Temporal noise sets a fundamental limit on image sensor performance, especially under low illumination and in video applications. In a CCD image sensor, temporal noise is well studied and characterized. It is primarily due to the photodetector shot noise and the thermal and 1/f noise of the output charge to voltage amplifier. In a CMOS APS several addition sources contribute to temporal noise, including the noise due to the pixel rest, follower, and access transistors. The analysis of noise is further complicated by the nonlinearity of the APS charge to voltage characteristics, which is becoming more pronounced as CMOS technology scales, and the fact that the reset transistor operates below threshold for most of the reset time. The paper presents an accurate analysis of temporal noise in APS. We analyze the noise for each stage of the sensor operation, and identify the noise contribution from each source. We analyze noise due to photodetector shot noise taking nonlinearity into consideration. We find that nonlinearity improves SNR reset transistor shot noise is at most half the commonly quoted value. Using HSPICE simulation, we find the noise due to the follower and access transistors. As expected we find that at low illumination reset noise dominates, while at high illumination photodetector shot noise dominates. Finally, we present experimental results from test structures fabricated in 0.35(mu) CMOS processes. We find that both measured peak SNR and reset noise values match well with the results of our analysis.
[1]
Bedabrata Pain,et al.
Optimization of noise and responsivity in CMOS active pixel sensors for detection of ultralow-light levels
,
1997,
Electronic Imaging.
[2]
E. Fossum,et al.
CMOS active pixel image sensors for highly integrated imaging systems
,
1997,
IEEE J. Solid State Circuits.
[3]
Hao Min,et al.
Test structures for characterization and comparative analysis of CMOS image sensors
,
1996,
Advanced Imaging and Network Technologies.
[4]
S. Decker,et al.
A 256/spl times/256 CMOS imaging array with wide dynamic range pixels and column-parallel digital output
,
1998,
1998 IEEE International Solid-State Circuits Conference. Digest of Technical Papers, ISSCC. First Edition (Cat. No.98CH36156).
[5]
C. Mead,et al.
White noise in MOS transistors and resistors
,
1993,
IEEE Circuits and Devices Magazine.
[6]
Johannes Solhusvik,et al.
Low-noise CCD signal acquisition techniques
,
1994,
Defense, Security, and Sensing.
[7]
Hao Min,et al.
Modeling and estimation of FPN components in CMOS image sensors
,
1998,
Electronic Imaging.
[8]
A. Ziel.
Noise in solid state devices and circuits
,
1986
.
[9]
Carver Mead,et al.
Analog VLSI and neural systems
,
1989
.
[10]
Abbas El Gamal,et al.
Method for estimating quantum efficiency for CMOS image sensors
,
1998,
Electronic Imaging.