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8/3/2019 2001 April Cmoc
http://slidepdf.com/reader/full/2001-april-cmoc 1/46
Photobit
CMOS Image Sensors
Dr. Eric R. FossumPhotobit Technology Corporation
Pasadena, California
© 2001 Photobit Technology Corporation Rev 1
8/3/2019 2001 April Cmoc
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Photobit
Timing &r ver
Circuits
DetectorPixelArray
Analog Signal ProcessorAnalog to Digital Converter
ASP
ADC
© 2001 Photobit Technology Corporation
Digital Signal Processor
DSP
8/3/2019 2001 April Cmoc
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Photobit CMOS Image Sensor
- - -
CMOS Active Pixel Color Imaging ArrayDigital Logic for
• User Interface
• Sensor Setup
• Timing Generator• Digital Signal
– Color Processing
– White Balance – Image Enhancement
• Data OutputFormatting
na og gnaProcessing
• Data Sampling
• Noise Reduction
© 2001 Photobit Technology Corporation
• Gain Analog-To-Digital Conversion
8/3/2019 2001 April Cmoc
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Photobit CMOS Image Sensor
•On-chip timing and control circuits•On-chi analo si nal rocessin
•Correlated double sampling•Local neighborhood image processing••Compression preprocessing
•Pixel defect correction••Window readout for electronic pan/tilt•Skip-mode for low resolution readout
• - - -•High speed digital output•On-chip DSP and digital sensor control
© 2001 Photobit Technology Corporation
, . , . …•Easier interface, easier board design
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Photobit
Vpd
Cpd
Ipd
Vssvoltage
© 2001 Photobit Technology Corporation
time
8/3/2019 2001 April Cmoc
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Photobit
• Each pixel gets covered by a colored filter
– e use re , green, ue - es ma c or
displays in “Bayer” pattern
– Could use complementary colors (cyan, yellow, magenta)
1
0.4
0.5
0.6
0.7
0.8
.
e r e s p o n s e
Silicon
0
0.1
0.20.3
400 500 600 700 800 900 1000 1100
R e l a t i
© 2001 Photobit Technology Corporation
Wa velength (nm)
8/3/2019 2001 April Cmoc
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Photobit
• A pixel is divided into a sensing portion and a readoutpor on
• Fill factor is the ratio of sensing area to total area and istypically about 20% for CCDs and CMOS APS
Total pixel area
Sensitive area
© 2001 Photobit Technology Corporation
8/3/2019 2001 April Cmoc
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Photobit
• Microlenses funnel li ht awa from non-sensitive ortions of
pixel
Color filter layerMetal opaque layer
Photodiode
Silicon substrate
© 2001 Photobit Technology Corporation
8/3/2019 2001 April Cmoc
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Photobit
• Ke to Inte rated Ima in S stem camera on a chi is
making a good pixel in a CMOS platform process.• Prior to CMOS active pixel was CMOS passive pixel.
• Simple and DRAM-like
• Not such a good pixelue o g rea no se
• Gets worse with smallixels lar e arra s and
M1RS
Vpd
CpdIpd
faster readoutVss
© 2001 Photobit Technology Corporation
Vout
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Photobit
• Add an am lifier inside each ixel.
• Not so obvious: – Reduces fill factor due to 3 transistors
– Adds fixed pattern noise due to offset variations in
each amplifier’ –
CCDs were invented.
• Non-CMOS active ixel sensors were demonstrated b
Olympus, Toshiba, Texas Instruments and others butsuffer from requiring a unique semiconductor fabrication
© 2001 Photobit Technology Corporation
8/3/2019 2001 April Cmoc
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Photobit
• CMOS state of the art is ripe for image sensors
–
– Defects and contamination well controlled – Threshold voltages stable and fairly uniform
– And now foundries offer specialized image sensor modules
• Customers demand low power, miniaturized systems-on-a-chip
• Circuit techniques developed for high performance
– Active pixel provides gain in pixel and lower noise
– Use of double-correlated sampling and double-delta sampling on-chi removes tem oral & fixed attern noise
– Column parallel architecture permits low analog bandwidths toreduce noise and artifacts and maintain high frame rate.
–
© 2001 Photobit Technology Corporation
8/3/2019 2001 April Cmoc
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Photobit
100
10
Im age SensorPixel Size
CCD Invente d
S i z
e ( u m )
PracticalO tical Lim it
1CMOS
Feature Size
0.11970 1975 1980 1985 1990 1995 2000 2005
Year
© 2001 Photobit Technology Corporation
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Photobit
20
14
16
18
Cheap Lens Resolution(30 lp/mm)
10
12
( m
i c r o n s )
Airy Disk Diameter=
4
6
8
S i z e
.
F/2.8
0
2
400 500 600 700 800 900 1000 1100
(120 lp/mm)
B G RB G R
© 2001 Photobit Technology Corporation
Wavelength (nm)
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Photobit
Quantum Efficiency of PB-0100 Rev. C
20
Blue pixels
Green pixels
Red ixels
10
15
f i c i e n c y ,
%
5
Q u a n t u m
E
300 400 500 600 700 800 900 1000 1100
0
© 2001 Photobit Technology Corporation
ave engt , nm
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Photobit
• PN junction photodiode (PD)
• RST switch M1 charges PD to
Vpix• Light-generated current Ipd M2
M1RST
ColBus
Vpix
• Voltage Vpd on PD is gatevoltage of in-pixel source-follower transistor M1.
Vpd
Cpd
• Row Select (RS) switch M3connects pixel transistor tocolumn bus and charges bus to
RSp
Vss
same vo tage as .• Voltage Vout picked off at
bottom of column.
Vout
IL
© 2001 Photobit Technology Corporation
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Photobit Physical Layout of
PD V D D
L B U S
PHOTODIODE
PD
PD
PD
C O
P
D
P
D
P
D
RESET
M1 RST
ROW
M2 SF
SELECT M3 RS PD
PD
PD
© 2001 Photobit Technology Corporation
8/3/2019 2001 April Cmoc
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Photobit
“Correlated” Double Sam lin
Photodiode Voltage
integration starts pixel reset level sampled
2V
signal sampled
0V
1V
ms ms
Pixel sampled twice to remove variations inthreshold volta e of ixel source follower and
© 2001 Photobit Technology Corporation
reset level.
8/3/2019 2001 April Cmoc
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Photobit
VDDPIXEL
RST
COL BUS
RS
CS GLOBAL
SHS
SHR
SIG
HOR BUS
VLP
RSTVLN
© 2001 Photobit Technology Corporation
PER COLUMN
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Photobit
ReadRead
ResetReset
Read
Reset
Row 1 Row 2 Row 3
2V
3V
1V
© 2001 Photobit Technology Corporation
0V
33 ms 66 ms
8/3/2019 2001 April Cmoc
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Photobit X-ray Sensor for Dental and
Osteo orosis A lications
• Total chi size: 37 x27 mm
• 900 (V) x 675 (H)elements
• μ • 2 μm CMOS process• Differential analog
output• On-chip timing and
control• Perhaps world’s
production
© 2001 Photobit Technology Corporation
Xue 1998
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Photobit Mammography Sensor
(3-Sides Buttable)
• x e ements• 30 μm pixel pitch• 0.8 μm process
• 3-sides buttable• P-channel PD-type pixel• Differential analog output
© 2001 Photobit Technology Corporation
• co umn oss
Xue 1997
• Some on-chip circuits
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Photobit
• Passive Pixel Sensor (PPS)
– o o o e
– Charge injection
– Photodiode (dates to 1968)
– Photo ate invented at JPL
– Pinned Photodiode (invented by JPL/Kodak)
– Floating gate (invented at JPL)
– Logarithmic (high dynamic range - low contrast) – Freeze-Frame (Photobit)
© 2001 Photobit Technology Corporation
– More complex amplifiers (from DoD infrared imagers)
8/3/2019 2001 April Cmoc
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Photobit
• 3 transistors per pixel
• Great QE• Logarithmic response -- good
VDD
range
• Poor contrast under flatg ng
• Log-response makes colorprocessing extremely
RS
comp ex• Susceptible to FPN• Slow response under low light COL BUS
© 2001 Photobit Technology Corporation
8/3/2019 2001 April Cmoc
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Photobit
• 4 transistor ixel VDD
• More complex fabrication• Susceptible to lag• Great QE
RST
• Low noise• Good scaling for large arrays•
TX
• First demonstrated by JPL/Kodak PPD
COL BUS
© 2001 Photobit Technology Corporation
8/3/2019 2001 April Cmoc
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Photobit
Photo ate Active Pixel
• 5 transistor ixel VDD
• Larger pixel• QE loss due to poly gate RST
• Lowest noise
– 5 e- rmsPG TX
• Good scaling for large arrays
• Good scaling for fast arrays
. , ,
COL BUS
© 2001 Photobit Technology Corporation
8/3/2019 2001 April Cmoc
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Photobit
-
•
• Permits on-chip DSP for camera control, colorinterpolation, etc.
• Suppresses noise pick up from EMI, crosstalk
• Simplifies interface• Permits faster readout
• Can reduce overall chip and/or system power
© 2001 Photobit Technology Corporation
8/3/2019 2001 April Cmoc
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Photobit
On-Chi ADC Choices
• One (or two or three) • Single-slope
– High data raterequirement (5-60
– slow
• Successiveapproximation
– Local high power
dissipation
– 8-10 b max
• Algorithmic
– needs ood o -am• ne per p xe
– Large pixels and low fillfactor
• Oversampled
– Filter takes lots of
• One ADC per column(column-parallel)
– Tall, skinny ADCs
• Flash and Folding
– More power
© 2001 Photobit Technology Corporation
8/3/2019 2001 April Cmoc
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Photobit
-
Digitizedin pixel Serial ADC(s)
at data rate Columnparallel
Columnparallel
ADCsMultiplexed
output
ADCsParallel
output ports
© 2001 Photobit Technology Corporation
8/3/2019 2001 April Cmoc
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Photobit
-
• Internet cameras, games
• 360x304 352x288 effective ixels
• 8b flash ADC
• 7.9 μm x 7.9 μm (1/5” optical format)
• Pro ressive scan window readout
• 15,000 gate on-chip logic
• >30 frames per sec (adj.)
• 3.3 V o eration
• <100 mW total power
• Built-in autoexposure control
• On-chi biasin
• On-chip CFA
• >20 dB SNR @ 1 lux, 30 fps
© 2001 Photobit Technology Corporation
Van Blerkom, Huang, Chan 1999
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Photobit
-
• Dual mode cameras, internet cameras
• 640x487 640x480 effective ixels
• 320 column-parallel 8b ADCs
• 7.9 μm x 7.9 μm (1/3” optical format)
• Pro ressive scan window readout
• 15,000+ gate on-chip logic
• >30 frames per sec (adj.)
• 5 V o eration
• <300 mW total power
• Built-in autoexposure control
• On-chi biasin
• On-chip CFA
• >20 dB SNR @ 1 lux, 30 fps
© 2001 Photobit Technology Corporation
Panicacci, Cho 1999
8/3/2019 2001 April Cmoc
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Photobit Example:
• Digital stillcameras
• 2 Mpixels
• 3.9 um ixel pitch
• Microlenses
© 2001 Photobit Technology Corporation
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Photobit Major Advantages of CMOS Image
• Lower power
– ower supp y vo ages , . , . , ….
– Integration reduces parasitics – Clever mixed si nal desi n and di ital si nal rocessin
• Increased functionality
– Increased integration on chip and smaller form factor – Higher dynamic range, better image quality
– Smart digital signal processing and local sensor control
•
– High throughput with on-chip ADC and digital output
• Lower system cost
© 2001 Photobit Technology Corporation
– Fewer system components, lower wafer costs
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Photobit 3-Pin Self-Clocked Micropower
Camera on a Chi
• World’s lowest power camera- Timing andon-a-chip
• Portable electronics such asPDAs, cell phones, games
control logic8b ADC
• QCIF format
• 0.35 um process technology
•
176x144
5 um pixels
• 550 uW total power
• Watch battery operation
• n-c p c oc• On-chip 8b ADC
• 1.5 volt operation
Analog signalprocessor
© 2001 Photobit Technology Corporation
• Serial digital data output30 fps output
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Photobit
• Pixel Format: 256 X 256
. .
• xe ze: µm µm
• Frame Rate: 2 fps
• ADC: On-Chip, 8 bits
View inside smallintestine
© 2001 Photobit Technology Corporation
• ower upp y:2.8
• Power: 3 mW
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Photobit Ultra-High Intrascene Dynamic
Ran e Sensor for Automotive
High SensitivityAny one 8b image does not coverfull intrascene dynamic range:
Output 8b
ynam c mapp ngASPADCs
Logic
• Proprietary pixel design allows very high
• Preserves contrast unlike logarithmicsensors
• Low susce tibilit to FPN com ared to
© 2001 Photobit Technology Corporation
logarithmic sensors
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Photobit High Speed Linear Sensor
• 4096 x 1 linear array
• 7 um pixel pitch (28 mm long)
-
• 4 analog output ports, each 40 MHz
• 160 Mpix/sec total output rate
• 35,000 lines/sec• 5 V operation
• Subwindowing allowed, from center
© 2001 Photobit Technology Corporation
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Photobit
• 1000 dpi scan density
• > 9 V / lux-sec• 10b ADC
• <150 mW operation
• on-chi FIFO buffer
• 40 Mbytes/s readout rate• SPI compatible serial interface
© 2001 Photobit Technology Corporation
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Photobit SmartBeamTM
• Pseudo-random accessreadout
• High sensitivity photogate
pixels• 8b ADC
• SPI interface
© 2001 Photobit Technology Corporation
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Photobit
• x array
• Photodiode-type pixel withradiation tolerant readoutc rcu try
• 1 MHz analog output
• Individual pixel resetcircuitry for ultra highdynamic rangemanagement
• Initial results shows sensorstill working after 30Mrads
© 2001 Photobit Technology Corporation
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Photobit 1024x1024 (1.0 Mpix), 500 fps ERS
• 1024x1024 elements
• 0.5 μm CMOS• 1024 on-chip 8b ADCs
• 8x8b digital output (64 pins)
• Open architecture
• 3.3 volt operation• Power: 95 mW @ 60 fps
• Power: 450 mW @ 500 fps
• -
© 2001 Photobit Technology Corporation
Krymski, Van Blerkom, Bock, Anderson 1998
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Photobit PBMV40 (in development)2352x1728 4.1M ix 240f s ERS
• 4.1 Mpixel sensor• 7 μm x 7 μm pixel pitch• 16x10b digital output• 240 fps ERS• y es sec a z• 4000 bits/lx-sec• 3.3 volt operation
© 2001 Photobit Technology Corporation
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Photobit Shuttered Node Active Pixel
• 6 transistor ixel VDD
• Larger pixel
• QE loss due to poly gateRST
across all pixels (freeze-motion)
• Shutter efficiency issue PG TXSH
COL BUS
© 2001 Photobit Technology Corporation
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Photobit
Shutter closed Shutter open
1 frame period (Tperiod)
timeTopen
Ideal: Signal = Topen / Tperiod Signal0
= open per o0
-ε 0where ε is the shutter efficiency
© 2001 Photobit Technology Corporation
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Photobit
• Proprietary Photobittechnology, 5-T pixel
• Normal photodiode
• Si nal transferred to
Col
storage node in N-well
• Stora e node read RSRGRP TXout in usual way
• Diffusinghotoelectrons do not -
n+
affect storage• Very high shutter
efficienc >99.9%
© 2001 Photobit Technology Corporation
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Photobit 1280x1024 (1.3Mpix) 600fps
• 1.3 Mpixel sensor
•
• 0.35 μm CMOS
• High efficiency (>99.9%) freezeframe shutter
• Shutter speeds from 1/30th to1/100,000th sec
• 10x10b digital output (100 pins)
Color image withrotating fan
1/605 sec=1652 usecRolling shutter
• Open architecture
• 3.3 volt operation
• Power: <500 mW @500 fps
• 1000 bits/lx-s• Color or monochrome
© 2001 Photobit Technology Corporation
1/33,000 sec = 30 usec
Freeze frame shutter
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Photobit Discussion
r m a n c
CCDs
s
t / P e r f
APS
s t e m
C
S
© 2001 Photobit Technology Corporation