CMOS active pixel sensors (APS) have performance competitive with charge-coupled device (CCD) technology, and offer advantages in on-chip functionality, system power reduction, cost, and miniaturization. This paper discusses the requirements for CMOS image sensors and their historical development, CMOS devices and circuits for pixels, analog signal chain, and on-chip analog-to-digital conversion are reviewed and discussed.

CMOS image sensors: electronic camera-on-a-chip

Recent advancements in CMOS image sensor technology are reviewed, including both passive pixel sensors and active pixel sensors. On-chip analog to digital converters and on-chip timing and control circuits permit realization of an electronic camera-on-a-chip.

CMOS image sensors: electronic camera on a chip

In this article, we provide a basic introduction to CMOS image-sensor technology, design and performance limits and present recent developments and future directions in this area. We also discuss image-sensor operation and describe the most popular CMOS image-sensor architectures. We note the main non-idealities that limit CMOS image sensor performance, and specify several key performance measures. One of the most important advantages of CMOS image sensors over CCDs is the ability to integrate sensing with analog and digital processing down to the pixel level. Finally, we focus on recent developments and future research directions that are enabled by pixel-level processing, the applications of which promise to further improve CMOS image sensor performance and broaden their applicability beyond current markets.

CMOS image sensors

CMOS image sensors: Electronic camera-on-a-chip

http://eia.udg.es/%7Eqsalvi/papers/2006-MJ.pdf

Review of CMOS image sensors

This paper describes the implementation in silicon of a retina-like sensor characterized by a space-variant resolution similar to that of the human retina. Besides the actual implementation using CMOS technology, the design peculiarities of retina-like sensors are compared with the use of software or hardware electronic remappers. The paper also describes the realization of a retina-like digital camera and its applications for real-time control and image transmission.

/pdf/a-retina-like-cmos-sensor-and-its-applications-47csq9ft7s.pdf

A retina-like CMOS sensor and its applications

A method is disclosed for obtaining a read-out signal of a MOS-based pixel structure having at least a photosensitive element with an output node and a memory element with a first switch therebetween. The method comprises the steps of while acquiring charge carriers on said output node of said photosensitive element, said charge carriers being converted from electromagnetic radiation on the photosensitive element, after a first time period creating a first signal, and after a second time period, creating a second signal, said read-out signal being a combination of at least said first and said second signals. According to the present invention, there is no limitation to the amount of collected charges in none of the integrated periods. The signal collected during the first period is memorized by a switch which shortly opens and closes between the period. The switch is thus in the same state in both period of time. After a second period, there are thus two charge packets, each obtained during a different time. In order to read-out, these two charge packets are then combined into one reading. This combination is known either by adding or subtracting this charge packets, e.g., by adding or subtracting them in the circuitry external to the sensor.

Method for obtaining a high dynamic range read-out signal of a CMOS-based pixel structure and such CMOS-based pixel structure

A new foveated CMOS image sensor has been designed and fabricated. The photocell elements transform the light into current, and then, in a continuous way, into voltage without charge integration. This kind of sensing cell has been already employed in image sensors for normal cameras, but never in foveated sensors. The presented sensor tries to emulate the human eye pixel resulting in a sensor with a space variant distribution of pixels. Consequences of this distribution are the different size of the sensing elements in the pixel matrix, the non orthogonal shapes of the different elements that integrate the pixel, and, as a result, the different response of every cell in the sensor. A scaling mechanism is needed due to the different pixel size from circumference to circumference. A mechanism for current scaling is presented. This mechanism has been studied along with other effects, as the narrow channel effect on submicron MOS transistors, and the influence of the logarithmic response of these special kinds of sensing cells. The chip has been fabricated using standard 0.7 /spl mu/m CMOS technology.

Response properties of a foveated space-variant CMOS image sensor

In one embodiment, an image sensor (290) for an x-ray imager (200) includes a photodiode (223) and a readout circuit. A deep well (232) formed below the readout circuit may be configured as a diode to drain away parasitic electrons, which would otherwise induce noise in images. The parasitic electrons may be drained away to a power supply or a measuring circuit for dosimetrie purposes, for example.

Minimizing the effect of directly converted x-rays in x-ray imagers

A new image sensor, using CMOS technology, has been designed and fabricated. The pixel distribution of this sensor follows a log-polar mapping, thus the pixel concentration is maximum at the center reducing the number of pixels towards the periphery, having a resolution of 56 rings with 128 pixels per ring. The design of this kind of sensors has special issues regarding the space-variant nature of the pixel distribution. The main topic is the different pixel size that requires scaling mechanisms to achieve the same output independently of the pixel size. This paper presents some study results on the scaling mechanisms of this kind of sensors. A mechanism for current scaling is presented. This mechanism has been studied along with the logarithmic response of these special kind of sensing cells. The chip has been fabricated using standard 0.7 micrometer CMOS technology.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Design issues on CMOS space-variant image sensors

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