CCD vs CMOS technology

- Nov 06, 2017-

 A micrograph of the corner of the photosensor array of a ‘webcam’ digital camera

 Image sensor on the motherboard of a Nikon Coolpix L2 6 MP

Most digital cameras use a CMOS sensor, because CMOS sensors perform better than CCDs, offering faster speeds with lower power consumption. Most CMOS sensors incorporate an integrated circuit, helping reduce costs; CCD sensors are still in use for cheaper cameras, but can demonstrate comparatively diminished performance (e.g. weakness in burst mode).Both types of sensor accomplish the same task of capturing light and converting it into electrical signals.

 Each cell of a CCD image sensor is an analog device. When light strikes the chip it is held as a small electrical charge in each photo sensor. The charges in the line of pixels nearest to the (one or more) output amplifiers are amplified and output, then each line of pixels shifts its charges one line closer to the amplifier(s), filling the empty line closest to the amplifiers(s). This process is then repeated until all the lines of pixels have had their charge amplified and output.

 A CMOS image sensor has an amplifier for each pixel compared to the few amplifiers of a CCD. This results in less area for the capture of photons than a CCD, but this problem has been overcome by using microlenses in front of each photodiode, which focus light into the photodiode that would have otherwise hit the amplifier and not be detected. Some CMOS imaging sensors also use Back-side illumination to increase the number of photons that hit the photodiode.CMOS sensors can potentially be implemented with fewer components, use less power, and/or provide faster readout than CCD sensors. They are also less vulnerable to static electricity discharges.

 Another design, a hybrid CCD/CMOS architecture (sold under the name "sCMOS") consists of CMOS readout integrated circuits (ROICs) that are bump bonded to a CCD imaging substrate – a technology that was developed for infrared staring arrays and has been adapted to silicon-based detector technology.Another approach is to utilize the very fine dimensions available in modern CMOS technology to implement a CCD like structure entirely in CMOS technology: such structures can be achieved by separating individual poly-silicon gates by a very small gap; though still a product of research hybrid sensors can potentially harness the benefits of both CCD and CMOS imagers.