated	O
with	O
CMOS	B-Device
rather	O
than	O
PMOS	B-Architecture
transistors	I-Architecture
.	O
</s>
<s>
It	O
was	O
the	O
first	O
CMOS	B-Architecture
sensor	I-Architecture
with	O
intra-pixel	B-General_Concept
charge	O
transfer	O
.	O
</s>
<s>
Photobit	O
's	O
CMOS	B-Architecture
sensors	I-Architecture
found	O
their	O
way	O
into	O
webcams	B-Protocol
manufactured	O
by	O
Logitech	O
and	O
Intel	O
,	O
before	O
Photobit	O
was	O
purchased	O
by	O
Micron	O
Technology	O
in	O
2001	O
.	O
</s>
<s>
The	O
early	O
CMOS	B-Architecture
sensor	I-Architecture
market	O
was	O
initially	O
led	O
by	O
American	O
manufacturers	O
such	O
as	O
Micron	O
,	O
and	O
Omnivision	O
,	O
allowing	O
the	O
United	O
States	O
to	O
briefly	O
recapture	O
a	O
portion	O
of	O
the	O
overall	O
image	B-Algorithm
sensor	I-Algorithm
market	O
from	O
Japan	O
,	O
before	O
the	O
CMOS	B-Architecture
sensor	I-Architecture
market	O
eventually	O
came	O
to	O
be	O
dominated	O
by	O
Japan	O
,	O
South	O
Korea	O
and	O
China	O
.	O
</s>
<s>
The	O
CMOS	B-Architecture
sensor	I-Architecture
with	O
PPD	O
technology	O
was	O
further	O
advanced	O
and	O
refined	O
by	O
R	O
.	O
M	O
.	O
Guidash	O
in	O
1997	O
,	O
K	O
.	O
Yonemoto	O
and	O
H	O
.	O
Sumi	O
in	O
2000	O
,	O
and	O
I	O
.	O
Inoue	O
in	O
2003	O
.	O
</s>
<s>
This	O
led	O
to	O
CMOS	B-Architecture
sensors	I-Architecture
achieve	O
imaging	O
performance	O
on	O
par	O
with	O
CCD	B-Algorithm
sensors	I-Algorithm
,	O
and	O
later	O
exceeding	O
CCD	B-Algorithm
sensors	I-Algorithm
.	O
</s>
<s>
By	O
2000	O
,	O
CMOS	B-Architecture
sensors	I-Architecture
were	O
used	O
in	O
a	O
variety	O
of	O
applications	O
,	O
including	O
low-cost	O
cameras	O
,	O
PC	B-Protocol
cameras	I-Protocol
,	O
fax	O
,	O
multimedia	O
,	O
security	O
,	O
surveillance	O
,	O
and	O
videophones	B-Application
.	O
</s>
<s>
The	O
video	O
industry	O
switched	O
to	O
CMOS	B-Architecture
cameras	I-Architecture
with	O
the	O
advent	O
of	O
high-definition	O
video	O
(	O
HD	O
video	O
)	O
,	O
as	O
the	O
large	O
number	O
of	O
pixels	B-Algorithm
would	O
require	O
significantly	O
higher	O
power	O
consumption	O
with	O
CCD	B-Algorithm
sensors	I-Algorithm
,	O
which	O
would	O
overheat	O
and	O
drain	O
batteries	O
.	O
</s>
<s>
Sony	O
in	O
2007	O
commercialized	O
CMOS	B-Architecture
sensors	I-Architecture
with	O
an	O
original	O
column	O
A/D	O
conversion	O
circuit	O
,	O
for	O
fast	O
,	O
low-noise	O
performance	O
,	O
followed	O
in	O
2009	O
by	O
the	O
CMOS	B-Device
back-illuminated	B-Algorithm
sensor	I-Algorithm
(	O
BI	O
sensor	O
)	O
,	O
with	O
twice	O
the	O
sensitivity	O
of	O
conventional	O
image	B-Algorithm
sensors	I-Algorithm
and	O
going	O
beyond	O
the	O
human	O
eye	O
.	O
</s>
<s>
CMOS	B-Architecture
sensors	I-Architecture
went	O
on	O
to	O
have	O
a	O
significant	O
cultural	O
impact	O
,	O
leading	O
to	O
the	O
mass	O
proliferation	O
of	O
digital	B-Device
cameras	I-Device
and	O
camera	O
phones	O
,	O
which	O
bolstered	O
the	O
rise	O
of	O
social	O
media	O
and	O
selfie	O
culture	O
,	O
and	O
impacted	O
social	O
and	O
political	O
movements	O
around	O
the	O
world	O
.	O
</s>
<s>
By	O
2007	O
,	O
sales	O
of	O
CMOS	B-Device
active-pixel	B-Architecture
sensors	I-Architecture
had	O
surpassed	O
CCD	B-Algorithm
sensors	I-Algorithm
,	O
with	O
CMOS	B-Architecture
sensors	I-Architecture
accounting	O
for	O
54%	O
of	O
the	O
global	O
image	B-Algorithm
sensor	I-Algorithm
market	O
at	O
the	O
time	O
.	O
</s>
<s>
By	O
2012	O
,	O
CMOS	B-Architecture
sensors	I-Architecture
increased	O
their	O
share	O
to	O
74%	O
of	O
the	O
market	O
.	O
</s>
<s>
As	O
of	O
2017	O
,	O
CMOS	B-Architecture
sensors	I-Architecture
account	O
for	O
89%	O
of	O
global	O
image	B-Algorithm
sensor	I-Algorithm
sales	O
.	O
</s>
<s>
In	O
recent	O
years	O
,	O
the	O
CMOS	B-Architecture
sensor	I-Architecture
technology	O
has	O
spread	O
to	O
medium-format	O
photography	O
with	O
Phase	O
One	O
being	O
the	O
first	O
to	O
launch	O
a	O
medium	O
format	O
digital	O
back	O
with	O
a	O
Sony-built	O
CMOS	B-Architecture
sensor	I-Architecture
.	O
</s>
<s>
In	O
2012	O
,	O
Sony	O
introduced	O
the	O
stacked	B-Architecture
CMOS	I-Architecture
BI	O
sensor	O
.	O
</s>
<s>
There	O
have	O
been	O
several	O
research	O
activities	O
ongoing	O
in	O
the	O
field	O
of	O
image	B-Algorithm
sensors	I-Algorithm
.	O
</s>
<s>
One	O
of	O
them	O
is	O
the	O
quanta	O
image	B-Algorithm
sensor	I-Algorithm
(	O
QIS	O
)	O
,	O
which	O
might	O
be	O
a	O
paradigm	O
shift	O
in	O
the	O
way	O
we	O
collect	O
images	O
in	O
a	O
camera	O
.	O
</s>
<s>
In	O
the	O
QIS	O
,	O
the	O
goal	O
is	O
to	O
count	O
every	O
photon	O
that	O
strikes	O
the	O
image	B-Algorithm
sensor	I-Algorithm
,	O
and	O
to	O
provide	O
resolution	O
of	O
less	O
than	O
1	O
million	O
to	O
1	O
billion	O
or	O
more	O
specialized	O
photoelements	O
(	O
called	O
jots	O
)	O
per	O
sensor	O
,	O
and	O
to	O
read	O
out	O
jot	O
bit	O
planes	O
hundreds	O
or	O
thousands	O
of	O
times	O
per	O
second	O
resulting	O
in	O
terabits/sec	O
of	O
data	O
.	O
</s>
<s>
Boyd	O
Fowler	O
of	O
OmniVision	O
is	O
known	O
for	O
his	O
work	O
in	O
CMOS	B-Architecture
image	I-Architecture
sensor	I-Architecture
development	O
.	O
</s>
<s>
His	O
contributions	O
include	O
the	O
first	O
digital-pixel	O
CMOS	B-Architecture
image	I-Architecture
sensor	I-Architecture
in	O
1994	O
;	O
the	O
first	O
scientific	O
linear	O
CMOS	B-Architecture
image	I-Architecture
sensor	I-Architecture
with	O
single-electron	O
RMS	O
read	O
noise	B-Algorithm
in	O
2003	O
;	O
the	O
first	O
multi-megapixel	O
scientific	O
area	O
CMOS	B-Architecture
image	I-Architecture
sensor	I-Architecture
with	O
simultaneous	O
high	O
dynamic	O
range	O
(	O
86dB	O
)	O
,	O
fast	O
readout	O
(	O
100	O
frames/second	O
)	O
and	O
ultra-low	O
read	O
noise	B-Algorithm
(	O
1.2e	O
-	O
RMS	O
)	O
(	O
sCMOS	O
)	O
in	O
2010	O
.	O
</s>
<s>
He	O
also	O
patented	O
the	O
first	O
CMOS	B-Architecture
image	I-Architecture
sensor	I-Architecture
for	O
inter-oral	O
dental	O
X-rays	B-Library
with	O
clipped	O
corners	O
for	O
better	O
patient	O
comfort	O
.	O
</s>
<s>
By	O
the	O
late	O
2010s	O
CMOS	B-Architecture
sensors	I-Architecture
had	O
largely	O
if	O
not	O
completely	O
replaced	O
CCD	B-Algorithm
sensors	I-Algorithm
,	O
as	O
CMOS	B-Architecture
sensors	I-Architecture
can	O
not	O
only	O
be	O
made	O
in	O
existing	O
semiconductor	O
production	O
lines	O
,	O
reducing	O
costs	O
,	O
but	O
they	O
also	O
consume	O
less	O
power	O
,	O
just	O
to	O
name	O
a	O
few	O
advantages	O
.	O
</s>
<s>
HV-CMOS	O
devices	O
are	O
a	O
specialty	O
case	O
of	O
ordinary	O
CMOS	B-Architecture
sensors	I-Architecture
used	O
in	O
high-voltage	O
applications	O
(	O
for	O
detection	O
of	O
high	O
energy	O
particles	O
)	O
like	O
CERN	O
Large	O
Hadron	O
Collider	O
where	O
a	O
high-breakdown	O
voltage	O
up	O
to	O
~	O
30-120V	O
is	O
necessary	O
.	O
</s>
<s>
HV-CMOS	O
are	O
typically	O
implemented	O
by	O
~	O
10	O
µm	O
deep	O
n-doped	O
depletion	O
zone	O
(	O
n-well	O
)	O
of	O
a	O
transistor	B-Application
on	O
a	O
p-type	O
wafer	B-Architecture
substrate	B-Architecture
.	O
</s>
<s>
APS	O
pixels	B-Algorithm
solve	O
the	O
speed	O
and	O
scalability	B-Architecture
issues	O
of	O
the	O
passive-pixel	O
sensor	O
.	O
</s>
<s>
Unlike	O
CCDs	O
,	O
APS	O
sensors	O
can	O
combine	O
the	O
image	B-Algorithm
sensor	I-Algorithm
function	O
and	O
image	O
processing	O
functions	O
within	O
the	O
same	O
integrated	O
circuit	O
.	O
</s>
<s>
They	O
have	O
also	O
been	O
used	O
in	O
other	O
fields	O
including	O
digital	O
radiography	O
,	O
military	O
ultra	O
high	O
speed	O
image	O
acquisition	O
,	O
security	O
cameras	O
,	O
and	O
optical	B-Device
mice	I-Device
.	O
</s>
<s>
Manufacturers	O
include	O
Aptina	O
Imaging	O
(	O
independent	O
spinout	O
from	O
Micron	O
Technology	O
,	O
who	O
purchased	O
Photobit	O
in	O
2001	O
)	O
,	O
Canon	O
,	O
Samsung	B-Application
,	O
STMicroelectronics	O
,	O
Toshiba	O
,	O
OmniVision	O
Technologies	O
,	O
Sony	O
,	O
and	O
Foveon	O
,	O
among	O
others	O
.	O
</s>
<s>
CMOS-type	O
APS	O
sensors	O
are	O
typically	O
suited	O
to	O
applications	O
in	O
which	O
packaging	O
,	O
power	O
management	O
,	O
and	O
on-chip	O
processing	O
are	O
important	O
.	O
</s>
<s>
CMOS	B-Device
type	O
sensors	O
are	O
widely	O
used	O
,	O
from	O
high-end	O
digital	O
photography	O
down	O
to	O
mobile-phone	O
cameras	O
.	O
</s>
<s>
A	O
primary	O
advantage	O
of	O
a	O
CMOS	B-Architecture
sensor	I-Architecture
is	O
that	O
it	O
is	O
typically	O
less	O
expensive	O
to	O
produce	O
than	O
a	O
CCD	B-Algorithm
sensor	I-Algorithm
,	O
as	O
the	O
image	O
capturing	O
and	O
image	O
sensing	O
elements	O
can	O
be	O
combined	O
onto	O
the	O
same	O
IC	O
,	O
with	O
simpler	O
construction	O
required	O
.	O
</s>
<s>
A	O
CMOS	B-Architecture
sensor	I-Architecture
also	O
typically	O
has	O
better	O
control	O
of	O
blooming	O
(	O
that	O
is	O
,	O
of	O
bleeding	O
of	O
photo-charge	O
from	O
an	O
over-exposed	O
pixel	B-Algorithm
into	O
other	O
nearby	O
pixels	B-Algorithm
)	O
.	O
</s>
<s>
In	O
three-sensor	B-Algorithm
camera	I-Algorithm
systems	I-Algorithm
that	O
use	O
separate	O
sensors	O
to	O
resolve	O
the	O
red	O
,	O
green	O
,	O
and	O
blue	O
components	O
of	O
the	O
image	O
in	O
conjunction	O
with	O
beam	O
splitter	O
prisms	O
,	O
the	O
three	O
CMOS	B-Architecture
sensors	I-Architecture
can	O
be	O
identical	O
,	O
whereas	O
most	O
splitter	O
prisms	O
require	O
that	O
one	O
of	O
the	O
CCD	B-Algorithm
sensors	I-Algorithm
has	O
to	O
be	O
a	O
mirror	O
image	O
of	O
the	O
other	O
two	O
to	O
read	O
out	O
the	O
image	O
in	O
a	O
compatible	O
order	O
.	O
</s>
<s>
Unlike	O
CCD	B-Algorithm
sensors	I-Algorithm
,	O
CMOS	B-Architecture
sensors	I-Architecture
have	O
the	O
ability	O
to	O
reverse	O
the	O
addressing	O
of	O
the	O
sensor	O
elements	O
.	O
</s>
<s>
CMOS	B-Architecture
Sensors	I-Architecture
with	O
a	O
film	O
speed	O
of	O
ISO	O
4	O
million	O
exist	O
.	O
</s>
<s>
Since	O
a	O
CMOS	B-Architecture
sensor	I-Architecture
typically	O
captures	O
a	O
row	O
at	O
a	O
time	O
within	O
approximately	O
1/60	O
or	O
1/50	O
of	O
a	O
second	O
(	O
depending	O
on	O
refresh	O
rate	O
)	O
it	O
may	O
result	O
in	O
a	O
"	O
rolling	O
shutter	O
"	O
effect	O
,	O
where	O
the	O
image	O
is	O
skewed	O
(	O
tilted	O
to	O
the	O
left	O
or	O
right	O
,	O
depending	O
on	O
the	O
direction	O
of	O
camera	O
or	O
subject	O
movement	O
)	O
.	O
</s>
<s>
A	O
frame-transfer	B-Algorithm
CCD	I-Algorithm
sensor	O
or	O
"	O
global	O
shutter	O
"	O
CMOS	B-Architecture
sensor	I-Architecture
does	O
not	O
have	O
this	O
problem	O
;	O
instead	O
it	O
captures	O
the	O
entire	O
image	O
at	O
once	O
into	O
a	O
frame	O
store	O
.	O
</s>
<s>
A	O
long-standing	O
advantage	O
of	O
CCD	B-Algorithm
sensors	I-Algorithm
has	O
been	O
their	O
capability	O
for	O
capturing	O
images	O
with	O
lower	O
noise	B-Algorithm
.	O
</s>
<s>
With	O
improvements	O
in	O
CMOS	B-Device
technology	O
,	O
this	O
advantage	O
has	O
closed	O
as	O
of	O
2020	O
,	O
with	O
modern	O
CMOS	B-Architecture
sensors	I-Architecture
available	O
capable	O
of	O
outperforming	O
CCD	B-Algorithm
sensors	I-Algorithm
.	O
</s>
<s>
The	O
active	O
circuitry	O
in	O
CMOS	B-Device
pixels	B-Algorithm
takes	O
some	O
area	O
on	O
the	O
surface	O
which	O
is	O
not	O
light-sensitive	O
,	O
reducing	O
the	O
photon-detection	O
efficiency	O
of	O
the	O
device	O
(	O
microlenses	O
and	O
back-illuminated	B-Algorithm
sensors	I-Algorithm
can	O
mitigate	O
this	O
problem	O
)	O
.	O
</s>
<s>
But	O
the	O
frame-transfer	B-Algorithm
CCD	I-Algorithm
also	O
has	O
about	O
half	O
the	O
non-sensitive	O
area	O
for	O
the	O
frame	O
store	O
nodes	O
,	O
so	O
the	O
relative	O
advantages	O
depend	O
on	O
which	O
types	O
of	O
sensors	O
are	O
being	O
compared	O
.	O
</s>
<s>
The	O
standard	O
CMOS	B-Architecture
APS	I-Architecture
pixel	B-Algorithm
consists	O
of	O
a	O
photodetector	O
(	O
pinned	O
photodiode	O
)	O
,	O
a	O
floating	B-Algorithm
diffusion	O
,	O
and	O
the	O
so-called	O
4T	O
cell	O
consisting	O
of	O
four	O
CMOS	B-Device
(	O
complementary	O
metal	B-Architecture
–	I-Architecture
oxide	I-Architecture
–	I-Architecture
semiconductor	I-Architecture
)	O
transistors	B-Application
,	O
including	O
a	O
transfer	O
gate	B-Algorithm
,	O
reset	O
gate	B-Algorithm
,	O
selection	O
gate	B-Algorithm
and	O
source-follower	O
readout	O
transistor	B-Application
.	O
</s>
<s>
The	O
pinned	O
photodiode	O
was	O
originally	O
used	O
in	O
interline	O
transfer	O
CCDs	O
due	O
to	O
its	O
low	O
dark	O
current	O
and	O
good	O
blue	O
response	O
,	O
and	O
when	O
coupled	O
with	O
the	O
transfer	O
gate	B-Algorithm
,	O
allows	O
complete	O
charge	O
transfer	O
from	O
the	O
pinned	O
photodiode	O
to	O
the	O
floating	B-Algorithm
diffusion	O
(	O
which	O
is	O
further	O
connected	O
to	O
the	O
gate	B-Algorithm
of	O
the	O
read-out	O
transistor	B-Application
)	O
eliminating	O
lag	O
.	O
</s>
<s>
The	O
use	O
of	O
intrapixel	O
charge	O
transfer	O
can	O
offer	O
lower	O
noise	B-Algorithm
by	O
enabling	O
the	O
use	O
of	O
correlated	O
double	O
sampling	O
(	O
CDS	O
)	O
.	O
</s>
<s>
The	O
Noble	O
3T	O
pixel	B-Algorithm
is	O
still	O
sometimes	O
used	O
since	O
the	O
fabrication	B-Architecture
requirements	O
are	O
less	O
complex	O
.	O
</s>
<s>
The	O
3T	O
pixel	B-Algorithm
comprises	O
the	O
same	O
elements	O
as	O
the	O
4T	O
pixel	B-Algorithm
except	O
the	O
transfer	O
gate	B-Algorithm
and	O
the	O
photodiode	O
.	O
</s>
<s>
The	O
reset	O
transistor	B-Application
,	O
Mrst	O
,	O
acts	O
as	O
a	O
switch	O
to	O
reset	O
the	O
floating	B-Algorithm
diffusion	O
to	O
VRST	O
,	O
which	O
in	O
this	O
case	O
is	O
represented	O
as	O
the	O
gate	B-Algorithm
of	O
the	O
Msf	O
transistor	B-Application
.	O
</s>
<s>
When	O
the	O
reset	O
transistor	B-Application
is	O
turned	O
on	O
,	O
the	O
photodiode	O
is	O
effectively	O
connected	O
to	O
the	O
power	O
supply	O
,	O
VRST	O
,	O
clearing	O
all	O
integrated	O
charge	O
.	O
</s>
<s>
Since	O
the	O
reset	O
transistor	B-Application
is	O
n-type	O
,	O
the	O
pixel	B-Algorithm
operates	O
in	O
soft	O
reset	O
.	O
</s>
<s>
The	O
read-out	O
transistor	B-Application
,	O
Msf	O
,	O
acts	O
as	O
a	O
buffer	O
(	O
specifically	O
,	O
a	O
source	O
follower	O
)	O
,	O
an	O
amplifier	O
which	O
allows	O
the	O
pixel	B-Algorithm
voltage	O
to	O
be	O
observed	O
without	O
removing	O
the	O
accumulated	O
charge	O
.	O
</s>
<s>
Its	O
power	O
supply	O
,	O
VDD	O
,	O
is	O
typically	O
tied	O
to	O
the	O
power	O
supply	O
of	O
the	O
reset	O
transistor	B-Application
VRST	O
.	O
</s>
<s>
The	O
select	O
transistor	B-Application
,	O
Msel	O
,	O
allows	O
a	O
single	O
row	O
of	O
the	O
pixel	B-Algorithm
array	O
to	O
be	O
read	O
by	O
the	O
read-out	O
electronics	O
.	O
</s>
<s>
Other	O
innovations	O
of	O
the	O
pixels	B-Algorithm
such	O
as	O
5T	O
and	O
6T	O
pixels	B-Algorithm
also	O
exist	O
.	O
</s>
<s>
By	O
adding	O
extra	O
transistors	B-Application
,	O
functions	O
such	O
as	O
global	O
shutter	O
,	O
as	O
opposed	O
to	O
the	O
more	O
common	O
rolling	O
shutter	O
,	O
are	O
possible	O
.	O
</s>
<s>
In	O
order	O
to	O
increase	O
the	O
pixel	B-Algorithm
densities	O
,	O
shared-row	O
,	O
four-ways	O
and	O
eight-ways	O
shared	O
read	O
out	O
,	O
and	O
other	O
architectures	O
can	O
be	O
employed	O
.	O
</s>
<s>
A	O
variant	O
of	O
the	O
3T	O
active	O
pixel	B-Algorithm
is	O
the	O
Foveon	B-Algorithm
X3	I-Algorithm
sensor	I-Algorithm
invented	O
by	O
Dick	O
Merrill	O
.	O
</s>
<s>
In	O
this	O
device	O
,	O
three	O
photodiodes	O
are	O
stacked	O
on	O
top	O
of	O
each	O
other	O
using	O
planar	B-Algorithm
fabrication	I-Algorithm
techniques	I-Algorithm
,	O
each	O
photodiode	O
having	O
its	O
own	O
3T	O
circuit	O
.	O
</s>
<s>
A	O
typical	O
two-dimensional	O
array	O
of	O
pixels	B-Algorithm
is	O
organized	O
into	O
rows	O
and	O
columns	O
.	O
</s>
<s>
Pixels	B-Algorithm
in	O
a	O
given	O
row	O
share	O
reset	O
lines	O
,	O
so	O
that	O
a	O
whole	O
row	O
is	O
reset	O
at	O
a	O
time	O
.	O
</s>
<s>
The	O
row	O
select	O
lines	O
of	O
each	O
pixel	B-Algorithm
in	O
a	O
row	O
are	O
tied	O
together	O
as	O
well	O
.	O
</s>
<s>
The	O
outputs	O
of	O
each	O
pixel	B-Algorithm
in	O
any	O
given	O
column	O
are	O
tied	O
together	O
.	O
</s>
<s>
The	O
size	O
of	O
the	O
pixel	B-Algorithm
sensor	O
is	O
often	O
given	O
in	O
height	O
and	O
width	O
,	O
but	O
also	O
in	O
the	O
optical	B-Algorithm
format	I-Algorithm
.	O
</s>
<s>
There	O
are	O
two	O
types	O
of	O
active-pixel	B-Architecture
sensor	I-Architecture
(	O
APS	O
)	O
structures	O
,	O
the	O
lateral	O
APS	O
and	O
vertical	O
APS	O
.	O
</s>
<s>
For	O
applications	O
such	O
as	O
large-area	O
digital	O
X-ray	B-Library
imaging	O
,	O
thin-film	O
transistors	B-Application
(	O
TFTs	O
)	O
can	O
also	O
be	O
used	O
in	O
APS	O
architecture	O
.	O
</s>
<s>
However	O
,	O
because	O
of	O
the	O
larger	O
size	O
and	O
lower	O
transconductance	O
gain	O
of	O
TFTs	O
compared	O
with	O
CMOS	B-Device
transistors	B-Application
,	O
it	O
is	O
necessary	O
to	O
have	O
fewer	O
on-pixel	O
TFTs	O
to	O
maintain	O
image	O
resolution	O
and	O
quality	O
at	O
an	O
acceptable	O
level	O
.	O
</s>
<s>
A	O
two-transistor	O
APS/PPS	O
architecture	O
has	O
been	O
shown	O
to	O
be	O
promising	O
for	O
APS	O
using	O
amorphous	O
silicon	O
TFTs	O
.	O
</s>
<s>
In	O
the	O
two-transistor	O
APS	O
architecture	O
on	O
the	O
right	O
,	O
TAMP	O
is	O
used	O
as	O
a	O
switched-amplifier	O
integrating	O
functions	O
of	O
both	O
Msf	O
and	O
Msel	O
in	O
the	O
three-transistor	O
APS	O
.	O
</s>
<s>
This	O
results	O
in	O
reduced	O
transistor	B-Application
counts	O
per	O
pixel	B-Algorithm
,	O
as	O
well	O
as	O
increased	O
pixel	B-Algorithm
transconductance	O
gain	O
.	O
</s>
<s>
Here	O
,	O
Cpix	O
is	O
the	O
pixel	B-Algorithm
storage	O
capacitance	O
,	O
and	O
it	O
is	O
also	O
used	O
to	O
capacitively	O
couple	O
the	O
addressing	O
pulse	O
of	O
the	O
"	O
Read	O
"	O
to	O
the	O
gate	B-Algorithm
of	O
TAMP	O
for	O
ON-OFF	O
switching	O
.	O
</s>
<s>
Such	O
pixel	B-Algorithm
readout	O
circuits	O
work	O
best	O
with	O
low	O
capacitance	O
photoconductor	O
detectors	O
such	O
as	O
amorphous	O
selenium	B-Library
.	O
</s>
<s>
Many	O
different	O
pixel	B-Algorithm
designs	O
have	O
been	O
proposed	O
and	O
fabricated	O
.	O
</s>
<s>
The	O
standard	O
pixel	B-Algorithm
uses	O
the	O
fewest	O
wires	O
and	O
the	O
fewest	O
,	O
most	O
tightly	O
packed	O
transistors	B-Application
possible	O
for	O
an	O
active	O
pixel	B-Algorithm
.	O
</s>
<s>
It	O
is	O
important	O
that	O
the	O
active	O
circuitry	O
in	O
a	O
pixel	B-Algorithm
take	O
up	O
as	O
little	O
space	O
as	O
possible	O
to	O
allow	O
more	O
room	O
for	O
the	O
photodetector	O
.	O
</s>
<s>
High	O
transistor	B-Application
count	O
hurts	O
fill	O
factor	O
,	O
that	O
is	O
,	O
the	O
percentage	O
of	O
the	O
pixel	B-Algorithm
area	O
that	O
is	O
sensitive	O
to	O
light	O
.	O
</s>
<s>
Pixel	B-Algorithm
size	O
can	O
be	O
traded	O
for	O
desirable	O
qualities	O
such	O
as	O
noise	B-Algorithm
reduction	O
or	O
reduced	O
image	O
lag	O
.	O
</s>
<s>
Noise	B-Algorithm
is	O
a	O
measure	O
of	O
the	O
accuracy	O
with	O
which	O
the	O
incident	O
light	O
can	O
be	O
measured	O
.	O
</s>
<s>
the	O
pixel	B-Algorithm
is	O
not	O
fully	O
reset	O
.	O
</s>
<s>
The	O
voltage	O
noise	B-Algorithm
variance	O
in	O
a	O
soft-reset	O
(	O
gate-voltage	O
regulated	O
)	O
pixel	B-Algorithm
is	O
,	O
but	O
image	O
lag	O
and	O
fixed	O
pattern	O
noise	B-Algorithm
may	O
be	O
problematic	O
.	O
</s>
<s>
In	O
rms	O
electrons	O
,	O
the	O
noise	B-Algorithm
is	O
.	O
</s>
<s>
Operating	O
the	O
pixel	B-Algorithm
via	O
hard	O
reset	O
results	O
in	O
a	O
Johnson	O
–	O
Nyquist	O
noise	B-Algorithm
on	O
the	O
photodiode	O
of	O
or	O
,	O
but	O
prevents	O
image	O
lag	O
,	O
sometimes	O
a	O
desirable	O
tradeoff	O
.	O
</s>
<s>
One	O
way	O
to	O
use	O
hard	O
reset	O
is	O
replace	O
Mrst	O
with	O
a	O
p-type	O
transistor	B-Application
and	O
invert	O
the	O
polarity	O
of	O
the	O
RST	O
signal	O
.	O
</s>
<s>
The	O
presence	O
of	O
the	O
p-type	O
device	O
reduces	O
fill	O
factor	O
,	O
as	O
extra	O
space	O
is	O
required	O
between	O
p	O
-	O
and	O
n-devices	O
;	O
it	O
also	O
removes	O
the	O
possibility	O
of	O
using	O
the	O
reset	O
transistor	B-Application
as	O
an	O
overflow	O
anti-blooming	O
drain	O
,	O
which	O
is	O
a	O
commonly	O
exploited	O
benefit	O
of	O
the	O
n-type	O
reset	O
FET	O
.	O
</s>
<s>
Next	O
,	O
a	O
soft	O
reset	O
is	O
done	O
,	O
causing	O
a	O
low	O
noise	B-Algorithm
reset	O
without	O
adding	O
any	O
lag	O
.	O
</s>
<s>
Specifically	O
,	O
pseudo-flash	O
reset	O
and	O
hard-to-soft	O
reset	O
both	O
add	O
transistors	B-Application
between	O
the	O
pixel	B-Algorithm
power	O
supplies	O
and	O
the	O
actual	O
VDD	O
.	O
</s>
<s>
A	O
more	O
radical	O
pixel	B-Algorithm
design	O
is	O
the	O
active-reset	O
pixel	B-Algorithm
.	O
</s>
<s>
Active	O
reset	O
can	O
result	O
in	O
much	O
lower	O
noise	B-Algorithm
levels	O
.	O
</s>
<s>
The	O
tradeoff	O
is	O
a	O
complicated	O
reset	O
scheme	O
,	O
as	O
well	O
as	O
either	O
a	O
much	O
larger	O
pixel	B-Algorithm
or	O
extra	O
column-level	O
circuitry	O
.	O
</s>
