Optical Image Sensors
- Basic Description
-
The basic purpose of an optical image sensor is to convert light to electrical signals.
In automobiles these sensors are used in various systems including accident recorders,
lane departure warning systems, sign detection systems, parking assistance and collision avoidance.
Optical sensors are generally based on one of two technologies CCD
(Charge Coupled Device)
or CMOS (Complementary Metal Oxide Semiconductor). Both types of sensors consist of an array
of picture elements (pixels)
that produce a current proportional to the illumination intensity.
CCD: CCD sensor elements are basically tiny capacitors that collect charge directly
proportional to the amount of light that strikes the sensor. After an array of sensors has been exposed
to an image, charge is shifted from one capacitor to its neighbor and the last capacitor in the array
dumps its charge into a charge amplifier which produces a voltage proportional to the charge. This analog
voltage level represents the brightness of the image at the corresponding pixel location.
CCD Imaging System
CMOS: CMOS image sensors have digital circuitry next to each photosensitive pixel
that converts the light intensity striking the pixel to an analog voltage.
Additional circuitry on the chip converts
that voltage to a digital value.
CMOS Imaging System
CCD sensors are a more mature technology and have traditionally enjoyed an advantage
over CMOS sensors in terms of their dynamic range and resolution. However CMOS sensors require less power
to operate and can be built on the same silicon using the same processes as the digital circuitry
that controls the sensor. Newer CMOS sensors rival CCD sensors in terms of dynamic range and resolution.
- Manufacturers
-
Aptina,
Bosch,
Delphi,
Dynamax,
Fairchild Imaging,
Hamamatsu,
Hynix,
Melexis,
Mitsubishi Electric,
New Imaging Technologies,
Omnivision,
ON Semiconductor,
Panasonic,
Samsung,
Sony,
ST Microelectronics,
Teledyne Dalsa,
Truesense,
Toshiba
- For More Information
- [1] What is a Sensor?, SensorCleaning.com.
- [2] Image Sensor, Wikipedia.
- [3] Simple CMOS, YouTube, May 2, 2008.
- [4] OmniVision's High Dynamic Range (HDR) camera sensors, YouTube, Oct. 21, 2008.
- [5] Video ABC's Part 2 - CCD vs CMOS, YouTube, Aug. 3, 2010.
- [6] CCD vs. CMOS, Teledyne Dalsa website.
- [7] The Growing World of the Image Sensors Market, Rajender Thusu, Sensorsmag.com, Feb. 1, 2012.
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