Lecture 11 CMOS Imaging Sensor - The Hong Kong University of ...

Lecture 11 

CMOS Imaging Sensor 

George Yuan 

Hong Kong University of Science and Technology 

Fall 2010 

© George Yuan, HKUST 

1

Outline 

• Introduction 

• CMOS imaging sensors 

– Passive pixel sensor 

– Photogate-based active pixel sensor 

– Photodiode-based active pixel sensor 

– Logarithmic pixel sensor 

– Noise 

• Analog processing 

– CDS 

– ADC 

– Spatial filtering 

• Wide dynamic range imaging sensor 

• High speed imager 


2

Temporal Noise 

Shot noise 

Trap noise 

Read-out noise 

SNR 

q 

2 

i 

phTint 

 

2 2 

i 

i T 

q 

ph 

dc 

int 

rd 


3

Temporal Noise Sources 

• Dark current shot noise 

• Trapping noise in the diode 

• kTC noise at the diode or floating drain 

• Read-out circuit noise 

• Photo-current shot noise 


4

Fixed-Pattern Noise (FPN) 

© George Yuan, HKUST Fall 2008, Lecture 9 

5

Fixed Pattern Noise Sources 

• Additive factors 

– Buffer transistor Vt mismatch 

– Column current source 

mismatch 

– Column buffer transistor Vt 

mismatch 

– Column amplifier offsets 

• Multiplicative factors 

– Photodiode size mismatch 

– Floating drain size mismatch 

– Column amplifier gain 


6

Outline 







– Noise 


– CDS 

– ADC 



• High speed imaging sensor 


7

CDS 

• 1k×1k imager, 

30Hz 

– Column circuit 

speed? 

– Global shutter 

– Rowing shutter 

• Noise 

– kT/C: 1pF, 60uV rms 

– OPAMP noise? 

• 3T-APS? 


8

Double CDS 


9

An CIS Example 

• 1k×1k imager, 30Hz frame rate, 

72dB dynamic range, read-out 

temporal noise

Low-noise Amplifier 

C 1 

C 0 


11

Wide Dynamic Range 

C 1 

C 0 


12

ADC 

• Successive approximate ADC 

• Cyclic ADC 

• Single-slope ADC 


13

Cyclic ADC 


14

Noise Cancellation Phase 

Input Sampling 

Charge Transfer 


15

Cyclic Algorithm 

Odd Phase 

Even Phase 


16

Single-slope ADC 

Column voltage 


17

Comparator 

1.1uA 


18

Outline 







– Noise 


– CDS 

– ADC 





19

Imaging Processing 

Spatial Template 


20

On-Chip Spatial Filtering 


21

On-Chip Spatial Filtering 


22

Outline 







– Noise 


– CDS 

– ADC 




© George Yuan, HKUST Fall 2008, Lecture 9 

23

Dynamic Range 

• CMOS imaging sensor: 40-60dB 

• CCD imaging sensor: 60-70dB 

• Human eyes: 90dB 

• Natural scenes: > 100dB 


24

Dynamic Range 

V 

 

T 

int 

ph 

I ph 

Cint 

DR 

 

V 

w 

C 

I 

int 

min 

T 

int 

V w 

: potential well capacity 

I min 

: determined by I dark 

, 

read-out circuit noise 

Well-Capacity Adjustment 


26

DR Compression 

V 

 

T 

int 

ph 

I ph 

Cint 


27

DR Improvement 

Linear low light Linear high light DR compression 


28

SNR 


29

Multiple Sampling 


30

Scheme 

V 

 

T 

int 

ph 

I ph 

Cint 

Sample1 Sample2 Sample3 

Exposure T, 2T, 4T, …, 2 k T Quantization: m bits Pixel resolution: m+k 


31

SNR 


32

Pixel-Level Quantization 


33

Time-to-Saturation 

V 

T 

 

int 

ph 

I ph 

Cint 


34

Pixel Circuit 


35

Pixel ADC 

3T APS Pixel 

V 

T 

 

int 

ph 

I ph 

Cint 


36

Pixel Circuit 


37

Lateral Overflow Integration 

Capacitor 

Low light: S1+N1 – N1 

High light: S2+N2” – N2 


38

Improved Lateral Overflow 

Integration Capacitor 

Low light: S1+N1 – N1 

High light: S2+N2 – N2 


39

CDS Readout 


40

Outline 







– Noise 


– CDS 

– ADC 





41

High Speed Pixel 

SWS 

SWR 


42

Performance 

14-bit Column-wise cyclic ADC read-out, 2MHz, 0.43mW 


43

References 

1. A. Gamal, and H. Eltoukhy, “CMOS image sensors”, IEEE Circuits & Devices Mag., pp. 6-20, May 2005 

2. S. Mendis, S. Kemeny, R. Gee, B. Pain, C. Staller, Q. Kim, and E. Fossum, “CMOS active pixel image sensors for highly 

integrated imaging systems”, IEEE J. Solid-State Circuits, Vol. 32, pp. 187-197, Feb. 1997 

3. S. Decker, R. McGrath, K. Brehmer, and C. Sodini, “A 256×256 CMOS imaging array with wide dynamic range pixels and 

column-parallel digital output””, IEEE J. Solid-State Circuits, Vol. 33, pp. 2081-2091, Dec. 1998 

4. D. Yang, and A. Gamal, “Comparative analysis of SNR for image sensors with enhanced dynamic range”, Proc. SPIE, San 

Jose, CA, 1999, vol. 3649, pp. 197-211 

5. D. Yang, A. Gamal, B. Fowler, and H. Tan, “A 640×512 CMOS image sensor with ultrawide dynamic range floating-point 

pixel-level ADC”, IEEE J. Solid-State Circuits, Vol. 34, pp. 1821-1834, Dec. 1999 

6. D. Stoppa, A. Simoni, L. Gonzo, M. Gotardi, and G. Betta, “Novel CMOS image sensor with a 132-dB dynamic range”, IEEE 

J. Solid-State Circuits, Vol. 37, pp. 1846-1852, Dec. 2002 

7. N. Akahane, S. Sugawa, S. Adachi, K. Mori, T. Ishiyuki, and K. Mizobuchi, “A sensitivity and linearity improvement of a 100- 

dB dynamic range CMOS image sensor using a lateral overflow integration capacitor”, IEEE J. Solid-State Circuits, Vol. 41, 

pp. 851-858, Apr. 2006 

8. S. Adachi, W. Lee, N. Akahane, H. Oshikubo, K. Mizobuchi, and S. Sugawa, “A 200uV/e- CMOS image sensor with 100-kefull 

well capacity”, IEEE J. Solid-State Circuits, Vol. 43, pp. 823-830, Apr. 2008 

9. H. Takahashi et. al, “A 1/2.7-in 2.96 MPixel CMOS image sensor with double CDS architecture for full high-definition 

camcorders”, IEEE J. Solid-State Circuits, Vol. 42, pp. 2960-2967, Dec. 2007 

10. 12. M. Futura, Y. Nishikawa, T. Inoue, S. Kawahito, “A high-speed, high-sensitivity digital CMOS image sensor with a global 

shutter and 12-bit column-parallel cyclic A/D Converters”, IEEE J. Solid-State Circuits, Vol. 42, pp. 766-774, Apr. 2007 

11. 13. M. Snoejj, A. Theuwissen, K.. Makinwa, and J. Huijsing, “A CMOS imager with column-level ADC using dynamic column 

fixed-pattern noise reduction”, IEEE J. Solid-State Circuits, Vol. 41, pp. 3007-3015, Dec. 2006 

12. 14. L. McIlrath, “A low-power low-noise ultrawide-dynamic-range CMOS imager with pixel-parallel A/D converters”, IEEE J. 

Solid-State Circuits, Vol. 36, pp. 846-853, May 2001 


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