CMOS IMAGE SENSORSA 200dB Dynamic Range Iris–less CMOS Image Sensor with Lateral Overflow

Integration Capacitor and Current Readout OperationNana 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

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. 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

.

Schematic of the circuit.[3]

Timing for CMOS APS readout.[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)

Over-saturated

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 operationTiming.[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

Sensor block diagram[1]Performance summary[1]

Sample Images

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

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.

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