1. ISSCC Dig. Tech. Papers, Feb. 2006
CMOS IMAGE SENSORS
A 200dB Dynamic Range Iris–less CMOS Image Sensor with Lateral Overflow Integration Capacitor and Current Readout Operation
Nana Akahane, Rie Ryuzaki, Satoru Adachi, Koichi Mizobuchi, Shigetoshi Sugawa
ISSCC Dig. Tech. Papers, Feb. 2006
Presented by: Katayoun Zand
Advanced VLSI Course Class Presentation, Fall 2006

2. Outline Introduction Imag Sensor Architecture Pixel circuits
Non-idealities and Performance measures
CMOS Active Pixel Image Sensors
Using a Lateral Overflow Integration to Improve the Dynamic Range of the Sensor
“A 200dB Dynamic Range Iris –less CMOS Image Sensor with Lateral Overflow Integration Capacitor and Current Readout Operation”

3. The Imaging System Pipeline.[5]
Introduction
Mobile imaging, digital still and video cameras, Internet-based video conferencing, surveillance, and biometrics
Over 230 million parts shipped in 2004
Estimated annual growth rate of over 28%
The Imaging System Pipeline.[5]

4. IMAGE SENSOR ARCHITECTURES
A cross-section photograph of an image sensor.[5]
(a) Readout architectures of interline transfer CCD and (b) CMOS image sensors.[5]

5. Pixel Circuits Passive Pixel Sensor.[5]
3- and 4-T active pixel sensor.[5]

6. Diagram pixel sensor.[5]
Pixel Circuits (Cont.)
Diagram pixel sensor.[5]
Logarithmic pixel.[6]

7. Non-Idealities and Performance Measures
Three important aspects of image sensor performance are:
SNR (signal to noise ratio): higher than 40 dB required
DR (dynamic range): range of illumination that can be detected by the image sensor.
Standard CMOS Image sensors have a DR of dB, While human eye exceeds 90 dB.
Spatial Resolution: determined by the Nyquist sampling theorem.

8. CMOS Active Pixel Image Sensor
Timing for CMOS APS readout.[3] .
Schematic of the circuit.[3]

9. Pixel schematic diagram, Timing and Potential diagram.[2]
Using a Lateral Overflow Integration to Improve the Dynamic Range of the Sensor
Pixel schematic diagram, Timing and Potential diagram.[2]

10. Using a Lateral Overflow Integration to Improve the Dynamic Range of the Sensor ( Cont.)
System Block Diagram[2]
Signal Processing Diagram[2]
The gain of the signal S2 is matched with the gain of S1 by multiplying the capacitance (CFD+CCS)/CFD ratio by S2.

11. Using a Lateral Overflow Integration to Improve the Dynamic Range of the Sensor ( Cont.)
Switching concept from S1 signal to S2 signal.[2]

12. Over-saturated signal
Using a Lateral Overflow Integration to Improve the Dynamic Range of the Sensor: Sample Image
Non-saturated signal (S1)
Over-saturated signal
(S2)
Wide dynamic range signal
[2]

13. ISSCC Dig. Tech. Papers, Feb. 2006
A 200 dB Dynamic Range Iris-less CMOS Image Sensor with Lateral Overflow Integration Capacitor using Hybrid Voltage and Current Readout Operation
Nana Akahane, Rie Ryuzaki, Satoru Adachi, Koichi Mizobuchi, Shigetoshi Sugawa
ISSCC Dig. Tech. Papers, Feb. 2006

14. The sensor features a hybrid readout operation to improve DR:
voltage-readout operation based on the lateral overflow integration capacitor in the pixel.
Current-readout operation based on current amplification and logarithmic compression
The voltage-readout circuit with a lateral overflow integration capacitor in the pixel is the same as the one described previously, leads to an extension of the DR keeping a high sensitivity and a high SNR.
The current-readout circuit achieves further extension of the DR on the bright end of the range by reading out the logarithmic compression of the photocurrent amplified in each pixel and column.

15. Current readout operation
Schematic of the pixel
Current readout operation
Timing.[1]
[1]

16. The voltage-readout operation incorporates the electrical shutter operation, the electric shutter time is sequentially varied as 1/30s, 1/500s, 1/8ks, and 1/30ks:
[1]

17. Photoelectric conversion characteristics:
The hybrid operation of the voltage and the current readout extends the DR over 200 dB
[1]

18. The Sensor Block Diagram
Performance summary[1]
Sensor block diagram[1]

19. Sample Images
The Image sensor is capable of capturing various scenes with the incident light ranging from about to 108 lx.
[1]

20. Summary and Conclusion
An introduction CMOS Image sensors was provided, the APS structure was explained.
It was shown that:
SNR, DR and Spatial resolution are the three main performance measures of image sensors.
a lateral overflow integration capacitor would enhance the dynamic range of APS and improve the circuit sensitivity and linearity : It integrates the overflowed charges and improves the DR at the bright end, and reduce noise so the dynamic range would increase at the dark end.
using a hybrid readout operation of the voltage and current would increase the dynamic range because the current readout circuit achieves further extension of the DR on the bright end.
A 64x64 pixel, 200dB dynamic range CMOS image sensor using 0.35 μm technology with lateral overflow integration capacitor using hybrid readout operation was described.

21. Selected References
[1] N.Akahane, et al.,“A 200dB Dynamic Range Iris-less CMOS Image Sensor with Lateral Overflow Integration Capacitor using Hybrid Voltage and Current Readout Operation” ISSCC Dig. Tech. Papers, 2006
[2] N. Akahane, et al., “A Sensitivity and Linearity Improvement of a 100dB Dynamic Range CMOS Image Sensor Using a Lateral Overflow Integration Capacitor,” Symp. on VLSI Circuits, pp.62-65, 2005.
[3] S.K.Mendis, et al. , “A 128x128 CMOS Active Pixel Image Sensor for Highly Integrated Imaging Systems”, IEEE IEDM Tech. Dig., 1993
[4] E.R.Fossum, “CMOS Image Sensors Electronic Camera-On-A-Chip”, IEEE Trans. on Electron Devices, Vol. 44, No.10, Oct. 1997
[5] A.E.Gamal, et al. “CMOS Image Sensors”, IEEE Circuits and Device Magazine, May. 2005
[6] B.Choubey, et. al.,”An Electronic-Calibration Scheme for Logarithmic CMOS Pixels,” IEEE Sensors Journal, Vol.6, No. 4,August 2006