1. DR. QUAZI DELWAR HOSSAIN
a SELF-ADJUSTING LIN-LOG ACTIVE PIXEL FOR WIDE DYNAMIC RANGE CMOS IMAGE SENSOR
PRESENTED BY
Md.Akramul Islam Minhaz Ibna Abedin
ID no ID no
SUPERVISED BY
DR. QUAZI DELWAR HOSSAIN
ASSOCIATE PROFESSOR
DEPARTMENT OF EEE,CUET.
Department of EEE, CUET

2. OUTLINE Objectives Pixel Literature Review Dynamic Range
DR Extension by Logarithmic Response
Proposed Pixel
Simulation Results
Layout Design
Summary
Future Works
Conclusion
Department of EEE, CUET

3. Objectives
To design a pixel to increase Dynamic Range maintaining high Fill Factor.
Simulation and Comparison with the standard linear and logarithmic response pixels.
11.5 µm× 11.5 µm layout design of the proposed pixel in 180nm technology.
Department of EEE, CUET

4. Pixel Pixel is short of Picture Element.
Thousands of Pixels form an image.
PHOTODIODE
RESET TRANSISTOR
SOURCE FOLLOWER READ-OUT CIRCUIT
Figure: Basic components of a Pixel
“Review of CMOS image sensors “M. Bigas, E. Cabruja, J. Forest, J. Salvi Microelectronics Journal 37 (2006) 433–451
Department of EEE, CUET

5. Literature Review Logarithmic Active Pixel Sensor
Linear Active Pixel Sensor
Logarithmic Active Pixel Sensor
Advantage: Low illumination,
good performance
Advantage: High illumination,
good performance
Disadvantage: High illumination,
bad performance
Disadvantage: Low illumination,
bad performance
“Wide-Dynamic-Range Pixel with Combined Linear and Logarithmic Response and Increased Signal Swing”,Eric C. Fox, Jerry Hynecek, and Douglas R. Dykaar DALSA
Department of EEE, CUET

6. Figure:The pixel with comparator and its reference signal .
Literature Review
Comparator
Reference signal
Figure:The pixel with comparator and its reference signal .
Advantage : Wide Dynamic Range.
Disadvantage: Additional in-pixel comparator decreases Fill Factor and
external analog signal required.
“A High-Dynamic-Range Integrating Pixel With an Adaptive Logarithmic Response” Hsiu-Yu Cheng,, Bhaskar Choubey, and Steve Collins, IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 19, NO. 15, AUGUST 1, 2007
Department of EEE, CUET

7. Literature Review (a) (b)
Figure: (a) A schematic circuit with PMOS reset and switch transistors (Mp1 and Mp2) [1] and (b) A schematic circuit with NMOS isolator (M4) [2].
[1]“A Wide Dynamic Range CMOS Image Sensor with an Adjustable Logarithmic Response” Bhaskar Choubey, Hsiu-Yu Cheng and Steve Collins, IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 56, NO. 11, NOVEMBER 2009
[2]“On Threshold Comparing Biomorphic Image Sensors” Waqas Mughal Luiz Carlos Gouveia, and Bhaskar Choubey University of Glasgow,Glasgow, U.K. Procedia Computer Science Volume 41, 2014, Pages 140–145
Department of EEE, CUET

8. Dynamic Range
Dynamic Range can be defined as the ratio of maximum unsaturated photocurrent to the minimum detectable photocurrent.
Techniques for Dynamic Range extension
Logarithmic Response
Well Capacity Adjustment
Time to Saturate
Multiple Capture
Department of EEE, CUET

9. DR Extension by Logarithmic Response
Figure: Pixel output voltage of Linear and Logarithmic APS to show their responses
throughout the illumination (Photocurrent) range.
Department of EEE, CUET

10. Proposed Pixel Reset Transistor to provide linear response
Vdd
Reset Transistor to provide linear response
Row Select
Vout
Photodiode N1 N2 P1 N3 N4
Gate to Drain connected NMOS
to provide logarithmic response
Reset
Source Follower Transistor
PMOS to allow or block
logarithmic response
Row Select Transistor
Figure: Schematic diagram of Proposed Pixel.
Department of EEE, CUET

11. Pixel in Logarithmic Mode
Proposed Pixel
Vdd
Row Select
Vout
Photodiode N1 N2 P1 N3 N4
PMOS in
“On” state
PMOS in
“Off” state
Pixel in Linear Mode
Pixel in Logarithmic Mode
Reset
Gate Voltage
Figure: DC Analysis of PMOS in Cadence Virtuoso shows the source to drain current versus gate voltage.
Department of EEE, CUET

12. Simulation Results Photo Current Linear APS Logarithmic APS
Table : Pixel Output Voltage of Linear APS, Logarithmic APS and Proposed Pixel
Photo Current
Linear APS
Logarithmic APS
Proposed Pixel
250n A
0 V
814m V
17.59m V
25n A
893m V
79.84m V
2.5n A
965m V
176m V
250p A
1 V
285m V
25p A
365m V
1.089 V
400m V
2.5p A
588m V
1.11 V
578m V
250f A
650m V
1.12 V
734m V
25fA
789m V
798m V
2.5f A
801m V
Department of EEE, CUET

13. And dynamic range of 120dB for Logarithmic APS.
Simulation Results .
Figure: Pixel output voltage versus Photocurrent of linear and logarithmic active pixels. It shows dynamic range of 100dB for Linear APS
And dynamic range of 120dB for Logarithmic APS.
Department of EEE, CUET

14. Simulation Results .
Figure: Pixel output voltage versus Photocurrent of the Proposed Pixel. It shows a wider
dynamic range of 160dB. It shows better response in both high and low illumination.
Department of EEE, CUET

15. Layout Design Photodiode Source Follower Reset Transistor PMOS
Gate to Drain connected NMOS
Figure: 11.5µm × 11.5µm layout design of the proposed pixel in 180nm CMOS Technology.
It has a Fill Factor of 45%.
Department of EEE, CUET

16. Layout Design Photodiode a) b) Metal Layer 2 Metal Layer 1 c)
Figure: a) 3D view of the pixel b) Top view of the pixel c) Cross-sectional view of the pixel.
Department of EEE, CUET

17. 180nm CMOS Technology Node
Summary
Technology
180nm CMOS Technology Node
Pixel Size
11.5µm × 11.5µm
Photo Detector
Photodiode
Transistor Per Pixel 5
Fill Factor
45%
Dynamic Range
160dB
Department of EEE, CUET

18. Future Works
To design and fabricate a 512 x 512 pixel array to analyze the performance of the proposed pixel.
To design Double Sampling circuit for column readout.
Reduction of FPN and Image lag.
Implementation of Anti-Blooming transistor or In-pixel current calibration.
Department of EEE, CUET

19. Conclusion
A simple technique has been found for self adjusting Linear-Logarithmic response.
A Wide Dynamic Range of 160dB and Fill Factor of 45% has been found which satisfies the objective of the project.
Department of EEE, CUET

20. Thank You
Department of EEE, CUET