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CCD or CMOS image sensors for consumer digital still ... · -overview CCD vs. CMOS-summary and...
Transcript of CCD or CMOS image sensors for consumer digital still ... · -overview CCD vs. CMOS-summary and...
1
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
CCD or CMOS image sensorsCCD or CMOS image sensors
for consumer digital still for consumer digital still
photography ?photography ?
Prof. dr. ir. Albert J.P. THEUWISSENPhilips Semiconductors Image Sensors, Eindhoven (NL)
Technical University, Delft (NL)
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Outline
• Introduction
• Principle of CCD and CMOS imagers
• Imager requirements
• Overview CCD vs. CMOS : resolution, signal-to-noise ratio, angular response, dark
current, dynamic range, linearity, pixel
uniformity, architecture
• Summary and Conclusions
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
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2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Introduction
• CMOS is challenging CCD
• Digital still is a continuously growing imaging
market
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Introduction
• CMOS is challenging CCD
• Digital still is a continuously growing imaging
market
• Today : almost exclusively CCD in DSC
• Tomorrow : CCD or CMOS ?
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
3
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Outline
• Introduction
• Principle of CCD and CMOS imagers
• Imager requirements
• Overview CCD vs. CMOS : resolution, signal-to-noise ratio, angular response, dark
current, dynamic range, linearity, pixel
uniformity, architecture
• Summary and Conclusions
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
CCD principle (1)
0 V
p-Si
10 V 0 V 0 V
0 V
p-Si
10 V 10 V 0 V
0 V
p-Si
0 V 10 V 0 V
ΦΦΦΦ
ΦΦΦΦ
ΦΦΦΦ
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
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2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
CCD principle (2)
out horizontal CCD output register
photosensitive CCD array
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
CMOS principle (1)
vertical scan circuit
photodiode array + MOS switches
horizontal scan circuit
A/D
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
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2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
CMOS principle (2)
p-Sin+
Photogate APS
RS
Col bus
RST
TXPG
p-Sin+
Photodiode APS
RS
Col bus
RST
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Outline
• Introduction
• Principle of CCD and CMOS imagers
• Imager requirements
• Overview CCD vs. CMOS : resolution, signal-to-noise ratio, angular response, dark
current, dynamic range, linearity, pixel
uniformity, architecture
• Summary and Conclusions
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
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2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Image Sensor Aspects (1)
IMAGER
PARAMETER
resolution
signal-to-noise ratio
angular response
dark current
CAMERA
SPECIFICATION
sharpness
ISO speed
min. F-stop
max. exp. time
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Image Sensor Aspects (2)
IMAGER
PARAMETER
dynamic range
linearity
pixel uniformity
architecture
CAMERA
SPECIFICATION
latitude
colour fidelity
granularity
features
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
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2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Outline
• Introduction
• Principle of CCD and CMOS imagers
• Imager requirements
• Overview CCD vs. CMOS : resolution, signal-to-noise ratio, angular response, dark
current, dynamic range, linearity, pixel
uniformity, architecture
• Summary and Conclusions
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Resolution Requirements
0
200
400
600
0 2 4 6 8 10
Image Size [Mpixels]
Print Resolution [pix/inch]
3.5"x5"
4"x6"
5"x7"
8"x10"quality level
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
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2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Resolution Requirements
0
200
400
600
0 2 4 6 8 10
Image Size [Mpixels]
Print Resolution [pix/inch]
3.5"x5"
4"x6"
5"x7"
8"x10"
disc 110 APS 35 mm
quality level
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Resolution Requirements
0
200
400
600
0 2 4 6 8 10
Image Size [Mpixels]
Print Resolution [pix/inch]
3.5"x5"
4"x6"
5"x7"
8"x10"
disc 110 APS 35 mm
cons. CMOS
cons. CCDprof. CCD
quality level
prof. CMOS
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
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2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Trend in Resolution
0
2
4
6
8
10
0 2 4 6 8 10
Pixel Size [um]
Resolution [Mpixels] 2/3" (8.8mmx6.6mm)
1/2" (6.4mmx4.8mm)
1/3" (4.4mmx3.3mm)
decrease chip size
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Trend in Resolution
0
2
4
6
8
10
0 2 4 6 8 10
Pixel Size [um]
Resolution [Mpixels] 2/3" (8.8mmx6.6mm)
1/2" (6.4mmx4.8mm)
1/3" (4.4mmx3.3mm)
decrease chip size
lens limitation
CCDCMOS
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
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2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Signal-to-Noise ratio (1)
0.001 0.01 0.1 1 10 10010
100
1k
100kNumber of Electrons
Light Intensity (µµµµW/cm )
10k
photon shot
read noise (20)
total (40)darkshot (35)
signal
saturation (100k)
dynamic range (68 dB)
2
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Signal-to-Noise ratio (2)
p-Sin+
Photogate APS
RS
Col bus
RST
TXPG
p-Sin+
Photodiode APS
RS
Col bus
RST
NOT FREE of reset noiseFREE of reset noise
LOW light sensitivity HIGH light sensitivity
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
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2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Signal-to-Noise ratio (3)
QEAISO40
⋅∝
ISOx = ISO-speed @ S/N=x
Hx = exposure to get S/N=x
A = pixel area
QE = quantum efficiency
nr = read noise
x
xH
10ISO =
r
10n
QEAISO
⋅∝
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Signal-to-Noise ratio (4)
0
20
40
60
80
100
0 1 2 3 4 5 6 7 8 9 10
Pixel Size [um]
QE in green [%]
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
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2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
0
20
40
60
80
100
0 1 2 3 4 5 6 7 8 9 10
Pixel Size [um]
QE in green [%]
CCD
Signal-to-Noise ratio (4)
CCD
CMOS
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Improvement QE (1)
micro-lenspixels
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
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2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Improvement QE (2)
lens
iris
micro-lenspixels
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Angular Response (1)
0
5
10
15
20
25
1.2 1.4 1.8 2 2.8 3.5 4 5.6 8 16
F-number
Incident Angle [deg.]
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
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2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Angular Response (2)
0
0.2
0.4
0.6
0.8
1
0 5 10 15 20 25 30
Incident Angle [deg.]
Rel. Imager Response
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Angular Response (3)
0
5
10
15
20
25
1.2 1.4 1.8 2 2.8 3.5 4 5.6 8 16
F-number
Incident Angle [deg.]
micro-lens limit
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
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2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Dark Current (1)
• prof. CCD
• cons. CCD
• standard CMOS
Dark current doubles every 6…8oC.
Example : @ 60oC : 32 times higher !
@ -100oC : 32,000 times lower !
1...3 pA/cm2 @ RT
5...10 pA/cm2 @ RT
200...500 pA/cm2 @ RT
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Dark Current (2)
• Compensation for dark current is possible !
• Compensation for dark-current non-
uniformities is possible !
• Compensation for dark-current shot-noise is
NOT possible !
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
16
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Dynamic Range (1)
2
dark
2
r
darksat
nn
NNDR
+
−=
DR = dynamic range
Nsat = saturation signal [e-]
Ndark = dark signal [e-]
nr = read noise [e-]
ndark= dark shot noise [e-]
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Dynamic Range (2)
0
0.5
1
1.5
2
2.5
3
2 3 4 5 6 7 8 9 10
Pixel Size [um]
Charge Handling [ke/um2]
Nsat = 30 ke-
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
17
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Dynamic Range (2)
0
0.5
1
1.5
2
2.5
3
2 3 4 5 6 7 8 9 10
Pixel Size [um]
Charge Handling [ke/um2]
CMOS
CCD
Nsat = 30 ke-
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Linearity (1)
RAWdata
inter-polation
whitebalance
colourmatrixing
gammacurve
RGBdata
R = R x 1.40G = G x 1.00B = B x 1.46
RGB
1.424-0.0460.090
-0.5001.431-0.390
0.076-0.4911.302
RGB
= xγγγγ = 1.8
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
- linearity
18
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Linearity (2)
• Due to sampling in colour space :
Interpolations,
• Filters do not match perfectly : Colour
corrections.
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
- linearity
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Linearity (2)
• Due to sampling in colour space :
Interpolations,
• Filters do not match perfectly : Colour
corrections.
• Linearity CCD : 99 % (for 70 % of Nsat),
• Linearity CMOS : 97 % (for 85 % of Nsat).
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
- linearity
19
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Pixel Random Non-
Uniformity
• PRNU CCD :
• PRNU CMOS :
< 0.7 … 1.0 %,
< 2.0 … 5.0 %,
(column + pixel FPN)
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
- linearity
- p.r.n.u.
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Pixel Random Non-
Uniformity
• PRNU CCD :
• PRNU CMOS :
• Can be corrected by means of LUT,
• To be non-visible : PRNU and FPN < photon shot
noise (0.5 % for 40 ke-).
< 0.7 … 1.0 %,
< 2.0 … 5.0 %,
(column + pixel FPN)
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
- linearity
- p.r.n.u.
20
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Architecture
• CCD : parallel integration/reset
• CMOS : rolling integration/reset
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
- linearity
- p.r.n.u.
- architecture
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Architecture
• CCD : parallel integration/reset
• CMOS : rolling integration/reset
• Can be solved by 1 T and 1 C extra in every
pixel extra …
• Costs sensitivity, charge capacity, noise, ...
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
- linearity
- p.r.n.u.
- architecture
21
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Outline
• Introduction
• Principle of CCD and CMOS imagers
• Imager requirements
• Overview CCD vs. CMOS : resolution, signal-to-noise ratio, angular response, dark
current, dynamic range, linearity, pixel
uniformity, architecture
• Summary and Conclusions
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
- linearity
- p.r.n.u.
- architecture
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Summary (1)
• Resolution : pixel size of CCD smallest
• Noise : CMOS pixels suffer from reset noise
• Quantum efficiency : CMOS and CCD can be
similar
• Angular response : limits set by micro-lenses
• Dark current : CCD outstanding
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
- linearity
- p.r.n.u.
- architecture
- summary
22
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Summary (2)
• Saturation level can be similar
• Dynamic range of CCD is higher
• Linearity of CCD is better
• Pixel uniformity of CCD is better
• Device architecture of CCD gives more
flexibility
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
- linearity
- p.r.n.u.
- architecture
- summary
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Conclusions (1)
CCD or CMOS image sensor
for consumer digital still
photography ?
CCD ? YES !
CMOS ? YES, provided that noise and
dark current problems can be solved !!!
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
- linearity
- p.r.n.u.
- architecture
- summary
- conclusions
23
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Conclusions (2)
• Main issue : S/N performance
• Then benefit from :
– low power of CMOS,
– low driving voltages of CMOS,
– on-chip functionality,
– selective read-out mechanism,
– cost advantage.
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
- linearity
- p.r.n.u.
- architecture
- summary
- conclusions
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Important Remark
This presentation was about digital
still photography.
For video applications the situation
changes completely !!!
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
- linearity
- p.r.n.u.
- architecture
- summary
- conclusions
- remark
24
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
References
• R. Baer : IEEE workshop on CCD & AIS, Karuizawa,
1999,
• J. Bosiers et.al. : IEDM, San Francisco, 1998,
• M. Kriss : ICPS, Antwerp, 1998,
• A. Theuwissen : “Solid-state imaging with Charge-
Coupled Devices”, 1995
• E. Fossum : “Camera-on-a-chip”, IEEE-ED, Oct.,
1997.
- introduction
- principle ofimagers
- imager requirements
- overview CCD vs. CMOS
- summary andconclusions
- CCD
- CMOS
- resolution
- S/N ratio
- angular resp.
- dark current
- dyn. range
- linearity
- p.r.n.u.
- architecture
- summary
- conclusions
- remark
- references