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 sensors 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 with 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 requires 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, Omnivision

For More Information

[1] What is a Sensor?, SensorCleaning.com.

[2] The New Foveon Sensors, Vincent Bockaert, Digital Photography Review.

[3] Image Sensor, Wikipedia.

[4] Sony Unveils 'Exmor R' Back-Illuminated CMOS Technology, Digital Photography Review, Aug. 6, 2009.