CCD and CMOS image sensors

Source

Both CCD (charge-coupled device) and CMOS (complimentary metal-oxide semiconductor) image sensors start at the same point -- they have to convert light into electrons. If you have read the article How Solar Cells Work, you understand one technology that is used to perform the conversion. One simplified way to think about the sensor used in a digital camera (or camcorder) is to think of it as having a 2-D array of thousands or millions of tiny solar cells, each of which transforms the light from one small portion of the image into electrons. Both CCD and CMOS devices perform this task using a variety of technologies.

The next step is to read the value (accumulated charge) of each cell in the image. In a CCD device, the charge is actually transported across the chip and read at one corner of the array. An analog-to-digital converter turns each pixel's value into a digital value. In most CMOS devices, there are several transistors at each pixel that amplify and move the charge using more traditional wires. The CMOS approach is more flexible because each pixel can be read individually.
CCDs use a special manufacturing process to create the ability to transport charge across the chip without distortion. This process leads to very high-quality sensors in terms of fidelity and light sensitivity. CMOS chips, on the other hand, use traditional manufacturing processes to create the chip -- the same processes used to make most microprocessors. Because of the manufacturing differences, there have been some noticeable differences between CCD and CMOS sensors.

• CCD sensors, as mentioned above, create high-quality, low-noise images. CMOS sensors, traditionally, are more susceptible to noise.
• Because each pixel on a CMOS sensor has several transistors located next to it, the light sensitivity of a CMOS chip tends to be lower. Many of the photons hitting the chip hit the transistors instead of the photodiode.
• CMOS traditionally consumes little power. Implementing a sensor in CMOS yields a low-power sensor.
• CCDs use a process that consumes lots of power. CCDs consume as much as 100 times more power than an equivalent CMOS sensor.
• CMOS chips can be fabricated on just about any standard silicon production line, so they tend to be extremely inexpensive compared to CCD sensors.
• CCD sensors have been mass produced for a longer period of time, so they are more mature. They tend to have higher quality and more pixels.

Based on these differences, you can see that CCDs tend to be used in cameras that focus on high-quality images with lots of pixels and excellent light sensitivity. CMOS sensors traditionally have lower quality, lower resolution and lower sensitivity. CMOS sensors are just now improving to the point where they reach near parity with CCD devices in some applications. CMOS cameras are usually less expensive and have great battery life.
These links will help you learn more:

• Patent# 5,841,126: CMOS active pixel sensor type imaging system on a chip
• Patent# 5,471,515: Active pixel sensor with intra-pixel charge transfer
• Patent# 6,005,619: Quantum efficiency improvements in active pixel sensors
• PhotoCourse.com: CCD and CMOS Image Sensors
• BeyondLogic: CMOS Digital Image Sensors
• Vision Sensing: CCD, CMOS or other image capturing sensors
• CMOS technology demonstration

Sensor sizes
Digital Camera Image Sensors

Image Sensor Type	Used in... (some examples, not meant to be a comprehensive list)	Width mm	Height mm	Diagonal mm (equals 'normal' lens focal length)	Focal length Factor
1/4"		3.2	2.4	4.0	11.3
1/3.6"		4.0	3.0	5.0	9.0
1/3.2"	Canon A100, A200	4.5	3.4	5.7	7.9
1/3"	Nikon Coolpix 100, 300 Casio QV-8000SX	4.8	3.6	6.0	7.5
1/2.7"	Nikon Coolpix 2500, 3500 Sony DSC-P31 Pentax Optio 230, 330GS Canon A40 Olympus C-730 Minolta Dimage X, Xi	5.3	4.0	6.6	6.8
1/2.5"	Olympus C-740, C-750 Ricoh R3, R4, R5 Canon SD700, SD800
1/2"	Nikon Coolpix 950	6.4	4.8	8.0	5.6
1/1.8"	Nikon Coolpix 995, 4300, 4500, 5400 Canon Powershot G2, G3, G5, S30, S40, S45 , SD900 Kodak DX3900, 4900 Pentax Optio 330RS, 430RS Olympus C-5050, C-5060, C-8080 Ricoh GR-D, GX8	7.2	5.3	8.9	5.0
1/1.76"	Leica Digilux 1 Panasonic DMC-LC5	?	?	9.0	4.7
2/3"	Nikon Coolpix 5000, 5700 Sony DSC-F717 Minolta 7i, 7Hi	8.8	6.6	11.0	4.1
1"		12.8	9.6	16.0	2.8
4/3"	Kodak-Olympus-Fuji-Panasonic-Sigma new digital standard. This system uses the same standard lens mount for any brand camera and lens. Maybe this is the digital system for the future. First model is the Olympus E-1 with the 5 megapixel chip as displayed above. Second model is the Olympus E-300 with an 8 megapixel chip also made by Kodak. Now also E-500, E-330 and E-400. Visit the 4/3 site for more information.	18.0	13.5	22.5	2.0
	Canon D30, D60, 10D	22.7	15.1	27.3	1.6
	Nikon D1, D1H, D1X, D100	23.7	15.6	28.4	1.5
	Pentax *ist D	23.5	15.7	28.3	1.5
	Canon 1D	28.7	17.8	33.8	1.4
APS	Advanced photo system film cameras (various crops in camera) APS-H here at 16:9 ratio	30.2	16.7	34.5	1.2
35mm	35mm film cameras. Full frame digital SLRs such as Contax N, Canon 1Ds, Kodak DCS14n	36.0	24.0	43.3	1.0
645	Medium format 120 roll film	56.0	41.5	69.7	0.6