Analysis of self-correcting active pixel sensors (original) (raw)
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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.
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.