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Does CMOS technology have advantages over CCD technology?

CCD sensors use devices called shift registers to transport charges out of the sensor cells and to the other electronic devices in the camera. The use of shift registers has several disadvantages:

  • Shift registers must be located near to the photosensitive cells. This increases the possibility of blooming and smearing.
  • The serial nature of shift registers makes true area of interest image capture impossible. With shift registers, the readings from all of the sensor cells must be shifted out of the CCD sensor array. After all of the readings have been shifted out, the readings from the area of interest can be selected and the remaining readings are discarded
  • Due to the nature of the shift registers, large amounts of power are needed to obtain good transfer efficiency when data is moved out of the CCD sensor array at high speed.

CMOS sensors and CCD sensors have completely different characteristics. Instead of the silicon sensor cells and shift registers used in a CCD sensor, CMOS sensors use photo diodes with a matrix oriented addressing scheme. These characteristics give CMOS the following advantages:

  • The matrix addressing scheme means that each sensor cell can be accessed individually. This allows true area of interest processing to be done without the need to collect and then discard data.
  • Since CMOS sensors don't need shift registers, smear and blooming are eliminated and much less power is needed to operate the sensor (approximately 1/100th of the power needed for a CCD sensor).
  • This low power input allows CMOS sensors to be operated at very high speeds with very low heat generation

The quality of the signals generated by CMOS sensors is quite good and can be compared favorably with the signals generated by a CCD sensor. Also, CMOS integration technology is highly advanced; this creates the possibility that most of the components needed to produce a digital camera can be contained on one relatively small chip. Finally, CMOS sensors can be manufactured using well-understood, standardized fabrication technologies. Standard fabrication techniques result in lower cost devices.