CMOS Image Sensors Information on GlobalSpec

CMOS image sensors (complementary metal oxide semiconductors) operate at lower voltages than CCDs, reducing power consumption for portable applications. Each CMOS active pixel sensor cell has its own buffer amplifier, and can be addressed and read individually. A commonly used cell has four transistors and a photo-sensing element. The cell has a transfer gate separating the photo sensor from a capacitive "floating diffusion," a reset gate between the floating diffusion and power supply, a source-follower transistor to buffer the floating diffusion from readout-line capacitance, and a row-select gate to connect the cell to the readout line. All pixels on a column connect to a common sense amplifier.

In addition to their lower power consumption when compared with CCDs, CMOS image sensors are generally of a much simpler design; often just a crystal and decoupling. For this reason, they are easier to design with, generally smaller, and require less support circuitry.

There are two categories of CMOS sensors, analog and digital, as defined by their manner of output. Analog sensors feed their encoded signal in a video format, such as PAL, NTSC, etc. The signal can be fed directly to standard video equipment. Digital CMOS image sensors provide digital output, typically via a 4/8 or 16 bit bus. The digital signal is direct, not requiring transference or conversion via a video capture card.

The video and imaging equipment and components category covers devices that either use video technology to record or display data, or read data or are powered by imaging technologies such as lasers and infrared scanners. In industrial applications, these products are used for automated inspection and measurement, quality control, image sensing; and in specific applications, reading, analyzing and displaying data. Video and imaging equipment and components are divided into seven different families: machine vision and inspection equipment, video cameras and lenses, video equipment, image sensors – including CMOS image sensors, bar code equipment, and meters, readouts and indicators.

Video equipment includes those devices used to process or display captured video data. This family includes digital video recorders (used to transform the video data into digital output), monitors, multiplexers (to handle a number of signals at one time) and switchers (to control video camera sequence).

Video cameras and lenses include all video devices that are used in industrial applications – including CMOS image sensors. These items are different from the consumer market camcorders and lenses in that they are structured to survive in rigorous factory or industrial environments. Video cameras and lenses include not only video cameras and vision sensors for visual inspection and surveillance, but thermal and infrared imagers to track heat changes within systems, or in security operations.

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Engineering Web: CMOS Image Sensors - TechBriefs

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