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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
Outline
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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”
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]
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]
Pixel Circuits
Passive Pixel Sensor.[5]
3- and 4-T active
pixel sensor.[5]
Pixel Circuits (Cont.)
Diagram pixel
sensor.[5]
Logarithmic pixel.[6]
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.
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Standard CMOS Image sensors have a DR of
40-60 dB, While human eye exceeds 90 dB.
Spatial Resolution: determined by the
Nyquist sampling theorem.
CMOS Active Pixel Image Sensor
Timing for CMOS
APS readout.[3]
.
Schematic of the circuit.[3]
Using a Lateral Overflow Integration to
Improve the Dynamic Range of the Sensor
Pixel schematic diagram, Timing
and Potential diagram.[2]
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.
Using a Lateral Overflow Integration to Improve
the Dynamic Range of the Sensor ( Cont.)
Switching concept from S1 signal to S2 signal.[2]
Using a Lateral Overflow Integration to Improve
the Dynamic Range of the Sensor: Sample Image
Non-saturated
signal (S1)
Oversaturated
signal
(S2)
Wide
dynamic
range signal
[2]
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
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.
Schematic of the pixel
Current readout operation
Timing.[1]
[1]
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]
Photoelectric conversion
characteristics:
The hybrid
operation of the
voltage and the
current readout
extends the DR
over 200 dB
[1]
The Sensor Block Diagram
Performance summary[1]
Sensor block diagram[1]
Sample Images
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The Image
sensor is
capable of
capturing
various scenes
with the
incident light
ranging from
about 10-2 to
108 lx.
[1]
Summary and Conclusion
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An introduction CMOS Image sensors was provided, the APS structure
was explained.
It was shown that:
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SNR, DR and Spatial resolution are the three main performance measures
of image sensors.
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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.
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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.
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