Image sensor
Overview
An image sensor is a device that converts an optical image into an electronic signal. It is used primarily in digital cameras and other imaging devices. Early sensors were video camera tubes but a modern one is typically a charge-coupled device (CCD) or a complementary metal–oxide–semiconductor (CMOS) active pixel sensor.
History
The first image sensors were based on video camera tube technology. These devices were used in early television systems, and were later adapted for use in video cameras. The first practical video camera tube, the Iconoscope, was developed by Vladimir Zworykin at RCA in 1931. This was followed by the development of the Orthicon and Vidicon tubes.
The development of solid-state image sensors started in the 1960s. The first solid-state device to capture an image was a charge-coupled device (CCD), invented by Willard S. Boyle and George E. Smith at Bell Labs in 1969. The CCD would later be used in the first digital cameras.
The complementary metal–oxide–semiconductor (CMOS) active pixel sensor (APS) was later developed by Eric Fossum and his team at the NASA Jet Propulsion Laboratory in the 1990s. The CMOS APS has since become the dominant image sensor technology, replacing the CCD in most applications.
Types of Image Sensors
There are two main types of image sensors: CCD and CMOS. Each type has its own advantages and disadvantages.
Charge-Coupled Device (CCD)
A CCD is a device that moves electrical charge, usually from within the device to an area where the charge can be manipulated. This is achieved by "shifting" the signals between stages within the device one at a time. CCDs move charge between capacitive bins in the device, with the shift allowing for the transfer of charge between bins.
Complementary Metal–Oxide–Semiconductor (CMOS)
A CMOS sensor is an electronic chip that converts photons to electrons for digital processing. CMOS sensors are used in digital cameras, digital video cameras and digital CCTV cameras. CMOS sensors are also used in various scientific applications including DNA sequencing, spectrometry and radiography.
Image Sensor Formats
Image sensors come in various sizes. The size of the sensor is often expressed as optical format in inches. Other measures are also used, such as the diagonal in millimeters or the area in square millimeters.
Image Sensor Performance
The performance of an image sensor is determined by several factors, including its resolution, dynamic range, and sensitivity to light. These factors are interrelated, and an improvement in one may lead to a decrease in another.
Future Developments
The future of image sensor technology is likely to involve further improvements in resolution, dynamic range, and light sensitivity. There is also ongoing research into new types of image sensors, such as the quantum image sensor.