CCD or CMOS image sensors for consumer digital still photography ? Prof. dr. ir. Albert J.P. THEUWISSEN Philips Semiconductors Image Sensors, Eindhoven (NL) Technical University, Delft (NL)
[email protected]
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Outline
- introduction - principle of imagers - imager requirements - overview CCD vs. CMOS - summary and conclusions
• • • •
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 2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
1
- introduction - principle of imagers - imager requirements - overview CCD vs. CMOS - summary and conclusions
Introduction • CMOS is challenging CCD • Digital still is a continuously growing imaging market
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers - imager requirements - overview CCD vs. CMOS - summary and conclusions
Introduction • CMOS is challenging CCD • Digital still is a continuously growing imaging market • Today : almost exclusively CCD in DSC • Tomorrow : CCD or CMOS ?
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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Outline
- introduction - principle of imagers - imager requirements - overview CCD vs. CMOS - summary and conclusions
• • • •
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 2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers
CCD principle (1)
- CCD
- imager requirements - overview CCD vs. CMOS - summary and conclusions
0V
10 V
0V
0V
Φ
p-Si
0V
10 V
10 V
0V
Φ
p-Si
0V
0V
10 V
0V
Φ
p-Si 2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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- introduction - principle of imagers
CCD principle (2) photosensitive CCD array
- CCD
- imager requirements - overview CCD vs. CMOS - summary and conclusions
out
horizontal CCD output register
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers
CMOS principle (1)
- CCD
vertical scan circuit
photodiode array + MOS switches
- CMOS
- imager requirements - overview CCD vs. CMOS - summary and conclusions
A/D horizontal scan circuit
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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CMOS principle (2)
- introduction - principle of imagers - CCD - CMOS
- imager requirements - overview CCD vs. CMOS - summary and conclusions
Photodiode APS
Photogate APS RST PG
p-Si
TX
RST RS n+
RS Col bus p-Si
n+ Col bus
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Outline
- introduction - principle of imagers - CCD - CMOS
- imager requirements - overview CCD vs. CMOS - summary and conclusions
• • • •
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 2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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- introduction - principle of imagers
Image Sensor Aspects (1)
- CCD - CMOS
- imager requirements - overview CCD vs. CMOS - summary and conclusions
IMAGER PARAMETER resolution signal-to-noise ratio angular response dark current
CAMERA SPECIFICATION sharpness ISO speed min. F-stop max. exp. time
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers
Image Sensor Aspects (2)
- CCD - CMOS
- imager requirements - overview CCD vs. CMOS - summary and conclusions
IMAGER PARAMETER dynamic range linearity pixel uniformity architecture
CAMERA SPECIFICATION latitude colour fidelity granularity features
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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Outline
- introduction - principle of imagers - CCD - CMOS
- imager requirements - overview CCD vs. CMOS - summary and conclusions
• • • •
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 2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers
Resolution Requirements
- CCD
- resolution
- summary and conclusions
Print Resolution [pix/inch]
- CMOS
- imager requirements - overview CCD vs. CMOS
600
400
3.5"x5" 4"x6" 5"x7" 8"x10"
200
quality level
0 0
2
4
6
8
10
Image Size [Mpixels]
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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- introduction - principle of imagers
Resolution Requirements
- CCD
- resolution
- summary and conclusions
Print Resolution [pix/inch]
- CMOS
- imager requirements - overview CCD vs. CMOS
600
400
3.5"x5" 4"x6" 5"x7" 8"x10"
200
quality level
0 0
disc
2
110
4
APS
6
8
35 mm
10
Image Size [Mpixels]
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers
Resolution Requirements
- CCD
- resolution
- summary and conclusions
Print Resolution [pix/inch]
- CMOS
- imager requirements - overview CCD vs. CMOS
600 prof. CCD cons. CCD prof. CMOS cons. CMOS
400
3.5"x5" 4"x6" 5"x7" 8"x10"
200
quality level
0 0
disc
2
110
4
APS
6
8
35 mm
10
Image Size [Mpixels]
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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Trend in Resolution
- introduction - principle of imagers - CCD - CMOS
- resolution
- summary and conclusions
10 Resolution [Mpixels]
- imager requirements - overview CCD vs. CMOS
2/3" (8.8mmx6.6mm)
8
1/2" (6.4mmx4.8mm) 1/3" (4.4mmx3.3mm)
6 decrease chip size
4 2 0 0
2
4
6
8
10
Pixel Size [um]
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Trend in Resolution
- introduction - principle of imagers - CCD - CMOS
- resolution
- summary and conclusions
10 Resolution [Mpixels]
- imager requirements - overview CCD vs. CMOS
lens limitation
2/3" (8.8mmx6.6mm)
8
1/2" (6.4mmx4.8mm) 1/3" (4.4mmx3.3mm)
6 decrease chip size
4 2
CCD
CMOS
0 0
2
4
6
8
10
Pixel Size [um]
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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- introduction - principle of imagers
Signal-to-Noise ratio (1)
- CCD - CMOS
- S/N ratio
- summary and conclusions
dynamic range (68 dB)
- resolution
saturation (100k)
100k
Number of Electrons
- imager requirements - overview CCD vs. CMOS
10k signal
1k
photon shot
100
total (40)
10 0.001
dark read noise (20) shot (35)
0.01
0.1
1
10
100
Light Intensity (µ µW/cm2 )
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers
Signal-to-Noise ratio (2)
- CCD - CMOS
Photogate APS
- imager requirements - overview CCD vs. CMOS - resolution - S/N ratio
RST PG
- summary and conclusions
p-Si
TX
Photodiode APS RST
RS n+
RS Col bus p-Si
n+ Col bus
FREE of reset noise
NOT FREE of reset noise
LOW light sensitivity
HIGH light sensitivity
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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- introduction - principle of imagers
Signal-to-Noise ratio (3)
- CCD - CMOS
- imager requirements - overview CCD vs. CMOS
ISO x =
- resolution
10 Hx
ISOx = ISO-speed @ S/N=x Hx = exposure to get S/N=x
- S/N ratio
- summary and conclusions
A = pixel area QE = quantum efficiency nr = read noise
ISO40 ∝ A ⋅ QE ISO10 ∝
A ⋅ QE nr
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers
Signal-to-Noise ratio (4)
- CCD - CMOS
- imager requirements - overview CCD vs. CMOS - S/N ratio
- summary and conclusions
QE in green [%]
- resolution
100 80 60 40 20 0 0
1
2
3
4
5
6
7
8
9
10
Pixel Size [um]
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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- introduction - principle of imagers
Signal-to-Noise ratio (4)
- CCD - CMOS
- imager requirements - overview CCD vs. CMOS - S/N ratio
- summary and conclusions
QE in green [%]
- resolution
100 80 60 40
CCD CCD
20
CMOS
0 0
1
2
3
4
5
6
7
8
9
10
Pixel Size [um]
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers
Improvement QE (1)
- CCD - CMOS
- imager requirements - overview CCD vs. CMOS - resolution - S/N ratio
- summary and conclusions
microlens pixels
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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Improvement QE (2)
- introduction - principle of imagers - CCD - CMOS
- imager requirements - overview CCD vs. CMOS
lens
- resolution - S/N ratio
iris
- summary and conclusions
microlens pixels
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers
Angular Response (1)
- CCD - CMOS
- resolution - S/N ratio - angular resp.
- summary and conclusions
25 Incident Angle [deg.]
- imager requirements - overview CCD vs. CMOS
20 15 10 5 0 1.2
1.4
1.8
2
2.8
3.5
4
5.6
8
16
F-number
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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- introduction - principle of imagers
Angular Response (2)
- CCD - CMOS
- resolution - S/N ratio - angular resp.
- summary and conclusions
1 Rel. Imager Response
- imager requirements - overview CCD vs. CMOS
0.8 0.6 0.4 0.2 0 0
5
10
15
20
25
30
Incident Angle [deg.]
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers
Angular Response (3)
- CCD - CMOS
- resolution - S/N ratio - angular resp.
- summary and conclusions
25 Incident Angle [deg.]
- imager requirements - overview CCD vs. CMOS
micro-lens limit
20 15 10 5 0 1.2
1.4
1.8
2
2.8
3.5
4
5.6
8
16
F-number
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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- introduction - principle of imagers
Dark Current (1)
- CCD - CMOS
- imager requirements - overview CCD vs. CMOS - resolution - S/N ratio - angular resp. - dark current
• prof. CCD • cons. CCD • standard CMOS
1...3 pA/cm2 @ RT 5...10 pA/cm2 @ RT 200...500 pA/cm2 @ RT
- summary and conclusions
Dark current doubles every 6…8oC. Example : @ 60oC : 32 times higher ! @ -100oC : 32,000 times lower !
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers
Dark Current (2)
- CCD - CMOS
- imager requirements - overview CCD vs. CMOS
• Compensation for dark current is possible !
- resolution - S/N ratio - angular resp. - dark current
- summary and conclusions
• Compensation for dark-current nonuniformities is possible ! • Compensation for dark-current shot-noise is NOT possible !
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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Dynamic Range (1)
- introduction - principle of imagers - CCD - CMOS
- imager requirements - overview CCD vs. CMOS - resolution
DR =
Nsat − Ndark 2 nr2 + ndark
- S/N ratio - angular resp. - dark current - dyn. range
DR = dynamic range Nsat = saturation signal [e-] Ndark = dark signal [e-] nr = read noise [e-] ndark= dark shot noise [e-]
- summary and conclusions
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Dynamic Range (2)
- introduction - principle of imagers - CCD
- resolution - S/N ratio - angular resp. - dark current - dyn. range
- summary and conclusions
Charge Handling [ke/um2]
- CMOS
- imager requirements - overview CCD vs. CMOS
3
Nsat = 30 ke-
2.5 2 1.5 1 0.5 0 2
3
4
5
6
7
8
9
10
Pixel Size [um]
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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Dynamic Range (2)
- introduction - principle of imagers - CCD
- resolution - S/N ratio - angular resp. - dark current - dyn. range
- summary and conclusions
Charge Handling [ke/um2]
- CMOS
- imager requirements - overview CCD vs. CMOS
3
Nsat = 30 ke-
2.5 2 1.5
CCD
1
CMOS
0.5 0 2
3
4
5
6
7
8
9
10
Pixel Size [um]
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Linearity (1)
- introduction - principle of imagers - CCD - CMOS
- imager requirements - overview CCD vs. CMOS - resolution - S/N ratio
RAW data
- angular resp. - dark current
R 1.424 -0.500 0.076 R G = -0.046 1.431 -0.491 x G B 0.090 -0.390 1.302 B
γ = 1.8
- dyn. range - linearity
- summary and conclusions
interpolation
white balance
colour matrixing
R = R x 1.40 G = G x 1.00 B = B x 1.46
gamma curve
RGB data
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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- introduction - principle of imagers
Linearity (2)
- CCD - CMOS
- imager requirements - overview CCD vs. CMOS - resolution - S/N ratio - angular resp. - dark current - dyn. range
• Due to sampling in colour space : Interpolations, • Filters do not match perfectly : Colour corrections.
- linearity
- summary and conclusions
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers
Linearity (2)
- CCD - CMOS
- imager requirements - overview CCD vs. CMOS - resolution - S/N ratio - angular resp. - dark current - dyn. range
• Due to sampling in colour space : Interpolations, • Filters do not match perfectly : Colour corrections.
- linearity
- summary and conclusions
• Linearity CCD : • Linearity CMOS :
99 % (for 70 % of Nsat), 97 % (for 85 % of Nsat).
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
18
- introduction - principle of imagers - CCD
Pixel Random NonUniformity
- CMOS
- imager requirements - overview CCD vs. CMOS - resolution
• PRNU CCD : • PRNU CMOS :
- S/N ratio - angular resp.
< 0.7 … 1.0 %, < 2.0 … 5.0 %, (column + pixel FPN)
- dark current - dyn. range - linearity - p.r.n.u.
- summary and conclusions
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers - CCD
Pixel Random NonUniformity
- CMOS
- imager requirements - overview CCD vs. CMOS - resolution - S/N ratio - angular resp.
• PRNU CCD : • PRNU CMOS :
< 0.7 … 1.0 %, < 2.0 … 5.0 %, (column + pixel FPN)
- dark current - dyn. range - linearity - p.r.n.u.
- summary and conclusions
• Can be corrected by means of LUT, • To be non-visible : PRNU and FPN < photon shot noise (0.5 % for 40 ke-).
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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- introduction - principle of imagers
Architecture
- CCD - CMOS
- imager requirements - overview CCD vs. CMOS - resolution
• CCD : parallel integration/reset • CMOS : rolling integration/reset
- S/N ratio - angular resp. - dark current - dyn. range - linearity - p.r.n.u. - architecture
- summary and conclusions
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers
Architecture
- CCD - CMOS
- imager requirements - overview CCD vs. CMOS - resolution
• CCD : parallel integration/reset • CMOS : rolling integration/reset
- S/N ratio - angular resp. - dark current - dyn. range - linearity - p.r.n.u. - architecture
- summary and conclusions
• Can be solved by 1 T and 1 C extra in every pixel extra … • Costs sensitivity, charge capacity, noise, ...
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
20
Outline
- introduction - principle of imagers - CCD - CMOS
- imager requirements - overview CCD vs. CMOS - resolution - S/N ratio - angular resp. - dark current - dyn. range - linearity - p.r.n.u. - architecture
- summary and conclusions
• • • •
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 2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers
Summary (1)
- CCD - CMOS
- imager requirements - overview CCD vs. CMOS - resolution - S/N ratio - angular resp. - dark current - dyn. range - linearity - p.r.n.u. - architecture
- summary and conclusions
• 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
- summary
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
21
Summary (2)
- introduction - principle of imagers - CCD - CMOS
- imager requirements - overview CCD vs. CMOS - resolution - S/N ratio - angular resp. - dark current - dyn. range - linearity - p.r.n.u. - architecture
- summary and conclusions
• • • • •
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
- summary
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
Conclusions (1)
- introduction - principle of imagers - CCD - CMOS
- imager requirements - overview CCD vs. CMOS - resolution - S/N ratio - angular resp.
CCD or CMOS image sensor for consumer digital still photography ?
- dark current - dyn. range - linearity - p.r.n.u. - architecture
CCD ?
YES !
- summary and conclusions - summary - conclusions
CMOS ? YES, provided that noise and dark current problems can be solved !!! 2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
22
- introduction - principle of imagers
Conclusions (2)
- CCD - CMOS
- imager requirements - overview CCD vs. CMOS - resolution - S/N ratio - angular resp. - dark current - dyn. range - linearity - p.r.n.u. - architecture
- summary and conclusions - summary - conclusions
• 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.
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
- introduction - principle of imagers
Important Remark
- CCD - CMOS
- imager requirements - overview CCD vs. CMOS - resolution - S/N ratio - angular resp. - dark current - dyn. range - linearity - p.r.n.u. - architecture
- summary and conclusions - summary
This presentation was about digital still photography. For video applications the situation changes completely !!!
- conclusions - remark
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
23
- introduction - principle of imagers
References
- CCD - CMOS
- imager requirements - overview CCD vs. CMOS - resolution - S/N ratio - angular resp. - dark current - dyn. range - linearity - p.r.n.u. - architecture
- summary and conclusions - summary
• 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 ChargeCoupled Devices”, 1995 • E. Fossum : “Camera-on-a-chip”, IEEE-ED, Oct., 1997.
- conclusions - remark - references
2001 Albert J.P. Theuwissen, Philips Semiconductors Image Sensors
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