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CMOS (Complementary Metal Oxide Semiconductor) Image Sensors
Like CCDs, these imagers are made from silicon, but as the name implies, the process they are made in is called CMOS, which stands for Complementary Metal Oxide Semiconductor. This process is today the most common method of making processors and memories, meaning CMOS Imagers take advantage of the process and cost advancements created by these other high-volume devices.
Like CCDs, CMOS imagers include an array of photo-sensitive diodes, one diode within each pixel. Unlike CCDs, however, each pixel in a CMOS imager has its own individual amplifier integrated inside. Since each pixel has its own amplifier, the pixel is referred to as an "active pixel". In addition, each pixel in a CMOS imager can be read directly on an x-y coordinate system, rather than through the "bucket-brigade" process of a CCD. This means that while a CCD pixel always transfers a charge, a CMOS pixel always detects a photon directly, converts it to a voltage and transfers the information directly to the output. This fundamental difference in how information is read out of the imager, coupled with the manufacturing process, gives CMOS Imagers several advantages over CCDs.
Applications
CMOS use both positive polarity (PMOS) and negative polarity (NMOS) circuits. This is beneficial because only one of the circuit types is on at any given time. This results in less power being needed in comparison to chips that have only one type of transistor. Since they rely on less power, CMOS chips have become incredibly attractive when building portable computers or other devices that require a stronger battery life. However, even personal computers contain a battery-powered CMOS memory to keep the data, time and system setup specifications kept in case the computer is unplugged or lose electricity.
And also CMOS use in following applications,
Microcontrollers
Static RAM
Image sensors
Data converters
Certain transceivers
Advantages
CMOS chips have several advantages. Unlike the CCD (Charge-coupled Device) sensor, the CMOS
chip includes amplifiers and A/D-converters, which lowers the cost for cameras since it contains all
the logics needed to produce an image. Every CMOS pixel contains conversion electronics.
Compared to CCD sensors, CMOS sensors have better integration possibilities and more functions.
CMOS sensors also have a faster readout, lower power consumption, and a smaller system size.
It is possible to read individual pixels from a CMOS sensor, which allows ‘windowing’, which implies that parts of the sensor area can be read out, instead of the entire sensor area at once. This way a higher frame rate can be delivered from a limited part of the sensor, and digital PTZ (pan/tilt/zoom) functions can be used. It is also possible to achieve multi-view streaming, which allows several cropped view areas to be streamed simultaneously from the sensor, simulating several ‘virtual cameras’.
A CMOS imager converts charge to voltage at the pixel, and most functions are integrated into the chip. This makes imager functions less flexible but, for applications in rugged environments, a CMOS camera can be more reliable. Responsively, the amount of signal the sensor delivers per unit of input optical energy. CMOS imagers are marginally superior to CCDs, in general.
Disadvantages
Since CMOS chip includes amplifiers and A/D-converters inside the chip can lead to a risk of more structured noise, such as stripes and other patterns. This cause to higher noise immunity. Calibrating a CMOS sensor in production, if needed, can be more difficult than calibrating a CCD sensor. CMOS imagers were traditionally much worse under both regimes where between uniformity under illumination and uniformity at or near dark.
