Analysis of self-correcting active pixel sensors (original) (raw)
Analysis of self-correcting active pixel sensors
Storage and Retrieval for Image and Video Databases, 2004
This paper evaluates the operation of self-correcting active pixel sensors presented in [6] using Signal-to-Noise Ratio. The evaluation is based on a simplified Active Pixel Sensing (APS) model. We show that in the absence of stuck faults (i.e., no errors) the performance of the system suffers from considerable degradation especially at low illumination (i.e., typical indoor scenes). We use the
Noise analysis of fault tolerant active pixel sensors with and without defects
Sensors, Cameras, and Systems for Scientific/Industrial Applications VII, 2006
As the sizes of imaging arrays become larger both in pixel count and area, the possibility of pixel defects increases during manufacturing and packaging, and over the lifetime of the sensor. To correct for these possible pixel defects, a Fault Tolerant Active Pixel Sensor (FTAPS) with redundancy at the pixel level has been designed and fabricated with only a small cost in area. The noise of the standard Active Pixel Sensor (APS) and FTAPS, under normal operating conditions as well as under the presence of optically stuck high and low faults, is analyzed and compared. The analysis shows that under typical illumination conditions the total noise of both the standard APS and FTAPS is dominated by the photocurrent shot noise. In the worst case (no illumination) the total mean squared noise of the FTAPS is only 15.5% larger than for the standard APS, while under typical illumination conditions the FTAPS noise increases by less than 0.1%. In the presence of half stuck faults the noise of the FTAPS compared to the standard APS stays the same as for the FTAPS without defects. However, simulation and experimental results have shown that the FTAPS sensitivity is greater than two times that of the standard APS leading to an increased SNR by more than twice for the FTAPS with no defects. Moreover, the SNR of a faulty standard APS is zero whereas the SNR of the FTAPS is reduced by less than half.
CMOS ACTIVE PIXEL SENSOR DESIGNS FOR FAULT TOLERANCE AND BACKGROUND ILLUMINATION SUBTRACTION
2005
As the CMOS active pixel sensor evolves, its weaknesses are being overcome and its strengths start to surpass that of the charge-coupled device. This thesis discusses two novel APS designs. The first novel APS design was a Fault Tolerance Active Pixel Sensor (FTAPS) to increase a pixel's tolerance to defects. By dividing a regular APS pixel into two halves, the reliability of the pixel is increased, resulting in higher fabrication yield, longer pixel life time, and reduction in cost. Photodiode-based FTAPS pixels were designed, fabricated in CMOS 0.18 micron technology, and tested. Experimental results demonstrated that the reliability of the pixel is increased and information that would have been lost without fault tolerance is recovered.
IEEE Transactions on Electron Devices, 2006
CMOS photodetectors are compact, cheap, and of low power, making them good candidates for many biomedical applications. However, many of these applications require the capability of detecting low-level light. Therefore, the noise in CMOS sensors must be carefully considered. This paper presents a detailed analysis of the signal and noise properties in active pixel sensor (APS) elements. An optimum signal-to-noise ratio (SNR) of 54 dB is achieved by varying the integration time. Based on a rigorous reset-time analysis of the APS, the dc level of the sense node is proposed as the new output signal, which is more sensitive to low-level light than existing APS techniques. By varying the reset time, an optimum SNR of 56 dB is achieved for a 30-ms integration time. This approach can achieve higher SNR for the same APS structure than the previous reports found in the literature.
High-dynamic-range active pixel sensor
SPIE Proceedings, 2004
We are implementing a new pixel test structure in a 0.25 µm CMOS process. This new structure is based on an internal pixel circuit that resets the pixel each time the well-capacity nears saturation and an analogue memory (counter), implemented in the pixel itself, records the number of resets per integration period. The increase in the dynamic range (DR) is (m+1) where m is the number of resets per period. The peak signal-to-noise ratio (SNR) will be increased due to the effective increase in the well capacity.
A Comparative Analysis of Active and Passive Pixel CMOS Image Sensors
CMOS imagers performance becomes critical whenever illumination reaches very low and very high optical energy levels because of the reduced signal-to-noise ratio (SNR) and blooming immmunity, respectively. In this paper we present a comparative analysis with respect to the above issues of the two major architectures used in implementing optical sensor arrays in CMOS technology: the Active Pixel Sensors (APS) and Passive Pixel Sensor (PPS) schemes. Based on both physical simulation and circuit analysis, the trade-offs between the two architectures with respect to the design constraints are highlited.
Optimization of noise and responsivity in CMOS active pixel sensors for detection of ultra low light
In this paper, we present results of the investigation of the design and operation of CMOS active pixel sensors for detection of ultra-low light levels. We present a detailed noise model of APS pixel and signal chain. Utilizing the noise model, we have developed APS pixel designs that can achieve ultra-low noise and high responsivity. We present results from two test chips, that indicate (1) that less than 5 electrons ofread noise is possible with CMOS APS by reducing the size of the pixel transistors, and (2) that high responsivity can be achieved when the fill-factor of the photodiode is reduced.
Modelisation and Simulation of Noise in CMOS Active Pixel Sensor for Low light Applications
Temporal and spatial noise sets a fundamental limit on image sensor performance, especially for low light applications. The temporal noise in CMOS APS is due to the reset noise, low frequency noise and thermal noise, and the spatial noise which associated to threshold voltage variations in transistors in the readout circuit. In this paper, analytical noise analysis of temporal noise in APS sensors is presented. We analyse the noise, for each stage of the sensor operation, taking nonlinearity into account. Using PSPICE simulations, we find the noise due to the readout circuit versus MOS dimensions and bias voltage of the load transistor of the first follower stage.
A chip and pixel qualification methodology on imaging sensors
2004 IEEE International Reliability Physics Symposium. Proceedings
This paper presents a qualification methodology on imaging sensors. In addition t o overall chip reliability characterization based on sensor's overall figure of merit, such as Dark Rate, Linearity, Dark Current Non-Uniformity, Fixed Pattern Noise and Photon Response Non-Uniformity, a simulation technique is proposed and used to project pixel reliability. The projected pixel reliability is directly related to imaging quality and provides additional sensor reliability information and performance control.
CMOS-Based Active Pixel for Low-Light-Level Detection: Analysis and Measurements
IEEE Transactions on Electron Devices, 2007
An analysis of the active pixel sensor (APS), considering the doping profiles of the photodiode in an APS fabricated in a 0.18 µm standard CMOS technology, is presented. A simple and accurate model for the junction capacitance of the photodiode is proposed. An analytic expression for the output voltage of the APS obtained with this capacitance model is in good agreement with measurements and is more accurate than the models used previously. A different mode of operation for the APS based on the dc level of the output is suggested. This new mode has better low-light-level sensitivity than the conventional APS operating mode, and it has a slower temporal response to the change of the incident light power. At 1 µW/cm 2 and lower levels of light, the measured signal-to-noise ratio (SNR) of this new mode is more than 10 dB higher than the SNR of previously reported APS circuits. Also, with an output SNR of about 10 dB, the proposed dc level is capable of detecting light powers as low as 20 nW/cm 2 , which is about 30 times lower than the light power detected in recent reports by other groups.
Linear Current-Mode Active Pixel Sensor
IEEE Journal of Solid-State Circuits, 2000
A current mode CMOS active pixel sensor (APS) providing linear light-to-current conversion with inherently low fixed pattern noise (FPN) is presented. The pixel features adjustable-gain current output using a pMOS readout transistor in the linear region of operation. This paper discusses the pixel's design and operation, and presents an analysis of the pixel's temporal noise and FPN. Results for zero and first-order pixel mismatch are presented. The pixel was implemented in a both a 3.3 V 0.35 µm and a 1.8 V 0.18 µm CMOS process. The 0.35 µm process pixel had an uncorrected FPN of 1.4%/0.7% with/without column readout mismatch. The 0.18 µm process pixel had 0.4% FPN after delta-reset sampling (DRS). The pixel size in both processes was 10 X 10 µm 2 , with fill factors of 26% and 66%, respectively.
Temporal noise analysis and measurements of CMOS active pixel sensor operating in time domain
2013 26th Symposium on Integrated Circuits and Systems Design (SBCCI), 2013
Image sensors in standard CMOS technology are increasing used for consumer, industrial and scientific applications due to their low cost, high level of integration and low power consumption. Further, image sensors in mainstream complementary metal-oxide-semiconductor (CMOS) technology are preferred because they are the lowest cost and easiest/fastest option to implement. For CMOS image sensors, a key issue is their noise behavior. Therefore, we have studied the noise characteristics of CMOS image sensors operating in time domain. Two important noise sources are the reset noise and integration noise. The reset noise is due to the reset in CMOS image sensors operating in voltage domain. The integration noise is that accumulated during light integration and was found to be the constant, independent of light intensity. Our circuit analysis shows that the signal-to-noise ratio (SNR) is also constant and independent of light intensity. At low light levels the constant SNR is higher compared to others CMOS image sensors presented in the literature. We have implemented a time domain CMOS image sensor in AMS CMOS 0.35um technology. Our measurements results show that the SNR level is approximately constant to 43dB.
MODELING AND CHARACTERIZATION OF LOGARITHMIC CMOS ACTIVE PIXEL SENSORS
We present a detailed analysis of logarithmic active pixel sensors (Log-APS) to be used in CMOS imagers for real-time on-chip motion detection. Based on an equivalent circuit model for CMOS-compatible photodiodes, an HSPICE simulation has been used to characterize different configurations of these sensors under various conditions of light intensities and switching speeds. These investigations are supported by the experimental results obtained from the chip fabricated with standard 0.5 µm CMOS technology. It is concluded that more robust on-chip motion detection in CMOS imagers can be achieved with careful design of its Log-APS photocircuits that consider the issues discussed here.
Photoresponse analysis and pixel shape optimization for CMOS active pixel sensors
IEEE Transactions on Electron Devices, 2003
In this work, a semi-analytical model, based on a thorough analysis of experimental data, is developed for photoresponse estimation of a photodiode-based CMOS active pixel sensor (APS). The model covers the substrate diffusion effect together with the influence of the photodiode active-area geometrical shape and size. It describes the pixel response dependence on integration photocarriers and conversion gain and demonstrates that the tradeoff between these two conflicting factors gives an optimum geometry enabling extraction of maximum photoresponse. The parameter dependence on the process and design data and the degree of accuracy for the photoresponse modeling are discussed. Comparison of the derived expression with the measurement results obtained from a 256 256 CMOS APS image sensor fabricated via HP in a standard 0.5m CMOS process exhibits excellent agreement. The simplicity and the accuracy of the model make it a suitable candidate for implementation in photoresponse simulation of CMOS photodiode arrays.
Normalized differential detection by use of smart pixels with smart illumination
Applied Optics, 2005
Smart pixels permit rapid signal processing through the use of integrated photodetectors and processing electronics on a single semiconductor chip. Smart pixels with smart illumination can increase the dynamic range and functionality of smart pixels by employing optoelectronic feedback to control the illumination of a scene. This combination of smart pixels and optoelectronic feedback leads to many potential sensor applications, including normalized differential detection, which is modeled and demonstrated here.
Standard CMOS active pixel image sensors for multimedia applications
arvlsi, 1995
The task of image acquisition is completely dominated by CCD-based sensors fabricated on specialized process lines. These devices provide an essentially passive means of detecting photons and moving image data across chip. We argue that line widths in standard ...